What are the HVAC sizing rules for adding a basement suite furnace under the Alberta Building Code?

Adding a basement suite furnace in Alberta requires careful sizing calculations and must comply with specific Alberta Building Code requirements for separate dwelling units.

When creating a secondary suite, the Alberta Building Code treats it as a separate dwelling unit, which means it typically requires its own heating system or a properly designed shared system with zone controls. The key is ensuring adequate heating capacity while meeting all safety and code requirements.

Heating Load Calculations and Sizing

The furnace must be sized based on a proper heat loss calculation for the basement suite area. In Calgary's climate (Zone 7A), basement suites typically require 25-35 BTU per square foot for heating, but this varies significantly based on insulation levels, window area, ceiling height, and exposure to exterior walls. A 600-square-foot basement suite might need a 15,000-25,000 BTU furnace, while a larger 1,000-square-foot suite could require 30,000-40,000 BTU capacity.

The Alberta Building Code requires that each dwelling unit maintain a minimum temperature of 22°C (72°F) during design winter conditions. For Calgary, the design temperature is typically -34°C (-29°F). Your HVAC contractor must perform Manual J load calculations to determine the exact heating requirements. Oversizing is wasteful and can cause short cycling, while undersizing means the suite won't stay warm during Calgary's coldest days.

Code Requirements for Separate Systems

Under the Alberta Building Code, secondary suites are considered separate dwelling units and typically require independent heating systems. This means a separate furnace, ductwork, and thermostat control. The furnace must be installed by a licensed gas contractor and requires both a gas permit and building permit from your municipality. All work must be inspected by accredited Safety Codes Officers under the Safety Codes Council of Alberta system.

The furnace location must meet clearance requirements - typically 24 inches in front for service access, 6 inches on sides, and proper clearances from combustibles. Basement installations need adequate combustion air supply and proper venting. High-efficiency condensing furnaces (90%+ AFUE) are standard in Alberta and require condensate drainage to a floor drain or condensate pump.

Ventilation and Air Quality

The suite requires mechanical ventilation meeting Alberta Building Code requirements - typically an HRV (Heat Recovery Ventilator) or bathroom exhaust fans with adequate CFM ratings. The heating system must integrate with the ventilation strategy to maintain proper air quality. Many contractors install combination heating/ventilation systems that provide both space heating and fresh air circulation.

Next Steps

Start with a licensed HVAC contractor who can perform proper load calculations and design the system. They'll handle the gas permit application and coordinate with your general contractor on the building permit. Expect 2-4 weeks for permit approval and $8,000-$15,000 for a complete furnace installation including ductwork, depending on complexity and accessibility. The City of Calgary requires inspections at rough-in and final stages - never operate the system before final approval.

Find verified HVAC contractors experienced with secondary suite installations in our Calgary Construction Network directory.