The short answer
Frequently, yes. A great many Calgary and Edmonton homes carry a fully legal secondary suite on an existing 100 A service. The instinct that "two kitchens means 200 amps" is wrong, and acting on it can cost you five figures you didn't need to spend.
What decides it is your calculated load under Canadian Electrical Code Rule 8-200 — not the number of dwelling units, not the square footage on its own, and not what your neighbour was told.
Rule 8-200 applies demand factors across dwelling units. The largest unit's basic demand counts in full; additional units count at a reduced percentage, because two households don't peak simultaneously. A house and suite showing 180 A of raw connected load can calculate out comfortably under 100 A.
What actually pushes you over
In our experience these are the loads that decide the question, roughly in order of impact:
| Load | Why it matters |
|---|---|
| Electric space heating in both units | The single biggest driver. Gas heat changes the answer dramatically. |
| A second electric range | Adds a substantial block to the suite's demand. |
| Tankless electric water heater | Very large, and the most commonly forgotten load on DIY calculations. |
| EV charging equipment | Counted at 100% of rating unless load management is installed. No diversity allowance. |
| Hot tub or spa | Full nameplate. Often added later, after the calculation was done. |
Any two of these together will usually settle the question one way or the other. A gas-heated house with a gas range in the suite and no EV charger is very likely fine on 100 A. An all-electric house with a suite, a tankless heater and a Level 2 charger almost certainly is not — without load management.
Get your actual number
Rather than guessing, run the real calculation. Every demand factor is shown, so you can see exactly which load is driving the result — and what to change if you're close.
Run the free calculator →If you're over: three options before upgrading
1. Change the equipment
The cheapest fix is usually specification, not infrastructure. Gas instead of electric for the suite's range, or a conventional tank water heater instead of tankless electric, can move the calculated load by more than you'd think. If you're marginally over, this is the first place to look.
2. Add load management (EVEMS)
If EV charging is what tipped you over, an electric vehicle energy management system lets the charger throttle back when the rest of the house is drawing. This reduces the charger's contribution to the calculated load and is typically far cheaper than a service upgrade — often by an order of magnitude. For a lot of Calgary suite projects, this is the answer.
3. Upgrade the service
Sometimes it's simply the right call, particularly if you're planning further electrification. Be aware that a service size change involves ENMAX as well as the City of Calgary, so it carries lead time and coordination cost beyond the electrical work itself. Identify this early rather than at rough-in.
We regularly see homeowners quoted for a 200 A service upgrade on projects that calculate out fine at 100 A. The calculation takes minutes and is free. Do it before you accept a quote that's premised on needing more service.
What about 60 amp services?
A 60 A service is a different conversation. For a single dwelling of 80 m² or more excluding basement, the Code sets 100 A as the minimum service ampacity — so most Calgary houses on 60 A will need an upgrade to add a legal suite regardless of what the demand calculation says. If you're on 60 A and planning a suite, budget for the upgrade.
Frequently asked questions
Can a 100 amp service handle a secondary suite?
Frequently yes. Under CEC Rule 8-200 the two dwelling units are not simply added together — demand factors reduce the contribution of the smaller unit. Many Calgary and Edmonton homes carry a legal suite on an existing 100 A service. Whether yours can depends on your specific connected loads, particularly electric heat, ranges, tankless water heaters and EV charging. Our Calgary secondary suite guide covers the permit side.
What most often pushes a 100 amp service over the limit?
In order: electric space heating in both units, a second electric range, a tankless electric water heater, EV charging equipment counted at 100 percent, and a hot tub. Any two of these together will usually decide the question.
Can I avoid a service upgrade with load management?
Often, yes — particularly where EV charging is the deciding load. An EVEMS reduces the charger's contribution to the calculated load by backing it off when the rest of the house is drawing, and is usually far cheaper than a service upgrade.
Is 100 amps the minimum service for a house with a suite?
For a single dwelling of 80 square metres or more excluding basement, the Code sets 100 A as the minimum service ampacity. In practice nearly every Calgary house with a legal suite is on 100 A or larger, so 100 A is the realistic starting point rather than a comfortable ceiling.
Close to the line? Get a second opinion.
If your result lands within a few amps of your service size, that's exactly when a master electrician's review is worth having before you commit to a plan.
Get it signed off →General information for planning purposes only — not a code ruling or a substitute for a permit submission. Final acceptance rests with the authority having jurisdiction.