What are the ventilation and HVAC requirements for a legal secondary suite in New Brunswick — does it need its own furnace?

A legal secondary suite in New Brunswick doesn't necessarily need its own dedicated furnace, but it does need a code-compliant heating system that can maintain a minimum indoor temperature of 22°C — and how you get there depends heavily on your existing setup and the suite's configuration.

The National Building Code of Canada 2020 (now mandatory for new applications in NB as of May 1, 2025) treats secondary suites as separate dwelling units, which means each unit must be capable of being heated independently. If your main home has a forced-air furnace with ductwork running into the suite, that shared ductwork creates a fire separation problem — ducts penetrating the required fire separation between units must have fire dampers installed, and the duct system must be designed so that smoke and fire can't travel freely between units. Many older NB homes with oil furnaces simply can't meet this requirement without significant modification, which is why a separate heating system for the suite is often the practical solution.

The most common approach in New Brunswick right now is a cold-climate mini-split heat pump. A single-zone or multi-zone mini-split handles both heating and cooling, operates independently from the main unit, and avoids the fire separation headache entirely. With NB winters regularly hitting -25°C to -30°C inland (Fredericton, Woodstock, Edmundston) and cold-climate units rated to -25°C or below now widely available, this is a realistic primary heat source — though electric baseboard backup is worth including for extreme cold snaps. NB Power's Total Home Energy Savings Program offers rebates on qualifying heat pump installations, so factor that into your budget planning.

If you're keeping an oil furnace as the primary heat source for the suite, it needs its own combustion air supply, proper venting, and — critically — it must be in a space that meets the fire separation requirements from the main dwelling. A shared mechanical room between units requires careful fire-rated construction.

Ventilation is where a lot of secondary suite projects in NB fall short. NBC 2020 requires mechanical ventilation in all dwelling units — natural ventilation alone doesn't cut it for a legal suite. Each unit needs its own ventilation system capable of meeting the required air exchange rates. For a suite, this typically means either a heat recovery ventilator (HRV) dedicated to the suite, or at minimum an exhaust-only system with makeup air provisions. Bathrooms and kitchens must have exhaust fans vented to the exterior (not into the attic or wall cavity — a common shortcut that inspectors catch). If the suite shares an HRV with the main unit, the ductwork again crosses the fire separation issue.

Carbon monoxide and smoke alarms are non-negotiable. Interconnected smoke alarms are required throughout both units, and CO detectors are required near sleeping areas and adjacent to any fuel-burning appliances. The two units' alarm systems must be interconnected so an alarm in one unit triggers audible warning in both.

On the permit side: your building permit comes from your local municipality (Fredericton Development Services at 506-460-2020, Moncton Planning & Development at 506-856-4375, Saint John Growth & Community Services at 506-658-2835, etc.) or your Regional Service Commission if you're in a rural area. Electrical work for the suite — including the heat pump wiring and panel upgrades — requires a licensed electrical contractor, an NB Power wiring permit, and a TIS inspection before occupancy. Plumbing for a bathroom or kitchen in the suite requires a licensed plumber and TIS permit as well.

Budget roughly $8,000–$18,000 for a standalone heating and ventilation system for a typical suite (heat pump unit, electrical panel upgrade if needed, HRV, exhaust fans, permits), depending on the size of the suite and the condition of your existing electrical service. Homes with older 100-amp panels often need an upgrade to 200-amp service when adding a suite — that alone runs $3,500–$6,500 in the NB market.

Before finalizing any design, have a licensed HVAC contractor assess your existing system and a licensed electrician evaluate your panel capacity. You can find qualified trades in the New Brunswick Construction Network directory — it's worth getting two or three quotes given the range of approaches available.