Operating temperature is only part of the story
A heat pump may run at a low outdoor temperature without producing enough heat for a particular home at that temperature. Ask for both heating capacity and efficiency data for the exact proposed equipment combination at your location’s winter design temperature.
As it gets colder, your home generally needs more heat. Equipment output and efficiency also change. A room-by-room load calculation helps an installer match those needs to the system; floor area alone is not enough.
Technical background: Department of Energy: air-source heat pumps ↗.
Plan for every room
A warm living room does not establish that a closed bedroom, distant bathroom, or basement is adequately heated. Ask how the design distributes heat and protects plumbing in spaces that previously benefited from a boiler or furnace.
Insulation, air leakage, duct condition, and indoor-unit placement affect results. Discuss planned weatherization before finalizing equipment size.
Agree on a supplemental-heat plan
Some installations can meet the home’s full heating load; others are designed to work with another heat source. Ask the installer to explain any capacity shortfall, control settings, and when additional heat is needed. There is no universal outdoor temperature at which every homeowner should switch systems.
Also discuss outages: heat pumps require electricity, and many boilers and furnaces do too. Have a qualified professional assess any backup-power arrangement.
Maine context: Efficiency Maine: homeowner FAQs ↗.
Understand defrost and outdoor clearance
Heat pumps can periodically defrost the outdoor coil during heating. Check your manual for normal behavior. Ice that persists, obstructed airflow, a blocked fan, or a recurring fault calls for professional attention. Do not chip away ice or pour hot water onto the unit.
Keep the manufacturer’s airflow clearances and address snow accumulation around the unit. Ask your installer about drainage and exposure to roof snow before winter arrives.
Compare costs for your situation
Efficiency and cost are different questions. Your electric rate, alternative fuel price, home heat loss, and seasonal system performance all influence the bill. Request an annual estimate with its assumptions stated, including any supplemental heat, instead of relying on a promised percentage saving.
Bring the installer checklist to your next conversation.