Panel sizing questions almost always arrive attached to a project — an EV charger, a heat pump, a basement apartment — and the right answer comes from a load calculation, not a rule of thumb. But the rules of thumb tell you what to expect.
When 100 amps is genuinely enough
A 100-amp service comfortably runs a small-to-mid-size home (under roughly 2,000 sq ft) with gas heat, gas hot water, gas stove, and central air as the only big electrical load. Millions of GTA homes fit this profile, and there's no safety issue with a healthy, properly installed 100A panel — insurers accept them without question.
The math changes the moment large electrical loads stack up. A 48-amp EV charger by itself consumes nearly half of a 100A service's capacity. An electric range, dryer, and air conditioner together eat most of the rest. This is why the Ontario Electrical Safety Code requires a load calculation before adding major circuits — it adds your square footage, heating type, appliances, and dedicated circuits into a worst-case demand figure and compares it against the service size.
The 200-amp threshold
We recommend upgrading to 200 amps when any two of these apply: EV charging, electric heating or a heat pump, a hot tub or pool, a basement apartment or in-law suite, a large kitchen renovation with electric cooking, or a workshop with heavy tools. The upgrade runs $3,200–$4,500 in the GTA including the ESA permit (full cost breakdown), and doing it once — with a 40-space panel — covers essentially any future the house has.
Heat pumps deserve a special mention because Ontario's electrification incentives are pushing thousands of homes from gas furnaces to electric heat pumps. A cold-climate heat pump with backup resistance heating is one of the largest loads a house can carry, and it routinely tips 100A homes over the line. If a heat pump is in your five-year plan, size the panel for it now.
When 400 amps enters the picture
Estate homes over 3,500–4,000 sq ft with electric heating, multiple EV chargers, pool equipment, and extensive lighting can exceed 200A on the load calculation. We install 400A services in Kleinburg, Oakville, and the Kingsway regularly. The tell-tale: if your project list includes two EVs, a pool, and a backup generator or battery, have the load calculation done before committing to equipment.
Not sure where your home lands? We run the load calculation as part of every free estimate — call 416-837-4038 and we'll give you the actual number, not a guess.