Homeowner Questions · Generators and electrical
What size standby generator does my house need?
Most homes should start with an essential-loads list rather than a generator size. Furnace or heat pump equipment, well pump, sump pump, fridge, lights, internet and a few outlets often point to roughly a 10 to 14 kW unit, while true whole-home coverage with large electric loads and air conditioning can require 18 to 24 kW or more. A load calculation decides.
Checked October 26, 2026 · Educational guide, not a quote.
Quick answer
Most homes should start with an essential-loads list rather than a generator size. Furnace or heat pump equipment, well pump, sump pump, fridge, lights, internet and a few outlets often point to roughly a 10 to 14 kW unit, while true whole-home coverage with large electric loads and air conditioning can require 18 to 24 kW or more. A load calculation decides.
The short version
- List essential loads before choosing kilowatts.
- Motor starting demand matters.
- Load management can reduce generator size.
- Fuel supply is part of sizing.
Essential circuits versus whole home
Essential coverage powers the furnace or heat system, well and sump pumps, fridge, some lights and outlets, and communications. Whole-home coverage adds major discretionary loads and air conditioning, and usually means a larger generator and transfer system.
Motor starts are the trap
A well pump, sump pump or compressor can draw several times its running power for a moment at startup. A proper load plan looks at both running watts and starting demand, and may stagger or manage loads.
Fuel and runtime
Natural gas offers continuous supply where available. Propane runtime depends on tank size and load. The generator size cannot be separated from the fuel plan during a multi-day outage.
What to do next
Mark the loads that must run during a long outage.
Record motor and HVAC nameplate data.
Have the installer complete a load calculation.
Read the full guide
This answer connects to Standby Generators, where the full topic is covered with the current Ontario figures and the next checker.
Size for the outage you need to survive
Decide what must run at hour 30 of an outage, not only what would be convenient at hour one.
Take the generator checkQuestions people also ask
What size standby generator does my house need?
Most homes should start with an essential-loads list rather than a generator size. Furnace or heat pump equipment, well pump, sump pump, fridge, lights, internet and a few outlets often point to roughly a 10 to 14 kW unit, while true whole-home coverage with large electric loads and air conditioning can require 18 to 24 kW or more. A load calculation decides.
Is 10 kW enough for most homes?
Many essential-circuit homes land in the 10 to 14 kW range, but pumps, heating equipment and load management can move the answer substantially.
Can a standby generator run central air conditioning?
It can be designed that way if the generator, transfer switch and load controls are sized for the AC's starting demand.