HVAC Electrical Calculators
Size wires, circuit breakers, and disconnects for HVAC equipment. Calculate MCA, MOP, voltage drop, and motor ampacity per CEC and NEC requirements. Tools for HVAC contractors pulling permits.
HVAC electrical: what the nameplate tells you
Every piece of HVAC equipment has a nameplate with 2 key electrical values: MCA (Minimum Circuit Ampacity) and MOP (Maximum Overcurrent Protection). These numbers drive every electrical decision on the installation.
MCA and MOP explained
MCA is the minimum wire ampacity required for the circuit. It's calculated as 125% of the largest motor FLA plus 100% of all other loads. Your wire must be rated at or above this value. MOCP is the maximum fuse or breaker size allowed. It protects the equipment. You can go smaller than MOCP but never larger. The MCA/MOCP calculator computes both from nameplate data when they're not printed directly.
Voltage drop: the silent equipment killer
Compressors are sensitive to low voltage. A compressor rated for 208-230V will run hot and draw excess current at 195V. CEC limits branch circuit voltage drop to 3%, but for long HVAC runs (over 50 ft) you should target 2% or less. The voltage drop calculator tells you exactly what gauge wire you need for any run length.
Heat pump installations and panel capacity
Adding a heat pump to an existing home often pushes a 100-amp panel close to its limit. A 3-ton heat pump draws 15-20 amps, plus 15-20 more for an electric auxiliary strip. Before sizing the electrical, check the electrical load calculation tool to confirm the existing service can handle it. If not, a 200-amp upgrade will be part of the project budget.