Electric baseboard heaters for an ICF house in Zone 6?
My husband and I are building a very air tight 2500 sq. ft. insulated slab on grade ICF rambler (6 inch concrete core with 2 inch foam on each side of wall) in Minnesota, and are wanting to avoid any natural gas hookup. Slab is already in so in-slab heat is no longer an option. At first we were thinking ductless Mini splits, but high up- front cost along with concern about performance during long periods of severe cold have us currently planning to put an electric baseboard heater in each room with a separate thermostat for each resistance heater. Will also have an HRV with ducts in conditioned space in built-in soffits. My husband did Manual J and also put our specs in REM/Rate and got room by room load report and figured we can heat entire home for around $1,500 per year this way because home is well insulated and designed for some passive solar. Would have generator in case of power outage. Maintenance and up-front cost are so low with the baseboards, that it seems more appealing and reliable even though not as efficient as other options we considered. Plan to install some solar down the road to help with load and could also add mini split later if not happy with electric baseboards alone. It is hard going it alone and not knowing others doing this, so looking for advice regarding this heating plan. One reason did not do in-slab heat was that I was afraid it was overkill and may actually be hard to keep house from feeling too warm since slab is a giant battery of heat even after you turn it off (a huge pro but also potential con?)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Was there a question in any of that, or just a comment?
In the spirit of "just comments"...
Not that you asked, but if you could heat our house for $500 /year with a few appropriately sized minisplits (probably can), it would "pay off" a lot quicker than roof top PV.
Putting the load numbers in BTU/hr or kw and the annual use in kwh or BTU it would provide more useful insights.
Thanks. Getting mixed reviews on Mini Splits for maintenance and defrost cycles is main reason we reconsidered and thought we could always install them later in addition to the electric baseboard radiators. For zone 6 would you recommend additional heat source with the mini splits? ( If we do solar panels we would be putting them on the ground and doing it on the cheap.)
Without the actual heat load numbers (particularly the room by room load numbers) it's not possible to make reasonable guesses as to whether additional heat sources would be necessary.
There are many houses in US climate zone 6 heated solely by ductless mini-splits.
A 2" + 2" EPS ICF (about R16.8) is only ~12% above the IRC 2015 code minimum R-15 for mass walls in US climate zone 6. It's usually cost effective to go significantly better than code minimum when the heating source is resistance electricity. See the whole-wall R values in the zone 6 row of Table 2, p10 of this document:
https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf
With siding, air films, the R-value of the concrete & interior finish wall added in you're looking at about R19-R20 whole wall for the 2" + 2" ICF. That's barely over half the R35 that would be the approximate limit of cost effectiveness on a lifecycle basis.
I suspect you are in a location with legacy hydro and 100 year contracts keeping electricity costs low. Building at barely better than code minimum and heating with electricity without leveraging at least part of it with a heat pump is placing a bet that future electricity cost will never rise (in inflation-adjusted terms.) Even though solar PV at utility scale is cheaper than new fossil-burner power, home-scale solar is probably dramatically more expensive than your current retail cost of electricity.
In most of zone 6 MN there are still significant cooling loads for most houses. A right-sized cold-climate minisplit sufficient to cover a major zone in the house is still a rational investment in year round comfort, and will pay for itself in offset heating costs, even at your likely low / very-low retail rates.
FWIW: There is a guy in US climate zone 7 location in Q who used to post here regularly under the handle Jin Kazama who heats his house with four cold-climate Fujitsu RLS2H series minisplits that keep up with the load even at -30F outdoor temps.
Have you thought about stick framing the walls with cavity insulation and exterior foam, for a higher overall assembly R-value, probably a lot of cost savings too. Throw the savings into the mini-split.
We are in a highly insulated slab on grade in a similar climate, no water lines in the slab for heating (and no regrets), and I comfortably walk on the slab all winter barefoot. I wouldn't lose any sleep over that.
I will say that unless you're in the high altitude southwest, passive solar and thermal mass are over rated. The days you need that kind of heat or 'battery power' it's going to be cold and gray, or you'll be losing the heat through those same windows at night.
Thanks! Helpful to hear you are happy with walking on floor with no in-slab heat. Great other points too. We do already have our walls poured though.
If you decide to go with electric heat, I'd suggest radiant cove heaters in place of baseboard heaters. They take up no floor space, pose no burn or fire risk.
4 inches of foam doesn't seem like a lot of insulation to me, but I guess it depends on your climate zone.
Thanks. Our concern is that the cove heaters will distribute as well throughout the room and radiate to the floor well enough to be our only heat system, but will take another look at it. Have never personally seen one in use
$1,500/year for electric heat for 2,500 square feet in Minnesota seems pretty cheap to me, but you haven’t provided many specifics. Remember too that in northern areas, you can’t count on solar to provide a lot of energy on the coldest days when you need it most. Our cold days tend to be gloomy cloudy skies and shorter daylight hours, both of which reduce the energy output from a solar installation. A big pile of snow on your solar panels doesn’t help either.
If you go the baseboard route, using hot water may be a better option over electric even though it will cost more to install. At least with hot water baseboards, you have a choice of fuel sources you can use if electric ends up costing too much. Natural gas (if you have it available), propane, and even wood fired boilers would be potential retrofit options you could use in the future.
Bill
Appreciate all the things you pointed out, thanks. The hot water does leave a lot more options. In our case, our concrete walls are already poured.
Sarah,
Your plan is fine. In the future, you will probably find that an investment in at least one ductless minisplit ($3,500 to $5,000) or any amount of PV you can afford (assuming your local utility offers net metering) would be money well spent.
Other GBA readers considering this question should take Nathan's advice: Skip the ICF walls, and instead choose a wall system that has a higher R-value and costs less. The lower cost walls will perform better and provide savings that can go to a minisplit.
I would seriously reconsider air source heat pumps with minisplits for your building.
I'm going through a similar design process in Zone 7, and there is no question this is the best solution. In my opinion, usually a separate system for each floor. Final design and shape of your house will determine whether you need multi heads per system. If you only need one head per floor, then cost goes down a fair amount.
Besides the significant reduction in operating costs you get air conditioning in the summer.
For extreme winter climates like ours, use electric baseboards/cover heaters for backup when the temperature drops below -15F.