One of the first questions homeowners ask when shopping for a standby generator is simple:
Will it run my air conditioner?
That's a particularly important question during a summer power outage. Keeping the refrigerator and lights running is helpful, but when outdoor temperatures climb, maintaining air conditioning can quickly become one of the most important reasons for having backup power.
Unfortunately, there's no universal rule that says a certain generator size will operate every 3-ton, 4-ton or 5-ton air conditioner.
To understand why, we need to look at how an air conditioner uses electricity.
Why Air Conditioners Are Different From Ordinary Household Loads
An air conditioner doesn't consume exactly the same amount of power every second it's operating.
The outdoor unit contains a compressor motor. When that compressor starts, it can briefly require substantially more electrical capacity than it needs once it's running.
This creates two different considerations:
Running load — the electrical demand while the equipment is operating normally.
Starting load — the temporary electrical demand associated with starting the compressor.
A generator needs to handle both.
This is why simply adding up the normal wattage of your appliances can result in an inaccurate generator recommendation.
Does AC Tonnage Determine Generator Size?
Not by itself.
Air-conditioning capacity is normally expressed in tons.
One ton of cooling equals approximately 12,000 BTU per hour, so:
2 tons = 24,000 BTU
3 tons = 36,000 BTU
4 tons = 48,000 BTU
5 tons = 60,000 BTU
Those numbers describe cooling capacity. They don't tell you exactly how much electrical power the equipment requires.
Two 5-ton air conditioners can have very different electrical characteristics depending on compressor design, efficiency, equipment generation and other factors.
That's why we recommend looking at the actual equipment rather than relying exclusively on tonnage.
What Information Should I Look For?
Check the data plate on the outdoor condenser or heat pump.
Depending on the equipment, you may find specifications including:
- Voltage
- Phase
- Minimum Circuit Ampacity (MCA)
- Maximum Overcurrent Protection (MOCP)
- Rated Load Amps (RLA)
- Locked Rotor Amps (LRA)
For generator sizing, compressor starting characteristics can be particularly important.
If you're unsure how to interpret the nameplate, take a clear photograph of it and have the equipment evaluated as part of the generator-sizing process.
Can a 13kW Generator Run Central Air?
Potentially, but there is no universal answer.
A smaller central air-conditioning system may have very different starting requirements from a large 5-ton system.
You also need to account for everything else operating at the same time.
The generator isn't powering the air conditioner in isolation. It may also be powering refrigerators, lights, a furnace blower or air handler, pumps and other household loads.
Can an 18kW Generator Run Central Air?
An 18kW generator provides considerably more capacity, making central HVAC operation possible in many properly designed applications.
But again, don't make the decision based solely on the generator's kW rating.
The compressor's starting requirement and the home's other simultaneous loads need to be considered.
Can a 22kW Generator Run Central Air?
A 22kW standby generator provides substantial residential capacity and may be suitable for homes where central air conditioning is an important backup load.
This size can provide more room for normal household equipment alongside HVAC operation.
The correct answer still depends on the particular AC system.
Can a 26kW Generator Run a 5-Ton Air Conditioner?
This is where motor-starting capability becomes particularly important.
Briggs & Stratton's PowerProtect 26kW family is designed with high motor-starting capability and the manufacturer specifically positions applicable models for demanding residential loads, including large air-conditioning systems.
That doesn't mean every 5-ton HVAC installation can automatically be connected without evaluation.
The AC's electrical specifications, other household loads, generator configuration, fuel and transfer system all matter.
But if operating a large central air conditioner is one of your priorities, motor-starting performance should be high on your generator-shopping checklist.
What About Two Air Conditioners?
Homes with two HVAC systems require another level of planning.
Suppose a house has an upstairs and downstairs air conditioner.
The generator might have enough capacity to operate both systems once they're running but still encounter difficulty if both compressors attempt to start simultaneously.
A properly designed installation may use load-management or sequencing strategies to control when large electrical loads are allowed to operate.
This is why generator design involves more than comparing the generator's kW number with estimated running wattage.
Can a Generator Run a Heat Pump?
Yes, a properly sized standby generator can operate many heat-pump systems.
However, heating mode creates another important consideration.
Some heat pumps use electric auxiliary heat when outdoor conditions require additional heating capacity.
Electric resistance heat can consume a substantial amount of power.
A generator capable of starting and running the compressor may not necessarily have enough capacity to operate every stage of auxiliary electric heat at the same time as the rest of the house.
For heat-pump homes, the complete heating configuration should be reviewed.
What About Variable-Speed HVAC Systems?
Modern inverter and variable-speed HVAC equipment can have different electrical characteristics from traditional single-stage compressor systems.
Don't assume that an old rule of thumb applies to newer equipment.
Use the manufacturer's electrical specifications for the actual system.
This is especially relevant as homeowners move toward higher-efficiency inverter heat pumps and variable-capacity air conditioners.
Can a Soft Starter Help?
In some applications, a properly selected and approved soft-start device can reduce the electrical stress associated with compressor startup.
That can potentially make HVAC operation easier on a generator.
However, compatibility should be verified with the HVAC equipment manufacturer and generator system requirements. A soft starter shouldn't be treated as a universal solution.
What About R-32 Air Conditioners?
The refrigerant itself doesn't determine the generator size.
An R-32 air conditioner still needs to be evaluated based on the electrical requirements of its compressor, outdoor fan and associated indoor equipment.
This distinction is useful because homeowners sometimes assume refrigerant type determines electrical demand.
It doesn't.
Look at the equipment's electrical specifications.
Don't Forget the Indoor Unit
Your outdoor condenser isn't the entire HVAC system.
The generator may also need to power:
- Furnace blower
- Air handler
- Control transformer
- Thermostat/control equipment
- Condensate pump
- Zone controls
- Accessories
Heat-pump air handlers with electric heat kits deserve particularly careful attention because those heaters can represent substantial loads.
Start With Your HVAC Nameplate
If air conditioning is one of the main reasons you're buying a standby generator, start with the HVAC equipment—not the generator catalog.
Find your condenser or heat-pump model number and electrical specifications.
Then determine what other household equipment needs to operate simultaneously.
Only after that should you select the appropriate generator capacity.
Briggs & Stratton Standby Generators for HVAC Backup
ACUnitsForLess specializes in heating and cooling equipment, which gives us a useful perspective on backup-power selection.
We carry Briggs & Stratton residential standby generators ranging across several capacities, including models designed for demanding motor loads.
When comparing generators, don't ask only:
"How many kW is the generator?"
Also ask:
"Can this generator handle the starting characteristics of my HVAC equipment while supporting the other loads I need?"
That's the question that leads to a much better backup-power system.
Shop Briggs & Stratton Standby Generators at ACUnitsForLess.
Generator and HVAC compatibility should be evaluated using actual equipment specifications. Installation and electrical/fuel connections should be performed in accordance with manufacturer requirements, applicable codes and qualified-professional guidance.
