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How to Safely Increase Hot Water Temperature your Water Heater
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How to improve hot water water temperature without being scalded and burned
How to stop running out of hot water, How to make hot water hot enough

This article explains how to diagnose & improve the hot water water temperature that is too cool, and how to check water temperature safety in a building.

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This article describes various ways to improve hot water quantity, pressure, and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.

At ALTERNATIVE HOT WATER SOURCES we describe various water heating methods. The detailed characteristics of various water heaters themselves, such as life expectancy, cost, safety, and capacity are discussed at ALTERNATIVE WATER HEATER PROPERTIES

How to Correct Hot Water Temperature that is Too Low

If your hot water temperature is just not ever hot enough here are some things to check:

First Check the Water Heater Temperature Settings

Check the water temperature settings on the water heater control. You can increase the water temperature setting, but beware of scalding. See MIXING / ANTI-SCALD VALVES for a discussion of the installation and use of anti-scald valves to avoid hot water burns, and for a table of temperatures at which hot water burns occur.

The temperature control on the gas fired water heater shown in our photo at left has been set to "Low" and could be turned "up" to a hotter temperature if building hot water is found to be too cool.

Check for long runs of un-insulated hot water piping

Long hot water piping runs can mean not enough or not hot enough hot water, especially if the piping runs through cold walls, basements, crawl spaces, or attics.

If this is the cause of water not being hot enough, the problem will not usually occur suddenly, but it will vary by season, with "hot" water being "cooler" in cold weather.

Even sudden appearance of hot water running cooler could be caused by uninsulated water pipe runs if the water pipes happen to be located in an area normally protected from weather but suddenly left exposed, such as a basement door left open or a mobile home surrounding skirt falling off..

If the water is leaving your water heater at a high temperature but arriving too cool at the sink, shower, or tub, see Insulate Hot Water Piping for details.

Check for a leaky or bad water heater tank dip tube

Schematic of dip tube in a water heater tank (C) Carson Dunlop

(Sketch courtesy Carson Dunlop) at your water heater tank. If your water is heated by an electric, gas, oil, or even solar-heated water tank, the tank probably uses a dip-tube to direct incoming cold water to the bottom of the hot water tank.

If the dip tube is leaking (metal dip tubes are often intended to corrode) it may be leaking incoming cold water into the top of the water heater tank.

Or the dip tube may have corroded away or dissolved completely, or parts of it may have fallen into the water heater tank.

See WATER HEATER DEBRIS FLUSH for an example of a dip tube that dissolved and fell into the water heater interior.

Either of these dip tube problems means that cold water running into the water heater tank is no longer delivered to thte tank bottom. Rather it enters at the heater tank top where it mixes with and cools the "hot" water in the water heater.

Watch out: a bad dip tube or a burned out electric water heater lower heating element both give the symptom of tepid hot water output.

Details about water heater anodes and dip tubes, how they work and why they are needed, are at ANODES & DIP TUBES on WATER HEATERS.

Check for a burned out electric water heater heating element

Sketch of electric water heater parts (C) Carson Dunlop

if your water heater is electric it probably has two heating elements, an upper and a lower unit. It's easy to diagnose a bad electric water heating element, and you can suspect a problem with the heating elements in an electric water heater even before doing any testing: (Sketch courtesy Carson Dunlop)

If the hot water coming out of the electric water heater is hot but runs out more quickly than previously, we suspect that the lower heating element has burned out. The upper water heating element is heating up just the water in the top of the water tank. So you have just a small amount of hot water before you run out.

If the hot water coming out of the electric water heater has become tepid when it used to be hot (and no one has changed any other hot water settings), we suspect that the upper heating element has burned out.

When only the lower heating element in an electric water heater is working, it will warm the water but it will normally be unable to raise the temperature in the whole water tank to a high enough level. So you have plenty of tepid "hot" water.

Watch out: as we described just above, a failed water heater dip tube also causes "hot" water to come out tepid or at a lower temperature than normal.

Check for an oil fired water heater that needs oil burner service & cleaning

Oil fired water heater with backpressure soot stains (C) Daniel Friedman

Oil fired heating equipment, when properly adjusted, does not burn perfectly clean.

Burning heating oil produces soot which over time sticks to the interior surfaces of the water heater's interior. There the soot acts like an insulator, reducing the transfer of heat from the burning heating oil through the metal of the water heater's heat exchanger, into the hot water itself. You may have plenty of water but its temperature is not as hot as it used to be.

Often service people called to clean and tune an oil fired heating boiler do not clean and adjust the oil-fired water heater unless specifically asked (and paid) to do so.

Just as your oil fired furnace or boiler should be serviced annual (for safety and to lower heating costs), so should your oil-fired water heater be cleaned and tuned annually.

It's likely that this service will be earned back easily in reduced heating oil costs. See How To Cut Heating Costs for details.

Check Water Heater Mixing Valve Settings and Aquastat Settings

Aquastat low limit controls hot water minimum temp (C) Daniel Friedman

Check the temperature settings at the mixing valve installed on your water heating system. See MIXING / ANTI-SCALD VALVES for a discussion of the installation and use of anti-scald valves to avoid hot water burns, and for a table of temperatures at which hot water burns occur. At the top of this page we show a photo of a mixing valve on a heating boiler.

Check the temperature settings at the aquastat combination control if your hot water is made by a tankless coil on a heating boiler.

The "low limit" control shown in our photograph at left maintains hot water in the heating boiler to assure that the tankless coil can produce domestic hot water.

During the heating season, the "high limit" will control boiler operation and boiler temperatures will normally be hotter than what was set here at the "LO" control. See MIXING / ANTI-SCALD VALVES for a discussion of the installation and use of anti-scald valves to avoid hot water burns, and for a table of temperatures at which hot water burns occur.

Hot Water Temperature Safety Warning

Setting water temperature above 100 degF may cause serious scalding burns.

A.O. Smith, the manufacturer of this water heater warns about water temperatures over 125 degF.

See MIXING / ANTI-SCALD VALVES for a discussion of the installation and use of anti-scald valves to avoid hot water burns, and for a table of temperatures at which hot water burns occur.

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.

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.

Anti-Scald Valves & Hot Water Quantity - improve safety and meter hot water more slowly - makes it last longer
CLOGGED PIPING & Hot Water Flow - diagnose and correct poor hot water pressure and flow due to pipe clogging
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
High Efficiency Water Heaters - if replacing a water heater, consider a model that saves money in operating cost
Insulate Hot Water Piping - worth doing where piping is accessible, especially on piping running through cool areas
Insulate Hot Water Tank? - probably not worth doing except in special cases; important safety warnings
Larger Diameter Water Supply Piping - worth doing if replacing clogged pipes or building new construction
Tankless Coil Hot Water Increase - various tricks can significantly improve the safety and water quantity available
Temperature of Hot Water is Too Low - where to look for problems when the "hot water" is not hot enough

A Comparison of Alternative Hot Water Heaters & Sources

The following articles discuss alternative ways to produce domestic hot water for washing and bathing.

High Efficiency Water Heaters such as direct-vent gas-fired water heaters
Indirect-fired Water Heaters which use a separate heating boiler to produce a larger quantity of hot water
Instantaneous Water Heaters point of use systems that have little or no standby energy losses
Multiple water heaters in parallel to increase total hot water quantity
Multiple water heaters in series to stage hot water heating for varying levels of demand
Range Boiler Water Heaters an older form of indirect-fired hot water heating used with separate heating boilers
Side Arm Coil Water Heaters similar to instantaneous and tankless coil water heaters, often used with range boilers
Solar Water Heaters using solar collectors, an indoor water tank, pump and controls, using minimal "on-grid" energy
Tankless Coil Hot Water Increase a heat exchanging coil immersed inside of a heating boiler heats provides (somewhat limited) hot water. various tricks can significantly improve the safety and water quantity available

The characteristics of various water heaters such as life expectancy, cost, safety, and capacity are discussed at WATER HEATER PROPERTIES

Ways to improve total hot water quantity, pressure, temperature and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.

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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.

THERMOSTATS, WATER HEATER
  AQUASTAT CONTROL Functions
  Electric Water Heater Thermostats

HOT WATER QUANTITY IMPROVEMENT
  Alternative Hot Water Sources & Methods
  Anti-Scald Valves & Hot Water Quantity
  CLOGGED PIPING & Hot Water Flow
  Extra Tanks to Increase Hot Water
  Insulate Hot Water Piping
  Insulate Hot Water Tank?
  Larger Diameter Water Supply Piping
  Temperature of Hot Water is Too Low

MIXING / ANTI-SCALD VALVES

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
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 "

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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.