Whole House Generator Buying Guide: Everything You Need to Know Before You Buy

A Whole House Generator Is a Long-Term Home Investment

A permanently installed standby generator represents one of the largest single purchases most homeowners make — typically $8,000 to $15,000 installed. Unlike a portable generator you can return to the hardware store if it does not meet your needs, a standby generator is a permanent fixture that will be with your home for 20 to 30 years. Getting the buying decision right requires understanding a set of factors that manufacturers’ marketing materials often gloss over. This guide gives you everything you need before you sign with an installer.

Step 1: Determine Your Coverage Goal

The first and most important question is: what exactly do you want the generator to power? The answer drives every subsequent decision.

• Essential circuits only: Refrigerator, well pump, sump pump, furnace, a few lights and outlets. Typically requires 10 to 14kW. Lower installed cost. Works through a load center transfer switch that covers only the selected circuits.
• Whole-home coverage: Every circuit in the house, including central AC, electric dryer, electric range, and EV charger. Requires 20 to 22kW or more. Higher installed cost. Works through a 200-amp whole-house automatic transfer switch.
• Managed whole-home coverage: A 16 to 18kW generator with a smart transfer switch that monitors total load and automatically sheds non-critical circuits if consumption approaches the generator’s capacity. A middle option that provides whole-home coverage under normal loads at lower cost than maximum-output units.

Step 2: Choose Your Fuel Source

Whole home standby generators run on natural gas or liquid propane. The fuel choice affects installed cost, ongoing fuel cost, and runtime capability.

• Natural gas: The preferred fuel for most installations. Piped directly from the utility — no storage, no delivery, no running out. Runtime is essentially unlimited as long as gas service is active. Natural gas standby generators are typically $200 to $500 less expensive to operate annually than equivalent propane units due to fuel cost differences.
• Liquid propane: The right choice for homes without natural gas service. Requires a propane storage tank — typically 100 to 500 gallons. A 500-gallon tank provides approximately 100 to 200 hours of generator runtime at typical residential loads. Propane requires delivery scheduling and tank level monitoring.

Step 3: Select the Right Output (kW)

Use this framework to determine the output level your home needs:

1. Add up the running wattage of all appliances you want to run simultaneously — refrigerator, HVAC, well pump, lighting, electronics.
2. Identify the single appliance with the highest startup surge — typically central AC at 5,000 to 7,000W starting.
3. Add the startup surge of that appliance to the running load of everything else simultaneously active. This is your peak demand.
4. Divide peak demand by 0.80 (the 80% rule) to find the minimum recommended generator size.
5. Round up to the next available product size — more headroom is always preferable to a generator running at near-capacity continuously.

As a quick reference: most 2,000 to 2,500 sq ft homes with central AC need 16 to 20kW for essential-plus-comfort coverage. True whole-home coverage for larger homes typically requires 22kW or above.

Step 4: Understand the Transfer Switch

The automatic transfer switch (ATS) is as important as the generator itself. It monitors utility power and signals the generator to start when the grid fails — then transfers your home’s electrical load from utility to generator power within seconds. When utility power returns, it transfers back and shuts the generator down.

• 200-amp whole-house ATS: Connects at your main electrical panel service entrance. Backs up every circuit. More expensive but provides complete coverage.
• 100-amp or 50-amp load center: A sub-panel containing only the selected circuits that will be backed up. Lower cost but requires circuit selection at installation — circuits not in the load center receive no backup power.
• Smart load management switches: Newer transfer switch technology that monitors total generator load in real time and sheds lower-priority circuits automatically if consumption approaches capacity. Allows a smaller generator to handle whole-home loads by managing demand intelligently.

Step 5: Evaluate the Installer, Not Just the Generator

The installer you choose affects your experience more than the generator brand. A quality generator installed poorly will cause you more problems than a modest generator installed correctly. Key installer evaluation criteria:

• Manufacturer certification: Generac, Kohler, Cummins, and most major brands have dealer certification programs. A certified dealer has completed manufacturer training and met installation standards.
• Licensing and insurance: Your installer must hold electrical contractor licensing in your state and carry liability insurance. Ask for license numbers and verify with your state licensing board before signing.
• Permit pulling: A legitimate installer pulls permits for the electrical and gas work involved. If an installer offers to skip the permit “to save money,” decline and find someone else. Unpermitted generator installations can void your homeowner’s insurance and create liability.
• References: Ask for references from recent installations in your area. Call them and ask specifically about post-installation service responsiveness — how the installer handled any issues after the job was complete.
• Service agreement: Ask about annual maintenance service. A generator that receives no annual service will underperform and fail prematurely. Installers who offer service agreements are invested in the long-term performance of the units they install.

Step 6: Get Multiple Quotes and Compare Them Correctly

Get at least three quotes. When comparing, do not compare on price alone — a quote that is $2,000 cheaper may exclude the transfer switch, use a smaller generator than appropriate, or skip the permit and gas line work. Compare quotes on:

• Generator brand, model, and output (kW)
• Transfer switch type and amperage
• Gas line work included or excluded
• Concrete pad included or excluded
• Permit fees included or excluded
• Warranty terms on the unit and the installation workmanship
• Estimated installation timeline

What to Expect During and After Installation

A typical whole home generator installation takes one to two days for a crew of two. After installation, your installer schedules the electrical inspection, coordinates utility interconnection if required, and activates the weekly exercise cycle. The generator will run a self-test at the scheduled time each week — typically 5 to 10 minutes at no load — to keep the engine lubricated, battery charged, and confirm operational readiness.

First annual service is typically due at 12 months or 100 hours of operation — whichever comes first. Budget $150 to $300 for annual professional service.

Bottom Line

A whole home standby generator is a sound investment for homeowners in areas with regular multi-day outages, those with medical equipment needs, or anyone who values complete energy resilience. The buying decision comes down to four things: the right output for your home’s actual loads, the right fuel for your infrastructure, a quality automatic transfer switch sized for your coverage goal, and a certified, licensed installer with a service network you can rely on. Get that right and you will have a reliable system for decades.