NEC 424 — Fixed Electric Space Heating: Baseboards, Heat Pumps, and the 125% Continuous-Load Rule

NEC 424 covers fixed electric space heating equipment — baseboards, in-wall heaters, electric furnaces, mini-split heat strips, radiant ceiling/floor heat. The most-cited rules:

All fixed electric heat is a continuous load (424.3(B)): branch circuits supplying fixed electric heat must be sized at 125% of the total connected load. Same continuous-load multiplier as EV chargers. A 1500 W baseboard pulls 6.25 A continuous, so the calculation is 1500 × 1.25 = 1875 VA / 240 V = 7.8 A — fine for a 15 A branch.

Multiple baseboards on one circuit: total all the watts on the circuit, multiply by 1.25, divide by voltage to get circuit amps. A common Hudson County brownstone setup is 3 × 1000 W baseboards (3000 W total) on a 20 A circuit at 240 V: 3000 × 1.25 = 3750 VA / 240 V = 15.6 A. Fits a 20 A breaker; good.

Disconnect required (424.19): every electric heater needs a disconnect that can disconnect the heater AND any associated thermostat and motor (for forced-air units). The disconnect must be:

• Within sight of the heater AND its motor controller, OR
• Capable of being locked in the OPEN position (lockable breaker satisfies this)

For baseboards in a finished basement, the lockable breaker at the main panel typically satisfies this — provided the breaker has a permanent locking provision (a plastic OFF-position lock that stays attached to the breaker handle).

Mini-split heat strip add-ons: when a ductless mini-split has electric backup heat strips, those strips count separately in the load calc. NEC 220.82(C) treats HVAC as the LARGER of A/C OR HEAT — but if you have heat-strip backup PLUS A/C in the same air handler, the heat strips can run during a defrost cycle WHILE the heat pump is running. Verify the manufacturer's installation instructions for the worst-case combined load.

Electric furnace branch circuit: a 15 kW electric furnace on 240 V draws 62.5 A nominal × 1.25 = 78 A continuous. Requires an 80 A breaker minimum, with #4 CU or #2 AL conductors. NJ heat-pump-with-strip-heat installs frequently exceed the existing service capacity — always run the load calc before quoting an electric-heat addition.

For load-calc impact of fixed electric heat, the free Malfettone Load Calculator at /tools/load-calculator has presets for electric furnace, heat pump, baseboard heat, and mini-split — applying the 125% multiplier and the 220.82(C) larger-of-A/C-or-heat rule automatically.