Steps to Getting More Hot Water Pressure, Temperature & Quantity from your Water Heater InspectAPedia® -
How much hot water do we get out of a hot water heater tank?
How to improve hot water water quantity and hot water pressure
How to use extra water storage tanks to pre-heat hot water or to increase hot water quantity
High efficiency water heater suggestions for saving on water heating cost
Guide to adding insulation to hot water piping & insulating water heater tanks
How to use larger diameter supply piping to increase hot water quantity and flow at plumbing fixtures
Questions & answers about how to improve hot water pressure, temperature, flow, & quantity from a residential hot water heating system
This article explains how much hot water to expect from your water heater, and how to improve the hot water pressure, quantity, flow, and water temperature safety in a building.
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We explain how to increase the hot water quantity and flow obtained from a tankless coil as well as other methods of making domestic hot water.
Thanks to Carson Dunlop, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article.
How Much Hot Water Should I Expect to Get Out of My Water Heater Tank?
Question: My 40 gallon hot water tank is not giving me 40 gallons of really hot water. Why?
How much hot water should I expect from my new 50 gallon hot water heater? I'm getting 32 gallons before the next 4 gallon bucket starts cooling and runs cold. - J.
Reply: List of factors that determine how much hot water you get out of a water heater tank
You didn't indicate the type of water heater. If your heater is electric, and if the lower heating element has burned out, the total quantity of hot water from the heater would be significantly reduced. (By contrast if the upper element is burned out the total quantity may not be reduced but the temperature of the hot water will be lower).
Some other factors that determine just how much hot water you get out of a water heater of a given size (that is without changing the size of the water heater tank) are:
The setting of the water heater temperature dial - setting the water heater temperature up increases the heat, allows mixing in more cold (manually or at a tempering valve to avoid scalding), thus giving the effect of more total hot water that can be drawn
The temperature of the incoming water supply that enters the water tank - that is, how cold is the incoming water? Colder incoming water cools down water in the water heater tank. Therefore even if we start with a 50 gallon water heater whose water contents is fully heated, as soon as we start drawing off hot water (someone turns on a hot water faucet) cold water is entering the tank to make up the volume of hot water that was withdrawn. Typically cold water enters the bottom of the tank and hot water leaves at the top of the tank, assuring that the water drawn off is as hot as possible.
Condition of the water heater tank dip tube: Even so, especially at higher water pressures (or if the dip tube in the tank that carries incoming water to the tank bottom has been corroded, become leaky, or fallen off), the cold water entering the water heater can stir up water in the tank, mixing with and cooling down the water inside so that before a full 50 gallons of "hot" water has been drawn off, the outgoing water temperature will be cooler, or even tepid.
Exposure of the hot water pipes to cold temperatures where they pass through the building - losing heat to the building or to outdoors
The flow rate of water through the building piping in gallons per minute (larger diameter pipes, valves fully open, higher water pressure) means that hot water may be run out of the tank "faster" or "slower" - this does not change the total quantity available, just how fast you use it up. So there is a trade off between how long we can run hot water and hot water supply pressure, as we explain at Larger Diameter Water Supply Piping. Also see WATER PRESSURE & FLOW MEASUREMENT.
The recovery rate of the water heater - how fast the water heater can put heat back into water in the tank when the tank temperature drops below the "cut-in" setting on the water heater temperature control. A water heater with a fast recovery rate (such as oil) will put heat into the tank faster than a slow-recovery water heater (such as electric water heaters). A faster recovery rate water heater may be able to deliver a bit more hot water before the outgoing water feels tepid. See Water Heater Recovery Speed Comparisons for details.
How do we Improve the Hot Water Volume & Quantity?
As we discussed beginning in the previous section of this article, there are several different hot water problems:
Poor hot water flow, or bad hot water pressure, which is usually a piping or clogging problem or an overall building water pressure problem. See CLOGGED PIPING & Hot Water Flow and see
Poor hot water quantity: not enough hot water, or running out of hot water very quickly. Insufficient hot water quantity may be due to the way hot water is being made (a water heater that is too small, a tankless coil on a new small heating boiler, or an instantaneous water heater that is being asked to supply hot water too rapidly. We describe various ways to improve hot water quantity, pressure, and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.
Hot water temperature that is not hot enough: water temperature is just too cool. Insufficient hot water temperature may be due simply to the setting of a temperature control on a water heater or mixing valve, or it may be due to flowing water too fast through a tankless coil. Hot water that is not hot enough can be caused by quite a list of problems, some of which are easy to correct. See Temperature of Hot Water is Too Low for steps to correct water that just won't get hot.
Previously we explained how a tankless coil makes domestic hot water, how to get more hot water from a tankless coil, how to avoid scalding, and how to detect clogged hot water piping.
Below we discuss other steps that can be taken to improve hot water quantity. And having a greater quantity of hot water also opens the way to taking steps to improve hot water pressure. (If we increase hot water pressure but lack adequate hot water quantity the result is we run out of hot water faster than ever.)
Articles Describing Steps to Increase Hot Water Quantity
The articles listed below offer more details about steps one can take to increase hot water quantity, pressure, and flow in a building. Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
ANODES & DIP TUBES on WATER HEATERS discusses hot water tank sacrificial anodes and dip tubes whose problems can produce both sulphur smells and even reduced hot water pressure and flow.
Extra Tanks to Increase Hot Water- pre-heat your hot water absorbing ambient building heat or increase hot water quantity with cascaded, staged, multiple water heaters, possibly using more than one energy source
change home appliances and plumbing fixtures to install devices that consume less hot water. For example, replace showerheads that have a flow rate greater than 2.5 gallons per minute (the current National Energy Policy Act standard),
take shorter showers,
when replacing a clothes washer, install models that use less water by installing a high efficiency washing machine with a "low water factor" and always wash full loads rather than smaller loads in your washing machine
Water heater choices: The characteristics of various water heaters such as life expectancy, cost, safety, and capacity are discussed at ALTERNATIVE WATER HEATER PROPERTIES
WATER HEATER SCALE - De-Liming Procedure explains how mineral scale build-up in a water heater (or in building water piping) can result in both poor hot water quantity and Water Heater Scale Prevention explains how to prevent lime and scale formation in water heating equipment
WATER SOFTENERS & CONDITIONERS - how to install and adjust a water softener to avoid hot water piping or tankless coil clogging due to hard water and minerals
Using Extra Tanks to Increase Hot Water Pressure, Flow, and Volume in a Building
As we illustrate with Carson Dunlop's sketch, it is possible to install multiple active water heaters in a parallel design for simple increase in total hot water quantity, or these tanks could have been installed in series, leaving the first or up-stream tank turned off when less hot water need was anticipated.
Leaving a hot water tank turned "off" can still cut water heating costs a bit, as we discuss next.
Passive water pre-warming tank: Use a water tank or hot water tank or old water heater tank installed upstream from water entering the tankless coil (or primary water heating tank, whatever water heating method is used). Remove insulation from the holding or staging tank. Water sitting in this tank will absorb water from the indoor environment and in most locales will be warmer than water coming directly from a well or municipal water supply.
Often people will simply salvage an old water tank and use it for this purpose. By pre-warming water headed for the tankless coil, the coil itself will not have to raise the water temperature as much as otherwise. Thus when the occupants are drawing hot water in the building, heat will be drawn out of the heating boiler at the coil at a slower rate - you'll have more domestic hot water.
Active water pre-heating tank: install a water heater (oil, gas, solar, electric) on the water piping upstream, that is, before water enters the tankless coil (or primary water heating tank, whatever water heating method is used).
This water tank can be left off when there is not much demand for hot water, in which case it will function as a passive water pre-warming tank as we discussed above. When a greater quantity of hot water is going to be needed (say many weekend visitors to a building), turn on the water heater to permit it to "boost" hot water headed for the tankless coil.
As occupants in the building draw hot water out of the system, heat will be drawn from the heating boiler and tankless coil at a very low rate, possibly not at all, until we've exhausted the hot water that was stored in the separate water heater tank.
Some people install this system backwards: hot water is fed from the tankless coil into a water heater tank. This is a much less efficient way to make hot water as all of the water entering the water heater tank will always cause the heating boiler to run. We do not recommend this arrangement.
Be sure that the hot water supply piping in the building has been insulated throughout its run.
In our photo at left our client is pointing out that foam insulation applied over the hot water pipe leaving the water heater was placed too close to the water heater draft hood. Spillage at the draft hood was melting the water pipe insulation - indicating an unsafe flue gas spillage problem.
The length of hot water supply pipe running between the building hot water source and the building faucet or fixture where hot water is being delivered will affect the temperature of water received there.
A long run of un-insulated hot water pipe will deliver cooler water than a well-insulated water supply pipe of any length.
The reason that insulation on hot water piping increases the total hot water quantity (and temperature) is that the hot water is not giving up so much of its heat in the form of radiant losses during movement of hot water from the water tank to the destination plumbing fixture.
The foam insulation on hot water lines (or hot water heating pipes) in our photo at left is readily available at building supply stores.
This foam pipe insulation is purchased according to the diameter of the pipe it is going to cover. In residential applications that's usually 1/2" pipe or 3/4" copper or galvanized steel pipe. The insulation is split so that it can be simply pushed onto the pipe that is to be insulated.
We insulate hot water piping to minimize heat loss between the heater and the point of use.
We also like to insulate cold water piping in order to reduce condensation and dripping off of the cold water lines during warm humid weather.
Also see our advice and safety warnings about water tank insulation at Insulate Hot Water Tank?.
Install Larger Diameter Water Supply Piping to Improve Hot Water Pressure & Flow
As we discussed at Water pipe clog repair guide, and as we illustrate with Carson Dunlop's sketch shown here, installing larger diameter water supply piping makes a large difference in the water flow rate.
In fact you can improve hot water flow in a building by replacing only part of the supply piping - perhaps that portion which is easily accessible. Installing larger water supply piping feeding the water heater may alone improve the hot water pressure and flow in the building.
But beware: if your hot water is provided by a tankless coil, increasing water pipe diameter may not be of much use.
A tankless coil (and also an instantaneous water heater) is normally rated by its manufacturer as capable of increasing water temperature to a desired level only if water flow through the coil is limited to a specific rate, perhaps 5 gpm. Flowing water through the tankless coil or instantaneous water heater too fast will mean that the water temperature may be too low at the fixture.
In sum, larger diameter piping increases water pressure and flow. It does not increase the total volume of hot water that is available from a water heater. This improvement may be of most value where water pressure is poor and where water piping has previously become clogged by rust or mineral deposits.
You may regain some of this loss by insulating hot water supply piping or by setting water heater or boiler temperatures higher as well as by an adjustment at the Mixing Valve.
Questions & Answers regarding this article
Questions & answers about how to improve hot water pressure, temperature, flow, & quantity from a residential hot water heating system.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
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 Thanks to reader J. for discussing hot water tank quantity, temperature, and performance - January 2011
AO Smith produces AO Smith water heaters in addition to Reliance, State, Maytag and others.
www.aosmith.com/prod/wpc.htm. AOS's gas water heater manuals offering advice and safety warnings about adding water heater insulation are available at
www.statewaterheaters.com/lit/im/res-Elec/184671-000.pdf and at
www.hotwater.com/lit/im/res_gas/184123-000.pdf
Rheem who also makes electric water heaters provides a manual for electric water heaters at
waterheating.rheem.com/content/resources/documents/use_care/ResElecProfessional.pdf. Rheem says, as do other water heater producers, that their water heaters
meet the "National Appliance Energy Conservation Act
standards with respect to insulation and
standby loss requirements making an
insulation blanket unnecessary"
Rheem also warns consumers that adding an insulation product [or making any other modification to their equipment] is likely to void the product warranty and may be unsafe:
"The manufacturer’s warranty does not
cover any damage or defect caused by
installation, attachment or use of
any type of energy saving or other
unapproved devices (other than those
authorized by the manufacturer) into, onto
or in conjunction with the water heater.
The use of unauthorized energy saving
devices may shorten the life of the water
heater and may endanger life and property.
The manufacturer disclaims any
responsibility for such loss or injury
resulting from the use of such
unauthorized devices "
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.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
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