The clear answer

A furnace installation should be sized for the home and include compatible ductwork, controls, venting, required permits, commissioning and warranty information. Floor area alone is not enough to select capacity.

Size the furnace for the building

Ask the contractor how the home’s heating requirement was calculated. Insulation, windows, air leakage, layout and location affect the load. The capacity of the old unit is useful background, but it is not a substitute for assessing the home as it is now.

For an addition, a newly finished basement or a major insulation upgrade, describe the changes before equipment is selected. Ask how supply and return airflow will serve the rooms that matter to you.

Price the complete scope

Compare equipment model numbers and installed scope, rather than headline appliance prices. Venting routes, condensate disposal where applicable, gas or electrical work, duct changes, controls, access and old-equipment removal can all change the work.

Before approving a gas installation, verify the contractor’s current licence and confirm who obtains the required permit for your jurisdiction. For a strata property, establish the approval process before altering common property or exterior penetrations.

  • Equipment model and proposed capacity
  • Venting, combustion air and condensate arrangements
  • Duct, electrical and fuel-supply work
  • Permits, inspections and disposal
  • Startup checks, controls demonstration and warranty

Finish with commissioning and a handover

Ask for the startup and commissioning records appropriate to the system. Learn how to use the thermostat, where the filter is, what maintenance the manufacturer specifies and who to contact if a problem occurs. Keep the model, serial number, permit details and warranty records together.

Before you agree to the work

  • A documented sizing basis
  • A complete itemized installation scope
  • Permit responsibility and strata approvals
  • Commissioning records and owner orientation

Sources & further reading

Prepared by the BC Furnace Repair editorial team using the official sources linked above. Reviewed November 5, 2026. General planning information; a qualified contractor must assess the equipment and property.