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.

Short answer

Don't size a cold-climate heat pump from a BTU-per-square-foot chart — those were calibrated to oversized furnaces. Size it to your home's design-day heating load (an honest range that depends on floor area, climate, insulation, and air-tightness), then judge a specific unit by its certified capacity at your local 99% design temperature, not its nameplate "tons." A heat pump's output drops roughly 30–40% from 47°F down to 5°F, so a "3-ton" unit can deliver closer to 2 tons when it's well below zero. A model is right-sized when its capacity at your design temp covers the high end of your load band without running more than ~20% oversized (oversizing causes short-cycling and poor summer dehumidification). Estimate your load and check any model against it below; the methodology page shows every constant and source.

Last updated June 10, 2026 · methodology & sources · model data from EPA ENERGY STAR

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.

Frequently asked questions

What size heat pump do I need for a 2000 sq ft house?

There's no single square-foot answer — a cold-climate heat pump is sized to your home's design-day heating load, which depends on floor area, climate, insulation, and air-tightness, not floor area alone. Skip the BTU-per-square-foot charts and estimate an honest load range for your envelope and design temperature, then judge a unit by its certified capacity at that temperature. Estimate your load above.

How much capacity does a heat pump lose at 5°F?

A heat pump's heating output drops roughly 30–40% from 47°F down to 5°F. That's why a "3-ton" unit can deliver closer to 2 tons when it's well below zero — and why you size to certified capacity at your local design temperature, not the nameplate tons.

Should I use a BTU-per-square-foot chart to size a cold-climate heat pump?

No. Those charts were calibrated by decades of oversized furnaces. A heat pump's capacity shrinks as the temperature drops, and oversizing hurts it more than a furnace — causing short-cycling and poor summer dehumidification. Size to your design-day load and check the unit's capacity at your design temperature.

When is a heat pump the right size for my home?

A model is right-sized when its certified capacity at your local 99% design temperature covers the high end of your load band without running more than about 20% oversized. Oversizing causes short-cycling and poor summer dehumidification, so a modest margin beats a large one.

Does this tool replace a Manual J load calculation?

No. It gives you an honest load range and a capacity-versus-design-temperature check to get you to an informed conversation. It doesn't do room-by-room loads, duct design, multizone head selection, or final equipment selection — a proper ACCA Manual J + Manual S by a qualified contractor is the standard for the final call.