How the code counts heat pumps
- Standard method: heating and cooling are not added together. The code takes the larger of the two (220.60, noncoincident loads). A heat pump counts on both sides, so its compressor plus any backup strips usually sets the heating number.
- Optional method (220.82): the heating and cooling line is the largest of several choices, including 100% of the heat pump compressor plus 65% of the supplemental electric heat, or 100% of the air conditioning.
- Motors: 25% of the largest motor (usually the biggest compressor) is added (220.50, 430.24).
Mini-split systems with several outdoor units
In the detailed calc you add each outdoor unit with its nameplate rating and quantity. Air handlers, fan coils, ERVs and dehumidifiers go in as their own lines. Not sure of a rating? Upload the submittal or the mechanical schedule and we read it from there.
Con Edison and electric heat
Con Edison will not supply service to convert an existing dwelling to electric space heating unless the building meets minimum insulation standards: roof/ceiling insulation of at least R-19 (about 6 inches), storm or multi-glazed windows and storm or thermal doors, unless a waiver applies (Blue Book 2026, pp. 36-37). Check this before you buy equipment.
Count every unit and see your service size. Load calc, reviewed: $197, fixed price.
Start the detailed calc Free quick calcQuestions
Do I add heating and cooling together?
No. In the standard method the NEC takes the larger of the heating or cooling load (220.60). A heat pump counts toward both, plus any backup heat strips on the heating side.
Can I add mini-splits without upgrading my service?
Sometimes. It depends on everything else in the home. The free quick calc gives a first answer; the detailed calc counts each outdoor unit and your actual appliances.
Does Con Edison have rules for switching to electric heat?
Yes. Existing dwellings converting to electric space heating must meet minimum insulation standards unless a waiver applies (Con Edison Blue Book 2026, pp. 36-37).