My HVAC guy is suggesting a traditional water heater with the heat pump, with a small electric boiler to run only the basement radiant heat. I'd like to get some opinions on this. What facts do you need from me to make some comments? House is 3600 SF. basement is 1700SF. I put R10 around the basement. There will be R10 under the slab and R5 around the perimeter. There is 1.5XPS (R7.5) on exterior of shell. R21/R23 batts will be used. R38 cathedral. I calculated I believe 55k BTU load for the home using a temporary HVAC-Calc software.

Whoops forgot my question. I am wondering if the traditional water heater and small electric boiler should be combined...?

Surf
This does not make sense from a thermal perspective You heat the basement with an electric resistance boiler ~ 99% efficiency, Inside the basement is a heat pump water heater lets say it runs at 160% efficiency in the winter. The heat pump heats the water and cools the air- and then you reheat the air with the electric boiler at 100% efficiency. This totally negates the efficiency of the heat pump (in the winter).
 In the summer the heat pump WH helps you out with the cooling load. You could use the heat pump only in the summer if you installed it anyway. You might look into high efficiency conventional hot water heaters- basically they have much lower standby losses because they are much more highly insulated. Look at the Rheam marathon ones for an example.

Cheers,
Eric

Eric, elsewhere we did the math with an eye toward whether the heat pump water heater was detrimental in the winter in a heating dominated application and concluded it was not. For our purposes we had a mechanical room in which was also a geo heat pump harvesting btu's at up to 4 COP adding heat to help make the hot water at maybe 2 COP. The consequence to the heating was similar to a desuperheater.

So the question is Surf, is that a geo heat pump? Why use an electric water heater and an electric boiler? Well it does keep operating hours down on a more expensive appliance. What about a WTW geo or a Hybrid?

While I don't have the new quote showing the electric boiler to run only the pex system in the basement, the plan is to install:

Carrier Infinity FE5NB004T00 variable speed air handler with 15 KW electric heater 92%
Carrier Infinity 25VNA048A003 20 seer, 4 ton heat pump with matching TXV a-coil

It is not a geo thermal heat pump. Just a regular heat pump. So I'm looking at a heat pump, a small elec boiler for the pex system, and a DWH for domestic water. I am curious if I should combine the DWH and elec boiler. He suggested to keep them separate. Now you guys are saying not to have a heat pump and elect boiler?

Surf
My assumptions based on reading your comments is that the you were talking about using a heat pump water heater, in a basement heated by an electric boiler. My comments were directed at that, on re reading it, I think I had the wrong scenario.

So if you are heating the basement with an electric boiler, and then using a seperate electric storage tank type hot water heater. That is OK. You should consider a high efficiency tank type one. Look at the marathon tanks for example. More insulation, less standby losses.

So the real question is will an indirect storage tank coupled to your electric boiler do better than using a separate electric hot water heater. The answer is probably not, unless the indirect tank was much better insulated then the standard electric hot water heater, (DHW).

The reality is resistance heat is resistance heat.

Cheers, Eric

Ok good to know thanks so much.

The boiler is more expensive do not put hours on it making DHW.