The number on the box is a 47 degree number

HSPF2 is a season-long average. It rolls mild November evenings together with January mornings and reports one number, which is genuinely useful for estimating a winter’s electricity and completely useless for answering “will this room be warm at dawn on the coldest day of the year”. Those are different questions and they need different data.

The ENERGY STAR Cold Climate specification is the only widely available answer to the second question that comes with a published floor rather than a marketing claim. It sets three requirements a unit must meet together: a heating efficiency of at least 8.5 HSPF2 for a non-ducted split^[3], a capacity at 5 F of at least 70 percent of the capacity at 47 F ^[1], and a coefficient of performance at that same temperature of at least 1.75 ^[2]. There is also a controls verification step, so the unit has to hit those figures using the controls it will actually ship with rather than a laboratory configuration.

This is an ENERGY STAR Cold Climate certification minimum, not a model-specific capacity rating. The ordinary efficiency tiers used on this site do not establish a corresponding low-ambient capacity minimum, so this calculator prints no inferred fraction for them.

The draw column is the other half of the story and it is rarely mentioned. At a coefficient of performance of 1.75, delivering that reduced heat takes noticeably more electricity per unit of warmth than the seasonal figure implies. The certification floor therefore describes both minimum heat output and minimum low-ambient efficiency. Your exact model and electric rate determine the actual draw and cost at that hour.

The six states below have the highest heating degree-day totals in the NOAA statewide series for 2025. If you are in one of them and you are being quoted equipment without the Cold Climate designation, the ordinary certification tier does not supply the low-ambient capacity minimum used on this page. Ask for the exact model's table at your local design temperature rather than inferring cold-weather output from the nameplate.

In every one of those states the heating side is more than ninety percent of this annual degree-day comparison, so HSPF2 and model-specific low-ambient capacity deserve particular attention alongside cooling efficiency. Whether ENERGY STAR Cold Climate (non-ducted) is worth a higher installed price depends on the exact model, local design temperature, run hours, electric rate and backup-heat plan; this page does not calculate that payback.