Bob Holodinsky was hoping for a better outcome from the heat loss calculations he received for his new Peterborough, Ontario, home — calculations that appear to have upset his plans for heating with a ductless minisplit. “I thought I was on the right track,” he writes in a Q&A post at GreenBuildingAdvisor, “but now I am not so sure.”
The 1 1/2-story, slab-on-grade house will be built with 2×6 exterior walls, insulated with blown-in fiberglass and 2 1/2 inches of expanded polystyrene insulation (EPS). Conditioned space totals about 1,900 square feet.
There are lots of triple-pane windows on the northeast side of the house, which faces a lake. The living-dining-kitchen area alone is responsible for a heat load of 17,000 Btu/hour, and the house as a whole shows a heat loss of 42,000 Btu/hour.
Holodinsky’s builder says that insulation in the roof will equal R-75. Exterior walls will have R-24 insulation between the studs, with an additional R-10 in the exterior foam sheathing. The slab is insulated with 3 inches of EPS.
“I was hoping to heat it with a Fujitsu minisplit on each level,” he writes. “Is that still a viable option?”
Holodinsky’s misgivings are the topic for this Q&A Spotlight.
Heat pumps are not the right option
Although he can lower his energy demands by air-sealing and increasing the amount of insulation in the house, minisplits may not be the best fit for this Climate Zone 6 location, writes a GBA reader who calls himself Flitch Plate.
“I would be concerned with minisplits as the sole heat source in Peterborough, no matter what the BTUs are,” Plate says. “Heat pumps are the poorest performers and least efficient at the times you need them most: very low temperatures. I would design in a backup heating solution, such as a small…