Electrical Load Calculation

A load calculation tells you what your service can actually support

An electrical load calculation is not a quick look at empty breaker spaces. It is a structured review of the loads already connected to the home, the rating of the service equipment, and the demand created by the equipment you want to add.

We use it to answer practical questions: can a 100A service support a Level 2 EV charger, a heat pump, a hot tub, a second kitchen or a finished addition? Is load management enough, or is a 100A to 200A panel upgrade the safer and cleaner route? Should the work be staged so the service upgrade, new circuits and ESA inspection are coordinated instead of handled as separate surprises?

A proper capacity review normally includes:

• Main service rating, main breaker and panel condition
• Existing panel schedule and visible circuit loads
• Large nameplate loads such as range, dryer, water heater and air conditioning
• Proposed loads such as EV charging, heat pumps, hot tubs, saunas, workshops or suites
• Available breaker space and whether tandem breakers are being used appropriately
• Grounding and bonding conditions visible at the service
• Whether the existing service entrance, meter base or panel age affects the plan

The calculation is especially important when a panel looks “full” but still may have service capacity, or when a panel has empty spaces but the service is already near its practical limit. Breaker spaces and service capacity are related, but they are not the same thing.

You need it before EV chargers, HVAC changes, hot tubs, additions and suites

The best time to do an electrical load calculation is before buying equipment or opening walls. Many modern upgrades are not small plug-in loads. They change the home’s electrical demand and may also trigger ESA notification and inspection when new wiring is installed.

Common reasons to book a load calculation include:

• Adding a Level 2 EV charger in a garage or driveway
• Replacing gas equipment with electric HVAC or a heat pump
• Installing a hot tub, swim spa or sauna
• Building an addition, garage, workshop or laneway-related space
• Finishing a basement with new lighting, receptacles and dedicated circuits
• Planning a basement apartment, duplex conversion or second suite
• Adding electric cooking, laundry or water heating
• Buying an older home with a 60A or 100A service

For HVAC projects, the calculation helps coordinate the electrical side before the mechanical installation. Heat pumps, auxiliary heat, outdoor disconnects and branch circuits need to be planned together, not guessed at after the equipment arrives. See our page on electrical for HVAC and heat pump circuits if the load calculation is part of a heating or cooling upgrade.

For suites and multi-unit work, the load calculation helps identify whether the existing service can support the extra cooking, laundry, heating and life-safety loads. It is also useful when planning multi-unit residential electrical, where panel capacity, metering choices and future access all matter.

For additions and larger renovations, the calculation belongs early in the design conversation. If the home needs more capacity, it is better to know before framing, drywall and finish work. Our new construction electrical planning follows the same principle: confirm service capacity first, then design the circuits.

The calculation supports code-compliant permit planning

Ontario electrical work must follow the Ontario Electrical Safety Code. When new circuits, service changes or other notifiable work are involved, ESA notification and inspection are required. City Power Electrical Services completes electrical load calculations and related work as a Licensed Electrical Contractor, ECRA/ESA #7015314, with ESA permits and inspections where required.

A load calculation helps determine the safe and code-compliant path before the installation is started. It can support decisions such as:

• Whether the existing 100A service can remain
• Whether a load-management device is appropriate for a new high-demand load
• Whether the panel has enough physical space for the new breakers
• Whether a subpanel solves distribution only, not service capacity
• Whether the service should be upgraded before adding equipment
• Whether older service equipment should be corrected before new loads are connected

One common mistake is assuming a subpanel creates more capacity. It does not. A subpanel adds breaker space and better circuit organization, but the total home load still flows through the main service. If the calculation shows the service is overloaded or too limited for the planned equipment, the answer may be a service upgrade rather than just another panel.

Another common issue is older equipment. A 60A fuse service, damaged panel, crowded breaker layout, missing directory, questionable grounding or amateur additions can change the recommendation. If ESA defects or unsafe wiring are found during the review, we can separate the capacity planning from any required electrical code corrections and ESA defect repairs.

If the work requires documentation after correction or installation, we can also explain when an ESA electrical safety certificate process applies and what inspection paperwork is normally available for your records, insurer, landlord file or buyer’s lawyer.

The visit ends with clear options and written pricing

A load calculation visit starts with the panel and service equipment. We identify the main breaker or fuse rating, panel make and condition, service entrance details where visible, grounding and bonding conditions, available breaker spaces and any obvious red flags. We then review the equipment you want to add and gather nameplate information where available.

For planned equipment, useful information includes the EV charger model or amperage setting, heat pump electrical specifications, hot tub installation manual, addition drawings, suite layout, appliance list and any renovation plans. If you do not have all of that yet, we can still give planning guidance and note what must be confirmed before final installation.

After the review, you get practical next steps. The answer may be simple: the existing service is acceptable for the proposed circuit. It may be conditional: the project works if load management is installed or if other loads are not added later. Or it may be clear that the service should be upgraded before the new equipment is connected.

Electrical load calculation work is quoted in writing after a site visit. City Power provides free written estimates, and pricing depends on the property, access, documentation available and whether the calculation is part of a larger installation.

If the calculation shows that a service upgrade is required, the published GTA pricing is: a 100A-to-200A panel upgrade typically costs $3,200–$4,500 including the panel, labour, ESA permit, and inspection. A load calculation can confirm when a 60A fuse panel upgrade is needed; this typically costs $4,000–$6,000 since the service entrance and meter base often have to be replaced as well.

The goal is not to sell the largest panel. The goal is to make the next electrical decision safely: proceed with the circuit, add load management, redesign the scope, or upgrade the service before the permit and installation work begin.