HVAC Amp Draw Calculator — Free Online Calculator
Estimate the running load amps (RLA), minimum circuit ampacity (MCA), and maximum overcurrent protection (MOP) for any air conditioner or heat pump from its cooling capacity (BTU/h) and SEER2 rating. Results follow NEC 440.32 (MCA) and NEC 440.22 (MOP). Always verify against the unit nameplate before final wiring.
Enter equipment details
e.g. 24 000 BTU/h = 2 tons
Min 13 SEER2 per 2023 federal standards
Running Load Amps (RLA est.)
Min. Circuit Ampacity (MCA)
— A
Max. Overcurrent Protection (MOP)
— A
Input power (kW)
— kW
High Current Warning
Estimated RLA exceeds 80 A. Verify nameplate data and consult a licensed electrician for service-entrance conductor sizing and disconnect requirements.
Estimated from BTU/h and SEER2. Always verify against the unit nameplate before sizing wire, disconnect, or overcurrent protection devices.
How the HVAC Amp Draw Calculator Works
The calculator converts cooling capacity and SEER2 into an approximate input power draw, then derives running load amps from the supply voltage and phase. MCA and MOP are then calculated per NEC Article 440. All values are estimates — the unit nameplate is the authoritative source for final electrical design.
Why 0.95 power factor?
HVAC compressors are inductive loads. A power factor of 0.95 is a reasonable estimate for modern scroll compressors with run capacitors. Older reciprocating compressors may have PF closer to 0.85, which would result in higher actual amps.
SEER2 vs EER
SEER2 is a seasonal metric; EER is a steady-state rating at AHRI 95°F conditions. The 0.875 multiplier is an empirical approximation. For precise sizing, use the EER listed on the unit energy guide or nameplate.
NEC 440.32 — MCA
For a hermetic refrigerant motor-compressor circuit, the minimum conductor ampacity is 125% of the compressor nameplate RLA. Branch-circuit conductors must be sized to carry this ampacity continuously.
NEC 440.22 — MOP
The branch-circuit short-circuit and ground-fault protective device must not exceed 225% of the compressor RLA, rounded up to the next standard overcurrent device rating listed in NEC 240.6(A).
Worked example
A 3-ton residential split-system air conditioner rated at 16 SEER2 operating on a 230 V single-phase supply.
3-ton AC — 36 000 BTU/h, 16 SEER2, 230 V, single-phase
Result: A 15 A minimum circuit conductor with a 30 A breaker satisfies NEC 440 for this unit. Always confirm against the nameplate, which will show the actual MCA and MOP based on measured compressor and fan motor FLA.
Frequently asked questions
Common questions about HVAC amp draw, MCA, and MOP per NEC 440.
What is MCA for HVAC?
Minimum Circuit Ampacity (MCA) is the minimum wire rating required to safely power the unit. Per NEC 440.32, MCA = 1.25 × the largest motor FLA + all other loads. The conductor from the disconnect to the unit must be rated at least this ampacity. MCA is always on the unit nameplate.
What is MOP (MOCP)?
Maximum Overcurrent Protection (MOP or MOCP) is the largest fuse or circuit breaker that can protect the equipment circuit. It is listed on the unit nameplate and must not be exceeded. Using a breaker larger than MOP may not adequately protect the wiring against fault current.
Why is my calculated MCA different from the nameplate?
The calculator estimates MCA from BTU/h and SEER2. The nameplate MCA is calculated from the actual FLA of the compressor motor, fan motor, and controls combined. Nameplate values are authoritative — always use them for final wiring design.
Can I use this to size a heat pump?
Yes. A heat pump's cooling-mode electrical draw is similar to an equivalent AC. For heating mode, input power is lower (higher EER in heating). Use the cooling-mode figure to size the circuit, since it represents the maximum current draw.
Electrical sizing done. Now quote the installation.
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