What size cold-climate heat pump do you actually need?

Most online calculators multiply square feet by a folklore number calibrated to oversized furnaces. This one does what NEEP's sizing method does: estimates your design-day heating load as an honest range, then checks a unit's certified capacity at your design temperature — because a "3-ton" heat pump is not 3 tons at −10°F.

1 · Your location & home

Why "BTU per square foot" charts get cold-climate sizing wrong

The numbers on retail sizing charts were calibrated by decades of oversized furnaces. A heat pump is different in both directions: its capacity shrinks as the temperature drops — the certified rating points at 47°F, 17°F, and 5°F can differ by 30–40% — and oversizing hurts it more than a furnace, causing short-cycling and poor summer dehumidification. Honest sizing means two things: an honest load range for your specific envelope and climate, and the unit's capacity at your design temperature, not its nameplate tons. That's what this tool does, with every constant sourced.

What this tool refuses to do (on purpose): room-by-room loads, duct design, multizone head selection, below-5°F capacity claims from public data, and final equipment selection. A proper ACCA Manual J + Manual S by a qualified contractor is the standard for the final call — this tool gets you to that conversation informed, not sold-to.