Overview
Backup power, interlocks, and generator sizing
An interlock kit, a manual transfer switch, and an automatic transfer switch all prevent the generator and the utility from feeding the house at once. They are not interchangeable, and none of them makes a dryer-outlet backfeed safe.
Size the generator from the loads you will actually run, including motor starting, not from the square footage of the house. Honda’s published wattage table is the default for the calculator; well pumps and heat pumps need nameplates because Honda does not list them in that home table.
Portable generators kill people with carbon monoxide when they are run in a garage, in a basement, or too close to an opening. See the placement question for CPSC’s published guidance, including the 20-foot figure.
Open the generator size calculator
Questions in this cluster
- Interlock kit vs transfer switch: what’s the difference?
- Manual vs automatic transfer switch: which do I need?
- Can I use an interlock kit with a portable generator?
- Is it safe to backfeed a generator through a dryer outlet?
- Do I need an automatic transfer switch for a standby generator?
- What size generator do I need for a refrigerator, a gas furnace, and some lights?
- What size generator do I need for a well pump and a refrigerator?
- What size generator do I need to run central air conditioning?
- Do I need a soft start to run my air conditioner on a generator?
- 30-amp vs 50-amp generator inlet: which should I install?
- Portable generator with an interlock vs a standby generator with an automatic transfer switch
- Can a portable generator power a heat pump?
- Can I run an electric dryer on a portable generator?
- Where should I put a portable generator so carbon monoxide is not a risk?
- Whole-house vs essential-circuits generator sizing: what is the actual difference?
- Can I install an interlock kit on a 100-amp panel?
- Can I install an interlock kit on a 200-amp panel?
- Does an interlock kit meet code as transfer equipment?
- What size generator do I need for a sump pump, fridge, and furnace?
- What size generator do I need for a 10,000 BTU window air conditioner?
- Can I run a well pump, fridge, and lights on a 5,000-watt generator?
- Gasoline vs propane vs natural gas for a home backup generator
- Do I need an inverter generator for electronics and a furnace board?
- How do I keep a portable generator from overloading when I use an interlock?
- Can I use a generator interlock and an EV charger on the same panel?
- What size standby generator do I need for a whole house with a heat pump?
- Is a 7,500-watt generator enough for a fridge, furnace, and a well pump?
- Do I need a building permit for a generator interlock and inlet?
- How far from a window does a portable generator need to be?
- Can I back up a gas furnace without backing up the whole house?
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.