What type of heating system makes the most sense for a small, very well insulated home?
I am building a 1300 sq foot home in Durango, Colorado, in zone 5b. According to what I can find on line, we have a bit more than 7000 heating degree days here . The house I am building will have real (house is exterior foam wrapped for thermal break) R-30 walls and a little over R-50 ceilings. It will be tightly constructed and blower door tested. It will also have an simple bath fan exhaust system for air exchange (from three bath fans on the different levels). The house has three levels: a 450 sg ft daylight basement with 2 bedrooms, bath and office, a 550 sq ft level over that with living and kitchen space and a 300 sq ft third level over the attached garage that will be all master bedroom. Due to the three levels, I am struggling somewhat with a heating source decision, however. I plan to have a small woodstove on the kitchen and living space level, but what is the most efficient and cost effective way to heat the basement level and the master bedroom level as well as provide base heat for the whole house when the wood stove is not in use or the owners are not at home to stoke the fire in the dead of winter?
Thanks,
Eric
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Eric,
Here's an article that may help you:
Heating a Tight, Well-Insulated House
Thanks Martin,
I have read the article through several times and the included two pages of comments as well. It was what initially got me very interested in minisplits! The reason I posted a question was because of two factors: My house is essentially a three zone animal, making it harder to heat all of it from a single point source, and it is in a cold area (Durango, CO, zone 5), making the option of minisplits possibly questionable. Just like one of the comments on the article, the Mr Slim hyper heat models (which would cover the cold temps we see here) only come in single zone configurations, not multi zone, making the installation of three of the these units to cover my three zones rather expensive. Local heating contractors just suggest radiant or a hydronic system at $15000 install price tag, which is just not in touch with the whole idea of super insulation. I am very interested in the minisplits, but I am concerned that they might not provide the heat needed for our typical overnight winter temps. If I install a multi zone minisplit system that would be the most economical for three zone installation such as sanyo's multi zone system, they claim to produce heat only down to 4 F, and at a reduced percentage of capacity. I guess what I am asking is if you or anyone knows of any cases where a multizone mini split system has been used with success in a similar climate to Durango, Colorado (~7000 heating degree days) and of course all of the details on its usage: install cost, operating cost, success at low temperatures, etc.
Thanks again.
Eric,
Whatever type of heating system you choose, improvements in the home's envelope will lower your energy bills. Choose the best windows you can afford, and strive for a very low level of air leakage.
Any of the heating systems mentioned in my article will probably work successfully in your house. The choice is yours.
If you choose to install a multizone minisplit heat pump system, you can always install a few lengths of inexpensive electric-resistance baseboard units to provide supplemental heat on the rare nights when the outdoor temperature dips below -10 degrees F.
Eric,
Martin has good advice, of course. If your climate is so chilly, it probably makes sense to go a bit further with your thermal enclosure, say R-40 walls and R-60 ceiling, and pay careful attention to window and door details to minimize thermal bridging and ensure air tightness. That should help some with heat distribution, but it does seem unlikely that a single zone heat pump could evenly heat three levels. You could install two Hyper Heat units, one at the bottom level and one at the top.
I just installed a system in a home like what you describe. We used a used Burnham boiler from a recent boiler upgrade and tied it to the woodstove with an indirect tank as a buffer. This was mated to 2 Runtal flat panel radiators per floor. When they are home, the house is heated with wood and when they need supplemental heat, the 80% efficient cast iron boiler fires. The indirect tank has 2 heat exchangers, one for hydronics and one for solar, the water in the tank is DHW. This is a log home, so I'm not sure what the wall R-values are, but the ceiling is insulated with 8" of foam for about R-56. We are about 8000 HDD.
We've only used ductless minisplits in single-floor applications and when necessary have had good results with hi-lo stud-space chases to circulate air from room to room using small quiet low-energy fans. Using a similar principle of gentle forced-air circulation independent of the minisplit fan unit, it occurs to me that the natural stack effect in a well-insulated three-story structure might be beneficially exploited with a simple vertical contraflow duct and fan to return warm air to the lowest level to ensure even distribution of conditioned air. An amply-sized straight-shot chase with no elbows would minimize fan load. Thoughts?
I'm just finished up my own house (will it never end!?) that's similarly sized and insulated. Climate zone 6 for me (NW Iowa). The biggest difference is that mine is all one level (slab on grade). Interior size is about 950 sq. ft.
10" double stud walls with dense pack cellulose and R-70 attic.
A small wood stove (1.1 cu. ft. firebox) was planned to be my main heat source from the beginning but the question of what to do for a backup heat source gave me a lot of trouble. I looked hard at mini-splits but the cost, at least for me, got prohibitively expensive once I started looking at the units that could deliver enough BTU/hr at the cold temps we have. Especially for a heat source that will (hopefully) rarely be used.
In the end I decided to go electric baseboard. No, it's not the cheapest to run and it's not sexy, but it is cheap and easy to buy. Easy to install and easy to hook them up in zones. No moving parts. No maintenance. The house is small and well insulated so it's not like they're getting installed in a 2 story 100 year old drafty house.
I was able to buy enough for my house for about $250 (thermostats not included). That's at least $5k less than the mini-splits I was looking at. $5000 buys a lot of electricity.
I haven't installed them yet (finishing drywall now) so I don't know how good they're going to heat the place or how much energy they'll use to do it. Only the wood stove is running now and it's been heating the place like a champ. I realize you're wood stove won't do so well with your multi-level affair though.
Like I said, my baseboard is only there for a backup for when I leave town for a few days and can't feed the stove. You're situation is a little different. Still something to think about.
Good luck!
Alan
Pellet stove in the basement with electric baseboard backup. Pellets are low cost here and the stoves can run unattended for longer periods than a woodstove. Mini split main floor with woodstove. Electric baseboard back up in master. I bet a small pellet stove heats the whole place perfectly from the basement. And the mini split will cool all floors well enough too.
(Natural gas if available is a very low cost choice both to install and the cost of the fuel. There is one cost though, the monthly base cost that is too high if very little gas is needed such as in a superinsulated small home.)