July 14, 2026 · 5 min read
Amperage is the size of the pipe, not the amount of water you use. A 100-amp service can carry a lot of house — until it can't, and the point where that happens is more predictable than most homeowners expect.
What a 100 amp service comfortably supports
- Gas furnace, gas water heater and gas range
- Central air conditioning on a modestly sized home
- Normal lighting, receptacle and appliance loads
- One Level 2 EV charger, sometimes, with load management
What pushes a home past it
- Electric or heat-pump heating
- An induction range plus an electric dryer and electric water heater
- A hot tub
- Two EV chargers
- A large addition, ADU or finished basement with its own HVAC
The other limit: breaker spaces
Plenty of homes hit a wall that has nothing to do with amperage. The service is fine, but the panel is physically full — every slot occupied, tandems stacked in wherever the manufacturer allows. Adding a circuit means either a subpanel or a bigger panel, regardless of how many amps you're drawing.
How a real load calculation works
Electricians don't add up nameplate ratings and call it a day. The code applies demand factors, because your dryer, oven and air conditioner rarely all run at maximum simultaneously. A proper calculation accounts for square footage, fixed appliances, heating and cooling, and the largest motor load.
It's the difference between "you should probably upgrade" and a number you can act on.
When 100 amps is genuinely fine
If your home is gas-heated, moderate in size, has open breaker spaces and no EV or hot tub in your plans, an upgrade may buy you nothing. We will tell you that. Replacing a failing panel at the same 100-amp service is often the smarter spend.
Planning five years out
The one argument for upsizing early: doing it while the walls are open, or while you're already paying for a panel replacement, is far cheaper than doing it twice. If solar, a heat pump or an EV is anywhere in your plans, size for it now.
Want this answered for your panel?
A tech opens the panel, runs the load calculation and leaves you with a written price. No cost, no obligation.