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We are reconstructing an old house. Step1 is getting a fairly airtight envelope and a lot of insulation installed.

We have the designs and a heat load analysis, saying at peak delta (minimum -17C external temp, 20C internal) there will be a total heat loss of 6kW including ventilation.

The MHRV unit has an integrated air heater and recirculating air route but our design does not allow for large warm air heating duct work, so we don't think that we could get more than 1kW or 2kW from that.

To supplement it we were offered underfloor radiant, but the price is astronomical here and we don't like it much. We much prefer the minisplit ductless feel of heating and cooling.

We are looking at supplementing the heating with Mitsubishi hyperheat, and we would really like to know if we can get away with heads in the main rooms and upstairs hallway, or would every small room need its own head? My thinking is I could get away with an 8kW heat pump and 4 heads. One in each main area, while MHRV recirculating routes would cover bedroom thermal losses. Each bedroom has a heat load of only 400 watts. Bathrooms have radiator ladders.

Is this viable or am I looking at an indoor multisplit unit per room?,

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  • Happy to add any info. Winters are -17 lowest, though last decade it has been milder. It can get hot say 30s. – Sentinel Feb 16 '18 at 17:00
  • Frankly, would be happy to pay for HVAC second opinion, as in Central Europe aircon/air heating skills are hard to come by, and prices too high. Everything is hydronic here – Sentinel Feb 16 '18 at 17:12
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Having a split system will heat the home you do not need to have each room connected if you leave your doors open. In my area it is common to have 2 or 3 units in the large areas of the home like the dining room/ kitchen and one in the living room. And sometimes a small unit in the master bed/bath room. Your area gets colder than where I am at but it comes down to how uniform in tempature do you want the house, if you can live with doors open at night 2 inside units could do the job. If you want 1-2 degree range throughout then more small inside units would be needed.

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  • Thanks. I am thinking that with doors closed, the MHRV recirc circuit would cover losses. Specifically, I am looking at Atrea R5 Duplex, which has a separate blower for recirculating air through an integrated heater. While it can heat to 7kW, I think a low volume quiet airflow would cover a kW or so needed to maintain a night time comfortable temp.thoughts? – Sentinel Feb 16 '18 at 18:13
  • What size is the home you said well insulated, my last home I installed a 5 ton unit approx 17kw our low temps -10c max that home was 2 story 2800sf, I had a wood stove that did most of the heating. the heat pump unit did well until it got down to 0c then it used electric coil packs way expensive a 2 ton unit or 7kw would be pushing it if the home is 1500sf or larger with the -17 temp. Although if your calculations are correct it should work. – Ed Beal Feb 16 '18 at 20:00
  • The size is about the same actually I think - about 2800sf total floor space in a first story and a second story in attic space. I guess because the second floor has the gable roof the total volume to heat is less, so we could count about 2200 sf. The MHRV has up to 7kW heating, but we wouldn't use it. We'd only use about 1kW of that, and the heat source is different (hot water heat exchanger or direct electric). The rest, I am looking at Mitsubishi Hyper Heat of 8/9/10kW or more, and those heat pumps are for cold climates down to -25C, with 80% efficiency at those sorts of temps. – Sentinel Feb 16 '18 at 20:19
  • We have a wood stove too, but not sure how to distribute the heat. – Sentinel Feb 16 '18 at 20:20
  • I cut a hole in the ceiling above the stove and installed a tempature activated fan, in the winter I pushed air up from the stove and in the summer I reversed the fan it really helped to move the air up/down stairs, it worked best in the winter heating the upstairs, – Ed Beal Feb 16 '18 at 23:30

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