Buy a generator that is too small and it will stall when the well pump kicks in. Buy one far too large and you have paid for capacity you will never use. Sizing is about what you want to run at the same time.
Start with a list
Write down what must stay on during an outage. For most Michigan homes that is the furnace or boiler, the sump pump, the well pump if there is one, the refrigerator and freezer, some lights and outlets, and internet equipment. Then add the things you would like: the range, the dryer, central air.
Running watts and starting watts
Motors draw two to three times their running power for a moment as they start. Well pumps, sump pumps and air conditioners are the big ones. A properly sized generator covers the total running load plus the largest starting surge.
Rough guide
- Essentials only, in a gas-heated home: a smaller standby unit or a large portable with an interlock.
- Most of the house, with gas heat and one air conditioner: a mid-size air-cooled standby unit.
- Whole house with electric heat, multiple air conditioners or large electric appliances: a larger unit, sometimes liquid-cooled.
Load management modules can let a smaller generator serve a bigger home by keeping large appliances from starting together.
Fuel
Natural gas is the most convenient where it is available, because it never needs refilling. Propane is the usual choice in rural areas and up north, and tank size determines how long you can run.
The transfer switch
Every generator connection needs a transfer switch or interlock so power cannot flow back onto utility lines. For standby units it is automatic. This is not optional, and it is what makes the installation safe and legal.
We calculate the load for you as part of every quote. See generator installation, or compare with battery backup. Adding whole house surge protection at the same time is a sensible extra.