How to Calculate My Home’s Electrical Load Capacity

Adding an EV charger, a heat pump, an induction range, or a hot tub raises the same question every time: is my existing service big enough? The answer is a load calculation, which the Ontario Electrical Safety Code defines in detail and every licensed contractor runs before quoting a service upgrade. This guide walks a Toronto or GTA homeowner through a simplified version so you can estimate your own capacity before you call.

How to calculate your home’s electrical load capacity

A rough load calculation for a single-family home in Ontario works out the connected load in watts, applies demand factors from the Canadian Electrical Code, and compares the result to your service size at 240V. If the calculated load exceeds your service capacity (or leaves less than a comfortable margin for the loads you plan to add), you need a service upgrade. A full formal load calc is a task for a licensed electrical contractor, but the simplified back-of-envelope version below is close enough to know whether a 100-amp service will hold or a 200-amp is coming.

Common Ontario service sizes are 60-amp (older homes), 100-amp (most GTA homes built 1970s–2000s), 200-amp (modern renos and new builds), and 400-amp (larger or heavily-loaded homes).

Step 1: Determine your service size

• Look at the amperage rating stamped on your main breaker. Common values: 60, 100, 125, 150, 200, 400.
• Cross-check with the meter and service entrance conductors.
• Convert to watts: service amps × 240V = maximum service watts. A 100-amp service = 24,000 W. A 200-amp service = 48,000 W.

Homeowners can read the main breaker rating safely with the deadfront closed. Do not open the deadfront. For panel type identification, see what is a main breaker panel vs a main lug panel.

Step 2: Add up your basic loads (simplified CEC method)

Use these approximations. Real load calcs apply demand factors that reduce total connected watts based on statistical usage, but the simplified version below is generous and works as a first sanity check.

• Basic load for lighting and general receptacles in a typical home: allow 5,000 W plus 1,000 W for every 90 m² (or portion) of living area above 90 m². A 200 m² (about 2,150 sq ft) home comes in around 6,000–7,000 W.
• Electric range: 6,000 W (first 6 kW) at 100%, remainder at 40%. A typical 12 kW range works out to about 8,400 W in the calc.
• Electric water heater: add its nameplate rating (typically 3,000–4,500 W).
• Electric dryer: 5,000 W or nameplate, whichever is greater.
• Central AC: add compressor plus air handler nameplates (typically 3,000–5,500 W for a 2–3 ton unit).
• Electric heat (baseboards, furnace, or heat pump): full connected nameplate. This is often the biggest single load.
• EV charger: use the nameplate. A Level 2 charger at 48 A on a 60 A circuit contributes 11,520 W. On a shared load with heat, either the heat or the EV gets the higher of the two under CEC.
• Hot tub or pool heater: add nameplate. Typical hot tub is 5,000–8,000 W.
• Other loads over 1,500 W: add the full nameplate.

Sum the numbers. This is your rough calculated load in watts.

Step 3: Compare to your service capacity

Divide your calculated load by 240V to get amps.

Example: a 2,000 sq ft Etobicoke home with a 12 kW range, 4.5 kW water heater, 5 kW dryer, 4 kW central AC, no electric heat, and a planned 48 A Level 2 EV charger.

• Basic load: about 6,500 W
• Range: 8,400 W
• Water heater: 4,500 W
• Dryer: 5,000 W
• AC: 4,000 W
• EV charger: 11,520 W
• Total: about 39,920 W ÷ 240V = 166 amps

That home is well beyond a 100-amp service and is a candidate for a 200-amp upgrade before the EV charger goes in. A licensed contractor’s full CEC load calc will refine this number, but not by enough to change the conclusion.

What triggers a service upgrade in the GTA

• Adding a Level 2 EV charger to a 60-amp or 100-amp service.
• Switching from gas heat to a heat pump or electric heat.
• Adding central AC to a home that never had it.
• Adding an induction range in a home with existing electric heat and dryer.
• Adding a hot tub, pool heater, or workshop equipment.
• Any finished basement or coach house that adds significant load.
• Any “my breakers keep tripping” situation where the panel is chronically full. See how to tell if an electrical panel is overloaded.

Ontario homes built before the 1980s frequently have 60-amp or 100-amp services that no longer support modern loads. See how long does an electrical panel upgrade take for what a service upgrade actually involves.

Signs your service is already overloaded

• Main breaker trips occasionally under normal use.
• Lights dim when the AC or dryer starts.
• The panel is full — no empty slots left.
• Multiple double-tapped breakers.
• Warm main breaker or warm feeder cables.
• A hum or buzz from the panel under heavy load.

Any of these means it is time for a full load calculation by a licensed contractor.

When 200-amp is enough and when 400-amp is warranted

For most GTA single-family homes, 200 amps is the modern standard and comfortably supports central AC, EV charging, induction ranges, and even a moderate heat-pump conversion. 400-amp services show up in larger custom homes, homes with multiple EV chargers, or homes with pool and hot tub combinations plus a heat pump.

Overkill is rarely a mistake, but 400-amp is not free — utility hookup costs, service equipment, and permit-line coordination all step up. Do the load calc first.

Expert tip from our ESA-licensed electricians

The single biggest mistake we see homeowners make is planning an EV charger install off a 100-amp service without running the load calc first. On paper it looks like it fits. In real life the combination of AC, dryer, water heater, and Level 2 EV puts many older GTA homes over the wire. When the numbers come back tight, load management options (like an EV charger that curtails when the home load spikes) can sometimes save a service upgrade. But that is a conversation with a licensed contractor, not a decision to make from an internet forum. Run the numbers before you buy the charger.

Related reading from ezsmart.ca

• How to Tell If an Electrical Panel Is Overloaded
• How Long Does an Electrical Panel Upgrade Take?
• Can I Install My Own EV Charger?
• What Is a Subpanel and When Do I Need One?
• How Do I Know if My Panel Is Overloaded?

Frequently Asked Questions

What is the modern standard service size in Ontario?

200-amp for new construction. 100-amp is still common in older GTA homes but tight for modern loads.

Do I need a professional load calc?

Yes for any panel upgrade, EV install, or heat-pump conversion. Licensed contractors run the formal CEC calc.

Can smart load management extend my service?

Yes. EV chargers that curtail during home peaks can often keep a 200-amp service comfortable.

What triggers a service upgrade?

EV chargers on 60/100-amp services, gas-to-electric heat conversions, and finished basements adding significant load.

How do I read my current service size?

Look at the amperage stamped on the main breaker. Do not open the panel deadfront.

Contact us

Need a full CEC load calculation for a Toronto or GTA home before an EV, heat pump, or reno? Call ezsmart at 416-838-9006 or use our contact page. An ESA-licensed electrician will run the numbers, quote any needed upgrade, and file the notification.

Amir Azimipour

Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp