Generator Sizing Estimator for Ontario Homes
Add up the running and starting watts of what you want to keep on during an outage and get an estimated generator kW band, portable or standby.
The Estimator
- Running load
- 3,500 W
- Starting peak
- 5,500 W
Generator size: essential circuits: a portable of at least 5,500 W through a GenerLink or a transfer switch, or a small standby unit
a portable generator through a GenerLink or a transfer switch is workable for these loads, and a standby unit starts itself when you are away.
A generator's natural gas rating is below its propane rating on every brand we checked: size on the fuel you will use.
An estimate from typical figures and the manufacturer's published numbers; a licensed electrician's load calculation on site decides.
How This Estimate Works
The running load is the sum of the running watts of every load you tick, times its quantity. The starting peak adds the largest motor's extra draw as it starts, on the assumption that the largest motor starts alone while everything else runs. A load calculation on site checks which motors can start together.
The size bands come from our generator sizing guide. A starting peak up to 7,200 watts is the essential circuits range, which a portable generator can feed through a GenerLink or a transfer switch: 7,200 watts is 240 volts at 30 amps, the rating of the common GenerLink and 30 amp inlet. Above it the bands run up to 10 kW, 10 kW to 14 kW, 14 kW to 20 kW and 20 kW to 26 kW; above 26 kW a liquid-cooled unit or load management comes in.
A standby unit is suggested when the list holds central air conditioning, an electric range, an electric dryer, an electric water heater, a well pump above one horsepower or an EV charger, or when you choose the whole home and the starting peak passes 7,200 watts.
Typical figures: the site's generator sizing guide and general practice; the nameplate or spec sheet governs. Read the generator sizing guide →
Where the source is the sizing guide, the guide states a range that includes the figure; the ranges are in the linked guide.
| Load | Running | Starting | Source |
|---|---|---|---|
| Gas furnace blower | 800 | 2,400 | Sizing guide |
| Refrigerator | 400 | 1,200 | Sizing guide |
| Chest freezer | 300 | 900 | General practice |
| Sump pump | 1,000 | 3,000 | Sizing guide |
| Well pump | 1,500 | 4,500 | Sizing guide |
| Central air conditioning | 4,000 | 12,000 | Sizing guide |
| Lighting, whole house | 1,000 | 1,000 | Sizing guide |
| Electric range or oven | 4,000 | 4,000 | Sizing guide |
| Microwave | 1,200 | 1,200 | General practice |
| Electric water heater | 4,500 | 4,500 | General practice |
| Electric dryer | 5,000 | 5,000 | General practice |
| Level 2 EV charger, 32 A | 7,700 | 7,700 | General practice |
| Television, modem, router and chargers | 300 | 300 | General practice |
| Medical device (CPAP, oxygen concentrator) | 500 | 500 | General practice |
| Garage door opener | 600 | 1,800 | General practice |
A licensed electrician's load calculation or site visit decides the generator size; this estimate is where the conversation starts.
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