A generator with a capacity of at least 5,000 to 7,500 watts is typically needed to run a heat pump efficiently.
Powering a heat pump during outages requires careful generator sizing. The right generator keeps your home comfortable while avoiding equipment damage from insufficient power.
Generator Size Requirements for Heat Pumps
Most residential heat pumps need generators between 7.5kW-20kW. The exact size depends on your heat pump’s capacity and efficiency. Here are common pairings:
| Heat Pump Size | Minimum Generator Size | Recommended Generator Size |
|---|---|---|
| 2-ton (24,000 BTU) | 7.5kW | 10kW |
| 3-ton (36,000 BTU) | 10kW | 15kW |
| 4-ton (48,000 BTU) | 15kW | 20kW |
| 5-ton (60,000 BTU) | 20kW | 25kW |
Why Oversize Your Generator?
Heat pumps require 2-3 times more power during startup than during normal operation. This surge lasts just seconds but demands generator capacity. Undersized generators cause:
- Voltage drops that trip safety switches
- Compressor short cycling
- Potential equipment damage
Key Factors Affecting Generator Sizing
1. Heat Pump Specifications
Check your unit’s nameplate for:
- RLA (Rated Load Amps) – Continuous draw
- LRA (Locked Rotor Amps) – Startup surge
Example: A 3-ton Trane XL16i heat pump draws 14.75A continuously but needs 18A at startup according to user reports.
2. Additional Home Loads
Factor in other essential circuits:
- Refrigerator (600-800W)
- Lights (300-1000W)
- Well pump (750-1500W)
- Electronics (500-2000W)
3. Climate Conditions
Cold weather increases power demands:
- Oil viscosity affects compressor startup
- Defrost cycles add intermittent loads
- Lower COP (Coefficient of Performance) in winter
Special Considerations
Soft Start Kits
These devices reduce startup surges by up to 70%. A 3-ton unit with soft start might drop from 82A to 25A startup current.
Generator Types
Inverter generators respond faster to load changes than conventional models. For heat pumps, look for:
- Less than 5% THD (Total Harmonic Distortion)
- Automatic voltage regulation
- Surge capacity matching your LRA
Real-World Examples
Success Case
A homeowner with a 4-ton geothermal system runs it smoothly on a 20kW Generac with soft start. The system draws 5.7kW running but needed the larger generator for the 82A startup surge.
Failure Case
Another user’s 5kW generator couldn’t handle their 3-ton heat pump startup, despite adequate running capacity. The voltage dip caused immediate shutdowns.
Professional Recommendations
HVAC technicians suggest:
- Size generators at 150% of running load
- Prioritize units with clean power output
- Consider whole-house systems for larger homes
- Install transfer switches properly
For homes with supplemental heating systems, you may be able to use a smaller generator by alternating loads.
Maintenance Tips
Keep your backup system reliable:
- Exercise generators monthly
- Change oil every 50-100 hours
- Keep fuel stabilized
- Test under load annually
Proper sizing ensures your heat pump and generator work together seamlessly when you need them most.
