Heat Pumps & HVAC

Heat pumps are the single most important technology shift in residential building science in the last decade. The math has flipped: in most North American climates, a cold-climate air-source heat pump now beats fossil-fuel heating on operating cost, carbon, and comfort — and it cools too. For an owner-builder, this means your mechanical room shrinks, your fuel storage disappears, and your sizing math gets driven by the envelope, not the equipment catalog.

The decisions that matter most are sizing, distribution, and cold-climate performance. Oversizing is the most common mistake: a heat pump that's too big short-cycles, dehumidifies poorly, and runs less efficiently than its rating suggests. Get a real Manual J-style heat-loss calculation before you shop. Then pick a topology: ductless mini-splits are the easiest to install and the cheapest to run room-by-room, but they require a head per zone. Ducted units distribute more evenly and look better but lose efficiency to duct losses, especially when ducts run through unconditioned space. HSPF2 and COP at low ambient temperatures matter more than the nameplate rating — a unit rated at 47°F means little if you live somewhere it hits -15°F.

Good starting points in this hub:

• Air-source heat pump buying guide — sizing, brands, and cold-climate ratings.
• Ducted vs. ductless — the trade-off most homeowners flip a coin on, with the technical reasoning to make a real decision.
• Heat-loss calculator for sizing based on envelope and climate zone.

The honest pitfall: a heat pump can only do what your envelope lets it. A poorly insulated, leaky house will struggle with a heat pump on the coldest nights of the year regardless of which model you bought. Tighten the envelope first, then size the equipment — see NREL's residential cold-climate heat pump research for the underlying performance data.