OVER-thinking mechanicals for Zone 7 deep winter homestead
We are making a modest 25×28′ addition onto the 1bd/1ba cabin we live in, to convert it into a family home.
The current structure is 1400sq-ft and its sole automatic heat is radiant slab in the basement. We use a Jotul wood stove as our primary heat. This means when we are traveling in the winter, the upstairs bedroom 2 floors above the radiant slab is cold. This makes me uncomfortable from a building health standpoint, but also convenience since we often return from travels at night and the kids are freezing until I get a fire blazing. There is a Venmar HRV running, of course.
With the addition, the structure will ultimately be ~2700sq-ft with 4bd/3ba.
I am looking at the CERV2 to replace the HRV.
The Jotul (which we love) is being replaced with a fireplace, RSF Opel 2C (with the catalyst). It should provide more than enough heat, although it will be on the West wall and the addition is attaching on the East, so I don’t expect bedrooms to get heated by the fireplace directly.
Ultimately, my idea is to expand the hydronic system to keep the temps consistent throughout by adding a radiant zone in the tuck-under 2-car garage which will be at the addition basement level, and low-temp Jaga radiators in the bedrooms/bathrooms. But considering ductless units can now operate at very cold temps, should I be looking at them instead?
A basic requirement I have for this house is to consider possible future guests and even future owners should we ever sell for some reason. We love using wood as our primary heat, but realize a future owner may not do that. So between that reality, and the fact that the fireplace is at the far end of the house from the bedrooms, I need to make sure that between the CERV2 (or whatever HRV we use), possible hydronic, and possible ductless, the house is nice and comfortable even without a fire burning. The idea is that the automatic systems will just run more efficiently or not at all when there happens to be a fire!
I also have not figured out domestic hot water. I have experience in our (detached) workshop with the use of a Navien combi mod-con which provides 3 zones of heat plus DHW, so I considered a similar setup for the house. But I am exploring getting away from propane dependency.
So – here are my ‘dumb’ questions:
1. HPWH – what do they do when it is colder than they can get heat? They use their backup element like a traditional water heater, right? Would that still be cost-effective in northern Minnesota?
2. Could an air-to-water heat pump run the hydronic system (like the http://www.electromn.com/gen/noraire.htm which is made in MN), using an integrated boiler when it can’t get heat from the outside air? Or would that be totally impractical cost-wise for a theoretical future winter where for whatever reason nobody starts a fire?
3. I know this ultimately comes down to modeling, but with the CERV2 and assuming we’re building a pretty good envelope, can you see a need for cooling? I am thinking we’d get a single-head ductless unit just in case, but is that in conflict with adding the hydronic radiators? I feel like the radiators are better since the heat will go directly into the bedrooms, but I have zero experience with ductless.
4. Why is it so many folks are saying hydronic is just a thing of the past for passive/pretty good construction? just the efficiency and low cost of mini split units? Is it folly for me to be looking at expanding our system to another slab zone plus upstairs radiators?
Thanks all! I hope this discussion is helpful to other folks in my position.
P.S. FWIW regarding our energy costs:
1. We currently pay ~$2/gal for LP. So we have multiple reasons – cost, sustainability, and the simple fact that we have a sloped 1/4mi long driveway which is precarious in the winter, suggesting it would be wise to go all electric.
2. We pay ~0.12/kWh for electric from the local coop, and pay extra to source it from wind (I realize this is primarily for warm fuzzies…). Our homestead was originally 100% off grid solar, so we will be building that up again as a new grid-tied system over the next 1-5 years, so I feel like this further bolsters the all-electric idea, but I don’t want to shoehorn it if it will get us in a difficult financial position later in life, either.
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