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water heater recovery rates Electric Hot Water Heater For Hydronic/ Home Heating FAQs

Questions & answers about whether or not it makes sense to use a water heater for heating a home.

This article series explains using an electric water heater for heating a building occupied space, connecting an electric water heater to heating baseboards or radiators.

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Q&A on Using an Electric Water Heater for Home Heating

Sketch explaining hot water recovery rate (C) Carson Dunlop Associates

These questions and answers about using a water heater in hydronic applications - heating small building areas - were posted originally

at WATER HEATERS for HOME HEATING USE? - be sure to see the information and warnings given there.

[Click to enlarge any image]

On 2020-02-23 randy owens said:

me and my father installed this open direct system with an oil fired hot water heater under floor (pex pipe) hydronic system. There is no heat exchanger so the same hot water goes to the floor loops and to all other domestic hot water applications. On the web site you can see that according to them this is code compliant in most of the USA.

the interesting thing is this system will cool your house a little because as you use water in the summer it still circulates in the loops beneath the floor thus taking the heat from the house and dumping it back into the tank.

By the way the system had been running for twenty years until the oil water heater went up, the heating company convinced my dad it wasn't code and replaced it with a new boiler that cost $7000 to install (about twice as much as the whole system cost originally).

The boiler setup just doesn't work right, boiler has two outputs one for hot water one for heat, and never gives enough hot water for showers even though the contractors have tried adjusting it 5 different times.

My father swears hes going to throw the boiler away and put another hot water heater in its place.

Here is the ICC code that says heating with domestic hot water heater and heating hydronically with the same hot water heater is allowed without a heat exchanger:

On 2020 02 23 - by (mod) - a few caveats regarding the above

The posting above seems a bit of an advertisement but we've retained it to invite reader discussion.

We agree that particularly for small heating loads, using a domestic water heater as the primary heating source for space heating can be economical and efficient.

Randy's criticism that "the boiler system just doesn't work right" is misleading and incompletely informed..

A tankless coil domestic hot water supply on a heating boiler is perfectly satisfactory for some homes but has limited hot water production quantity as we explain

at TANKLESS COILS

Other domestic hot water systems that use the home's heating boiler as the heat source are very efficient and can produce very large quantities of domestic hot water supply, as we explain

at INDIRECT FIRED WATER HEATERS

The concept of running the domestic hot water supply first through a radiant heat floor tubing system and then on to plumbing fixtures is a different approach [this sounds like Radiantech's version 3: Open Direct System, for which we invite citation of supporting research and reader experience to add to the home page for this topic:

WATER HEATERS for HOME HEATING USE?

Watch out: while some water heaters are rated by their manufacturer as suitable for use in hydronic heating applications, others are not and that use will both void water heater warranty and may also result in a short water heater life.

On 2019-12-11 - by (mod) -

Yep - sounds too good to be true. The "annual operating cost" surely varies depending on the size and construction and insulation level and air leakage rate of the specific building. No single heating cost claim is going to be "right" for all situations.

On 2019-12-04 by Todd

As an updated question:

How about using one of the new "hybrid" hot water tanks that have the heat pump on top to heat one's whole house? Under normal use, they are only supposed to cost like $110 a year to operate. Even if it cost 10 times that it would be cheaper than my annual oil heating bill.

On 2018-12-02 by (mod) - CIPH warnings on using water heaters in hydronic applications

David:

Thank you for referring us to the CIPH bulletin - I've made it available in the article above. You may have to clear your browser cache to see the updated page.

On 2018-12-02 by David

See CIPH Bulletin and read very carefully.

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.'

Other warnings and limitations on the use of water heaters for space heating are detailed at WATER HEATERS for HOME HEATING USE?

On 2018-11-21 01:04:41.845917 by Daniel Utecht

is it better to switch pump on and off or electric hot water heater in my floor heat system

On 2018-03-28 20:17:44.081030 by Clarence

Also, would the pump be better on the return or on the supply side of the heating circuit?

On 2018-03-28 by Clarence

I'm interested in using an electric 40 gal DHW tank in an exclusive closed loop system to supply HW for an infloor radiant heat installation.

The space is about 840 sq ft in 4 zones. My thought is to make it a single zone, where a pump runs continuously cycling the hot water out from the tank and returning it cooler to the tank. I'm not sure about what pump size to buy, or if this idea even makes sense.

Once the system is fully charged and the air is bled, do I shut off the cold supply inlet from the city water to the HW tank?

On 2018-01-06 by (mod) -

Peter

Some installers use a water heater for small radiant slab heating, and there may be SOME water heater models rated for that use. Most are not - so your heater could see a shorter life.

On 2018-01-06 by Peter

I have a newly built shop which is 40 X 20 feet. It is very well insulated & has the in floor heating pipes laid in to the floor. Could I use an electric water heater to heat this structure?

On 2017-03-14 by (mod) -

Scott I don't have the details nor expertise to give an exact specification but sure you can do what you want; at most you'll have to install a switching relay so that your controller switches a relay that switches what you want to turn off: a pump or a 240V electric water heater - each gets its own relay.

On 2017-03-14 by Scott Rookes

Hi there. I have a question regarding relays for a heating system. I have a 120 gallon heat exchanger tank that runs with one loop to my solar hydronic collector system and another loop to my infloor heating loops.

The pump for the solar system is on an automatic controller and the pump for the floor loops is wired to a thermostat on the wall so that it will shut off if not needed in the spring/fall/summer.

I would like to be able to allow the controller to relay the heating element of the tank to "off" whenever the pump for the solar is on during the day, to save energy ( I think now what happens is that the tank senses any loss of heat to the floor and then 'tops up' the heat in the tank right away.

I would like to allow the tank to shut off and allow the solar to slowly heat the tank on the sunny days without using electricity. This will also allow the solar to not overheat on days when the tank is already too hot and the sun is good.

There is a relay 2 built into the controller which, if wired in would allow the element to be turned on/off through this setting, but I am unsure of how to do this.

Do I need an additional relay off of the element in the tank to allow for the 240 V. Not sure now to reconcile the fact that the power to the element is different than what would be running through the controller.

Also I would have to keep the tank's power separate due to just the load on that breaker.

Any ideas? maybe I'm overthinking it, there is probably a simple solution.?

On 2016-07-18 by (mod) -

Jim, yes it's possible to use a water heater to heat small areas or zones. Your temperature limit of 50F is certainly within the setting range of most wall thermostats. The article above summarizes the approach and the questions about this heating method. Let me know if any of that seems unclear or incomplete.

On 2016-07-17 by Jim W

I want to heat my basement with hot water heater (circulator pump and heater unit)i live in upstate New York and don't plan on running heat above 50 degrees in winter so pipes will not freeze in sub zero weather my water heater is 40 gal electric and heater is rated at 80,000 btu(used unit from friend)can this be done?

I plan on hiring a plumber to do work or is this not capable of being done.Any help would be great.

On 2016-01-25 by David Davis

I never thought of putting more than one water heater in my house. I want to get a electric water heater, but I wasn't sure if it would work for our house.

We generally aren't trying to run laundry, dishes, and showering all at once anyways. Putting in two units could definitely help, maybe just one for each floor. But I'm cautious because they run on electricity, would that be practical than the gas types?

On 2015-06-08 by Greg Phiopps

I live in the Sonoma the win country of California. I want to use an direct electric hot water heater using photovoltaic panels The existing heater is 125,0100 BTUs and I want to use the cheap power to run the system instead of gas. I have eight zones and 35,000sf of house

On 2015-03-05 by (mod) -

Thanks Steve & Gavin, we've updated the article above and added some comments to the CMHC article. We welcome your comments. Daniel


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