Whole House Generator Guide: Cost, Sizing, Fuel & Installation

How it works: A whole house standby generator is a permanently installed, fuel-powered generator that sits outside your home (like an AC unit). It is connected to your electrical panel and a fuel source (natural gas line or propane tank). When utility power goes out, an automatic transfer switch (ATS) detects the outage and starts the generator within 10-30 seconds. The generator powers your home until utility power is restored. When power returns, the ATS switches back to utility power and shuts down the generator. The entire process is automatic — you don't need to be home.

Standby vs portable: Standby generators are permanently installed, automatic, and power the whole house (or selected circuits). Portable generators are temporary, manual (you must start them, run extension cords, and refuel), and power limited items. Standby generators cost more upfront ($5,000-$15,000+ installed) but provide true whole-house backup with zero effort during an outage. Portable generators cost less ($500-$2,000) but are limited, inconvenient, and carry carbon monoxide risks if used improperly.

Who benefits most: Areas with frequent or prolonged power outages. Homes with sump pumps (flooding risk without power). Homes with well water (no water without power). Homes with medical equipment. Homes in extreme climates (loss of heating or cooling can be dangerous). Remote or rural areas where utility restoration takes longer. Anyone who works from home and can't afford downtime.

By generator size (installed): 10-14 kW (essential circuits only): $4,000-$8,000. 16-20 kW (most of the home): $5,000-$10,000. 22-24 kW (whole house, moderate loads): $6,000-$12,000. 30-48 kW (large home, all loads including central AC and electric heat): $10,000-$20,000+.

Cost breakdown: Generator unit: $3,000-$15,000 (depending on size and brand). Automatic transfer switch (ATS): $500-$1,500 (often included with the generator). Installation labor: $1,500-$3,000. Concrete pad: $200-$500. Electrical work (connecting to panel, wiring ATS): included in installation. Gas line extension (natural gas): $500-$2,000. Propane tank (if using propane): $500-$2,500 (for a 250-500 gallon buried or above-ground tank). Permit: $100-$500.

Ongoing costs: Fuel: natural gas $0.50-$1.50/hour at full load; propane $1.50-$3.00/hour at full load. Annual maintenance: $200-$400 (oil change, filter, spark plugs, inspection). Exercise cycle: the generator runs automatically for 10-15 minutes weekly to stay ready (minimal fuel cost). Propane refill: varies by usage and tank size.

Popular brands and price ranges: Generac (market leader, ~75% market share): $4,000-$15,000. Kohler: $5,000-$18,000 (premium). Briggs & Stratton: $4,000-$10,000. Cummins: $5,000-$15,000. Champion: $3,500-$8,000 (value option).

How to size a generator: Add up the wattage of everything you want to power during an outage. Key loads: central AC (3,500-5,000 watts running, 7,000-10,000 starting), furnace/blower (500-700 watts), refrigerator (100-400 watts), sump pump (800-1,500 watts), well pump (1,000-2,000 watts), lighting (1,000-2,000 watts for the whole house), electric water heater (4,500 watts), electric range/oven (3,000-5,000 watts), electric dryer (5,000-6,000 watts), washer (500 watts), and miscellaneous (TVs, computers, garage door, security system: 1,000-2,000 watts).

General sizing guidelines: Small home (1,000-1,500 sq ft), gas heat, no central AC: 10-14 kW. Medium home (1,500-2,500 sq ft), gas heat, central AC: 16-22 kW. Large home (2,500-3,500 sq ft), gas heat, central AC: 22-30 kW. Large home with electric heat, electric water heater, or multiple AC units: 30-48 kW.

The right approach: Have the installing contractor perform a load calculation. They will review your electrical panel, identify all circuits, and calculate the total load. This ensures proper sizing — too small and the generator overloads; too large and you overspend. Most homes (2,000 sq ft, gas heat, central AC, standard appliances) are well-served by a 22 kW generator ($6,000-$12,000 installed).

Natural gas: Best choice if you have a gas line to the house. Unlimited fuel supply (connected to the utility gas line — no tank to refill). Cleanest-burning fuel (less maintenance). No fuel storage concerns. Slightly lower energy density than propane (natural gas generators are rated slightly lower in output). Cost: natural gas is typically the cheapest fuel per BTU. Downside: if the gas utility goes down during a disaster (rare but possible), the generator won't work.

Propane (LP): Best choice for homes without natural gas service (rural areas). Requires a dedicated propane tank (250-1,000 gallons). Higher energy density than natural gas (slightly more power per unit). The tank stores fuel on-site (independent of utility infrastructure). Tank options: above-ground (cheaper, visible) or buried (out of sight, more expensive to install). Downsides: the tank must be refilled (you need to monitor the level and schedule deliveries), propane costs more per BTU than natural gas, and the tank takes up yard space.

Diesel: Less common for residential standby. More fuel-efficient than gas or propane. Diesel fuel stores well long-term. Louder and produces more emissions. Requires a dedicated fuel tank. Used more often in commercial/industrial applications.

Dual fuel: Some generators can run on either natural gas or propane. Provides flexibility (e.g., primary fuel is natural gas, but a propane tank provides backup if the gas utility fails). Slightly more expensive than single-fuel models. Brands: Generac and Cummins offer dual-fuel options.

Installation process: Site assessment: the contractor evaluates your home's electrical system, fuel source, and generator placement options. Permits: electrical permit and sometimes a building permit. Pad: pour a concrete pad or install a composite pad for the generator to sit on. Placement: the generator must be at least 5 feet from windows, doors, and vents (to prevent exhaust from entering the home) and at least 18 inches from the house. Generator delivery and placement. Fuel connection: extend the natural gas line or install a propane tank and line. Electrical connection: install the automatic transfer switch at the main panel and wire it to the generator. Startup and testing: the installer programs the ATS, sets the exercise schedule, and tests under load. Inspection: the local inspector verifies code compliance. Timeline: 1-2 days for installation (after the pad is cured and permits are in hand).

Maintenance: Weekly exercise: the generator runs automatically for 10-15 minutes per week. This keeps the engine lubricated and the battery charged. You set the day and time. Oil and filter change: every 200 hours of run time or annually (whichever comes first). Air filter: inspect annually, replace as needed. Spark plugs: replace every 2-3 years. Battery: inspect annually, replace every 3-5 years. Coolant (liquid-cooled models): check annually, replace per manufacturer schedule. Annual professional maintenance: $200-$400 (highly recommended). Most dealers offer maintenance plans.

Noise: Modern standby generators are quieter than older models. Typical noise level: 60-70 dB at 23 feet (comparable to a normal conversation or a dishwasher). Generac models with their Quiet-Test mode run at reduced RPM during weekly exercise (even quieter). Placement away from bedrooms and neighbor windows reduces noise impact.