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How to Calculate Building Heat Loss Rate, Insulation Values & Heating Efficiency
- HEAT LOSS R U & K VALUE CALCULATION - How to calculate the rate of heat loss (or gain) in a building through insulation, walls, etc.
- 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?
- Questions & Answers about how to calculate building heat loss rate, R-values, Insulation Values, Heating Efficiency
- References
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How to calculate building heat loss rates R, U and K. This article gives details and formulas for calculating R-values, U-values U-coefficient of heat loss resistance, and K-values, all ways of looking at insulation values or building heat loss rates. Our page top photo of above-ground building perimeter & foundation insulation using styrofoam board was observed at a home Maine - Ed.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Definition of & How to Calculate the R value or R-coefficient of Resistance to Heat Loss in a Building or its Insulation
 The "R" value of a material is defined as the material's resistance to heat flow through the material. For purposes of insulation, you might think of "R" value as the opposite of thermal conductance, since it's described as thermal resistance or resistance to heat flow. And you'd be correct. If thermal resistance to heat flow is "resistance" we can say that the thermal conductivity of a material is equal to the reciprocal of its thermal resistance.
More practically, by convention we use thermal resistance or R-value 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. [Assuming all other fadctors like air leakage are either equal or have been factored into the R-value calculation.]
Mathematically, but in painfully circular reasoning, "R-value" is simply the reciprocal of the two measures of resistance to heat flow "K-value" (R = 1/K) or "U-value" (R(whole building) = 1/U) that we define further below.
What do U and K values have to do with R-values?
As you'll read below "K" measures the heat flow through an individual substance and "U" as most folks use it measures the overall building heat loss by adding all of the
various areas and substances together. U-values measure the thermal transmittance of heat in or out of a building and combines heat movement by all principles that are occurring at a building: radiation, convection, and conduction. So you can see that "U" values are more complex but really more complete than "R" values.
Escaping the Circular Reasoning of R=1/K
We can escape the horrible circular reasoning that appears in some writing about heat loss measurements if any one of the three values, R, U, K is defined independently. We'll take a stab at this just below.
The R-value of a material is typically expressed as R [resistance to heat flow] per inch of material thickness. More technically, "R-value" is measured in mete Watt [metric system] or h/Btu [U.S. measurement system].
Materials may be rated in R per inch or R per meter or similar measures.
Here are Some Basic Formulas for Calculating R-Values
R-value = temperature difference [in degF] x area [sq ft] x time [in hours] / heat loss[in BTUs]
Calculating R-Value [U.S. metrics]
R = (Heat Resistance x Degrees F x square feet) / BTUs
or stated in metric: (R-value) = t/k, measured in [editing needed]
Definition of & How to Calculate the U value or U-coefficient of heat loss resistance
Computing "K" values 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".
U-value = BTUs / (hours x Degrees F x Square Feet)
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".
Formulas Used to Calculate the Rate of Building Heat Loss Per Hour for a Building Using it's "R" Values or "U" Values
Formulas and an explanation of how we use R U or K values to determine the rate of heat loss at a building (or heat gain if we are cooling it) are at HEAT LOSS in BUILDINGS or within that articler at section Formulas to Calculate the Rate of Heat Loss Per Hour for a Building Using it's "R" Values or "U" Values.
Definition of & How to Calculate 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.
Computing "K" values 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.
Sorting out the Definitions of U.S. k-values, lambda or λ values, and European k-values
Note: In the U.S. k-value when discussing the heat loss resistance of window glazing is equivalent to lamda λ value in Europe, and in case that's not confusing enough, an older European k-value (the total insulation value of a building) is currently referred to in Euripe as U-value. You'll recall from our notes above that U-value is a reciprocal or 1/R-value. - Wikipedia web search 03/11/2011 see "Thermal Conducitivity".
To convert U.S. R-values to European U-values:
[ (1 / R-value USA) x 0.176 ] / 1 = U Europe
and
U Europe = [watts / kelvin x meters2]
Related Building Heat Loss Articles
Beginning at HEAT LOSS in BUILDINGS article series explains how to insulate a building and how much insulation is needed 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
Also see HEAT LOSS INDICATORS (where is the building losing heat during the heating season, or gaining un-wanted heat during the cooling season),see HEAT LOSS DETECTION TOOLS for both tools and procedures, and see HEAT LOSS R U & K VALUE CALCULATION for a guide to calculating heat loss (or gain) rates for buildings and building insulation. At INSULATION R-Values & Properties we give a detailed table of insulating material R-values & properties.
Be sure to review the definitions of R, U, & K Values at Definition of Heating & Cooling Terms. Because no amount of insulation can keep a drafty building warm, also review ENERGY SAVINGS PRIORITIES. Also see our detailed table of Insulation R-Values & Properties and our list of building HEAT LOSS INDICATORS (where is the building losing heat during the heating season, or gaining un-wanted heat during the cooling season).
Formula-R™ and Owens Corning™ which may be visible in this photograph of pink Styrofoam™ insulation boards are registered trademarks of Owens Corning® and were photographed at a Home Depot® building supply center.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Thanks to Sanjiv Malkan for correcting our formula for R-values 3/22/2009.
- Thanks to Steven Muscato for correcting our formula for U-Values 7/31/2009
- Asbestos pipe insulation in buildings
- Brick "Insulation" in Building Walls
- HEAT LOSS CALCULATIONS, Insulation Properties, Definitions of R, K, U values, Insulation Design
- How to Choose an Air Conditioner - BTU Chart
- How to Detect and Correct Attic Condensation & Prevent Ice Dam Leaks in buildings
- How to Inspect Building Interiors and Building Insulation/Ventilation list of articles about building insulation inspection, defects, design, and ventilation requirements
- Insulation Materials as Indicators of Building Age
- Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
- Insulation Identification Photographs - Cellulose insulation photos, Mineral wool insulation photos, rock wool insulation photos, cotton insulation photos, balsam wool insulation photos
- Insulation Identification Photographs - Vermiculite insulation photos
- LP or Natural Gas Pressures & BTUH per Cubic Foot
- Insulation Properties, Table of R-Values, density, moisture permeability, fire safety, aging effects on various insulation materials
- Mold in Fiberglass in Insulation
- Radiant Heat Floor Mistakes to Avoid
- Rated Cooling Capacity - How to Determine Air Conditioning Equipment Rated Cooling Capacity
- Un-Vented Roof Solutions - How to Prevent Attic Condensation, Ice Dam Leaks, Roof Mold, & Roof Structural Damage in buildings with Un-vented Roof Cavities
- Vermiculite Building Insulation & Asbestos
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 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 Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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.
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- Asbestos: How to find and recognize asbestos in Buildings - visual inspection methods, list of common asbestos-containing materials
- Asbestos HVAC Ducts and Flues field identification photos and guide
- 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
- 1993 ASHRAE Handbook Fundamentals (Hardcover), ISBN-10: 0910110964 or ISBN-13: 978-091011096
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- 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 used as soundproofing is mentioned in this article on Popular Forest
- 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.
- Photo of very rough in-wall brick nogging at an architects website
- 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
- From the walls in, Charles Wing
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?InspectAPedia Bookstore (Amazon.com)
- 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: Adding Insulation to an Existing Home," U.S. Department of Energy - tips on how to do your own check for the presence of absence of insulation in a home
- 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
- Nogging: See this photo of exposed bricks on a building exterior on a building exterior in Canada. [Thanks to Carson Dunlop, Toronto - see References below].
- 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.
- Super-Insulated Retrofit Book: A Homeowner's Guide to Energy-Efficient Renovation, Robert Argue
- The super-insulated retrofit book: A homeowner's guide to energy-efficient renovation (Sun builders series), Brian Marshall
- 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.
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