A load calculation is the first step in most electrical projects that add equipment, and homeowners often hear the term for the first time partway through a quote. It adds up what a house can demand and compares that total with what the service can supply, so the result decides whether a new hot tub, EV charger, or generator fits on the existing panel. The City of Calgary’s homeowner permit rules say that load calculations must be completed by a qualified electrician, and for rowhouse projects that add a Level 2 EV charger, heat pump, air conditioner, hot tub, or battery storage it asks for a professional electrician or engineer to complete one. That is why this step appears early in a project.
What A Load Calculation Measures
The Canadian Electrical Code sets out the method. For a house it starts with a basic load tied to the home’s living area, then adds the demand of space heating and cooling, the range, the water heater, and large loads such as an EV charger or a hot tub. The total is compared with the rating of the service, commonly 60, 100, or 200 amps, and the difference is the headroom left for the next addition. Floor area is one input, but the equipment in the house matters just as much, which is why two homes of the same size can produce different results.
How The Numbers Get Counted
Not every load is counted the same way. Electric space heating has its own demand factors under Section 62 of the code, and where heating and air conditioning will not run together, only the larger of the two is added. EV charging equipment and hot tubs are counted at their full rating, while other loads, such as the range, receive demand factors because everything in a house does not run at its maximum at the same moment. Getting those factors right separates an accurate result from one that either oversells the panel or recommends more capacity than the house needs, which is why a guess from a photo of the panel label is not a substitute.
What A Panel Rating Does And Does Not Tell You
A panel marked 100 or 200 amps shows the maximum its main breaker allows, not the room left once existing circuits and equipment are counted. Two homes with the same panel can have very different headroom depending on the furnace, range, dryer, water heater, and any additions made over the years. Older panels often show less room than expected for the same reason, since a garage heater here and a charger there were added without anyone recalculating the total. Our breaker capacity post covers the signs that a panel is already running near its limit.
What The Result Means For Your Project
If the calculation shows room, the new circuit goes in as planned. If it comes back tight, there are usually two paths: upgrade the service, or add a load management device that reduces power to lower priority loads when the house nears its limit. Our permit and inspection guide outlines both options for a service that is maxed out, our load management service page and load shedding devices post compare them in more detail, and load management in Coventry Hills looks at the same question for homes in that neighbourhood.
The calculation comes before the quote because it sets the scope. Installing equipment on a guess can mean breakers that trip regularly, a panel found to be undersized after the new circuit is in, a second visit, and rework on the circuit just completed. An accurate number up front also shows how much headroom remains for the next addition.
Where A Generator Fits
A generator is sized with the same method applied to a different question: which circuits must keep running during an outage. The answer decides whether a unit covers the furnace, sump pump, and refrigeration or the whole house, and it prevents buying a unit that is too small for the circuits that matter or larger than the house needs. Our standby generator installation page covers how this feeds into sizing.
Book your load calculation before adding a hot tub, a generator, or any equipment that draws significant current, and you will know what your panel can carry before you commit. We serve homes across Calgary, and you can reach us here.