Whole House Generator Types: Complete Guide

Standby generators are permanently installed outside the home on a concrete pad, connected to the home's electrical panel via an automatic transfer switch (ATS), and supplied by a natural gas line or propane tank. When utility power fails, the ATS detects the outage within seconds and signals the generator to start. The generator reaches operating speed and the ATS transfers the electrical load to generator power, typically within 10 to 30 seconds. The whole process is automatic: you do not need to be home, start the generator manually, or run extension cords. Standby generators run on natural gas or propane, which means they can operate indefinitely (natural gas supply is not interrupted in most outages; a 250-gallon propane tank provides 2 to 5 days of continuous operation). Sizes range from 10kW (covering essential circuits only) to 48kW or larger for whole-house coverage including central air conditioning. Brands include Generac, Kohler, Briggs and Stratton (Standby), and Cummins.

Portable gasoline generators are the most accessible form of backup power. They must be started manually and run outside the home (carbon monoxide risk makes indoor operation life-threatening). They power devices via extension cords or, with a manual transfer switch or interlock kit, selected circuits in the home. A 3,500 to 5,000-watt portable generator ($500 to $1,000) can power a refrigerator, several lights, a phone charger, and a window AC unit. A 7,000 to 12,000-watt unit ($800 to $2,000) can run most of a home's essential loads but typically not a central air conditioning system. Fuel consumption is significant: a 5,000-watt generator running at 50 percent load consumes about 0.5 gallons of gasoline per hour. For a 48-hour outage, you need 24 gallons of stored fuel. Gasoline stored more than 30 days degrades without a fuel stabilizer. Portable generators are adequate for occasional outages but are not a whole-house solution.

Inverter generators produce what is called clean power: output with less than 3 percent total harmonic distortion, which is safe for sensitive electronics including computers, televisions, and medical equipment. Standard portable generators produce noisier power that can damage delicate electronics. Inverter generators also throttle the engine speed to match the actual load, making them significantly quieter (50 to 60 decibels at 23 feet versus 65 to 75 decibels for standard portables) and more fuel-efficient at partial loads. The main limitation is output capacity: most inverter generators produce 1,000 to 7,000 watts. Two units can often be parallel-connected to double the capacity. At $800 to $3,000, they cost more than standard portables but less than standby generators. Inverter generators are the best choice for powering a home office, essential appliances, and sensitive electronics during an outage when a standby unit is not in the budget.

Natural gas standby generators connect to the utility natural gas supply line. The fundamental advantage is unlimited fuel: natural gas service is rarely interrupted during power outages (the gas distribution system operates independently of the electrical grid). A natural gas generator can run for days or weeks without any intervention or refueling. Natural gas is also the least expensive fuel option, typically costing 50 to 75 percent less per kilowatt-hour of generated power than propane and significantly less than diesel or gasoline. The installation requires a gas line connection from the main to the generator location ($300 to $800 if nearby, $500 to $1,500 if a long run is needed). Natural gas generators require slightly more regular maintenance than propane units because natural gas burns with slightly more residue, but the difference is minor in practice. This is the most popular fuel choice for residential standby generators in areas with natural gas service.

Propane standby generators work identically to natural gas models from a performance standpoint. The difference is fuel supply: propane is stored in an on-site tank (typically 250 to 500 gallons for residential use) rather than drawn from a utility line. A 250-gallon propane tank costs $800 to $1,500 installed. A 22kW generator running continuously uses approximately 2 to 3 gallons of propane per hour. A full 250-gallon tank provides 3 to 5 days of continuous operation -- enough for most extended outages. Before hurricane season or periods of elevated outage risk, schedule a propane delivery to ensure the tank is full. Propane costs more per BTU than natural gas but is available anywhere regardless of utility infrastructure. Propane generators are the standard choice for rural homes without natural gas service.

Diesel generators are the dominant choice for commercial and industrial standby power but are less common in residential applications. They are more fuel-efficient than gas generators at equivalent output and have a longer engine life under heavy continuous use. Diesel fuel stores better than gasoline but degrades after 12 to 24 months without treatment (add a fuel stabilizer to stored diesel). The drawbacks for residential use are cost (diesel units cost $1,000 to $5,000 more than equivalent gas units), noise (diesel engines are louder), and fuel storage requirements (a substantial above-ground or underground tank). In residential applications, natural gas or propane standby generators are almost always the better choice unless the homeowner has an existing diesel fuel infrastructure or requires a very high output generator (above 48kW) that is not readily available in gas versions.