Sizing a Dual-Fuel Generator: Running Watts vs. Starting Watts
Last verified: September 2026
Everything you actually need to know, in plain English — no jargon, no rabbit holes. If you'd rather have someone help in person, my number is (330) 200-8042.
Sizing a Dual-Fuel Generator: Running Watts vs. Starting Watts
Picking the right size generator trips people up more than almost anything else in this subject — and it shouldn't. You don't need to be an engineer or do algebra at the kitchen table. You need two numbers: what your essentials use to run, and the single biggest jolt one of them needs to start. Add those together, account for your fuel, and you're done. Here's the plain-English worksheet, and there's a printable, 29-page guide up top if you'd like the full deep-dive.
Common Questions
1 What's the difference between running watts and starting watts?
Running watts is the steady power something uses once it's up and going — a lamp, a phone charger, a fridge that's already humming. Starting watts is a short burst, often just a second or two, that a motor needs to get moving from a dead stop.
Anything with a motor — a fridge compressor, a pump, a furnace blower — has both numbers. Anything that just glows or heats steadily usually only has running watts.
2 How do I find my own numbers instead of guessing?
Look for a small metal or sticker tag, usually on the back or bottom of the appliance. Pumps and blowers are often labeled on the unit itself or by horsepower (HP). Your generator's own spec plate lists its running and starting watts, often broken out by fuel.
If a label is worn off, a licensed electrician — or I — can often look it up by model number.
3 Does my fuel choice really change the size I need?
Yes, and it surprises a lot of people. The big number on the box is almost always the gasoline rating. On propane you'll typically get somewhere around 5–15% fewer running watts (about 10% is common), and natural gas trims it a bit further. If propane or natural gas is your real outage plan, size against that number, not the gasoline headline.
4 Do I need to add up the starting watts for everything on my list?
No — just the single biggest one. Motors rarely all start at the exact same instant, so the usual recipe is: add up everyone's running watts, then add only the largest starting-watt jolt among them on top.
5 What if a well pump is part of the picture?
Well pumps deserve their own careful look — they're usually 240-volt with a big starting surge, often several times their running watts. We have a whole guide just on backing up a well pump, with the typical ranges and the 240-volt catch explained.
6 This still feels like a lot of homework. Can you just size it for me?
Happily — this is one of the most common house calls I get. Bring me your appliance labels (or let me find them with you), and I'll help you land on a size that fits your home, your budget, and your fuel plan, no sales pressure. $99 flat. Call or text (330) 200-8042.
Want Me to Help With Yours?
Getting a backup generator picked, set up, and safe is one of the things I'm glad to do in person. I bring the patience and the know-how — you keep your seat. We'll get it starting, sort out the fuel and the safe hookup, walk through running your essentials, and make sure everyone knows the carbon-monoxide basics. $99 flat, and every visit is 30-day come-back-free. (330) 200-8042.
Would you rather I just do this for you?
No shame in it — plenty of folks would rather hand it off, and that's what I'm here for. I'll come to your home, set it up right, and make sure it's working before I leave. Flat $99 per visit — no jargon, no upsell, and every visit is 30-day come-back-free.
Not a hardware job? I can often fix it remotely for $49 — a secure screen-share, up to 2 hours, that you watch the whole time and can end whenever (included free for $39/mo Support Plan members, and it counts toward the $99 if it turns out I need to come out).