Is your 100A panel actually full?

A full-looking panel and a full panel are different things. Slots can run out while capacity is fine, and capacity can run out while half the slots sit empty. What matters is the load calculation — the same math the Ontario Electrical Safety Code uses to decide what a house can safely draw.

The signs worth paying attention to

Breakers that trip when two big appliances run at once. A panel that hums or feels warm. Lights that dip when the dryer starts. None of these prove the service is undersized, but together they’re the classic picture of a house pushing its limits.

What a load calculation actually adds up

Square footage sets a base heating and lighting load, then the big fixed loads stack on top: electric heat or a heat pump, the range, the dryer, air conditioning, a hot tub, and — the one that changes everything lately — an EV charger. A 100A service that handled a gas-heated 1990s house comfortably can be genuinely out of room after a heat pump and Level 2 charger arrive.

When you don’t need the upgrade

Sometimes the honest answer is a sub-panel for slots, a load-management device for the EV, or nothing at all. A good electrician shows you the arithmetic before quoting anything — if the numbers say your service is fine, that should be the quote.

If the numbers say 200A

Expect the job to take about a day, include an ESA notification and inspection, and involve your utility briefly disconnecting service. Get the certificate at the end — your insurer may ask for it, and the next buyer’s home inspector definitely will.