Heat loss and cold-climate heat-pump sizing for a Winnipeg townhouse

Prairie Hearth owns 24 townhouses built in 1978. Each home is two storeys, 112 m² of heated floor over a heated basement, with a 22-year-old gas furnace that is reaching the end of its life. The co-op board wants to replace all 24 with cold-climate air-source heat pumps over two summers, using federal and provincial rebates. A sister co-op in Minneapolis is watching to see if it works.

The board has two worries. A contractor quoted a 5-ton heat pump per home "to be safe", which seems large. And some members fear the heat pumps will not cope at −33 °C, so their electric backup heat will run all winter and bills will rise.

You will work out the answer for one typical end-unit: - set the design conditions for Winnipeg from climate data; - calculate heat loss through walls, windows, roof, basement, air leakage and ventilation; - size a heat pump from a manufacturer-style capacity table and find the balance point where backup heat starts; - estimate yearly energy use and cost with a temperature-bin method, comparing gas and the heat pump; - check whether air sealing or attic insulation first would let a smaller heat pump do the job.

The home's construction is in task 1. You need no site visit. All the work is done in a spreadsheet, with optional Python for the bin calculation.

Done looks like a design heat loss in kW, a recommended heat-pump size in tons with a reason, the share of yearly heat that backup provides, and a yearly cost comparison in Canadian dollars. The board wants a one-page answer they can read at the next members' meeting.