3 Ton Heat Pump Amp Draw: Typical Running and Startup Amps Explained

A 3 ton heat pump equals 36,000 BTU and its amp draw varies with efficiency, compressor type, and supply voltage. This article explains typical running and startup amps, how to calculate expected current, recommended breaker and wire sizes, and practical tips for measurement and troubleshooting. Key Takeaway: Typical running amps for a 3 ton heat pump on 240V single-phase range from about 9A to 30A depending on technology; startup (inrush) can be several times higher and dictates breaker sizing and surge considerations.

Unit Type	Typical Running Amps (240V)	Typical Startup/Inrush	Recommended Breaker
High-Efficiency Inverter/Variable Speed	8–15 A	1.5–3x Running	30 A
Modern Single-Stage Scroll Compressor	15–25 A	2–4x Running	30–40 A
Older Standard-Stage Compressor	20–30 A	3–6x Running	40–50 A

What “3 Ton” Means And Why It Matters For Amps

“3 ton” indicates cooling capacity equivalent to melting three tons of ice in 24 hours: 36,000 BTU per hour. Electrical load depends on how much electrical power the heat pump needs to move that heat, not the tonnage alone.

A heat pump’s electrical consumption is governed by its coefficient of performance (COP) or EER/SEER ratings, compressor efficiency, and whether the unit uses variable-speed electronics. Higher efficiency reduces amp draw for the same cooling/heating capacity.

Basic Calculation: How To Estimate Amp Draw

Estimate amps by converting BTU to input kW and dividing by voltage. Use the instantaneous efficiency measure (EER) for cooling load calculations: Input kW = BTU ÷ (EER × 3412). Then Amps = kW × 1000 ÷ Voltage.

Example: 36,000 BTU with an EER of 10 on 240V: Input kW = 36,000 ÷ (10 × 3412) ≈ 1.055 kW. Amps = 1,055 W ÷ 240 V ≈ 4.4 A. This low number is theoretical because real-world EER, heat pump heat mode COP, and auxiliary heat change results; typical units show higher nameplate amps.

Why The Simple Calculation Often Underestimates Real Amps

Manufacturers list compressor and total unit nameplate amps (RLA, MCA, MOCP). RLA (Running Load Amps) and LRA (Locked Rotor Amps) differ from simple EER-based math because motors, fans, reversing valves, defrost heaters, and auxiliary electric heat draw additional current.

Electric backup heat (strip heat) in many heat pumps can add significant amps when active; a 3 ton unit might include 5 kW of strip heat drawing ~20.8 A at 240V, which must be included when sizing circuits and breakers.

Typical Amp Ranges For 3 Ton Heat Pumps

Modern inverter-driven heat pumps: 8–15 A running on 240V due to high efficiency and variable compressor speed. Startup is modest because soft-start electronics reduce inrush.

Single-stage scroll compressor units: 15–25 A running. Startup inrush can be 2–4 times running amps briefly.

Older or lower-efficiency units: 20–30 A running, with high locked-rotor currents requiring larger breakers and robust wiring.

Nameplate Terms And What They Mean

RLA (Rated Load Amps or Running Load Amps) shows typical continuous running current for the compressor only. MCA (Minimum Circuit Ampacity) is the minimum conductor size requirement. MOCP (Maximum Overcurrent Protection) indicates the maximum allowed breaker size for protection.

When evaluating expected amp draw, use MCA for conductor sizing and size breakers according to MOCP or NEC rules, considering continuous vs non-continuous loads and 125% multiplier where applicable.

Recommended Breaker And Wire Sizes

General guidelines: many 3 ton heat pumps use a 30–50 A breaker depending on model. Typical wiring choices are 10 AWG copper for up to 30 A, 8 AWG for up to 50 A. Always follow the unit’s MCA and MOCP nameplate and local code.

Typical Running Amps	Typical Breaker	Typical Wire
8–15 A	30 A	10 AWG Copper
15–25 A	30–40 A	8–10 AWG Copper
20–30 A	40–50 A	8 AWG Copper

Startup (Inrush) Current And Its Impact

Startup current can be multiple times the running current for a short period. Inrush is highest for single-stage compressors and lower for inverter-driven units. Breakers do not trip on short inrush if within the breaker’s time-delay characteristics, but frequent large inrush may stress electrical systems.

Hard starting can also cause nuisance tripping on weak circuits or shared loads. Using a time-delay fuse or proper HVAC-rated breaker prevents nuisance trips while protecting equipment.

How To Measure Actual Amp Draw

Use a clamp-on ammeter or a true-RMS meter with current measurement. Measure at the outdoor unit’s disconnect while the unit is running in both heating and cooling modes and during compressor startup if safe to do so.

Measure with no auxiliary heat running to capture base heat pump amp draw; then measure during backup heat to capture worst-case circuit demand. Record running amps, and if possible capture peak inrush to compare with MOCP and breaker ratings.

Examples With Typical EER And SEER Values

Using EER yields better instantaneous amp estimates than SEER. Example A: 36,000 BTU at EER 11, Input kW ≈ 36,000 ÷ (11×3412) ≈ 0.96 kW → ~4 A at 240V for compressor only. Real total unit running amps rise after adding fans and controls.

Example B: 36,000 BTU at EER 8, Input kW ≈ 36,000 ÷ (8×3412) ≈ 1.32 kW → ~5.5 A. Add blower, reversing valve, and defrost elements and currents add up, bringing practical running amps into the ranges previously given.

Auxiliary Electric Heat And Its Effect On Amp Draw

Many heat pumps include auxiliary electric resistance heat for very cold weather or defrost. Auxiliary heat elements often add 2.5–10 kW, adding up to 41.7 A per 10 kW at 240V. This can more than double circuit demand and requires separate or appropriately sized circuits.

Important: When auxiliary heat runs, the total current may exceed the heat pump compressor’s MOCP, so NEC and manufacturer guidance on wire and breaker sizing must be followed.

Common Causes Of Higher-Than-Expected Amp Draw

• Dirty coils, restricted airflow, or low refrigerant charge causing compressor to work harder.
• Failing compressor motor bearings or electrical faults raising coil current draw.
• Short cycling or frequent defrost cycles increasing average amps.
• Incorrect voltage supply leading to higher current draw; low voltage increases amps for same power.

Troubleshooting Steps For High Amp Draw

Check for dirty air filters and outdoor coils and restore airflow. Verify correct refrigerant charge and inspect for leaks. Measure supply voltage under load; low voltage can raise current draw and harm compressor.

Inspect contactor, capacitor, and motor condition. Replace failing capacitors or contactors. If electrical problems persist, consult an HVAC technician or licensed electrician for diagnosis and repairs.

NEC And Safety Considerations

Follow the National Electrical Code and manufacturer nameplate when sizing conductors and overcurrent protection. NEC requires 125% of continuous load for conductor ampacity in many HVAC applications; breakers are sized per MOCP but must coordinate with wire ampacity.

Always work with or consult a licensed electrician for service, wiring changes, or breaker upgrades. Disconnect power before inspecting or working on HVAC equipment to avoid electrocution or equipment damage.

When To Replace A Unit Or Upgrade Service

Consider replacement if the unit consistently draws higher current than specified, has repeated compressor failures, or the home electrical service cannot support auxiliary heat without costly upgrades. Newer heat pumps offer significantly lower running amps due to improved inverter technology and higher efficiencies.

When upgrading to a modern inverter heat pump, evaluate service capacity, surge requirements, and whether a dedicated circuit or subpanel is needed to meet NEC and manufacturer recommendations.

Summary: Practical Guidance For Homeowners And Technicians

Estimate amps using nameplate MCA and RLA rather than raw BTU math. Typical running amps for 3 ton heat pumps on 240V usually fall in the 8–30 A range depending on technology. Startup inrush can be multiple times running current and influences breaker selection and nuisance trips.

Measure directly with a clamp meter for accurate assessment. Account for auxiliary heat when planning circuits. Always follow manufacturer nameplate values and NEC rules, and hire licensed professionals for electrical or refrigerant work.

Resources And Further Reading

Refer to manufacturer specification sheets for exact RLA, LRA, MCA, and MOCP values of specific models. Consult the National Electrical Code (NEC) and local amendments for circuit sizing and protection requirements.

For measurement and diagnostics, consider HVAC training materials and guides from industry organizations such as AHRI and NATE for correct procedures and safety practices.