Thought I would pass along some observations about heating my nearly completed ICF house. It's 2000 SF with a 780 + SF garage. Sealed and conditioned crawl space and attic with nominal 10" of spray foam on the underside of the roof. During construction the garage to kitchen door has been open all the time.

Total power consumption from 11/20/08 to 12/19/08 was just over 3500 kwh. This is for lighting, power tools, a temporary electric resistance heater, and the indoor unit in the garage of the Daikin heat pump. Virtually all the power gets converted into heat eventually. Temps in that time frame ranged from a low of about 5F to maybe 40F, with most nights in the teens and most days below freezing. The power consumption converts to about 16,600 Btuh average. There would be, at most, about 6000 Btuh additional provided by the indoor heat unit in the garage, which ran pretty much full time. The heat pump unit in the house hadn't been turned on yet because of all the dust that was being generated, hence the temporary electric furnace. The house is pretty well sealed except for the two overhead garage doors not tight at the top yet, and a couple of construction man doors with a canvas at one and an old shirt at another for draft stops! The electric furnace had only two elements connected (5 kw ea?) and was fed by a 40 amp breaker. It ran less than about 25% of the time except the very coldest days, or whenever the garage doors were open!

I turned on the indoor Daikin heater just before Christmas and took out the electric furnace. I also installed a pellet stove just before Christmas. This week a couple of days have been in the 30s and 40s during the daytime. Yesterday the house temp was 69F in the morning and 72F in the evening. Neither the heat pump unit in the house nor the pellet stove ran all day. The garage unit ran part of the day. Heat was supplied by sunlight, 5 workers' bodies, lights, and power tools! This morning the outdoor temps rose from about 31F to 40F by noon. The house was 74F this morning, and by about 1 pm had dropped to 72F. The pellet stove and both heat pump indoor units had not run, and there were only 3 workers providing body heat.

It looks like the heat load calcs my HVAC nephew did are holding up, 36,000 Btuh at 9F outdoors, and 20,000 Btuh at 29F.

My ERV isn't operational yet. I need to get it going for the balmy days of 50F to help get rid of the internally generated heat! I didn't think I would ever need to run a/c much at all but now I'm beginning to wonder if I'm not going to have to run it on 50+F days just to get rid of the normal heat of living!!

Mac, How much of a factor is the 10" of roof deck insulation on the performance of your HVAC system? Would 5" been sufficient and keep you from having to run your A/C at 50* outdoors (somewhat tongue in cheek here)?

Give your HVAC nephew a gold star for his load calcs.

By the way, how is the hose sill under your garage doors working? Dave

Mac,
Just wait til you get moved in and on one of those 5 degree mornings when you lay your hand on an exterior wall and it's the same temperature as the interior wall. You just dont get that in a stick house.
By the way, what kinnd of "R" value do you get with 10 inches of spray foam? 70+?

Greg

" lay your hand on an exterior wall and it's the same temperature as the interior wall."

I don't understand this analogy?

Jim, I've noticed on cold days with a 2x4 framed house you can feel the cold radiating through the walls, probably due to air leakage. With ICF, the walls are as warm as the rest of the house.

Greg

This house is a day vs. night difference from a house I lived in near Pittsburgh over 30 years ago. The first floor was clay tile construction with stucco exterior and plaster interior. No insulation at all! On cold days you could feel the heat radiate from your body to the wall! Talk about a cold feeling. No cold feeling in this ICF house!!

The foam is Icynene, 1 1/2 lb density, with an R rating about 3.8/in, so that gives something on the order of an 35 to 40 R value. The foam is quite uneven, like the surface of a brain, so it's impossible to know accurately what its net value is. It could easily be on the order of 50 in some spots, and 15 in others.
 

The 10" makes a big difference, but I don't know how much. We never ran calcs for less than R35 or 38 since R38 is the minimum per Northwest Energy Star specification. Incidentally I won't be getting an Energy Star rating because the governing body here in the NW has no provision to recognize using the crawl space as a supply plenum. They tell me they don't have the time or staff to pursue a technical option, so I won't push it.

The accuracy of the load calcs is in great part a result of the fact that my nephew has invested in a multi-thousand dollar program called Right Suite from Wrightsoft.

The hose sill isn't. I couldn't find a hose that would work right and I decided I didn't want to have a barrier in the door way for sweeping water out of the garage. The seal on the bottom of the garage door, an Amaar Olympus, seems to work pretty good. I have a 3/4" foam thermal break between the garage slab and the threshold right under the door, which I need to replace. When I put sealer on the garage slab it spilled over the foam and melted it!!