A Generac standby generator needs more than "a gas line."
It needs a fuel system capable of delivering the required:
- Pressure
- Flow
- Pipe capacity
- Meter capacity
at full generator demand.
Current Generac air-cooled product pages commonly publish minimum natural-gas pressure around:
3.5 inches water column
with exact acceptable ranges depending on model.
For example, the current 10kW lists:
3.5-7.0 in. water column
while several larger current product pages publish a 3.5 in. water-column requirement field.
The exact model installation manual controls.
Current Natural-Gas Consumption Matters
Approximate current published full-load consumption:
| Model | NG Full Load |
|---|---|
| 10kW | 132 ft³/hr |
| 14kW | 243 ft³/hr |
| 18kW | 235 ft³/hr |
| 22kW | 311 ft³/hr |
| 26kW | 316 ft³/hr |
| 28kW | 297 ft³/hr |
The fuel system must support the generator plus other gas appliances that may run simultaneously.
Why Pipe Size Cannot Be Given From kW Alone
Gas-pipe sizing depends on:
- Generator BTU demand
- Pipe length
- Pipe material
- Supply pressure
- Pressure drop
- Number of fittings
- Other gas appliances
- Local code
So there is no honest universal answer such as:
"A 22kW Generac always needs a 1-inch line."
The same generator can require different pipe sizing on two different homes.
Gas Meter Capacity
A generator can have a correctly sized branch line and still be starved if the gas meter cannot supply total demand.
Total system load may include:
- Generator
- Furnace
- Water heater
- Range
- Dryer
- Pool heater
The utility or licensed gas fitter may need to verify or upgrade the meter/regulator.
Symptoms of Inadequate Gas Supply
Possible symptoms include:
- Overcrank
- Starts then shuts down
- Runs unloaded but struggles under house load
- Underspeed/RPM faults
- Poor performance when other gas appliances run
These symptoms do not prove gas pressure is the cause.
They make it worth testing.
Static vs Running Pressure
A gas system can look fine with no generator load and fail once the engine demands full fuel flow.
That is why diagnosis often needs pressure checked:
- At rest
- During starting
- Under load
This is qualified gas-technician work.
22kW Gas Demand
Current 22kW published NG consumption:
- 221 ft³/hr at 50%
- 311 ft³/hr at 100%
Rated NG output:
21 kW
That is a significant appliance load.
Do not add it to an old residential meter without checking capacity.
26kW Gas Demand
Current 26kW:
- 182 ft³/hr at 50%
- 316 ft³/hr at 100%
Rated NG output:
24 kW
28kW Gas Demand
Current 28kW:
- 182 ft³/hr at 50%
- 297 ft³/hr at 100%
Rated NG output:
25 kW
Can You Reuse an Existing Generator Gas Line?
Maybe.
Verify:
- Diameter
- Length
- Material
- Supply pressure
- New generator demand
A line that worked for a 14kW may not automatically be suitable for a 26kW.
High-Pressure Gas Systems
Some homes use elevated gas pressure with a regulator near appliances.
That changes the sizing calculation.
Do not copy pipe sizing from a low-pressure installation.
Natural Gas vs Propane Pressure
Propane uses different pressure requirements.
Current Generac model pages commonly show propane around:
10 inches water column
or a model-specific range.
Do not use natural-gas settings for propane or vice versa.
Who Should Size the Gas Line?
Use a qualified:
- Licensed plumber
- Gas fitter
- Generator installer
working from:
- Exact Generac manual
- Local gas code
- Utility conditions
This is not the place to optimise cost by guessing one pipe size smaller.
Bottom Line
For current Generac air-cooled standby generators, think of 3.5 in. water column as a common published natural-gas minimum/reference point, not a universal complete design specification.
The actual installation must be sized from:
pressure + flow + distance + total connected gas load + local code
A generator that is fuel-starved can look like an engine or controller problem.
Size the gas system correctly from the beginning.
Read Generac fuel consumption →