looking to build a ICF house. 2500 Sf home slab on grade radiant floor with at least 36" frost wall. Have done a Manual J with heat load Pro and came up with 62300 BTU/hr heat loss, 70 inside and 0 outside. Weather numbers used are for the Spokane Wa. Would like to do GEO but the return on investment verses using an electric boiler, Nextgen makes more sense. Power is cheap lots of hydro at $.065 KWH. I'm I on the right track. Jess

Also from my understanding this type of house is very air tight. Air needs to be turned over every so often. Why not use a small forced air electric for secondary heat.

That heat load seems pretty high for ICF. If 2500 is a footprint instead of a total sq ft and you're doing multiple stories, maybe not. But if that's total conditioned square footage, I'd be skeptical, understanding I'm saying that without knowing anything else about the house. Being over 20 BTU/sq ft for a design load in an ICF house is pretty rare though.

Air doesn't need to be moved around within the house, it needs to be exchanged with the outside. an ERV or HRV is important (energy or heat recovery ventilator). You'll also need to be very careful with any exhaust air requirements (kitchen hoods, fireplaces, etc).

Electric rates like that can work for electric heat. If you expect to be cooling though a heat pump is probably a better choice. I don't personally favor GSHP for residences, but I do like Air to Water units and the one I'm most interested in right now is the spacepak Solstice Extreme. Or you can do a few minisplits if spot cooling is all you need.

Absent cooling at that electric rate the air water's payback would probably still make sense in the medium term, but it's not as hard of a slam dunk.

yes I to thought 62,300 BTU/hr seamed high. This is going to be a single story house.

I have also researched ERV and HRV and still trying to get my head wrapped around the right one to use.

The exact location of the house will be Deer Park just north of Spokane. Summer time two months out of the year will average 80 ish but it cools down real fast at night to mid to high 60. We have a RV trailer, poor insulation in it. On hot days at night we turn on a fan to pull the cool air in and it cools down fast.I don't think we will need much cooling and if we do, get a standalone.

I also looked at air to water heat pumps, seems like Europe is way ahead of US. Had a hard time finding a source in the US let alone an installer.

I might be wrong here but heat pumps loose efficiency when the temps drop below 30 ish. I would think that you would need a second source of heat on the very cold days.
Don't get me wrong I do like the Air to water heat pumps
I'll check out your recommendations.

One thing I have noticed in DP was when the snow was on the ground and starting into the winter spring melt radiant heat off of objects would melt the snow around them. So maybe one could install a heat pump that would take advantage of this. Run the pump during the day and let the radiant coast throuth the night.
Thank You
NRT.Rob

I would at least look at www.chiltrix.com (rated to -14F). Or a low-temp mini-split. Maybe just one to handle the load most of the time and then supplement with electric heat.

A while back I was thinking water to water geo hydronic floor. Having to be careful Dew point for circulating cooled water in the floor. Why not insrtall a forced air system with a hydronic A coil for cooling. Then install an electric heat type ECM air handler to move the air and for a secondary heat source when needed along with a ERV or HRV exchanger. I was shot down on this Idea, I be leave on this forum. So again why not do the same thing but with a Chiller like NTRRob or Jonr systems. Yes up front would be expensive but the back end would be very flexible. So say you have a Deer Park week where there is 60 degree weather the hydronic floor is turned down. then you hit a 30 deg day you can flip on the electric to catch the house heating up. Also the benefit of forced air cooling. Just thinking out loud.
Thanks again to NRTRob and Jonr

There are ducted heat pumps out there that don't require a Chiller, they just do refrigerant right to the A coil, and if you're going to end up with forced air heat only they would probably make more sense unless you're trying to do a lot of zones and/or incorporate DHW production with the heat pump. My go-to there is the Daikin SkyAir system, but there are others. There are zoned air systems out there too but in generally I think zoning air system is a bad idea with most current technology... less bad if you are doing the hydronic coil technique though.

The combination of radiant and forced air does give you everything you could want, it's true. It's just a question of whether it's necessary.. you're investing in two heating systems really to solve one problem when other tactics, like operating the radiant floor at a consistent temperature, might solve it instead. Some people would prefer to dodge the additional cost for what you get (faster response, maybe some backup) and some aren't concerned with that. In most cases I would tend to avoid a fully redundant air heat system unless ducted cooling is a goal.

Many modern heat pumps are rated to deep subzero temperatures... old school technology starts to dwindle in the 30's, the newer units work to the negative teens.

Your heat load is the same as a similar walk-out I just designed in Minneapolis, except it has vaulted ceilings and a walk-out. You should have a professional Manual 'J'. I'm guessing half.

I'm with Rob on the GSHP, especially in mild climates. The NextGen looks like a nice unit. Mine is not installed yet. Rheem Marathon 80-105 gallon and an ERV.

Cooling should not be an issue if you exhaust the heat sources and control solar gain, wait you don't have solar :-).

I your loads are very low the floor will not "feel" warm, but they will not feel cold, unless you have tile everywhere. I keep my bathrooms set a couple degrees above the rest and find it's all good.

Once you get to R-50 ceilings and R-25 walls the need for central air diminishes rapidly. Then it is more a matter of controlling humidity. I have been using more dehumidifiers and steamers lately.

Even IRC 2012 code-min 2500' houses typically come in well under 35K @ 0F these days. As a point of reference my ~2400' 1.4 story 2x4 framed 1920s antique with 1500' of insulated basement comes in at about 40KBTU/hr @ 0F when I bump all the temps to 70F, including the basement. The windows are primarily antique single pane wood sash + clear storm windows, and the only insulation that actually meets IRC code min is the basement walls (part ICF, the rest retrofit foam on antique poured concrete.)

So how do you even come anywhere near twice that with an ICF structure? Is the place just over-glazed with code-min windows or something, or are there built-in ridiculously high ventilation rate assumptions or...??? If your real heat load is over 30K there has to be a glaring and correctable fault to the house design.

In a high-R high mass house in Spokane you can probably do just fine using nighttime ventilation approaches to cooling, due to the low to negative latent cooling loads in that climate. (I've lived in the Columbia basin in much crummier housing than that and did OK with a nighttime cooling approach, once I put exterior shutters on the west facing windows.) With reasonable roof overhangs on the south side to limit summertime gain and minimal glazed area on the west side to severely curtail afternoon/evening gains at the much lower sun angle, the peak sensible cooling loads can be brought down to something between small & tiny.

Humidity can (almost) always be controlled by ventilation rates in your climate, unlike the eastern half of the US.

If you shade the roof with a solar array it brings the peak cooling load even lower, though in most of WA that approach isn't yet cost effective. It will be by 2030 though, given the double-digit learning curve of solar.

Bottom line, get a better handle on the real heating & cooling loads (or reduce them by design, if you're really looking at 60K+ for a heating load) before deciding which approach to take on mechanical systems.

Thank you Badger
Dana I screwed up, Originally I had come up with 36,000 BTU Changed my design and messed up somewhere on the manual J My bad.
Thank you Dana

Even 36K is pretty high for a 2500' ICF house unless you're assuming it leaks air like a barn.