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Use a water heater for heating a home: this article explains using an electric water heater for heating a building occupied space, connecting an electric water heater to heating baseboards or radiators. We describe using a water heater for small heating loads, and we explain the concerns for life expectancy of a water heater and on its warranty when the heater is used for other purposes. Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman. Advice on Using an Electric Water Heater for Home Heating by Baseboards or Radiators?Thanks to Carson Dunlop, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. Question: How Can I Improve the Efficiency and Reduce the Operating Cost of my Electric Water Heater Used to Heat my Entire Home?I'm looking for information on boilers and hydronic heat. I have read the 39 steps in the operation of a boiler and my problem is this: my "boiler" is a 60 gal hot water storage tank heated by 2 4500-watt elements each controlled by a tank thermostat set at 140 F. Each stat is hooked up to a 240 V 20 A breaker/ There are 5 loops. 4 of them have TRVs and one runs wide open. The installer was a plumber who loved this system and took out an oil-fired hot air furnace to install this system. When I bought the house he did not give me much information on how to operate it and now he is dead. The living-room has a loop with a TRV set at 4 (70 F according to a spare one he left me) AND a stat on the wall that turns on or off a GRUNDFOS UPS 20-42 3-speed circulator pump. I am wondering how to make this [water-heater based home heating] system work efficiently. None of the heating contractors I have contacted seem to understand this system and think that this water heater is a boiler and should be run at 180 F and my stats go up to 177 F. I am unable to find a discussion of this system anywhere on the internet with the use of electricity to heat the water. Any ideas? Thank you very much. -- Ben V, Canada. Answer: Electric Water Heaters Designed for Producing Domestic Hot Water
Also, take a look at your water heater's warranty and you may see that using the water heater to heat the home either voids the heater warranty or reduces the warranty period. (Also see APPLIANCE EFFICIENCY RATINGS). Electric water heaters can be the slowest to recover when cool - so the system may not be very responsive in cold weather unless it is staying on nearly all the time (even more costly). Carson Dunlop's sketch (left) explains recovery rate of water heaters. Also, water heaters are not expected to maintain internal water temperature much above 140 degF - domestic hot water over 120 degF is dangerously scalding hot. Of course, your heater may be capable of reaching the 177 degF. you mention, but it's going to have a still shorter life and higher operating cost at that level. We guess that your plumber/designer who loved using an electric water heater for heating the entire home expected that (as is common in Canada) the circulator pump(s) would run continuously during the heating season. Circulating water continuously at a lower temperature may be comfortable and may actually heat the home adequately. That's where his 70 degF. set point may have come from. But unfortunately, circulating cooler water (70 degF.) than would be produced by an ordinary hydronic heating boiler (operating at around 180 degF), is less efficient in both theory and practice for a less obvious reason that we learned from a heat transfer engineer who explained that "The thermal conductivity of finned copper baseboard, or of cast iron radiators, is exponentially greater at higher temperatures." In other words, the hotter the heating water you are circulating, the more efficiently heat is transferred into the living area. So dropping the temperature to 70 degF. may have helped the water heater life, but it probably increased the building heating cost still further. We wouldn't rule out using an electric (or other type) of domestic water heater to heat a small space that is not served by the main building heating system, but using any water heater as the permanent and main source of building heating in a cold climate is generally a bad idea. 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. We discuss the role of water heater use (for heating a home) and its effect on warranties at AGE of WATER HEATERS. Electricity is commonly used to heat water for hydronic heating systems as a backup heat source, such as in a heat pump system (see BACKUP HEAT for HEAT PUMPS), or in super-insulated buildings that use a tiny electric boiler and perhaps a radiant floor slab. ELECTRIC HEAT discusses typical electric heating systems In the water-heater based home heating system described in the question above, we would guess that the thermostats simply cause the hot water to circulate, and the built-in thermostat turns on or off the electric elements in the water heater tank. We doubt that there is any way to make this an efficient home heating system other than by removing it and installing a more economical heating source; you might however
Here is a rough guess at the relative life expectancy of several types of water heaters, provided all other water heater life factors (discussed at AGE of WATER HEATERS) are the same (comments are invited Contact Us) (shortest life first).
Conditions Affecting Water Heater LifeKeep in mind that conditions besides the type of water heater can dominate its life expectancy. Some of these water heater life expectancy factors include:
For complete information about water heater life and things that affect how long a hot water heater will last, see our full article at AGE of WATER HEATERS. As we illustrate with Carson Dunlop's sketches shown here, in order of speed of re-heating or hot water recovery time, listing slowest-recovery time to fastest recovery time we'd list water heater types as follows:
Don't confuse water heater recovery rates (how fast we can heat water) with water heater operating costs, which we discuss at Water Heater Operating Cost Comparisons. Recovery rate is measured in gallons per hour or gph. Water heater operating costs are compared using a standard measure of energy cost in therms. Frequently Asked Questions (FAQs)... Ask a Question or Search InspectApediaQuestions & answers or comments about using electric water heaters as home heating systems Ask a Question or Enter Search Terms in the InspectApedia search box just below. Technical Reviewers & ReferencesRelated Topics, found near the top of this page suggest articles closely related to this one.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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Carson, Dunlop & Associates Ltd.,
The Home Reference Book - the Encyclopedia of Homes
