Hot Water Heater Timer Recommendations for Energy Savings
InspectAPedia^®  -    

• Water heater timers: how to choose and use a water heater timer to save energy
• Guide to inspection of electric water heaters
• Timers for electric water heaters
• Timers for tankless electric water heaters
• How long should the "off" time be on an electric water heater
for a timer to save energy
• Comparing savings from water heater timers with other options
• Questions & answers about how to install, set, use, and troubleshoot electric water heater timer controls

The sketch above shows the basic components of an electric water heater and is provided courtesy of Carson Dunlop.

This article contains links to in-depth articles on inspecting, testing, and repairing problems residential hot water heaters of all types, including their parts, controls, and alternative sources for hot water as well as tips for improving hot water temperature, hot water pressure, and hot water quantity.

Also see Energy Efficient Water Heating, a US Department of Energy, a PDF file that provides tips on lowering your water heating bill.

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The link to the original Q&A article in PDF form immediately below is followed by an expanded/updated online version of this article.

• Q&A on Using Timers on Electric Water Heaters & Tankless Water Heaters - original PDF version, use your browser's back button to return to this page

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article, (see links just above) from Solar Age Magazine and written by Steven Bliss.

Water Heater Timers

Question:

Does it make sense to put a timer on an electric hot water tank to turn it off for most of the day if no one will be home?

How about using a timer on a tankless electric water heater if gas is not available? -- Bill Geary, Belfair WA

Answer:

Efficiency of Timers on Conventional Electric Water Heaters

According to Princeton Energy engineer Gautam Dutt, the idea of using a timer on an electric water heater will work fairly well if your daily hot water consumption is less than one water-tank load, or if the hot water heater will be shut off for several days at a time, such as over a long weekend.

For shorter time periods or for higher hot water consumption rates, in the 1980's Dutt thought that it would be more practical to insulate the water tank.

However modern hot water tanks come from the manufacturer with good insulation, and in some cases insulating a hot water heater tank may fail to follow the manufacturer's instructions, could void its warranty, or could make the water heater unsafe (if for example you covered the pressure-temperature relief valve). --DF

In the 1980's a typical stock electric water heater was about 73-percent efficient, including tank losses. If you included hot water delivery piping losses, the efficiency of the water heating system drops to about 60 percent. This is a good incentive to add insulation on your hot water piping, and it may help you decide on using a water heater timer too.

A Quick Comparison of Water Heater Types by Efficiency

By 2010, according to the American Council for an Energy-Efficient Economy, water heater efficiencies, organized by EF listed as:

• EF = 0.55 for conventional oil-fired water heaters
• EF = 0.60 for conventional gas fired water heaters
• EF = 0.65 for high efficiency gas water heaters,
• EF = 0.80 for pilotless gas fired water heaters
• EF = 0.86 for condensing gas storage type water heaters
• EF = 0.90 Minimum-efficiency electric water heater storage type tanks
• EF = 0.95 High-efficiency electric storage type water heaters
• EF = 1.20 for solar water heaters with electric backup, and a whopping
• EF = 2.20 EF for electric heat pump water heaters.

But, currently (2010) unless your electric utility company is offering preferential electricity rates (such as off-peak energy use or an "all electric home" discount), even though modern electric water heaters have a higher efficiency factor than oil or gas fired water heaters, don't assume that an electric water heater is the most sound environmental choice. Electric resistance heating is only as clean and efficient as the fuel (often coal) used at the electrical company's power plant.

These energy efficiency factor ratings do not include variations in life expectancy of the water heater, but ACEEE rated all of the water heaters at an expected 13-year life except oil-fired that they rated at 8 years. The shorter life of the oil fired equipment, combined with its lower EF (if these are accurate estimates) mean that the per-year operating cost of oil fired water heating equipment is more than its competitors. These ratings also do not compare BTUH input rates of the different equipment and thus don't say anything about the hot water recovery rate.

Also, the costs of these systems vary widely, from a low of $820. for a typical high-efficiency electric storage type (tank) water heater, to $4,800. for a solar water heater with electric backup. Costs do not include installation labor nor the effect of financial incentives, to this cost for solar hot water is over-stated.

Efficiency of Electric Tankless Water Heaters

Dutt said that tankless electric hot water heaters work best if the hot water demands are low, and if points of hot water use are clustered in the building (as opposed to having the tankless water heater deliver hot water through long pipe runs to distant points of use from the heater itself).

Obviously this is easier to achieve in new construction than in a hot water heating retrofit.

We add that because tankless water heaters have zero or very low stand-by losses, there would be typically be no gain achieved by installing a timer on an electric tankless water heater. -- DF

Drawbacks of electric tankless hot water heating systems are that they draw high electrical current (amperage) and supply low hot water flow rates. This means that from a modest-sized tankless electric hot water heater system you can't shower and wash dishes at the same time, and low hot water-demand appliances are in order as well.

Consumer Reports points out that a tankless water heater may be efficient but not necessarily economical to operate. What they mean is that it is certainly efficient to avoid heating water when no one is using it. But if water usage is high, a high-BTU tankless water heater may consume more total energy than a large but more conventional oil or gas fired hot water tank and burner.

See TANKLESS WATER HEATERS and Should I Convert to a Tankless Heater? for more about these systems.

Sketch (above) of a point of use tankless water heater courtesy of Carson Dunlop. Our OPINION is that readers looking for plenty of hot water heated efficiently should also consider the heater we describe at Indirect-fired Water Heaters.

Readers should also see ALTERNATIVE HOT WATER SOURCES to distinguish among these types of hot water producing systems and see Electric Shower Heaters for a discussion of point of use heaters at shower heads.

If your hot water is not working, check the water heater timer: Some electric water heaters are installed with a timer (photographs above) that saves electricity costs by turning off the heater during periods when no one will be using hot water. If a timer is installed for your heater, it might be in its "off" position. Instructions for setting the water heater timer are inside the timer cover.

WATER HEATER PROPERTIES discusses water heater types and their efficiencies; there we also note that using a water heater at a high duty cycle (such as heating a home) will shorten its life.

Also see Energy Efficient Water Heating, US Department of Energy, a PDF file that provides tips on lowering your water heating bill.

• 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.