Sizing a Standby Generator: Whole House vs. Essentials - A Plain-English Guide
Last verified: September 2026
Whole house, or just the essentials? The plain-English guide to sizing a standby generator — building your must-run list, understanding motor surges, and why the final call is a load calculation, not a chart. Rather talk it through? My number is (330) 200-8042.
Sizing a Standby Generator, at a Glance
Sizing a standby generator comes down to one honest question: do you want to back up your whole house, or just the circuits that matter most? The whole-house path means a larger unit, often with a whole-house transfer switch; the essentials path pairs a smaller unit with a transfer switch or load center feeding chosen circuits. Either way, it starts with a must-run list, accounts for the big starting surge that motors like a well pump need, and ends with a proper load calculation from your installer — never a guess from a chart. This guide walks the decision, with no invented numbers. There's a printable 29-page version up top.
Common Questions
1 What size standby generator do I need?
There's no honest one-size answer — it depends on your must-run list and the starting surges behind it. That's a load calculation your installer does; a chart only guesses. A good pro won't hand you a wattage without doing the math for your home.
2 Whole house or just the essentials — how do I choose?
Start with what you truly need running and your budget. Whole-house covers everything with a larger unit; essentials covers chosen circuits with a smaller one. Many folks are happiest, and spend less, with a well-chosen essentials setup.
3 Why do motors matter so much for sizing?
Motors — the well pump, AC compressor, furnace blower, sump — draw a big surge the instant they start, several times their running draw. The generator has to cover the biggest surge while running everything else, so motors often drive the size.
4 Can a smaller unit run my whole house?
Sometimes, with help. Load-management gear lets a smaller unit cover more by taking turns with the biggest loads, and a soft-start can tame an AC surge. Our load-management guide explains how — but the base size still comes from a load calculation.
5 What's the deciding load in a rural home?
Usually the well pump. Most home wells use a 240-volt pump with a big starting surge, often the largest single load — so it tends to set the size. Our well-pump guide digs into backing it up.
6 Do I really need a professional load calculation?
Yes. It's the difference between a system that works when you need it and one that stumbles or costs too much. Charts and rules of thumb guess; your installer's load calculation gets it right for your home.
Would You Rather I Just Help?
Building your must-run list and thinking through whole-house versus essentials is exactly what I love to help with, and I have nothing to sell you. I'll help you get ready for a proper load calculation and line up licensed pros I trust. $99 flat for a visit, 30-day come-back-free.
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).