Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AGE of WATER HEATERS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
ALTERNATIVE HOT WATER SOURCES
ANODES & DIP TUBES on WATER HEATERS
ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
AQUASTAT CONTROL Functions
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER, HEATER WATER FEEDER
CARBON MONOXIDE - CO
CHECK VALVES, WATER SUPPLY
CHEMICAL CONTAMINANTS in WATER
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CLOGGED SUPPLY PIPING
DEBRIS in WATER SUPPLY, Water Heater
DRAIN a WATER HEATER TANK
ELECTRIC WATER HEATERS
FLOODED HEATING EQUIPMENT REPAIR
FLOODED WATER HEATER REPAIR
GALVANIC SCALE & METAL CORROSION
GAS BURNER FLAME & NOISE DEFECTS
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
HOT WATER SUPPLY
INDIRECT FIRED WATER HEATERS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
NO HEAT - NO HOT WATER: HEATER DIAGNOSIS
NOISE / SOUND DIAGNOSIS & CURE
NOISE CONTROL for HEATING SYSTEMS
NOISE, PLUMBING CHECKLIST
NOISE, WATER HEATER
ODORS GASES SMELLS, DIAGNOSIS & CURE
ODORS IN WATER
PIPING IN buildings, Clogs Leaks Types
PLASTIC PLEXVENT ULTRAVENT RECALL
PLUMBING FIXTURES, KITCHEN, BATH
RELIEF VALVE LEAKS
RELIEF VALVE, WATER HEATER
SCALE REMOVAL, WATER HEATERS
SEWER GAS ODORS
SOLAR HOT WATER HEATERS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCH, FLUE GAS DETECTOR
TANKLESS WATER HEATERS
Temperature Pressure Relief Valves - Water Heaters
THERMOSTATS, WATER HEATER
TIMERS for ELECTRIC WATER HEATERS
WATER CONSERVATION MEASURES
WATER CONTAMINANT LEVELS
WATER HAMMER NOISE DIAGNOSE & CURE
WATER ODORS, CAUSE CURE
WATER PIPES, Clogs Leaks Types
WATER PRESSURE MEASUREMENT
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER QUANTITY IMPROVEMENT
WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
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. We also warn that using a water heater as the primary heat source for building space heating where heating loads are significant is likely to give a reduced water heater life and may also void the water heater warranty.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
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
We cannot imagine a more costly, short-lived heating system than using an electric water heater to heat an entire building, especially in Canada where winters can get pretty cold and a heater has to work hard. While electric or even some other water heaters are on occasion used for home heating, they are generally not applied where there is a high heating load and a long duty cycle.
Watch out: Also, take a look at your water heater's warranty and you may see as we have on review of a number of manufacturers, that using the water heater to heat the home either voids the heater warranty or reduces the warranty period.
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
Electricity is commonly used to heat water for hydronic heating systems as a backup heat source, such as in a heat pump system
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.
For your heating area where there are significant heating system loads, 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 Life
Keep 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.
Reader Comment: Water heaters used for radiant floor heating may make sense in areas with milder heating load
3 Feb 2015 Steve said:
This article, while containing factual information, is not entirely accurate by ommission. While most of Canada experiences cold winters, not all areas do.
Many Canadians live on the BC coast in a very mild climate where it only rarely drops below freezing in winter. It is not clear if the application is in-floor or radiator hydronic heating. There is very large difference, the primary one being the required fluid temperature. In-floor radiant heat works best with a low temperature, while radiators require high temps.
In fact an electric hot water tank can be used to heat a house with in-floor radiant and they are thousands of dollars cheaper than boilers, and if they fail cost very little to replace; also there is very little maintenance, which can be done by the homeowner. The saving are extraordinary. The heater should be dedicated solely to heating due to slow recovery and desire to avoid mixing heating with domestic hot water. Otherwise heating water must be isolated by an approved heat exchanger.
Thank you for your interesting comments, Steve. Indeed it’s a challenge to write accurate technical data covering much of the world in one article. Indeed when heating loads are small, small heating systems, even tankless water heaters, can make economic sense, as Steve Bliss points out at HEATING SMALL LOADS
We need to be careful when claiming that water heaters are enormously less expensive than heating boilers. It's not categorically so that water heaters are "thousands of dollars cheaper than boilers" - or ... it depends.
Cost comparisons between heating boilers and water heaters vs. replacement life are interesting. Boilers matching radiant heat specs well range from about $1,200 USD (Argo Electric AT2-series) to over $3,600 (Peerless PureFire condensing gas boiler).
Water heater prices also will range widely by type & fuel. At the low end are electric water heaters in the $225-400 USD range (simple electric, e.g. Kenmore) with prices easily zooming up to the same range as some pricey heating boilers (Rheem-Ruud 200 BTUH Gas unit) at $2,800. USD.
Making water heater vs. heating boiler cost comparisons needs to consider some additional expenses
My own views in the question of using a water heater for radiant heating were shaped by reading what the various manufacturers recommend regarding use of their equipment.
But I agree that for light heating loads a water heater, properly set up for that application, may perform just fine.
And it's worth noting that building codes do not prohibit using water heaters in these other heating applications.
Continue reading at WATER HEATER LIFE or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Questions & answers or comments about using electric water heaters as home heating systems
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References