Definitions Heating & Cooling Terms
BTU, Calorie, R U& K Values,
Design Temperature, Degree Day, Tons of Cooling Capacity etc

DEFINITION of HEATING & COOLING TERMS - CONTENTS: BTU, Calorie, R U& K Values,
Design Temperature, Degree Day, Tons of Cooling Capacity. How to measure or calculate heat loss (or gain) in a building. How to measure heat transmission in materials: definition of R-values, U-values, K-values, BTU, calorie, and rates of heat loss or gain. Building design temperatures & how to use a home energy audit or heat loss analysis. What insulation "R" values should be used in a building insulation?

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This article defines Heat Loss, R-value, U-value, & K-Value measures of heating loss rate or insulation effectiveness and provides basic building insulation and heat loss guidelines including how to measure or calculate heat loss in a building, defines thermal terms like BTU and calorie, provides measures of heat transmission in materials, gives desired building insulation design data, and shows how
to calculate the heat loss in a building with R values or U values.

Definitions of BTUs, BTUH, and Calories for Discussing Building Heat Gain or Heat Loss Analysis

When we are evaluating the quality and effectiveness of insulation in a building or the adequacy of a building heating
or cooling system, we need to use measurements that permit us to describe the rate at which a building loses heat under
various conditions (such as outdoor temperature, wind velocity, how leaky the building is, the area of its windows and
perhaps doors, and the amount of insulation in the building walls, floors, and ceilings.

[Click to enlarge any image]

Formula-R™ and Owens Corning™ which may be visible in the page top photograph of pink Styrofoam™ insulation boards are registered trademarks of Owens Corning® and were photographed at a Home Depot® building supply center.

A few of these critical definitions
is given just below, followed by some simple formulas used to calculate the heat loss in a building. Sketch at above left is provided courtesy of Carson Dunlop Associates.

Definition of AFUE

AFUE is an abbreviation for Annual Fuel Utilization Efficiency. In short, the AFUE tells you, for each dollar you spend on energy for heating by gas, oil, or another fuel, just how much of your dollar shows up inside the occupied space of your building as heat. Higher AFUE is better.
See AFUE DEFINITION, RATINGS for details & examples.

Definition of BTUs and BTUH

a BTU is one "British Thermal Unit" which is defined as the quantity of heat
that would be required to increase the temperature of one pound of water by one degree Fahrenheit.

A BTUH is defined as the number of BTU's lost (if we're talking about heat loss or air conditioning), or provided (if
we're talking about providing heat for a building) in one hour. You'll often see BTUH as a number on data plates on
air conditioners and on heating systems.

Also see our examples of BTU data used in air conditioning and heat pump calculations discussed at What is a BTU or British Thermal Unit? What is a Joule?for details about BTUs and various examples of BTU and BTUh calculations. There we give definitions of related terms such as latent heat, superheat, latent heat of condensation, sensible heat, and specific heat.

Complete details about the definition of BTUs and BTUH, and examples of uses & calculations using BTU numbers can be found at Definition of BTUs and Definition of BTUH

Energy Efficiency Ratio (EER): This is a measure of the instantaneous energy efficiency of cooling equipment. EER is the steady-state rate of heat energy removal (e.g., cooling capacity) by the equipment in Btuh divided by the steady-state rate of energy input to the equipment in Watts. This ratio is expressed in Btuh per Watt (Btuh/Watt). EER is based on tests performed in accordance with ARI 210/240.

Definitions of R-Value, U-Value, K-Value

R values and heat loss: The "R" value of a material is its resistance to heat flow through the material. When buying various insulation materials you will almost
always see an "R" value quoted for the material. In general, higher "R" means more resistance to heat loss and therefore lower heating or
cooling bills for the building.

Mathematically, "R" is simply the reciprocal of the two measures discussed in more detail below:

U - the measure of heat transfer (the ability of a substance to conduct heat) discussed above and also at "U"

K - the coefficient of heat transmission discussed at "K"

"K" (R = 1/K) or "U" (R_{(whole building)} = 1/U)

As you'll read below, the heat transmission coefficient "K" measures the heat flow through an individual substance and "U" measures the overall building heat loss by adding all of the
various areas and substances together.

Reader Peter J. Collins has noted in clarification of the definition of "R" value that

The R-value of a material is a measure of its thermal resistance.

The U-value (or U-factor), more correctly called the overall heat transfer coefficient

We add that R-value measures the resistance of a material to transfer heat (in any direction). Higher R-vales are more resistant to heat transfer. When we are discussing building insulation, an insulation with a higher R-value would be expected to resist heat loss more than one of a lower R-value, if all other factors such as air leakage or heat radiation are the same.

And as Mr. Collins elaborates,

R-value = resistance to the movement of heat

U = the ability to transfer heat, obviously an inverse condition, to resistance, or in other words, or to allow the transfer of heat

U-Factor measures how well a product prevents heat from
escaping a home or building. U-Factor ratings generally fall
between 0.20 and 1.20. The lower the U-Factor, the better
a product is at keeping heat in. U-Factor is particularly
important during the winter heating season. This label
displays U-Factor in U.S. units. Labels on products sold in
markets outside the United States may display U-Factor in
metric units.

Definition of Insulation R-Values or Building R-Values: Rate of Heat Loss Per Hour for a Building

How to Calculate the R value U value & K value for a Building & How to Use These Numbers

If you like, read below this section to see our details about "K" values, "U" values, and "R" values as measures of heat movement in buildings. Actually calculating a building's actual rate of heat loss is pretty simple - it's a "cookbook" process that uses the
following formula:
Also see HEAT LOSS in BUILDINGS

Heat Loss using "R" values:

(Building Heat Loss in BTU's per hour) =

(Building Total Surface Area in sq.ft.) / (Surface Area "R" value) x (Temperature Difference)

Temperature Difference = the difference in temperature in deg F. on the two sides of the building surface, typically indoors and outdoors

Surface Area "R" value = the "R" value of the surface area being evaluated (say an insulated wall).

Heat Loss using "U" values:
(Building Heat Loss in BTU's per hour) U = 1/R, - or in other words -

(Building Total Surface Area in sq.ft.) / (Surface Area "U" value) x (Temperature Difference)

More considerations when measuring home energy use or heat loss

But there's more work to do for a complete answer to building heat loss. We need to make up a simple table which will contain
the total surface area of each type of material (since each will have it's own "R" value) and then plug in the area's "R" value
and the temperature difference. Usually we assume the same temperature difference for all of the areas of the building though this might
be a simplification since that may not be exactly true.

How to include the effect of wind on home energy use or heat loss

We're also missing, from this simple calculation, the effects of wind on a building's heat loss, though a more sophisticated version of this approach might simply adjust the temperature difference to include
the wind factor.

For example, you could use a wind/temperature chart to derive the effective outdoor temperature when it's also windy.
In cold conditions, adding a wind velocity will lower the effective outdoor temperature and thus it will increase the temperature difference across the building wall.

Use any "wind chill factor" chart for this data. Still more sophistication
of measures of heat loss are possible by adding the effects of moisture on heat loss from a surface, but while this is important
for a (sweaty) human in cold conditions it is generally ignored when considering building heat loss.

Using a spreadsheet to accurately calculate building heat loss or heat gain

This is a perfect application for an Excel or similar spread sheet, listing each building surface type (wall, window, door),
it's R, K, or U value, and its total area. Adding temperature difference across these surfaces permits a calculation of the
heat loss (or gain) through each surface type. These are simply added together to represent the entire building's heat loss or gain.

Heat loss vs. heat gain in buildings: applying the simple laws of thermodynamics

You may have noticed we keep talking about heat loss and then we add "or heat gain" in the same sentences or headings.
That's because heat loss analysis works just fine for both building heating and building cooling. The only differences
between looking at heat loss and heat gain for a building are the direction of heat flow and the fact that we may
be using different equipment with different equipment efficiencies (a heating furnace or boiler versus an air conditioner).

If we're in a heating climate and are in the heating season, heat will flow from the building interior to the outdoors.

If we're in a cooling climate and are in the cooling season, heat will flow from the outdoors to the building interior. Just remember that (according to the
laws of thermodynamics), heat (or energy) always flows from the warmer (or more exited state) into the cooler (or less excited state) area of a building.

Definition of the K value or K-coefficient of heat transmission

A building's K value or K-coefficient of heat transmission is one way to express the heat loss in a building.
"K" is defined as the number of BTU's of heat moving through any material with these details:

Per square foot of area of the material

Per degree Fahrenheit of temperature difference

Per inch of thickness of the material

So "K" takes a lot of variables into consideration and gives us the rate of heat loss per square foot of building surface, per inch of thickness
of material in that building surface, per degree of temperature difference in Fahrenheit, in BTUs per hour.

By "degree of temperature difference in Fahrenheit" we mean that we are taking into consideration the difference in temperature
on the two sides of our building surface. For example, if the indoor temperature in a building is 68 deg. F. and the outdoor temperature is 48 deg. F., then we have a 20 degree temperature difference on the two sides of the building (wall or roof for example).

This temperature difference on the two sides of a surface, say an insulated building wall, for example, is very important in understanding
how a building loses heat (in the heating season) or gains heat (in the cooling season). That's because the rate of heat transfer through a material
increases exponentially as a function of the temperature difference. This is intuitively obvious and is confirmed by physicists.

For example, if
the temperatures on either side of a building wall were the same, there would be no heat loss or gain through the building wall.
As the temperature difference on either side of that same wall increases, say from one degree of difference to 20 degrees
of difference the rate of heat transfer increases.

An interesting version of this heat transfer theory was shared with the author in a class on how to minimize building heating costs when the instructor
told us that "the thermal conductivity of finned copper heating baseboard is exponentially greater at higher temperatures".

He was saying that if we
ran heating water from our heating boiler through the baseboards at 200 deg.F. we would see much more efficient heat transfer from the heating baseboards
into the building. There are other factors involved in heating system efficiency such as the length of boiler on cycle (longer is more
efficient), so there was more to think about, but the instructor was applying classic heat transfer theory that is reflected in the "K" values
of building insulation as we've discussed here.

Definition of U value or U-coefficient of heat loss resistance

U-value measures the ability to transfer heat, an inverse condition, to heat movement resistance, or in other words, or U-value measures the ability of a substance to allow the transfer of heat

The NFRC (National Fenestration Council) in discussing solar heat gain at windows, describes the U-Factor (U) as follows:

U-Factor measures how well a product prevents heat from
escaping a home or building. U-Factor ratings generally fall
between 0.20 and 1.20. The lower the U-Factor, the better
a product is at keeping heat in. U-Factor is particularly
important during the winter heating season. This label
displays U-Factor in U.S. units. Labels on products sold in
markets outside the United States may display U-Factor in
metric units.

Computing "K" values (discussed above) tells us the heat loss rate for a specific material, thickness, area, and temperature difference but while
we need to be able to calculate "K" values, those alone don't tell us what's going on in an actual building. We need to be able to combine all of the rates of heat loss (or gain) across all of the types of surfaces, insulation, and building material for the
whole building - at least for all of its external or perimeter surfaces including roofs, walls, and floors as well as windows and doors.
That's where the "U" value makes its appearance.

A building's "U" value or U-coefficient of resistance of heat loss is a related measure of resistance
to thermal energy or heat flow out of a building (if it's warmer inside than outside) or conversely
the same concept works in a warm climate where air conditioning is in use, except that we expect outside heat to be flowing into the building.

A building's "U" value is much more complete, and therefore useful than "K" values alone because
a building's "U" value combines the "K" factors for all of the building's surfaces and
materials. In other words, we add the effects of heat loss (or gain), still expressed in the
number of BTU's per hour per square foot of area, and still expressed per degree of Fahrenheit of temperature
difference and still expressed per inch of thickness of material (just as with "K" values), for
all of the substantial areas and surfaces of the exterior of a building's floors, walls, windows, doors,
ceilings, or roofs (if cathedral ceilings are present).

To calculate the "U" value, or overall heat loss (or gain if we're air conditioning) for a building, we need to
add the "R" values for each material in the structure, and to factor in the total area of each material in the structure.
We discuss this procedure in more detail below at "Calculating Heat Loss for a Building".

Seasonal Energy Efficiency Ratio (SEER): This is a measure of equipment energy efficiency over the cooling season. It represents the total cooling of a central air conditioner or heat pump (in Btu) during the normal cooling season as compared to the total electric energy input (in watt-hours) consumed during the same period. SEER is based on tests performed in accordance with ARI 210/240.48

Definition of Design Temperature for buildings and Building Insulation?

The "indoor design temperature" for a building refers to the assumed target indoor temperature that the building owner or occupants
want. Typically 70 deg.F. is used unless the owner specifies something different.

The "outdoor design temperature" for a building is (for heating purposes) assumed to be the average lowest recorded temperature
for each month between October and March (the heating season in most climates). If we are specifying a "design temperature" for
cooling climates we'd use the average outdoor highest recorded temperature during the heating season, perhaps April through September.

Watch out when calculating building or room heating needs. In a recent review of the number of linear feet of heating baseboard needed for a New York building addition we tried out an excellent heat loss analysis program provided by SlantFin. The program considers most of the key variables you'd want examined for an accurate and reliable heating design. But we found that our building had properties not considered by the heat loss software, including

The specific R-value of the insulation we used in a cathedral ceiling and in a floor as well as in 2x6-framed walls

The effects of the surprise by our plumber who installed 1/2-inch diameter heating supply and return piping instead of the 3/4" diameter pipes we anticipated, and his assumption that the flow rate was 1 gph through the system would be OK instead of the design point of 4 gph.

A designed variation in placement of windows to provide more solar gain on South and West walls and less glazing (and heat loss) through the building's North wall

Effects of using an insulation method and other building design features that minimized air leaks (foam insulation, and detailing around window and door openings, for example)

Fortunately simpler rules of thumb analysis by consultants at our heating equipment and parts supplier indicated that the modified design would adequately heat the space.

Definition of Heating Degree Day or Cooling Degree Day

Some building insulation designers and architects look at the number of "degree days" as an easy way to get at the average outdoor
temperatures for an area and a season. A Degree Day is the daily average number of degrees Fahrenheit that the outdoor temperature is below 65 deg.F.

The number of "degree days" during a heating season is easy to obtain: call your local oil delivery company or utility company. These energy
providers keep close tabs on degree days for their area since this number is used in planning for the automatic delivery of energy. It's the
number of "degree days" that have occurred in a given period, combined with a building's historic rate of heating oil use, for example, that
tells an oil company when to schedule that building for an automatic delivery of heating oil.

Definition of Tons of Cooling Capacity

"One ton" of cooling capacity, historically, referred to the cooling capacity of a ton of ice.
Re-stated we can define one ton of cooling capacity as the amount of heat energy absorbed in the melting of one ton of ice over a 24-hour period.

One ton of cooling capacity is the same as 12,000 BTU's per hour of cooling capacity or 288,000 BTUs of cooling capacity provided over a period of 24 hours (12,000 x 24 hours = 288,000).

What is the Relationship of Cooling Capacity and Dehumidification?

Tons of ice does not, however, explain an important factor in the comfort produced by air conditioning systems, reduction of indoor humidity -
that is, removing water from indoor air. Cool air holds less water (in the form of water molecules or gaseous form of H2O) than warm air.

Think of the warmer air as having more space between the gas molecules for the water molecules to remain suspended.
When we cool the air, we in effect are squeezing the water molecules out of the air.
When an air conditioner blows warm humid building air across an evaporator coil in the air handler unit, it is not only cooling the air,
it is removing water from that air. Both of these effects, cooler air and drier air, increase the comfort for building occupants.
One ton of cooling capacity equals 12,000 BTU's/hour of cooling capacity.

How do we measure cooling or heating efficiency: the relationship between BTUs and cooling or heating operating cost?

Note that the BTU rating of an air conditioner itself does not tell you how economically those tons of cooling capacity are being produced. For the answer to that question
see SEER RATINGS & OTHER DEFINITIONS for air conditioners and heat pumps.

Air Conditioning, Refrigeration, & Heating System Standard Definitions

What is a Watt Hour or Wh?

What's a WattHour? Watt hours (Wh), sometimes written W.h, can measure either electrical energy produced, say by a power station, or Watts
can measure the amount of electrical energy consumed (say at a light bulb or an air conditioner in our home).
For air conditioners, the A/C units' total Wh is the energy used in running the air conditioning
system for an hour.

How do we calculate watts, volts, and amperage for an electrical device like an air conditioner?

Watts (W) as used in a simplified manner here and by electricians, is a measure of electrical power and is expressed by any of the formulas shown below. [All forms of power are measured in units of Watts, W, but this unit is generally reserved for real power (see definitions further below.]

DC circuits: W = V x I (this is a simplified formula and is technically exactly correct for DC circuits. For AC circuits,

V*I=VA not watts. In an AC circuit, things are more complicated. An electrical load in an AC circuit will typically use both real power - P - and reactive power - Q - (definitions below).

AC circuits: Watts W=V*I*PF where PF = power factor

Also see AMPS & VOLTS DETERMINATION "How to estimate the electrical service ampacity and voltage entering a building".

Reader Daniel Mann adds that "Watts is correctly shown as Watts-Voltage times Current times power factor. Since power factor varies all over the place,..." [W = V x I] "perpetuates misinformation". We include additional more technical explanation of power factor, real power, apparent power, complex power, and reactive power as we elaborate
at DEFINITIONS of ELECTRICAL TERMS.

Lots of electrical appliances include a label providing the appliance's wattage, and in the case of heating and air conditioning equipment, lots of other details are provided too.
See A/C DATA TAGS for details.

Definition of BTUs & BTUH

A BTU is a measure of heat energy, or the amount of heat given off when a unit of fuel is consumed. One BTU is the amount of heat energy we need to raise the temperature
of one pound of water by one degree Fahrenheit. One BTU also is defined as 252 heat calories (this is not the
same as food calories).

When talking about air conditioners or heaters, we talk about the A/C unit's
BTUh capacity - the number of BTUs of cooling (lowering rather than
raising temperature) it can produce in an hour of running.

When we are heating a building BTUs describe heat given off by consuming fuel or energy from some source (electricity, natural gas, LP gas, oil, etc.) of which some portion is delivered to the building occupied space (see AFUE and HSPF).

When we are cooling a building, or when we are describing an air conditioner or heat pump's rated capacity (in BTUs), we are describing the removal of a quantity of heat from the building - or really from the building's air.

Complete details about the definition of BTUs and BTUH, and examples of uses & calculations using BTU numbers can be found at Definition of BTUs and Definition of BTUH

BTUH: Based on the definition of BTUs above, BTUH describes the number of BTUs of energy produced (as heat) or removed (by air conditioning) in one hour.

Latent heat is defined as the amount of heat absorbed by a substance with no change in a temperature - such as when a substance changes state (from water to steam, for example)

In other words, heat that is absorbed by a substance with no change in temperature is latent heat. For example when a substance changes state (liquid to gas) latent heat is involved.

Definition of Superheat: The latent heat of vaporization is defined as the number of BTUs to raise one pound of liquid to a pound of vapor (to a varying degree per BTU depending on the type of vapor - this is "superheat"). Our Sketch explaining latent heat of vaporization shown at left is provided courtesy of Carson Dunlop Associates.

The latent heat of condensation is defined as the number of BTUs necessary to change a state back from a vapor to a liquid

The latent heat of solidificationis defined as the amount of energy (or number of BTUs) needed to change a liquid to a solid (such as water to ice) while the temperature remains unchanged (at sea level, 32 °F).

Sensible heat is defined as the amount of heat that we can sense or feel or measure.

When an air conditioner system is working, the larger diameter tubing on the low-side of the system combined with the effects of the refrigerant metering device (cap tube or thermostatic expansion valve) results in a reduced pressure on the low side (compared with high side pressure). The reduced pressure causes vaporization of the liquid refrigerant inside the cooling coil, which in turn means that sensible heat is absorbed by the cooling coil.

When the same air conditioner system is working, the smaller diameter tubing on the high side reduces available volume so that (along with the effect of the compressor itself) we increase the pressure and temperature of the refrigerant so that sensible heat can be transferred to ambient outdoor air.

Specific heatis defined as the amount of heat required to raise the temperature of a given substance by one unit of temperature (in our examples by one °F.) Specific heat is also defined as the amount of heat (in calories) to increase the temperature of one gram of a substance by one deg C (Celsius).

The specific heat of water is defined as a constant and = 1

The specific heat of ice is is 5

A definition of one BTU is the energy required to raise one pound of water by one degree F (sensible heat).

In which direction does heat flow: heat energy always flows from the warmer substance to the cooler substance, down to -460 °F where all molecular movement stops.

A neat fact is that the heat flows more rapidly (efficiently) between two substances when there is a greater temperature difference between them. That's why the thermal conductivity of finned copper tubing heating baseboard is exponentially greater at higher degrees of heating water temperature, and that's why we like to run our heating boiler at a higher rather than a lower upper limit temperature.

Note: Outside of the U.S. and some other places, BTUs is being replaced with the SI unit of energy, the Joule. (J).
The English have beaten out the Scots by James Prescott Joule who defined this value. since there are 3600 seconds in an hour) the following formulas equating Watts, Joules, and Newton meters can be written:

1 Watt second (Ws) = 1 joule (J) = 1 newton meter
1 Watt hour (Wh) = 3600 Joules

1 kilowatt hour = 3.6 x 10^{6} Joules, since there are 1000 watts in a kilowatt.

We can think of an air conditioner's "efficiency" as expressed either in the total operating cost for a season of use,
or you may prefer to just express the air conditioner's efficiency as its operating cost to run
the system for one hour.

The equation shown at page top is designed to reduce all of the parameters describing air conditioning efficiency to a
single efficiency number, SEER. SEER numbers are useful when we're comparing one air conditioner with another.
But suppose we want to know the actual air conditioning cost per season, or air conditioning cost
per operating hour to operate our air conditioner?

To translate our air conditioners SEER rating into actual air conditioning operating costs we need to know:

How do We Translate BTUs to Tons of Air Conditioning or Cooling Capacity?

One ton of air conditioning capacity produces the same cooling ability as melting one ton of ice in 24 hours. Sketch courtesy of Carson Dunlop Associates.

288,000 BTUs / 24 hours = 1 Ton of cooling

12,000 BTUs / hour = a 1-ton air conditioning system

[Click to enlarge any image]

A one-ton air conditioner claims to remove 12,000 BTUs of heat from the building air per hour of operation.

Or if we know the total number of BTUs at which an air conditioning system is rated, since this number is usually given in BTUH or BTUs / hour, we just divide that number by 12,000 to get the number of tons of cooling capacity.

A 36,000 BTUh air conditioner is providing 36,000 / 12,000 or 3 Tons of cooling capability per hour.

If we know the number of tons of cooling capacity that an air conditioning system is rated for, we just multiply the number of air conditioning capacity in Tons by 12,000 to get the number of BTUs of cooling capacity of the system.

A 3-ton air conditioner is providing 3 x 12,0000 or 36,000 BTUs of cooling capability per hour.

To assist in choosing the right sized air conditioner, we provide a typical air conditioner chart
at AIR CONDITIONER BTU CHART.

Watch out: more is not always better. Don't buy an air conditioner that is too big: if you install a system that is too powerful (too many tons of cooling capacity) the building will be less comfortable than if you install a properly-sized air conditioner. Too many tons of air conditioning mean the system will shut off on short cycles and won't run long enough to reduce the indoor humidity to a comfortable level. Details are
at DEHUMIDIFICATION PROBLEMS

How Much Electricity Does An Air Conditioner Use Per Hour?

How much electricity our air conditioner uses
per hour is easy to calculate.
Let's assume that the data tag on our air conditioner
says that the unit is a 5000 BTUh device with a SEER rating of 10. This means our A/C unit will produce
5000 BTUs of cooling in an hour of running. Since SEER=10 means that 10 BTUs used per Wh, then

5000 BTUh / 10 SEER = 500 Watts per hour that our A/C unit will use.

How Much Electricity Does An Air Conditioner Use in one Cooling Season?

A common example we use (because the math is easy) is to assume we have 125 days of cooling
season during which we run the air conditioner for eight hours per day.

8 x 125 = 1000 hours of cooling operation over a season

500 Wh (watts used per hour) x 1000 (hours per season) = 500,000 Wh per season

So we are using 500,000 Watt Hours of energy (electricity) per cooling season. We
divide this by 1000 to convert to Kilowatts since that's how our electrical bill will
express our electricity usage.

500,000 Wh / 1000 = 500 kWh or kilowatt hours per season of use
That's how much electricity we're using over the cooling season.

What is the Definition of High Side and Low Side in Air Condition & Refrigeration Systems?

Definition of Low Side in an Air Conditioning System refers to the components on the low-temperature and low-pressure side of the compressor unit. In an air conditioner, the low side includes the suction or intake side of the compressor unit, suction piping connected to the evaporator coil, the evaporator or cooling coil, and the output-end of the metering device or TEV.

Definition of High Side in an Air Conditioning System refers to the components on the high-temperature (above ambient air temperature) and high pressure side of the compressor unit. In an air conditioner in cooling mode these include the output or high pressure side of the compressor unit, the high pressure gas refrigerant line connected to the condensing coil, the condensing coil itself, and the inlet side of the metering device located near the evaporator coil.

At OPERATING COST we determine the actual dollar cost of running an air conditioner
either by the hour of by the season of use. It's easy to get from
that data to actual air conditioning operating costs in dollars.

Other Heating & Air Conditioning System Performance Measurements & Standards

Definition of AFUE

The AFUE (Annual Fuel Utilization Efficiency) rating number for heating equipment is a measure of heating system efficiency. AFUE tells you, for each dollar you spend on energy for heating by gas, oil, or another fuel, just how much of your dollar shows up inside the occupied space of your building as heat.

See AFUE DEFINITION, RATINGS for more details and for current required AFUE percentages for U.S. & Canadian heating equipment.

Definition of Heating Seasonal Performance Factor - HSPF

HSPF is a heating performance measurement used to evaluate the efficiency of heat pumps when in heating mode. Higher HSPF numbers mean greater heating efficiency. Currently heat pumps in the U.S. should have an HSPF of 6.8 or higher.

Definition of Watt & Watt Hour: What is a Watt Hour or Wh?

What's a WattHour? Watt hours (Wh), sometimes written W.h, can measure either electrical energy produced, say by a power station, or Watts
can measure the amount of electrical energy consumed (say at a light bulb or an air conditioner in our home).
For air conditioners, the A/C units' total Wh is the energy used in running the air conditioning
system for an hour.

How do we calculate watts, volts, and amperage for an electrical device like an air conditioner?

Watts (W) as used in a simplified manner here and by electricians, is a measure of electrical power and is expressed by any of the formulas shown below. [All forms of power are measured in units of Watts, W, but this unit is generally reserved for real power (see definitions further below.]

DC circuits: W = V x I (this is a simplified formula and is technically exactly correct for DC circuits. For AC circuits,

V*I=VA not watts. In an AC circuit, things are more complicated. An electrical load in an AC circuit will typically use both real power - P - and reactive power - Q - (definitions below).

AC circuits: Watts W=V*I*PF where PF = power factor

Also see AMPS & VOLTS DETERMINATION "How to estimate the electrical service ampacity and voltage entering a building".

Reader Daniel Mann adds that "Watts is correctly shown as Watts-Voltage times Current times power factor. Since power factor varies all over the place,..." [W = V x I] "perpetuates misinformation". We include additional more technical explanation of power factor, real power, apparent power, complex power, and reactive power as we elaborate
at DEFINITIONS of ELECTRICAL TERMS.

Lots of electrical appliances include a label providing the appliance's wattage, and in the case of heating and air conditioning equipment, lots of other details are provided too.
See A/C DATA TAGS for details.

Because no amount of insulation can keep a drafty building warm, also review ENERGY SAVINGS PRIORITIES.

Continue reading at AFUE, DEFINITION or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

FAQs below discusses field reports of problems & solutions for this topic

...

Frequently Asked Questions (FAQs)

Question: What does 20 Amps mean?

What does 20 amps actually mean - Mary Riccio

Reply: ... it depends.
Amps is a measure of electrical current that we elaborate here:

In a residential electrical circuit, a 20-amp rated circuit means that the electrical wire and it's overcurrent protection (fuse or circuit breaker) are rated for a total load or total current draw of 20 amps. The sum of all of the electrical current drawn by everything connected to that circuit must be 20-Amps or less - else the circuit breaker will trip or fuse will blow to prevent overheating of the wire (and a fire hazard).

The definition of AMPS or ampacity and other electrical terms can be found at InspectAPedia either by using the search box found at the top and bottom of our pages, or by clicking on this link
to DEFINITIONS of ELECTRICAL TERMS.

Amperage or Amps provided by an electrical service is the flow rate of "electrical current" that is available. Mathematically, Amps = Watts / Volts. (Amps = Watts divided by Volts)

Speaking practically, the voltage level provided by an electrical service, combined with the ampacity rating of the service panel determine how much electrical demand, or in another sense how many electrical devices can be run at one time in the building.

Depending on what you are looking at, 20-Amps may be the rating of a particular piece of equipment. For example a 20-Amp circuit breaker means that that safety device will limit to 20 Amps the current drawn on the circuit that it is protecting. If you plug three 10-amp electric heaters into that circuit and they all are running simultaneously, their combined current draw (3 x 10 = 30Amps) should trip the circuit breaker and turn off the circuit to protect it from overheating and a possible fire.

...

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Thanks to reader Peter J. Collins for discussing and helping clarify definitions of R U and K - August 2010

Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com 11/06

Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.

Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

Asbestos: How to find and recognize asbestos in Buildings - visual inspection methods, list of common asbestos-containing materials

Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).

Asbestos Identification and Testing References

Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.

Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151

Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone

ASHRAE resources on building insulation, dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:

2005 ASHRAE Handbook : Fundamentals: Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707

2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."

1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."

Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929

Construction Waterproofing Handbook, Michael T. Kubal. Quoting:
... an all-inclusive, project-simplifying guide for waterproofing and construction professionals. This comprehensive answer-packed resource is loaded with the up-to-date, clearly-defined information you need on every project, including work on the building envelope, below-grade, above-grade, and remedial waterproofing.

Brick Nogging, Historical Investigation and Contemporary Repair, Construction Specifier, April 2006. Historical use of brick in timber-framed buildings, drawing on the investigations of the Kent Tavern in Calais, VT.
"Brick nogging is a European method of construction which was brought to the new world in the early-nineteenth century. It was a common construction method that employed masonry as infill between the vertical uprights of wood framing." -- quoting the web article review.

Dust from the World Trade Center collapse following the 9/11/01 attack: the lower floors of this building contained spray-on fire-proofing asbestos materials.

"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print

"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870

"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy

"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy

"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900

"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy

"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy

Fiberglass: Indoor Air Quality Investigations: Health Concerns About Airborne Fiberglass: Fiberglass in Indoor Air from HVAC ducts, and Building Insulation

Insulate & Weatherize (Taunton's Build Like a Pro), Bruce Harley. Review quoted:
An engineer who trains builders in energy-efficient construction, Harley offers a wealth of information that will allow readers to improve their home's efficiency, saving both money and natural resources. After an introductory section that explains the underlying principles of heat transfer, insulation, and air quality, Harley demonstrates basics such as weather-stripping and moves forward through advanced projects including insulation and major upgrades. Short "Pro Tips" as well as sections labeled "Trade Secrets," "What Can Go Wrong," and "In Detail" provide a great deal of helpful information. Increasing energy efficiency is one of the easiest ways for homeowners to save money

Insulation: Selecting Insulation for New Home Construction, U.S. Department of Energy - "Your state and local building codes probably include minimum insulation requirements, but to build an energy-efficient home, you may need or want to exceed them. For maximum energy efficiency, you should also consider the interaction between the insulation and other building components. This is called the whole-house systems design approach."

Insulation Types, table of common building insulation properties from U.S. DOE. Readers should see INSULATION R-VALUES & PROPERTIES our own table of insulation properties that includes links to articles describing each insulation material in more detail.

The National Institute of Standards and Technology, NIST (nee National Bureau of Standards NBS) is a US government agency - see www.nist.gov

"A Parametric Study of Wall Moisture Contents Using a Revised Variable Indoor Relative Humidity Version of the "Moist" Transient Heat and Moisture Transfer Model [copy on file as/interiors/MOIST_Model_NIST_b95074.pdf ] - ", George Tsongas, Doug Burch, Carolyn Roos, Malcom Cunningham; this paper describes software and the prediction of wall moisture contents. - PDF Document from NIS

Piquet Wall Construction: See this photo of
piquet wall construction - involving timber-framed wall construction with long top girts, diagonal timber bracing, and small diameter logs
placed vertically along with concrete chinking to fill in the wall plane.

Plank House Construction: weblog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
06/12/2007 documented at yurokplankhouse.com where scale model Museum quality Yurok Plank Houses are being sold to raise money for the Blue Creek - Ah Pah Traditional Yurok Village project.

Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 ASHRAE Handbook - Fundamentals, Harry J., Jr. Sauer, Ronald H. Howell, William J. Coad. Quoting
... textbook for college level HVAC courses or independent study and review, especially when combined with the 1997 ASHRAE Fundamentals Handbook. Contains the most current ASHRAE procedures and definitive, yet easy to understand, treatment of building HVAC systems -- from basic principles through design and operation. Dual units of measurement.

Re-Bath, tub lining products is a bath tub relining manufacturer and distributor located in Tempe, Arizona - see rebath.com

Rubblestone Wall Filler: See this Lartigue House using exterior-exposed rubblestone filler between vertical timbers of a post and beam-framed Canadian building.

Understanding Ventilation: How to Design, Select, and Install Residential Ventilation Systems, John Bower, Quoting:
Understanding Ventilation is the only book that covers all aspects of exchanging the air in houses: infiltration, equipment selection, design, heat-recovery ventilators, sizing, costs, controls, whole-house filters, distribution, and possible problems that a ventilation system can cause--all in easy-to-understand language.

"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE

Weaver: Beaver Board and Upson Board:
Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver,
APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.

...

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.

The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.

TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.

Special Offer: For a 10% discount on any number of copies of the Home Referen
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Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones.

Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones

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