Standby generators automatically activate during a power outage, supplying electricity to your home or business without manual intervention. Unlike portable generators that require manual setup and fuel transport, standby units are permanently installed and operate on natural gas or propane. Understanding how they work helps you choose the right capacity, fuel type, and maintenance plan for your specific needs.
How Standby Generators Detect Power Loss
Your standby generator includes an automatic transfer switch (ATS) that continuously monitors your main electrical panel. When the ATS detects a voltage drop—typically within 10 to 50 milliseconds—it sends a signal to the generator's control module to start the engine. This seamless handover means your lights, HVAC system, and refrigerator stay powered without interruption or manual effort.
The ATS also prevents backfeeding, which occurs when generator power flows backward into the utility grid. This protects utility workers and is required by electrical code in all jurisdictions.
Fuel Sources and Runtime Considerations
Natural gas is the most common choice for standby generators because it's delivered through existing utility lines—no storage tanks needed. These systems typically run indefinitely as long as the gas supply remains active. However, during major outages, gas pressure can drop if the utility experiences damage.
Propane requires an on-site storage tank (usually 500–2,000 gallons) and offers independence from utility infrastructure. A 500-gallon tank can run a 20 kW generator for 8–10 days of continuous operation, depending on load. Propane is ideal for rural properties or areas with unreliable gas service, though tank refilling logistics require planning during extended outages.
Diesel generators are less common for residential use but offer excellent fuel stability and long storage life—important if you anticipate weeks without refueling.
Sizing Your Generator: What Capacity Do You Need?
Generator capacity is measured in kilowatts (kW). Undersizing leaves essential loads unpowered; oversizing wastes money on equipment you don't need.
Calculate your needs by identifying essential loads:
- Whole-home backup: 15–25 kW (covers heating, cooling, hot water, kitchen appliances, and lights)
- Essential circuits only: 7–12 kW (refrigerator, sump pump, furnace blower, some lights, medical equipment)
- High-demand homes with electric heating: 30+ kW
Standby generators typically range from 7 kW (around $3,000–$5,000 installed) to 48 kW (around $15,000–$25,000 installed). The automatic transfer switch adds $1,500–$3,000 to your total project cost. Professional installation, permits, and electrical work usually run $2,000–$5,000 depending on your existing electrical setup.
Engine and Cooling System Design
Most residential standby generators use four-stroke engines with liquid cooling, similar to vehicle engines. Liquid cooling keeps operating temperatures stable and extends engine life compared to air-cooled portable models.
The generator's enclosure provides sound dampening—typically 70–80 decibels at 25 feet, roughly equivalent to a window air conditioner. If noise is a concern, request quotes that specify decibel ratings.
Maintenance Schedule and Costs
Standby generators require monthly load testing and annual service. Load testing simulates actual use to ensure the battery charges, the engine starts reliably, and fuel flows properly—critical because generators left idle can develop fuel line blockages.
Annual maintenance typically includes:
- Oil and filter changes
- Spark plug inspection
- Battery testing and cleaning
- Fuel filter replacement
- Coolant level checks
Budget $150–$300 annually for maintenance if you handle it yourself with the manufacturer's manual, or $300–$600 if you hire a licensed technician.
Permits and Inspections
Installing a standby generator requires electrical permits in nearly all jurisdictions. Your contractor should handle permit filing, which typically costs $200–$500 and takes 1–2 weeks. A final inspection ensures the ATS is wired correctly, the exhaust is properly vented, and fuel lines meet code.
Choosing a Provider
Compare standby generator quotes by verifying the kW rating matches your load calculation, confirming the fuel type aligns with your property's infrastructure, and checking whether the quote includes ATS installation and permits. Mercoly helps you compare trusted Generators & Backup Power providers in one place, so you can review multiple bids side-by-side without separate phone calls.
Ask prospective installers for references from customers with similar setups and confirm they're licensed electricians in your state.
Frequently Asked Questions
Q: How long does it take to install a standby generator? Installation typically takes 2–3 days for most residential systems, though timeline varies based on your electrical panel layout and fuel line routing.
Q: Can I transfer my standby generator to a new house? Transfer is possible but expensive—you'd need a new ATS, electrical work, and fuel connections at the new location, often costing as much as a new installation.
Q: What happens to my generator if the gas utility lines are damaged? A natural gas generator won't run if the utility is damaged; this is why propane systems appeal to some homeowners despite higher upfront costs.
Compare generator options tailored to your home's specific power needs today.