Checking Electrical Panel Capacity Before a Renovation

A common renovation surprise is discovering, partway through a project, that the existing electrical panel does not have enough capacity for the new circuits a renovation or addition requires -- new kitchen appliance circuits, an EV charger, a heat pump, or simply more general lighting and receptacle circuits than an older home was built for.

Panel capacity is limited by two separate things that are easy to confuse: the number of physical breaker slots available in the panel, and the total electrical service capacity coming into the house (commonly 100A, 125A, 150A, or 200A in Canadian homes, with many older homes still on 60A or 100A service). A panel can have open breaker slots but still lack the amperage capacity to safely add a large new load, and conversely a panel that looks 'full' of slots may still have amperage headroom if a load calculation is done properly.

A licensed electrician determines actual available capacity through a load calculation, not just a visual count of open slots -- this calculation accounts for the electrical code's demand factors, which recognize that not every circuit in a house draws its full rated load simultaneously.

When a load calculation shows insufficient capacity, the options are typically a full service upgrade (increasing the amperage coming from the utility, which usually requires utility coordination and a permit), or in some cases smart load management devices that can safely share capacity between large loads like an EV charger and other high-draw circuits without an anticipation upgrade. Either way, this is a decision to make early in renovation planning, not something to discover mid-project when the electrician arrives to install a new circuit.