Thanks in advance for any guidance... just using this as a check on whether I am crazy going down this path. I am just finishing a renovation on a 3 story, 1,400 sq. ft. rowhouse in DC. It has Warmboards throughout and closed cell to code. We have a separate AC system, but now I need to make a decision on heat source. I have had two load calculations done: 10,850 and 18,000 Btuh. The home has NG already. One of the engineers suggested I go with an electric boiler for I would have a really, really long time ever getting back the cost between elec. and NG. Some people have looked at me like I was crazy to ever go down this path. Thoughts?

The cost of power per therm for each fuel source?

Domestic hot water requirements e.g. Roman tub, body shower, the showers?

Do you have an extra 60 amps in the service?

I am not sure if I have the calculations right, for this sounds high, but all in my gas bill was $110 for 101.4 TH, so including taxes and fees, $1.08 a TH? On the electric side, electric was $47.59 for 331 kWh, so $0.14 kWh?

Two showers, standard 2.5gpm flow heads. Traditional size bath. Household of only two, so not a big load demand, save for the few times a year we have visitors.

You've got a great question on the extra amps. I just had a new panel put in, and he sized it to 150 instead of 200, saying I simply didn't need the bigger service. That $50 savings may come back to bite me. That being said, I may. The house doesn't look to have a big draw. I'd have to check.

What is the explanation for the widely differing load calculations? You might find this useful:

Borst Existing Building Energy Usage Analysis

Do the ROI analysis. If you have the electrical capacity, an electric boiler is likely the better solution. Electric boilers don’t have the mechanical failure issues associated with gas-fired boilers and are not bothered by short cycling either if that turns out to be an issue.

And since this is a green building forum…NG is still a fossil fuel and will never be green. Electric may be generated by burning fossil fuels or may be generated by using greener methods such as hydro, PV, and wind. “Green” in this context meaning not worsening our planet's global warming problem.

1 Therm=100,000 BTU (source fuel). Burned in an 95% efficiency boiler (or condensing combi hot water heater) it delivers 95,000 BTU / therm into the house. At a delivered retail rate of $1.08 / therm, every million BTU (MMBTU) costs $1.8 x (1M/95k) = $11.37 / MMBTU

1 kwh =3412 BTU. Used in an electric boiler at 100% efficiency it delivers 3412 BTU / kwh into the house. At a residential retail rate of $0.14 thats $0.14 x (1M/3.412K)= $41.03 / MMBTU

If you have an existing gas-fired hot water heater, it may be cost-effective to run the radiant floor off the hot water heater. If you don't have an existing hot water heater, there may be a lifecycle cost rationale for going with a heat pump water heater, but you won't be heating your house with it.

If you have reasonable access to the sun, you may do pretty well spending the difference in upfront cost of an electric boiler vs. any gas-fired alternative on a rooftop photovoltaic system. Some of that depends on how the net-metering or feed-in-tarriff deals work with your local utility.

For a heat load of less than 20,000 BTU/hr you do not need a 60 amp service (unless it's 110V). 20,000 BTU/hr = 20,000/3.412 = 5,861 watts. At 240V that's 24.4 amps- a 25A/240V drop would do it. But take a look at the heat load calculations and figure out which is more credible (or run your own numbers.) If the place is insulated, is reasonably tight, and has code-min or better windows rather than single-pane antiques my guess is that the 10,850 BTU/hr number is more accurate, in which case even 3500 watts of boiler would get you there with margin. Something like the 4.5kw Electric Mini Boiler Radiant EMB-S-5 would live comfortably on a 20A/240V circuit, and would be about 50% oversized for the more likely 10.8 KBTU/hr load. The boiler itself costs about $750-800, qty1 at internet pricing.

Nicely done Dana...really perfection!