Any thoughts on which heat source to go with for new construction? I am an electrician and could save a good amount by going with electric base board or electric "in floor" in each room. My thought for this is that each bedroom will have it's own programable thermostat allowing only one room to be on in stead of every room. I am guessing, this being a super insulated home I will not need many ft in each room to bring it up to temp. The first floor will be all open liv rm din rm and kitchen... in floor electric in this space or go with the heat pump? the mr slim units look good but what would the benefit be over infloor electric? for this open space??

In your previous thread and in this one you have been suggesting in-slab heating, and I wonder why. This comes up often in connection with a superinsulated house. One advantage of in-floor heat in a house with conventional construction is even distribution of the heat, and another is the "warm feet" feeling. In a superinsulated house, the inside temperature profile tends to be far more isothermal, with far less in the way of cold spots. That means that heat can be introduced in such a house almost wherever it is convenient to do so. Actually, if you want your bedrooms to remain cooler for sleeping, you'll find you have to keep those doors closed, or the rest of the house will heat them to practically the same temperature. This has been our experience so far (I'm also in NH).

As to the warm feet feeling, a concrete slab is very conductive, and without slippers on it won't feel warm unless its temperature is at least in the upper 70s (F). If you heat the slab that warm, the air temperature will rise to nearly that quickly, and that is too warm for comfort. You'll have to keep the slab temperature down in the low 70s to avoid overheating. My personal opinion is that in-slab heating isn't a good way to spend money in a superinsulated house, considering the cost of plumbing it and how you'd have to operate it. Resistance heating in a slab wouldn't carry the cost of plumbing, but it comes with the same drawbacks as with warm water through PEX as far as slab temperature and response time to thermostat changes.

Regardless of heating option, you'd be well advised to put at least 4" of foam under the slab, and more if you do heat the slab. You also need to address thermal isolation of the slab from frost walls.

As to mini split heat pumps vs straight resistance heating, obviously there is the tradeoff between operating cost and installed cost. The heat pump will cost less to operate by a factor equal to the averaged coefficient of performance. If you get say 3.0 for COP averaged over the heating system, you'd have to buy electric power at a third the cost for resistance heat to break even. On the other hand, installation of resistance heating is cheap, and distribution of the heat involves running just wiring to the strip locations. Without ducting, the heat pump dumps heat into the room where is is located. If ductwork is to be used for distribution, one way of avoiding ducts outside conditioned space is to use a service cavity up at ceiling level. There is a good thread running on this subject over on greenbuildingadvisor.com.

Posted By DickRussell on 21 Jan 2012 11:42 AM  There is a good thread running on this subject over on greenbuildingadvisor.com.

Can you provide a link?

What type of resistance heating do you recommend?

Thanks for the insite Dick. I have been looking into wood fired boilers to run for domestic and possibly infloor heat. I understand what you are saying about the whole house becoming balanced out with heat, because of the super insulating levels. My other beef with the heat pump is that when I really need it to crank some heat it will be in the teens or below and from what I hear the efficiency ratings drop drasticly at those temps and will kick on a resistance type heater to make up the differance.... could you in theory create a structure to mount the compressor of a heat pump in along with a small coil off the wood boiler to pre heat the incoming air to the heat pump?? or is that just non sence...

gusto
Mitsubishi makes a hyper heat model, that can provide 100% efficiency at 5 degrees and 70% (or something like that) below 0. It is rated down to -14 or so. They come in 9k btu and 12k btu models. They run around $1500-2000 online plus install. My plan for our SI house will be one of the 12k units on the main floor and another in the basement. 2' baseboard heaters will be placed about 1 in each bedroom for backup heat as needed. Hopefully they do not need to run often at all.
It is true as temps drop the COP of the HP lower as well. However they are typically still above 1, or what the electric baseboard heaters would be.
Either option comes much below the install cost as infloor heat.

Posted By lzerarc on 22 Jan 2012 11:33 AM
gusto
Mitsubishi makes a hyper heat model, that can provide 100% efficiency at 5 degrees and 70% (or something like that) below 0. It is rated down to -14 or so. They come in 9k btu and 12k btu models. They run around $1500-2000 online plus install. My plan for our SI house will be one of the 12k units on the main floor and another in the basement. 2' baseboard heaters will be placed about 1 in each bedroom for backup heat as needed. Hopefully they do not need to run often at all.
It is true as temps drop the COP of the HP lower as well. However they are typically still above 1, or what the electric baseboard heaters would be.
Either option comes much below the install cost as infloor heat.

Make that "100% of rated output at 5 degrees" and "70% of rated output at -13F".   At +5F they're running ~150-200% efficiency (COP 1.5-2.0), depending on compressor speed.  They come in more than the 3/4 ton & 1-ton models  too.  At mid-speed most heating mini-splits will run a COP better than 2.5 @ +17F.  

In most of US climate zones 5 & 6 a mini-split will have an average COP of 2.5 if sized exactly to the design condition heat load (which isn't always possible in zone 6, but can be in zone 5 in a superinsulated house.   Oversizing it by ~1.5x it will add ~0.5 or more to the average COP since it will spend most of it's time running at lower & more efficient compressor speed. In US climate zone 4 it's pretty easy to heat seasonal average COP > 3.0.

Electric baseboard have a COP of 1, which means it'll run use 2.5-3x the electricity of a mini-split.  Your electricity would have to be practically free for this not to make economic sense in a net-present value analysis, even with low heat loads & superinsulated houses.

You have to place the interior heads where they won't blow on humans, and this is even more so if you oversize, since the bigger you go, the more air it moves.  At some point oversizing becomes less comforatable, even if it's more efficient.

Posted By Lbear on 21 Jan 2012 10:16 PM

Posted By DickRussell on 21 Jan 2012 11:42 AM  There is a good thread running on this subject over on greenbuildingadvisor.com.

Can you provide a link?

What type of resistance heating do you recommend?

www.greenbuildingadvisor.com/blogs/dept/musings/service-cavities-wiring-and-plumbing

Thanks Dana Those efficiency ratings are really amazing! I am currently looking into using a gasification wood boiler for domestic and infloor heatfor my walkout basment floor and, most likely, will install a mini split on the main floor.