My house is old and has radiator heat, which is heated by a gas furnace from which the hot water is pumped through 7 radiators and back in. Hypothetically, and by no means would I ever want to do this to my system, if gas became unavailable in my area, would it be possible for me to adapt a regular electric water heater and mount a pump nearby to circulate water through the system like the present one does with gas?
Another way to ask is, what if I were designing a radiant hydronic floor heating system and my only source of energy were electric. I'm sure there are specialized heaters for that purpose that have a pump built in but, if I wanted to make my own (for experiment's sake), could I do it with a regular electric water heater and a pump?
At first thought, I don't see why not and I think the most complicated part would be designing a wiring control that works with the thermostat and connects the heater and the pump. I'm asking this primarily to understand the visceral concepts of heating and associated devices. Of course, unlike with a residential water heater that has open inlet for new water to come in, in this case it would have to be on a closed system which itself has a fill valve and a backflow adapter.
Best Answer
It's actually not uncommon to use a water heater for heating a well-insulated building (though an electric water heater is very UN-common, due to operating cost.) But....
This is not commonly done with radiators, which are typically designed to operate on 180F water. It is much more common with radiant floor heating, which can function quite well down at 100F water temperature in many cases.
The building must be well-insulated - the typical reason for using a hot water heater is the inability to get a "boiler" that's SMALL enough for the load of a well-insulated building. As designed, my shop will take about 30K BTUs/Hr to heat to 68F on a -20F "design day." (the minimum temperature used for the sizing the heating system.) A 100K BTU/Hr boiler would be massively oversized.
You need an expansion tank for a closed system, and you may need to use stainless steel pumps (rather than cast iron) if any part of the system allows oxygen to get in (non-oxygen barrier tubing, or an open system where the SAME water heater heats the floor AND the domestic hot water - in which case the floor tubing needs to be potable-water rated - not actually difficult to find in PEX tubing.)
Finally, if there is gas in your area now, it's stunningly unlikely to "become unavailable" in a future where you still have electricity. And if you are "heating with electricity" you really should be using a heat pump (in cold climates, a cold-climate air-to-air heat pump or a water-source/geothermal heat pump) since you get about 3 times the heat (depending on conditions and specific unit) for a given amount of electricity purchased. Heat pump water-heaters won't work without some other source of heat, as they are designed to operate from air that's 50F or more, typically.