What a whole house generator does
A whole house generator is a machine that automatically turns on when your power goes out and supplies electricity to your entire home until the grid comes back. Unlike a portable generator that you wheel out and plug into individual appliances, a whole house unit sits permanently outside (usually near your home's electrical panel), connects directly to your house's wiring, and switches on within seconds of detecting an outage—no manual setup required.
The generator runs on either natural gas, propane, or diesel fuel. Natural gas models draw from your home's existing gas line. Propane models need a tank installed on your property. Diesel models are less common for residential use but offer good fuel efficiency. The generator powers your lights, heating or cooling, refrigerator, well pump (if you have one), and other essential systems continuously until power returns, which can be days or weeks depending on the outage.
Key Takeaways
- A whole house generator automatically detects a power outage and starts within seconds, running on natural gas, propane, or diesel without any action from you.
- Installation requires a licensed electrician to connect the generator to your home's electrical panel and a gas or propane line, plus a concrete pad and permits from your city or county.
- Whole house generators cost between $3,000 and $15,000 installed, depending on size and fuel type, plus annual maintenance of $150 to $300.
- You will need to arrange fuel delivery (for propane) or may support your natural gas line can handle the generator's demand, and have a licensed technician service the unit yearly.
- Portable generators are cheaper upfront but require manual setup, produce carbon monoxide, and cannot power your whole home at once.
How installation works and what it costs
Installing a whole house generator involves several steps and requires permits from your local building department. A licensed electrician must run a new circuit from your home's electrical panel to the generator, install a transfer switch (the device that automatically detects the outage and switches power sources), and connect the generator to either your natural gas line or a propane tank. You will also need a concrete pad poured where the generator sits, usually on the side of your house near the electrical panel.
Total installation cost varies widely by region and generator size. A 20-kilowatt natural gas generator (the most common residential size) typically costs $3,000 to $6,000 for the unit itself, plus $2,000 to $5,000 for installation labor and materials. Propane models run similar prices but require an additional $500 to $2,000 for tank installation. Larger units (24 to 48 kilowatts) cost $6,000 to $15,000 installed. You will also pay permit fees, which vary by municipality but typically range from $100 to $500.
Before installation, your electrician will assess your home's electrical panel to confirm it can handle the generator's output, and your gas or propane provider will confirm your line can supply the fuel demand. If your home uses propane, you will need a new tank installed on your property, which adds to the upfront cost.
Fuel types and ongoing maintenance
Natural gas generators are the most popular choice because they connect to your existing gas line and require no tank storage. As long as the gas utility is running, your generator can run indefinitely. The downside is that natural gas is not always available during major disasters, and your generator depends on the utility's infrastructure.
Propane generators store fuel on-site in a tank, so they work even if the gas utility is down. You arrange delivery from a propane supplier, and the tank typically holds enough fuel for several days of continuous operation. Propane generators are more independent but require you to monitor fuel levels and arrange refills.
All whole house generators need annual maintenance: an oil change, filter replacement, spark plug inspection, and a test run. A licensed technician should perform this work, which costs $150 to $300 per year. Neglecting maintenance can cause the generator to fail when you need it most. Some manufacturers recommend a professional inspection every two years for propane models.
Sizing your generator: what you actually need
Generator size is measured in kilowatts (kW). A 20-kilowatt generator is the standard for most homes and can power essential systems: heating or cooling, refrigerator, water heater, lights, and well pump if you have one. A 24-kilowatt unit adds capacity for electric ranges or multiple large appliances running at once. Larger homes or those with electric heating may need 30 to 48 kilowatts.
Your electrician will calculate your home's peak electrical demand by reviewing your electrical panel and utility bills. This tells you the minimum size generator you need. Oversizing (buying a larger generator than necessary) costs more upfront and uses more fuel, but undersizing means some appliances will not run during an outage. Most homeowners find a 20-kilowatt natural gas generator sufficient for their needs.
How automatic transfer switches work
The transfer switch is the brain of the system. It constantly monitors your home's incoming power from the grid. When it detects an outage, it signals the generator to start and then switches your home's electrical load from the grid to the generator—all within 10 to 30 seconds. When power returns, the switch waits a few minutes to confirm the grid is stable, then switches back and signals the generator to shut down.
This automatic switching is why you do not have to do anything during an outage. You do not flip switches, unplug appliances, or manually start the generator. The transfer switch handles it. Some models allow you to manually override the automatic mode if needed, but most homeowners never touch it after installation.
Whole house generators versus portable generators
A portable generator is cheaper upfront—typically $500 to $2,000—and requires no installation. You store it in your garage or shed and wheel it out when the power goes down. You then plug extension cords into it to power specific appliances. The tradeoffs are significant: you must be home to start it, you cannot power your whole house at once, and they produce carbon monoxide, so they must run outside (meaning long extension cords and noise).
Portable generators are useful as a backup to a whole house system or for occasional use (camping, job sites, outdoor events). For permanent home backup power, a whole house generator is more convenient and safer, especially if you are elderly, disabled, or frequently away from home. The higher upfront cost is offset by the automatic operation and ability to power your entire home indefinitely.
Permits, inspections, and local rules
Most cities and counties require a permit before installing a whole house generator. The permit process typically involves submitting plans showing the generator location, electrical connections, and fuel line routing. Your local building department reviews these plans and may require an inspection after installation to confirm the work meets electrical and gas codes.
Permit requirements and costs vary by location. Some municipalities charge $100 to $300 for a generator permit; others charge more. Your electrician usually handles the permit process as part of the installation contract. Skipping the permit process can create problems when you sell your home (the new owner's inspector will flag unpermitted work) and may void your homeowner's insurance coverage if the generator causes damage.
Some neighborhoods have restrictions on generator placement or noise levels. Check your homeowner's association rules or local zoning code before purchasing. Generators produce noise (typically 70 to 80 decibels at 20 feet), which may violate local noise ordinances if placed too close to property lines.
Frequently Asked Questions
How long can a whole house generator run continuously?
A natural gas generator can run indefinitely as long as the gas utility is operating and supplying fuel. A propane generator can run continuously for as long as you have propane in the tank—typically several days to a week depending on tank size and fuel consumption. Most propane tanks for residential generators hold 500 to 1,000 gallons and use 2 to 5 gallons per hour during operation.
Will a whole house generator work if the natural gas utility is down?
No, a natural gas generator depends on the utility's gas lines. If the gas utility is shut down or damaged during a disaster, your natural gas generator will not run. A propane generator is independent and will work as long as you have propane in your tank, making it a better choice if utility outages are a concern in your area.
Can I install a whole house generator myself?
No. Installation requires a licensed electrician to connect the generator to your electrical panel and install the transfer switch, and a licensed gas fitter or plumber to connect the fuel line. These connections involve electrical codes and gas safety codes that vary by location. Improper installation can cause electrical shock, gas leaks, or fire. Your city or county will not issue a permit for unlicensed work.
What happens to my generator during a power outage if I do not maintain it?
A generator that has not been serviced may fail to start or run poorly when you need it. Oil breaks down over time, filters clog, and fuel can gum up inside the engine. Annual maintenance ensures the generator starts reliably and runs smoothly. Many manufacturers void the warranty if you skip scheduled maintenance.
How much does it cost to run a whole house generator for a week?
Fuel cost depends on your generator size, fuel type, and how many appliances are running. A 20-kilowatt natural gas generator running continuously costs roughly $10 to $20 per day in gas (varies by local gas prices and load). A propane generator costs roughly $15 to $30 per day in propane. These are estimates; actual costs depend on your specific situation and local fuel prices.