I built a new 1700 sq.ft. home last year in central lower michigan.It's a wood basement with r24 walls and has a walkout. Before the floor was poured I put down the heavy plastic,2" of the correct foam, and 7 circuits of 1/2" pex tubing.I have a forced air furnace and now I'm ready to finish my basement floor heat system. Being this is supplamental heat, could an electric water heater work? Unless it's too costly to operate I didn't want to have to vent out a gas one. This will also be a stand alone system too, not to be hooked in with my household water system.I also need to get the manifolds, circulating pump, etc. Any suggestions? Thanks

A water heater is only about 15,000 BTU/hr. The water heater probably wouldn't be very happy running all the time... You need to do a heat loss study with your inside and outside temps thru your R24 walls and see how much heat you need to maintain your desired temp, or provide whatever percentage of your overall heat you require

For maximum comfort, you want to put as much heat as is usable into the radiant floor (vs the forced air furnace). More than enough to justify using nat gas (assuming that is the gas you have available) vs electric.

I'd consider a Taco X-Pump to a shared gas tank water heater (probably ~40k btu/hr).

carguy - I hear you. As you are heating the rest of the house anyway with forced air, you just want to make the floor warm and maybe offset some cold air dump to the basement.

Assuming you have a few supply air runs in the basement for fresh air, a double element electric will handle your load. Probably a single will unless a large part of the basement is a walkout. As long as you have foam under the slab, the slab once warm, will not need much to maintain it. It might mean that the water heater runs full time for a period of time until the slab is up to heat, but once there, it take very little to keep it there.

How cost effective electricity is, is dependent on the difference you pay between gas and power. It is seldom worth the cost of doing an elaborate system if all you are doing is slab tempering. Are you heating the whole slab as one zone or do you want to have different areas?

What are your fuel options, and their local costs?

Is this 1700' of basement, half of which is below grade? Did anybody do a heat load calculation on that basement?

What is the construction of the above-grade portion of the basement walls, and how many square feet of windows & doors, at what U-factor?

Until the heat load is known, it's hard to say what a good solution might be. Unless the energy pricing is known it's hard to estimate whether it might be considered "...too costly to operate...".

It's sort of like asking what car you need for a drive to Detroit, given that the car in question has to be blue, and cheaper to run than your other car. A whole lot depends on how fast & how often you need to get there, and what you're hauling along with you, and what the other car is.

thanks for your replies. To answer veteren and senior members questions, I have lp gas at $1.20 a gallon, the walkout has only about 20' at basement floor grade with a pretty steep incline back up, there has been no heat load calculation done,the floor is done with 7 circuits in 1 zone, the basement is wood with 2x8's, 3/4" ply with all sealed seams and 1" foam board outside of that. With last winters extreme cold I was very happy with my electric and gas bills, but I know with the slab warmed and my open stairway from the basement to the mainlevel it will help more, besides the fact of feeling better on my feet in the basement.

Your torturing us here!

OK, you have buck-twenty propane...

...and the price of electricity in your neighborhood is... ? (Take the whole bill, divide by the total kwh.)

And the local 99% outside design temperature, roughly? (Not the coldest temp ever recorded, or even the coldest temp every year, just the 99th percentile temperature bin. Or just give a ZIP code for weather data purposes.)

https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf

https://www.captiveaire.com/CatalogContent/Fans/Sup_MPU/doc/Winter_Summer_Design_Temps_US.pdf?v=17112015

So, it's 2x8 studs on some unspecified spacing...

... with R24 cavity-fill and an inch of some unspecified type of foam on the exterior...

...and what type of siding?

Total square feet of above-grade wall?

Total square feet of above grade windows/doors?

U-factor of those windows & doors?

Given the scenario as described by OP, we can assume the F.A. heating is designed to keep the house AND the basement warm at design temp for his area.
What he wants is to know the cost of running the slab tempering.
So what is the upward heat loss of one square foot of basement floor given that the ambient air temp above it is 70ºF and the target temperature is 70º? That is a d-t of 0º.
And sure, he'll have a little heat loss through the foam but unless he has running water under the foam, even this diminishes the longer the system is in operation.

All he is asking for is to warm the slab, not the basement. Possibly ,it is for a children's play space. Maybe he wants to sit on the floor to play with his toy train set and not get his cheeks cold. In any case I don't think we are talking about the heat loss of the whole basement.
This is often done out here. It just takes the "basement feel" out of the basement. Given that he has an open stairwell, he may have a bit more "heat loss" then if it had a doorway but still, given that it's a wood basement with foam outside, even one 1500 watt element will probably meet his expectations.

Probably true.

But without the price of electricity how would we even estimate the operating cost?

We haven't gotten verification on the size of the basement slab yet.

Unless the forced hot air is zoned there's a high likelihood that the basement would overheat if the slab temp were raised very much over the stepoint temp of the thermostat, but if the total heat load is low enough an electric boiler may not have too high an operating cost.

First things first- get the heat load estimated with reasonable accuracy, then figure out the best way to deliver that heat.