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Community and Q&A

Mech Design for “Pretty Good” addition/retrofit

koselig | Posted in Mechanicals on

We are expanding a 1bd/1ba cabin into a “not too big” 4bd/3ba family home, and I am struggling to work out the mechanicals. We are working on modeling so that will obviously inform the selections, but I would like to hear from you folks if you have other suggestions we should be looking at as we get into modeling everything.

Zone 7 – near Two Harbors, MN.

For the mechanicals I have a mixed bag that I am guessing is overkill and needs editing:
1. “Right sized” Navien, Viessmann, or IBC boiler – Prep for solar collector preheat?
2. Expand existing slab-only hydronic to slab in addition and Jaga/Runtal/SlantFin radiators in bedrooms/bathrooms
3. Domestic Hot Water – Indirect tank? Heat pump water heater? 
4. RSF Opel fireplace (EPA2020 via catalyst)
5. CERV heat pump air exchanger
6. Ductless cool/heat (install one head upstairs in classroom/hall and pre-wire/plumb for second head on ground floor South elevation, opposite kitchen

We do have LP onsite but I aim to minimize our dependency on LP deliveries (not only for environmental concerns, we have a 1/4mi sloped driveway that gets icy and narrow in the late winter). I can’t entirely eliminate it because our shop/studio/office building has a mod-con boiler providing hydronic heat and DHW.   But the house will switch from LP to induction range, and from LP dryer to electric condensation.

When I look at these heat pump water heaters, they have an electric heating element as a “backup”. Why isn’t there an air-to-water heat pump that simply uses an electric element to do a final heating if the outside air is too cold, like when it is -20F here?
When we are here, we’d just be heating mostly with the fireplace. So I am guessing the fireplace plus the CERV should distribute heat pretty well. The radiators would just be to heat it up the rest of the way in the faraway bedrooms and bathrooms. Then when we are traveling 4-5wk in the winter, the radiators would come into play and provide primary heat. But even still, wouldn’t it be ideal to totally drop LP and have an air-to-water heat pump with some electric element?

We homeschool our 4 kids so we truly “live” here when we are not traveling, so getting a nice, consistent setup is really important. The previous owners were totally off-grid and I suspect they went for a time without running the air exchanger, and the result is the windows have been compromised. We are planning on replacing them all with Duxton triple-pane fiberglass. Between that and the fact that the only heat is from the radiant slab when we are not here feeding the stove (we currently have a Jotul we love), there is a bit temp delta between the basement and the upstairs bedroom where the kids currently sleep.

Thanks all!

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