What will a 12,000-watt generator run?
A 12,000-watt portable is the top of the portable range. It runs central AC, an electric dryer, or Level 2 EV charging each with headroom, and it will carry central AC + dryer + fridge + furnace together (about 13,100W peak) if you stagger the starts. Beyond that, all-electric whole-house loads running at once (AC, dryer, and the EV together) are home-standby territory, not portable.
The three tables sort common outage load lists by how a 12,000-watt handles each one. Every running and starting figure comes from the same engine the wattage picker and the wattage chart use. "Runs easily" means the list stays under 80% continuous with the start spike covered; "runs with load management" means it fits but you're near the ceiling or staggering starts; "won't run" means the running total or the start spike is over the line. Loads tagged 240V also need a 240V outlet, which starts at the 5,000W class.
Runs easily
| Load list | Running | Peak start |
|---|---|---|
| Lights, Wi-Fi, and phone or laptop chargers | 200 W | 200 W |
| TV, streaming box, Wi-Fi, and lights | 400 W | 400 W |
| A CPAP machine overnight | 60 W | 60 W |
| One 1,500W space heater | 1,500 W | 1,500 W |
| A microwave on its own | 1,400 W | 1,400 W |
| A refrigerator on its own | 700 W | 2,200 W |
| Fridge, freezer, and the keep-alive basics | 1,400 W | 2,900 W |
| Winter storm: fridge, furnace blower, lights, Wi-Fi | 1,700 W | 3,250 W |
| Flooding storm: fridge, furnace, 1/2 HP sump, basics | 2,750 W | 4,300 W |
| Well water: fridge, 1/2 HP well pump, basics | 1,900 W | 3,400 W |
| A 10,000 BTU window AC with fridge and basics | 2,100 W | 3,600 W |
| Kitchen morning: microwave, coffee maker, fridge | 3,100 W | 4,600 W |
| A 1 HP well pump with fridge and furnace 240V | 3,700 W | 5,700 W |
| An electric water heater with fridge and basics 240V | 5,400 W | 6,900 W |
| Central AC (3 ton) with fridge and furnace fan 240V | 5,200 W | 7,700 W |
| An electric dryer 240V | 5,400 W | 6,750 W |
| Level 2 EV charging (40A) 240V | 9,600 W | 9,600 W |
Runs with load management
| Load list | Running | Peak start |
|---|---|---|
| Central AC, electric dryer, fridge, and furnace together 240V | 10,600 W | 13,100 W |
Won't run on this size
| Load list | Running | Peak start |
|---|---|---|
| Central AC, dryer, and Level 2 EV all at once 240V | 20,000 W | 22,500 W |
How to read these tables for your own list
A 12,000-watt holds about 9,600 watts continuously (80% of its 12,000W rating) and survives a start spike up to 15,000W. Add the running watts of everything you'll have on at once, then add the single largest start surge on top of that total. If both numbers fit, so does the list. The wattage picker does that arithmetic for your exact appliances, and the wattage chart lists the per-appliance numbers behind these lists.
Anything that connects to your electrical panel (a furnace, well pump, central AC, or a whole-house transfer) is licensed-electrician work, wired through a transfer switch or interlock. A generator powers those through that equipment, never by backfeeding an outlet, and it always runs outside, well away from the house.
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Questions people ask
Will a 12,000-watt generator run central AC and an electric dryer at the same time?
Yes, with the fridge and furnace too, at about 13,100W peak, as long as you don't start both 240V loads in the same instant. Add Level 2 EV charging to that and you're over its rating; that combination is a standby generator's job.
How many appliances can a generator run at once?
As many as fit two limits at the same time: the running watts have to stay under about 80% of the rating (that is the 12,000W a 12,000-watt holds continuously, so roughly 9,600W of steady load), and the single biggest motor start has to land under the 15,000W peak. Add running watts for everything on, then add the largest one start spike on top. The tables above do that for the common lists.
Running watts or starting watts: which one sizes the generator?
Both, on different clocks. Running watts are what the generator holds for hours, so they set the continuous size; the starting spike is what it has to survive for about a second when the biggest motor kicks in. A unit that clears the running total but not the spike stalls at start; one that clears the spike but runs at 95% all night runs hot and drinks fuel.