Electrical design for a cold-climate heat-pump retrofit

The Harper family own a 1,250 ft² bungalow in Winnipeg with a finished basement. They want to replace their 80% gas furnace and gas water heater with a cold-climate air-source heat pump, electric backup heat and a heat-pump water heater, and they plan to buy an electric car next year. Prairie Comfort has sold them the mechanical side. The electrical side is now your job.

What you know: - Winnipeg's winter design temperature is about −33 °C, and the house loses about 11.5 kW of heat at that temperature. - The existing service is 100 A at 120/240 V, and the 24-space panel has 3 spaces free. The house already has a 12 kW electric range and a 5 kW dryer. - The proposed heat pump is a 3-ton cold-climate unit. Its nameplate gives a minimum circuit ampacity of 25 A and a maximum overcurrent protection of 40 A at 240 V. The backup is a 10 kW electric strip heater in the air handler. - The EV charger they want is a 7.2 kW Level 2 unit on a 40 A circuit. - The utility quoted about C$4,500 and 10 weeks for a 200 A service upgrade, and the panel would also need replacing.

The homeowners want to know three things: does everything fit on 100 A, what will it cost to run compared with gas, and what is the cheapest safe way to do it. Prairie Comfort needs a design its electrician can permit and install.

You will size the heat pump against the heat loss and find the balance point, survey the panel, do the single-dwelling load calculation under the Canadian Electrical Code, compare a service upgrade with a load-management device, size every new circuit, draw the panel schedule and single-line diagram, and estimate running cost. All of this is done on paper or in a spreadsheet, with manufacturer data and the code.

Done looks like a design pack for the electrician and a two-page report for the Harpers that they can read at the kitchen table.