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.

Advice on Using an Electric, Gas or Oil Water Heater for Home Heating

Question: How Can I Improve the Efficiency and Reduce the Operating Cost of my Electric Water Heater Used to Heat my Entire Home?

[Click to enlarge any image]

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.

However water heaters can be used for home heating - aka "hydronic applications" or "hydronic heating applications" provided that the specific water heater is rated by the manufacturer as approved for that use and provided that the heater is being used for "small heating loads" of 75,000 BTUh or less. (CIPH 2008).

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.

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 Associates' 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.

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

• Check with your electrical company 
  
  to see if they can give you preferential rates for using electric heat
• Be sure your home is draft free and super-insulated.
  
  See these articles that can help improve the energy efficiency of your building:
  • HEAT LOSS in buildings
  • AIR LEAK DETECTION TOOLS
  • AIR LEAK MINIMIZATION
  • ENERGY SAVINGS in BUILDINGS
  • ENERGY SAVINGS PRIORITIES
  • HEAT LOSS in buildings
  • INSULATION INSPECTION & IMPROVEMENT
  • SOLAR ENERGY SYSTEMS
• Set back your thermostats 
  
  as much as you can - see THERMOSTATS

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).

1. Electric water heaters (though individual heating elements may fail and need to be replaced before the tank fails)
2. Gas-fired water heaters, High Efficiency Models (LP gas or natural gas)
3. Gas-fired water heaters (LP gas or natural gas)
4. Oil-fired water heaters
5. Solar water heaters have a relatively high purchase cost but probably lower maintenance cost than oil and gas fired equipment

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:

1. The duty cycle or level of usage of the water heater (more use = shorter life). Using a water heater to heat a building in a cold climate is going to work that device harder than if it were just making domestic hot water for washing and bathing.
2. The chemistry of the water being heated (aggressive or corrosive water = shorter life)
3. The construction of the water tank, methods and materials used (look at the water heater warranty period; longer warranty probably means a more durable water heater tank)
4. Proper installation of the water heater; improper fuel or water piping connections or inadequate chimney venting on fossil-fuel fired water heaters can lead to safety problems or leaks and early heater failure. Improper location or improper position of the water heater (such as mounting some water heaters horizontally) can lead to early failure of the heater as well as voiding the manufacturer's warranty.
5. Proper maintenance; almost no one we've encountered drains and services their water heater on the schedule recommended by the manufacturer

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 Associates' 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:

1. Range boilers
2. Electric water heaters
3. Gas-fired water heaters
4. Gas-fired water heaters, High Efficiency Models
5. Solar water heating systems (depends on weather, season, and sun exposure)
6. Tankless coils (depends on heating boiler size, construction [steel/cast iron], thermal mass, and fuel type [oil/gas])
7. Indirect-fired or tankless water heaters (depends on heating boiler size, construction [steel/cast iron], thermal mass, and fuel type [oil/gas])
8. Oil-fired water heaters
9. Instantaneous water heaters

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.

Thanks to Carson Dunlop Associates, 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.

Reader Question: hot water is too hot when using the water heater to heat my home

I have a hot water tank which is connected into my central heating system. In the summer

I use it as an immersion heater using electricity. The problem is that the water is too
hot when I use the immersion heater. How can I adjust the water temperature. - John Newing 6/16/11

Reply:

For a water heater that is used for both domestic hot water and heating, I'd suggest adding an automatic mixing valve right at the water heater hot water outlet line. The valve can be set to the desired domestic water temperature for washing and bathing; the valve works by mixing cold in with the outgoing hot.

You can also permanently lower the electric water heater temperature setting by opening the access cover to the control and setting the temperature dial to a lower number.

Also take a look at ANTI SCALD VALVES

Support for Use of Electric Water Heaters for Space Heating Applications

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 omission. 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.

Reply:

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

• Operating expenses 
  
  affected by fuel costs: electricity prices vary widely around the world as do gas and oil
• Cost of additional controls 
  
  needed in some implementations (using a water heater) vs others (using boilers that include those controls).
  
  Add a few radiant heat floor controls to a water heater and the installed cost may quickly creep up to or even pass some heating boilers that include mixing valves and other economizer controls.
• Equipment life and warranty:
  
  A water heater used for radiant heating is not warranted at all by the companies we’ve surveyed.
  
  A Peerless PureFire gas boiler is warranted for 12-years though warranty coverage varies as the unit ages. Depending on brand, water chemistry, and usage duty cycle I’ve seen water heaters fail in a year and others last more than 20 years. Same with boilers.
• Heating load peak demand:
  
  Watch out: any limited BTUh capacity or duty cycle capacity heating device may be insufficient in areas where temperatures can be low and cold. Some DIY radiant floor articles we reviewed pointed out that in cold weather the water-heater-radiant-floor system had a clear upper limit on how warm it could make the building.
  
  See TANKLESS WATER HEATERS for details about these "instantaneous" water heating systems, their capacities, and uses.
  
  Also see RADIANT HEAT MISTAKES for other snafus that keep radiant heat from working as well as it could.

The life expectancy of a water heater is not calculated based on the duty cycle it will experience as a space heater but rather as a water heater.

On the other hand, an added difference in water heater performance when it’s used for heating is that in areas where water chemistry is aggressive (corrosive) a water heater used to make domestic hot water will have a more challenging time than the same unit used to heat the same volume of unchanging (and perhaps treated) water for space heating.

Things that affect water heater life are discussed

at AGE of WATER HEATERS.

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.

Also seeReferences or Citations where we cite independent research on the use of domestic water heaters for different heating applications including radiant flooring heating and ancillary heat.

Reader comment: water heater longevity improved in closed-systems

28 Feb 2015 Gavin said:

I'd like to add to Steve's comment regarding the use of an electric hot water tank in a 'closed' system. First the longevity of a hot water tank in this system is greatly increased due to the fact that the oxygen in the water is virtually non existent after a short time of use (assuming you've installed an air bleeder).

Secondly in this situation the water heater is only operating intensively for four month out of the year, and would be off for six months. This setup will outlive a domestic only or open system setup. The elements are typically around $30 each to replace.

There is also the some what controversial, but highly effective method of rewiring the water heater to operate both elements at the same time. Most master plumbers know about and have done this before. In this situation a 60 gallon typical hot water tank with 4500 watt elements will produce approximately 28,000 BTUs which is a substantial amount of heating potential from one tank.

Also some manufacturers recognize this wiring setup as a viable option where there is a higher demand for hot water. (You need heavier gauge wire and larger breaker, or second wire and breaker and wiring scheme for thermostats,

Reply:

Thanks Gavin, I agree about the oxygen, am nervous about the wiring changes, and remain a bit conservative on this general topic in part because I figure the manufacturers have a reason for voiding warranty if their water heater is used as a space heater.

Domestic Hot Water Tanks as Space Heating Appliances in Canada

5 March 2015 Gavin added:

Check out the last page of the Giant water heater brochure, it states the following,

"All models are suitable for combination potable water and space heating applications. Toxic chemicals, such as those used for boiler treatment, must NEVER be introduced into this system. These units must NEVER be connected to any existing heating system or component(s) previously used with a non-potable water heating appliance."

It appears the exception to the rule is actually Canada. Virtually all hot water tanks are certified for space heating here. Look at Canadian Mortgage and Housing Corporation's article [below]. CMHC made a study back in the 80's using domestic hot water heaters in place of boilers up in northern Canada. The findings are interesting and led to the approval of DHW heaters for space heating.

The approval we don't have is for the wiring for simultaneous energizing of the heating elements in electric water heaters. However, many of the commercial grade tanks do allow for either simultaneous or non.

Excerpting From & Comments on CMHC's Report on Pros & Cons of Using Electric Water Heaters as Space Heaters

A CMHC study performed for Yellowknife, included considerations such as transport cost as well as heating loads that will be different in different climates.

• With today's more energy efficient northern houses, the DHW load is beginning to exceed the space heating load. This opens the potential to use the DHW heater for both space and water heating.
• Advantages:
  • DHW tanks are less expensive to buy, install and maintain than boilers
  • DHW tanks use less space
  • Suitable for use with both hydronic and forced air distribution systems
• Disadvantages:
  • Energy costs may be higher because DHW heaters are less efficient than boilers
  • In Yellowknife, 3 DHW tanks in use for 6 years were examined and showed only typical wear for their age.
• The study recommended that CSA Standard B-140-12 be revised to approve DHW tanks as combined space and water heaters and that manufacturers improve the efficiency and lifespan of the equipment. - source cited in the table below.

The study reported the following installation cost comparisons:

Notes to the table above

Source:

• "DOMESTIC HOT WATER TANKS AS SPACE HEATING APPLIANCES", [PDF] CMHC / SCHL, Technical Series 90-226, retrieved 5 Mar 2015 original source: ftp://ftp.cmhc-schl.gc.ca/cmhc/90_226.html

Notes & comments from InspectApedia: these opinions are not quoted from the CMHC study.

Amounts are in $CDN

The study did not compare the effects of different heater fuel options: gas, oil, electricity - rates vary widely by area.

Watch out: the study did not comment on the BTUh output requirements as they vary considerably in different climates. A high BTUh output requirement in a cold climate may be beyond the output of many water heater models or may significantly reduce the service life of a DHW heater used for space heating. Certainly some water heaters are capable of a high input BTUh - 200-700 BTUh (more than a typical boiler needs to heat a home, since the water heater is shooting for a quick recovery time).

Watch out: This study omits reporting on the annualized cost of these two heating approaches to include differences in fuel cost, heater efficiency, and possibly significant differences in the typical service life of a heating boiler vs. a water heater. The authors noted that they assumed a typical 79% efficiency level for heating boilers and only a 58% efficiency level for domestic water heaters.

That 21% absolute percentage points difference means that if you converted your DHW heater (used for home heating) to a mid-efficiency heating boiler using the same fuel (presumably oil?) using the boiler you would see a 38% improvement in fuel efficiency over the original DHW heater!

Missing from the analysis was comparison of a direct-vented high efficiency boiler vs. a direct-vented high-efficiency water heater. For example, without going to extreme (and possibly fussy or hard-to-maintain equipment), U.S. Boiler Company offers the MPO-IQ, a 3-pass oil fired hydronic heating boiler with an 87% AFUE. That boiler can be direct-vented, avoiding the cost of installing a chimney in new construction.

• High efficiency oil-fired DHW water heaters that we found operated in the 82% efficiency range. (HTP SuperStor). Smarterhouse.org estimates water heater efficiencies ranging from 60% (conventional gas storage heater) all the way up to 1.20% for solar with electric backup. But they too end up at about 82% as the upper range for conventional water heaters, noting interestingly that larger water heater tanks tend to be less efficient.
• High efficiency AFUE heating appliances (boilers for example) operate in the 90% to 98.5% AFUE range.

Maintenance costs are also assumed to be different (probably lower for a water heater in general but possibly higher for a water heater used for space heating). The authors reported annual maintenance costs for Yellow Knife as:

• $298./ unit furnace maintenance cost
• $242./unit - Boiler maintenance cost
• $90./unit - DHW maintenance cost

Watch out: it may not make sense to compare a furnace installation or maintenance cost to a water heater installation and maintenance cost: where are the heating distribution system costs for the water heater vs. the duct work cost for a furnace. Or if a water heater is to be used in a water-to-air installation (which may be a neat approach to converting a forced warm air heat source) one needs to add to the DHW heater cost the cost of the water to air heat exchanger as well as additional controls. - Ed.

As well there are very significant price ranges for both heating boilers and water heaters. For example a cast-iron heating boiler might be expected to have a longer life than most water heaters of any design. - Ed.

Watch out: also missing from this analysis is the question of how domestic hot water is to be produced if the DHW heater is dedicated for home heating (thus claiming a longer life than otherwise). One might consider other alternatives and cost comparisons to obtain a more accurate picture of all of the cost implications of DHWs for space heaters such as:

• The requirement of a second water heater for domestic hot water
• Comparing two water heaters and their installation, operating cost, fuel efficiency, maintenance cost, and life with a high quality cast iron boiler with a high efficiency, attached to an indirect-fired water heater - operating as an additional zone off of the heating boiler.

The following note from the end of the article is also significant for what it says and implies (in our OPINION) - Ed.

Manufacturers of domestic hot water tanks should make design improvements in the area of efficiency and life span of the tanks. Side wall venting should also be incorporated into future designs.

Research: use of water heaters in hydronic applications

• CIPH, USE OF WATER HEATERS IN HYDRONIC APPLICATIONS [Home Heating] [PDF] (2008) CIPH Information Bulletin, Canadian Institute of Plumbing & Heating 295 The West Mall, Suite 504, Toronto, ON M9C 4Z4 Tel: 416.695.0447 | 1.800.639.2474 Email: info@ciph.com, Website: https://www.ciph.com, retrieved 2018/12/02 original source http://mail.ciph.com/themes/ciph_2013/pdfs/Information%20Bulletin%20-%20Use%20of%20WH.pdf - special thanks to reader David for posting this link.
  
  Excerpts:
  
  Only water heaters that are certified for dual purpose space heating and potable water use may be installed. If the appliance is not certified to one of the three possible Standards (ANSI Z21.10.1- 2004/CSA 4.1-2004; ANSI Z21.10.3-2004/CSA 4.3-2004; or CSA B140.12-03) and marked, indicating that it can be used in dual purpose applications, then installing it is an offence—and a safety hazard.
  
  There is not a single water heater manufacturer in Canada that allows its product to be used solely for space heating applications. In fact, manufacturers may void the warranty of the appliance if it is not installed appropriately.
  
  CSA B214-07 (Installation Code for Hydronic Heating Systems) states that water heaters may be used in combination space and domestic water heating to a maximum space heating load of 75,000 BTU/hr.
• CMHC, DOMESTIC HOT WATER TANKS AS SPACE HEATING APPLIANCES", [PDF] CMHC / SCHL, Technical Series 90-226, retrieved 5 Mar 2015 original source: ftp://ftp.cmhc-schl.gc.ca/cmhc/90_226.html
• Ahn, Byung-Cheon, and Jae-Yeob Song. "Control characteristics and heating performance analysis of automatic thermostatic valves for radiant slab heating system in residential apartments." Energy 35, no. 4 (2010): 1615-1624.
• Cho, S-H., and M. Zaheer-Uddin. "An experimental study of multiple parameter switching control for radiant floor heating systems." Energy 24, no. 5 (1999): 433-444.
• Chandler Design Build, "Synergy of Demand Water Heaters with Solar and Radiant Floor Heating", Green Building Details, Chandler Design Build, Mebane NC, USA, Web article, Tel: 919-304-5397, retrieved 3 Feb 2015, original source: chandlerdesignbuild.com/files/demandWaterHeaters.pdf Email: Michael@ChandlerDesignBuild.com
• Crawley, Drury B., Linda K. Lawrie, Curtis O. Pedersen, Frederick C. Winkelmann, Michael J. Witte, Richard K. Strand, Richard J. Liesen et al. "EnergyPlus: an update." Proceedings of SimBuild (2004): 4-6.
• RADIANTECH WATER HEATER HEATING SYSTEM ICC EVALUATION REPORT 2010 [PDF] (Subject to reevaluation in two years) Radiantech Co., PO Box 1111, Lyndonville, VT 05851 USA, PO Box 1111, Lyndonville, VT 05851 USA Tel 802-626-5564 Email: info@radiantech.com retrieved 2020/02/23 original source: www.radiantec.com/wp-content/uploads/Radiantec_ICC_ES_Evaluation_Report.pdf
  Excerpts:
  
  Radiantec has three basic designs: an indirect system, a closed system, and an open direct system.
  
  The indirect system provides both hot potable water and hydronic heating, using a heat exchanger to keep the two loops separate (Figure 1).
  
  The closed system provides only space heating. In this design, the water heater provides no potable water, and is used exclusively for hydronic heating (Figure 2).
  
  The open direct system provides both hot potable water and hydronic heating in a combination system which is also available in a supplemental solar energy design.
  
  The open direct system has a check valve which forces make-up water entering the system to pass through the heating loop before entering the water heater. This prevents water from stagnating in the heating loop (Figures 3 and 4).
  
  Filling connections for the indirect system and the closed system must be protected from flow from the hydronic piping loop.
  
  5.1 Radiantec’s closed, indirect, and open direct combination potable water heating and space heating systems must be designed and installed in accordance with Section 4.0 of this report and applicable provisions in the building, residential, plumbing, mechanical, electrical and energy conservation codes referenced herein.
  
  5.2 Evaluation of the specific components of Radiantec’s closed, indirect, and open direct systems is outside the scope of this report.
  
  5.3 Radiantec’s design details and calculations for the applicable closed, indirect, or open direct potable water heating and space heating system must be available at the jobsite during and after construction. The details and calculations must be stored in an identifiable, readily accessible and approved location.
  
  5.4 The indirect system must be installed to maintain fluid separation between the hydronic heating loop and the potable hot water system in accordance with the applicable code.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-09-20 by Dave

@InspectApedia-911, thank you for the reply. I feel the same way as you do... it .... may ..... work.

The good things about this problem are

1. It is only for one heating season
2. If the water heater elements do crap out on me during a -20 cold snap i can fall back on the heat pump ( concerned that with the exposed pipes i will be pumping the cold fluid into the relatively warm ground) severely reducing heating capacity.
3. The elements have never been used - purchased as a storage tank - so hopefully they are still in good working condition.

I have installed a smoke detector directly above the heater in the basement, and a double pole 30 amp switch upstairs -

1. To toggle the tank temp on and off if needed.
2. In case of emergency.
   

Did not do anything funky, like wiring both elements separately to get more btu. As i did not want to bypass the safety features in the top element.
Thanks again.

On 2022-09-19 by InspectApedia-911 (mod) - need more heat-loss data to conclude that water heater will work

@dave,

thanks for a very interesting question.

I'm not sure we have all the heat-loss data to conclude that your water heater will work, but I agree that in the upper outdoor-temperature range the rate of heat loss from your house ought to be less than when weather is colder, so the heater doesn't have to work as hard.

I note that not all water heaters survive a home-heating duty cycle.

On 2022-09-19 by dave - ground source heat pump pipes buried in my back yard

Hello. In the process of building a new home, and uncovered the ground source heat pump pipes buried in my back yard.

Here is where it gets interesting. The ground source heat pump is rated at 36,000 btu. On a - 20 day, it runs 20 minutes every hour. Which means on a -20 day, it takes 12,000 btu to heat my house.... correct ? 20 min ( x) 3 = 60 min.... or 36,000 ÷ 3 = 12,000 btu.

Once the outside temps reach 45 degrees ( same temp as the earth ) i would like to turn off the heat pump - with the exposed earth pipes ( which will be covered with insulation and hay bales) and heat the house with a 60 gallon water heater - that i happened to install many yeara ago as a storage tank.

This set up is because the concrete pour has been delayed a year, so the water heater will only have to carry the heating load for this winter ( temporary measure). Once the walls are up and backfilled, the pipes will be buried and back too normal.

What do you think ? I am reading that a 4,500 watt element will produce 15,000 btu - and sinve on the COLDEST day ( -20) i only use 12,000 ..... it should do the job.... correct ?

On 2022-08-19 by InspectApedia-911 (mod) - Radiant heat floor systems use a mixing valve

@Carl,

Radiant heat floor systems pretty much always use a mixing valve - else the floor is too hot and the heating cost too high.

Take a look at our radiant heat floor installation & design articles that begin at

RADIANT HEAT

On 2022-08-19 by Carl

I'm using a electric hot water heater for a small 560 sq ft radiant in-concrete floor, 2 zones. I am wondering if using a mixing valve would be beneficial. Thinking a higher tank temperature would assist the air eliminator remove air from the closed system.

On 2022-01-16 by Inspectapedia Com Moderator

@Smartin,

Good news indeed. Can you tell us what steps you did to get it working now?

Take a look at

EXPANSION TANK PRESSURE SETTINGS

About running your pump I'm not sure I have a clear picture of what you're doing but you certainly would use a pump when there's water in the system and you would avoid running a pump if there was a chance that you're running it's dry.

On 2022-01-16 by Smartin

We finally got it to work and it has been running fine for 24 hours now!

On 2022-01-15 by Smartin - gas fired hot water heater supplies both domestic and radiant floor heating in a closed loop

@Inspectapedia Com Moderator, Thanks for your reply. The water heater is running fine as the temp gauge shows 120. We feel the water heater shuts off because the cooler water from the floor is not circulating back to the water heater.

Questions:
If the cold water pressure reducer valve is set to 15lbs, what pressure should the expansion tank be set to? Since we just have radiant floor heat.

When we purge water from the floor, should we be running the pump? (Or does that add more air?)

The water from the cold fill can go left and/or right because of the tee.

This was the original set up from when we purchased the house

On 2022-01-15 by Inspectapedia Com Moderator

@Smartin,

Do you think that the fact that the return water starts and turns cold could be telling you that there's a controller problem?

On 2022-01-14 by Smartin

Hi! I hope someone can assist us as we cannot find very many resources where people are using a gas fired hot water heater (bradford white defender for hydronic) that supplies both their domestic and radiant floor heating in a closed loop.

Attached is a simple hand drawn design of our system. Our set up seems different (than ones with boilers) because we have a mixing valve and also our expansion tank and circulator pump are on the return side of the water heater.

The system was working beautifully (so we know it does work!). After we drained some water from the water tank (for maintenance on the domestic side) .. we drained a little dirty water from the hydronic side and we haven't been able to get it running since (2 weeks ago).

What is happening: When we turn on the pump, lines for loop 1 (shortest) will return warm water fairly quickly. Sometimes loops 2 & 4 will also be warm. Then after 5 - 10 mins it turns cold. Line 3 is the longest and still feel cool. Water temp is at 120 and pressure is 18lbs. Water heater turns off and doesn't start again.

What we have done: We have bled the floor lines individually multiple times to try and eliminate air (by only opening 1 valve at a time, we also increased the pressure with the cold fill to purge the air). We have tried this with and without the pump running - no difference in end result.

We replaced the maid-of-mist air bleeder and installed the air eliminator to help remove any additional air bubbles (and purged all the lines again).

We checked the expansion tank (it was at 10lbs, we have tried 12 lb and 15 lb).

Any help would be sincerely appreciated! Sonya

On 2021-02-10 by (mod) - Which Navien water heaters can be used for home heating (space heating) ?

George,

Above on this page we give the general considerations in deciding if a given water heater can be used for building heating systems including a radiant heat floor system.

I think there was a typo and that you mean Navian NPE-S 240 water heater.

Watch out: be sure that the Navian heater you are going to use for your radiant heat flooring is in fact the manufacturer's model that is approved for that application: the Navian Commercial or "Combi"

Check you water heater's data plate to confirm that your model can be used as you ask. An example from Navien's IO manual is shown just above.

For other tankless or any other water heater product, In my OPINION I'd be reluctant to ask a water heater to do double duty as providing both domestic hot water (washing and bathing) and building heating.

But the manufacturer, in this case Navien, are the people to ask. 1-800-519-8794

George,

Please find your question and our more-detailed reply now also found at

NAVIEN WATER HEATER AGE & MANUALS

and see this example of a Navien tankless heater for both domestic hot water and building heating:

• NAVIEN CH COMBINATION WATER HEATER / HEATING BOILER SERVICE MANUAL [PDF] (2010) Combination water heater / heating boiler. Models CH-180 CH-210 CH-240 CH-240 ASME

On 2021-02-10 by George Brisson

Hi. I have a tankless propane water heater Navien PNE-S 240 maximum rated output at 199000 BTU/H used to supply domestic hot water only. I would like to know if i can add a radiant heating system to it. It will be used to heat my basement concrete floor as a secondary heating system. The surface to be heated consist of 5 loops of 1/2'' pex for a total of 1085 ft. Thanks

On 2020-06-22 by David Lepsig

I am converting my home to solar. I am hooked into PUD and have a net meter arrangement. I have radiant floor heat in a 2500 sf home. I currently have a propane boiler and stainless tank. I want to convert to electric tankless if possible.

The research shows me 1 electric and 4 gas tankless as the highest rated. With the latest technology, will an electric HW heater run my heat in the winter. I live in WA state in snow country. I use heat from Mid September to early June.

...

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• ELECTRIC WATER HEATER REPAIR GUIDE
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• WATER HEATERS for HOME HEATING USE?

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