How much does it cost to add a second furnace for a basement suite versus just upgrading the existing one?

Adding a second furnace for a basement suite typically costs $4,000-$8,000 installed, while upgrading your existing furnace to handle the additional load runs $3,500-$6,500 — but the decision involves much more than just upfront cost.

Understanding Your Options

When creating a basement suite in Calgary, you have two main HVAC approaches. A separate furnace system gives your tenant complete control over their heating costs and comfort, which is often preferred for rental situations. You'll need a high-efficiency gas furnace (96%+ AFUE is standard in Calgary's climate), new ductwork throughout the basement, a separate thermostat, and potentially a second gas line if your current service isn't adequate. The installation requires gas permits, HVAC permits, and inspections by Safety Codes Council of Alberta accredited officers.

Upgrading your existing system means installing a larger furnace and extending ductwork to serve both levels. This approach costs less upfront but creates shared utility bills and potential comfort conflicts between floors. Your existing furnace may already be sized appropriately — many Calgary homes have oversized units that can handle additional square footage, especially if the basement was always intended for future development.

Calgary-Specific Considerations

Calgary's extreme temperature swings and -30°C winters put serious demands on heating systems. A properly sized system is critical — undersized equipment will struggle during cold snaps, while oversized units cycle frequently and waste energy. Most basement suites in Calgary require 40,000-60,000 BTU capacity depending on square footage, insulation levels, and window area. The city's expansive clay soils also mean many basements stay naturally cooler, which can actually reduce heating loads.

For separate systems, you'll need adequate gas service to your home. Many older Calgary homes have 3/4" gas lines that may need upgrading to 1" to supply two furnaces safely. ATCO Gas handles service upgrades, typically costing $800-$2,500 depending on distance from the meter.

Professional Requirements and Permits

Both options require licensed gas contractors and HVAC permits through the Safety Codes Council of Alberta system — this isn't DIY territory. Gas work must be done by certified technicians, and all installations need pressure testing and inspection before activation. Expect 2-3 inspections: rough-in, insulation, and final. The permit process typically takes 1-2 weeks, with installation requiring 2-4 days depending on ductwork complexity.

Long-Term Financial Considerations

While separate systems cost more initially, they often make financial sense for rental properties. Tenants pay their own heating bills (typically $80-$150/month in Calgary winters), and you avoid disputes about temperature settings. Separate systems also allow independent maintenance schedules and reduce wear on your primary furnace. However, you'll have two units to maintain, with annual servicing costing $150-$250 per furnace.

Making the Right Choice

Choose a separate furnace if you're creating a rental suite, want independent temperature control, or your existing system is near capacity. Upgrade your existing system if the suite is for family use, your current furnace is undersized for the main floor anyway, or budget is the primary concern. Have an HVAC contractor perform a proper heat loss calculation before deciding — this determines whether your existing system can handle the additional load effectively.

Find licensed HVAC contractors experienced with basement suite installations in our Calgary Construction Network directory to get accurate quotes based on your specific home and heating needs.