Tier 4 guide
Whole-house automatic standby generators
A 20–26 kW standby generator with a service-entrance ATS restores the whole house automatically, typically within seconds. The hard parts are gas supply capacity, code-compliant siting and an installed cost that is roughly double the equipment.
Data labels: Manufacturer stated Calculated Planning estimate Pending verification
Should I choose an air-cooled or liquid-cooled standby generator?
1. Air-cooled, 14–26 kW, 3,600 RPM - 2-cylinder V-twin (~800–1,000 cc), fan-cooled - Suited to typical residential outage hours - Cost baseline ~$5,500–$7,500 (unit + 200 A ATS) 2. Liquid-cooled, 25–150 kW, often 1,800 RPM - Automotive-style 4-cyl or V8 block, radiator cooling - Built for long runtimes; quieter at lower RPM (~58 dBA cited) - Cost baseline ~$14,000–$28,000+ (equipment only)
For many single-family homes, a 22–26 kW air-cooled unit can cover multiple AC compressors (with load management), an electric range, a well pump and lighting. Size against a load calculation by a licensed electrician.
Generac Guardian 22–26 kW
Representative air-cooled residential standby line. Confirm output per fuel in the spec sheet.
Kohler 20RCA / 26RCA
Representative air-cooled residential standby models.
Cummins QuietConnect 20 kW
Representative air-cooled residential standby model.
Can my existing gas service supply a standby generator?
A frequent failure point is not electrical but fuel delivery. Having gas service does not mean the existing line or meter can feed a generator at full load plus your other appliances.
The gas meter capacity problem
Many residential meters are around 250 CFH (about 250,000 BTU/h). A furnace might use 80,000–100,000 BTU/h, a tankless water heater 150,000–199,000 BTU/h, and a 24 kW generator at full load roughly 280,000–320,000 BTU/h. Planning estimate If all run at once on an undersized meter, pressure drops and the generator may shut down on low fuel pressure. The gas utility decides whether a larger meter is needed and what it costs.
Supply pressure and pipe sizing
Generators specify a supply pressure range in inches of water column; natural gas units often list ranges of a few inches WC and propane units higher. Use the exact range in your generator's manual. Long runs can require larger pipe than a standard 3/4" line. Pipe sizing is engineering for a licensed gas fitter using the locally adopted fuel gas code; the table below is illustrative, not an installation design.
| Generator capacity | Fuel | Load | Hourly consumption | Hourly BTU demand | Illustrative pipe, run under 30 ft | Illustrative pipe, run 30–70 ft |
|---|---|---|---|---|---|---|
| 18–20 kW | Natural gas | 50% | 165 CFH | 165,000 BTU/h | 3/4" IPS | 1" IPS |
| 18–20 kW | Natural gas | 100% | 245 CFH | 245,000 BTU/h | 1" IPS | 1.25" IPS |
| 18–20 kW | Propane | 50% | 1.8 gal/h | 164,000 BTU/h | 1/2" copper/poly | 3/4" copper/poly |
| 18–20 kW | Propane | 100% | 2.8 gal/h | 255,000 BTU/h | 1/2" copper/poly | 3/4" copper/poly |
| 24–26 kW | Natural gas | 50% | 205 CFH | 205,000 BTU/h | 1" IPS | 1.25" IPS |
| 24–26 kW | Natural gas | 100% | 310 CFH | 310,000 BTU/h | 1" IPS | 1.25" IPS |
| 24–26 kW | Propane | 50% | 2.3 gal/h | 210,000 BTU/h | 1/2" copper/poly | 3/4" copper/poly |
| 24–26 kW | Propane | 100% | 3.5 gal/h | 320,000 BTU/h | 3/4" copper/poly | 1" copper/poly |
On a 500-gallon propane tank filled to 80% (400 gallons), a 24 kW unit at 2.3 gal/h would run about 174 hours, roughly 7 days. Calculated Fuel is not infinite: propane deliveries can be delayed in storms, natural gas supply can be curtailed, and extended runs require oil and filter changes at the manufacturer's intervals.
How does an automatic transfer switch hand the house to the generator?
A service-entrance-rated ATS sits between the utility meter and your main panel.
- Utility power fails; a short confirmation delay ignores momentary blinks.
- The engine cranks and stabilises at 240 V / 60 Hz.
- The ATS breaks the utility connection and closes onto the generator.
- The house is energised, typically within roughly 10–20 seconds; load management modules stage large loads.
Service-entrance rated vs non-service rated
- Service-entrance (SE) rated: includes the service disconnect (e.g., 200 A) and can take utility power directly from the meter.
- Load management modules: rather than sizing for everything at once, controllers can temporarily shed a large 240 V load such as an AC compressor when the generator is near capacity, keeping critical circuits stable.
Where can a standby generator legally be installed?
Standby generators produce carbon monoxide, heat and noise. Siting follows the manufacturer's installation manual, NFPA 37 and the local authority having jurisdiction. NFPA 37 — Installation and Use of Stationary Combustion Engines
From operable windows, doors, window wells, vent intakes: often ~5 ft for tested enclosures From walls: from ~18 in to several feet, depending on wall material and manufacturer testing
- Foundation: a level pad (poured concrete or manufacturer-approved composite pad on compacted gravel) per the manual.
- Permits: typically an electrical permit for the ATS and wiring, and a gas/mechanical permit for piping, pressure test and shut-off.
- CO alarms: install battery-backed CO alarms in the home even with correct siting.
What does a whole-house standby generator really cost installed?
Advertised "starting at" prices often cover the equipment only. In this planning estimate the generator is roughly half the total.
| Line item | Scope | Typical contractor cost |
|---|---|---|
| Standby generator (22–26 kW) | Air-cooled enclosure with digital controls | $5,200–$6,800 |
| 200 A service-entrance ATS | Automatic transfer switch with load management | $900–$1,400 |
| Licensed electrician | ATS wiring, conduit, conductors, grounding | $2,200–$3,500 |
| Licensed gas fitter | Gas line, meter tie-in, shut-off, sediment trap | $1,200–$2,400 |
| Pad preparation | Gravel base, pad, anchoring | $350–$650 |
| Gas meter upgrade (if required) | Utility fee for higher-capacity meter | $150–$400 |
| Permits and inspections | Electrical and gas/mechanical | $300–$600 |
| Cold-weather accessories | Battery warmer, oil heater, as specified | $250–$450 |
| Gross total | Complete automatic infrastructure | $10,550–$16,200+ |
Which sources is this page based on?
- NFPA 37 — Installation and Use of Stationary Combustion Engines
- CDC — Carbon monoxide poisoning prevention
Figures marked Planning estimate are illustrative ranges for budgeting and comparison. They are not measured test results, quotes, or verified benchmarks. Reserve has not performed hands-on testing of the equipment named here.
Frequently asked questions
Do I need to upgrade my gas meter for a whole-house standby generator?
Often, but it depends on your meter and other gas appliances. Many residential meters are around 250 CFH, while a 22–26 kW generator at full load may need roughly 280–320 CFH by our planning estimates. Add the generator's maximum consumption from its manual to your other appliances and have the gas utility and a licensed gas fitter confirm meter, regulator and piping capacity under local code.
What is the difference between an automatic transfer switch and an interlock kit?
With an interlock, someone manually turns off the utility main, turns on the generator breaker and manages circuits. An automatic transfer switch monitors utility voltage, starts the generator when power fails and transfers the house automatically, typically within roughly 10–20 seconds after a short confirmation delay.
What clearances apply to a standby generator?
Clearances come from the manufacturer's installation manual, NFPA 37 and your local authority having jurisdiction. Distances of about 5 feet from operable openings are commonly cited for tested enclosures, with wall clearances that vary by siding material and manufacturer testing. Install CO alarms inside the home.
How much does it cost to install a whole-house standby generator?
As a planning estimate, roughly $10,500–$16,500 or more. The generator and 200 A transfer switch might be $5,500–$7,500, with electrical work, gas piping, possible meter upgrade, pad and permits adding about $5,000–$9,000. Get local quotes.