Is it legal to have a basement suite without a separate furnace, or does Calgary allow shared HVAC systems now?

Yes, it's legal to have a basement suite share the main home's HVAC system in Calgary, but there are specific requirements you must meet under the Alberta Building Code and City of Calgary bylaws.

The key requirement is that each dwelling unit must have independent temperature control. This means your basement suite needs its own thermostat and zone control, even if it's connected to the main furnace. You can't simply rely on heat rising from upstairs or use a single thermostat to control both units.

Shared HVAC systems are actually the most common setup for basement suites in Calgary homes. Most existing furnaces have adequate capacity to heat an additional 600-800 square foot basement suite, especially with Calgary's well-insulated basements. The system typically works by installing a separate zone with its own thermostat, dampers, and dedicated ductwork to the basement suite. This gives the basement tenant control over their heating and cooling while using the same furnace and air conditioning system.

However, there are important Alberta Building Code requirements to consider. The ductwork serving the basement suite must be properly fire-stopped where it penetrates the fire separation between units. You'll also need to ensure adequate return air circulation and that the shared system can maintain comfortable temperatures in both units simultaneously. An HVAC contractor will need to calculate the heat load and verify your existing furnace has sufficient capacity.

From a permitting perspective, you'll need both a development permit for the secondary suite and building permits for any HVAC modifications. The mechanical permit will require inspection by a Safety Codes Officer to ensure the shared system meets code requirements. Your HVAC contractor must be licensed and pull the appropriate permits - this isn't DIY work.

Utility considerations are also important. While you can share the HVAC system, you'll need separate electrical panels for each unit (or a properly configured sub-panel for the suite). Many landlords install separate gas and electrical meters to allow tenants to pay their own utilities, but this isn't required by code - it's a business decision.

The main advantage of a shared system is cost savings - you avoid the $8,000-$15,000 expense of installing a separate furnace and ductwork. The potential downside is that if the main furnace fails, both units lose heat. Some homeowners address this by installing a backup heating source like baseboard heaters or a mini-split heat pump in the basement suite.

Next steps: Consult with a licensed HVAC contractor to assess your current system's capacity and design the zone control setup. Apply for your development permit through Calgary Planning, then obtain the necessary building and mechanical permits before starting work.