Which Generac® Home Generator Size Do You Need? 10kW to 26kW, Explained

Shopping for a home standby generator usually starts with a number — 10kW, 18kW, 22kW, 26kW — and no clear sense of which one actually fits your house. The honest answer is that size comes down to three questions, not one spec sheet: what do you actually need to keep running during an outage, how big is your home's electrical service, and what's the single heaviest thing that generator will ever have to power. Get those three answers right and the correct size becomes obvious. Guess at them, or size off square footage alone, and you end up either underpowered on the coldest night of the year or paying for capacity you'll never use.

The first question is what has to stay on. Some homeowners only want the essentials protected — the refrigerator, a well or sump pump, the furnace blower, some lighting and outlets — and that's a fundamentally smaller, less expensive system than a homeowner who wants the whole house, including central air conditioning, to run exactly as if nothing happened. The second question is your electrical service size, typically 100A or 200A, which sets a ceiling on what the generator and transfer switch need to handle. The third, and usually the deciding factor, is your heaviest single load — and for most homes, that's central air conditioning. A generator that comfortably runs lights, a furnace, and a refrigerator can still stall out trying to start a large AC compressor, so the AC tonnage on your home is often the number that actually determines your tier, more than anything else on your circuit list.

In practical terms, home standby generators fall into a few well-worn tiers. Around 10–14kW covers essential-circuit protection for smaller and mid-size homes — refrigerator, well or sump pump, furnace, select lighting and outlets — without attempting to run full central air. Stepping up to roughly 18–22kW reaches genuine whole-home coverage for many average-size homes, including central AC in most cases; the 22kW class has for years been the best-selling home standby size in the country, which tells you it's the sweet spot for a large share of American houses. At the top end, 24–26kW units are built for larger homes with bigger AC loads or more square footage to condition, and the 26kW is the largest air-cooled home standby unit Generac makes — the ceiling before you're into liquid-cooled, more industrial-grade equipment entirely.

There's a genuinely useful trick that changes this math for a lot of homeowners: smart load management. A transfer switch with load-management modules can briefly cycle or shed non-critical circuits — say, an electric water heater or a second AC zone — for the few seconds it takes a big compressor to start, then bring everything back online. That means a smaller, less expensive generator can often run a whole home that would otherwise seem to require the next size up, simply by never asking every circuit to draw power at the exact same instant. It's frequently the difference between paying for an 18kW system with smart switching and a 22kW or 24kW system without it, for the same real-world outcome in your house.

Fuel choice matters alongside sizing, though it doesn't change the kW number itself. Natural gas generators run for as long as your utility keeps supplying gas — effectively unlimited runtime with no tank to monitor, which is why they're the default choice wherever gas service already reaches the house. Propane generators offer the same performance but depend on tank size for total runtime, so a longer expected outage means either a bigger tank or a refill plan. Neither fuel makes a generator more or less powerful — it's purely a question of how long you can sustain the load once the generator is already sized correctly for it.

The one sizing approach that reliably fails is going by square footage alone. A 2,800-square-foot home with a small AC system and a 100A panel can need meaningfully less generator than a 2,000-square-foot home with a large compressor and a 200A service — because it was never really about the floor plan. It's about the panel, the loads, and what you've decided has to keep running. That's exactly why we size every home generator over a video call rather than off a form: you show us your panel and walk us through your priorities, and we quote the specific unit, transfer switch, and accessories that actually fit your house — no guessing, no oversizing, no undersizing. This article is general guidance to help you understand the tiers; your quote is where the real sizing happens.