Natural Gas Comparison

18kW

  • 17 kW output
  • 164 ft³/hr at 50%
  • 235 ft³/hr at full load

22kW

  • 21 kW output
  • 221 ft³/hr at 50%
  • 311 ft³/hr at full load

The 22kW provides more capacity but demands substantially more gas at published full load.

Propane Comparison

18kW

  • 18 kW output
  • 1.65 gal/hr at 50%
  • 2.87 gal/hr at 100%

22kW

  • 22 kW output
  • 2.45 gal/hr at 50%
  • 3.71 gal/hr at 100%

If propane storage is limited, that difference can matter during a long outage.

Compare Generac fuel consumption →

Which Is Better for Central AC?

The 22kW gives more starting and running headroom.

But the correct answer depends on:

  • Compressor LRA
  • Soft-start equipment
  • Other active loads
  • Load management

If 18kW starts and carries the HVAC plus your priority loads, the 22kW may not add meaningful value.

Which Is Better on Natural Gas?

Do not compare only the model names.

The current ratings are:

  • 18kW model → 17kW NG
  • 22kW model → 21kW NG

So the natural-gas capacity difference is still 4kW.

That can be the difference between:

  • Managed AC and unrestricted AC
  • One extra large appliance
  • Greater motor-start headroom

Physical Size

Both current models use the same published enclosure dimensions:

46.4 × 26.3 × 30.7 inches

So moving to the 22kW does not require a physically larger next-generation enclosure.

Weight

  • 18kW: 426 lb
  • 22kW: 451 lb

Difference:

25 lb

Weight is not a serious decision factor once professional installation is assumed.

Price

The 22kW costs more, but installed project cost is often dominated by:

  • Electrical labor
  • Transfer switch
  • Fuel piping
  • Trenching
  • Permits

That means the generator price gap may be smaller than the total installed-project gap appears.

Get both quoted if the sizing calculation is close.

Pick the 18kW When

Choose the 18kW when:

  • 17kW NG / 18kW LP covers the actual load
  • One main HVAC system is manageable
  • You are comfortable shedding secondary loads
  • Lower fuel demand matters
  • You do not need the extra 4kW

Pick the 22kW When

Choose the 22kW when:

  • Load calculation genuinely exceeds 18kW
  • HVAC starting demand needs more headroom
  • More loads need to overlap
  • You want less aggressive load shedding
  • Gas system can support the higher demand

The Wrong Reason to Buy 22kW

Do not buy it simply because:

"More kW is always safer."

An oversized generator can create:

  • Higher equipment cost
  • Larger fuel-system requirements
  • More fuel burn potential

without adding practical value if the load never needs it.

Bottom Line

The current 22kW buys you a real:

+4 kW

over the 18kW on both fuels.

If that extra 4kW has a job, buy it.

If your calculated backup load fits comfortably inside the 18kW envelope, the 18kW is the cleaner buy.

Read Generac 18kW →

Read Generac 22kW →

Calculate generator size →

Find Generac dealers →