Question 1

Where does combustion air come from in Toronto?

Accepted Answer

In Toronto homes with gas-fired equipment, combustion air comes from one of two sources: the surrounding indoor air (for older, naturally aspirating appliances) or directly from outside (for modern sealed-combustion or direct-vent equipment). Understanding which type your home has is critical — getting this wrong creates a carbon monoxide risk.

Older Atmospherically Vented Appliances

Most pre-2000 Toronto homes have furnaces, water heaters, or boilers that draw combustion air from the mechani

Question 2

What is the best location to install a make-up air intake on a Toronto home exterior wall?

Accepted Answer

The best location for a make-up air intake on a Toronto home is on an exterior wall facing away from prevailing winds, at least 600mm (24 inches) above grade, well away from exhaust outlets, gas meters, and any combustion appliances — typically on the north or east wall of most GTA homes.

Placement is one of the most consequential decisions in a make-up air installation, and it directly affects system performance, combustion safety, and long-term durability in Toronto's climate. Getting it wron

Question 3

How does a negative pressure test determine if my Toronto home needs a make-up air system?

Accepted Answer

A negative pressure test measures how much depressurization your home experiences when exhaust systems run — if the house goes more than 5 Pascals negative relative to outdoors, you likely have a make-up air problem that Ontario Building Code may already require you to address.

Here's what's actually happening: every exhaust fan, range hood, dryer vent, and combustion appliance in your home moves air from inside to outside. That air has to be replaced from somewhere. In a leaky older home, repl

Question 4

How does a balanced make-up air system differ from a passive one in a Toronto home?

Accepted Answer

A balanced make-up air system actively controls and conditions incoming air through a dedicated fan and ductwork, while a passive system relies on natural air infiltration through cracks, gaps, and intentional openings to replace exhausted air. In Toronto's extreme climate, balanced systems provide far superior comfort, energy efficiency, and moisture control.

Balanced Make-Up Air Systems use a dedicated fan to bring in fresh outdoor air at a controlled rate, typically through a 6-8 inch insula

Question 5

Can a make-up air unit be tied into my Toronto home ERV system to reduce heating costs?

Accepted Answer

No, a make-up air unit should not be tied directly into your ERV system, as they serve different purposes and operate under different control strategies. However, there are ways to coordinate these systems to reduce heating costs while maintaining proper ventilation and combustion safety.

Make-up air units are designed to provide large volumes of replacement air (typically 300-600 CFM) when high-capacity exhaust systems like range hoods operate. In Toronto's climate, this incoming air must be h

Question 6

What happens to my Toronto home smoke detectors and CO alarms if make-up air is not installed properly?

Accepted Answer

Improperly installed make-up air systems can cause backdrafting of gas appliances, which may trigger carbon monoxide alarms and create life-threatening conditions in your Toronto home. When make-up air is undersized, poorly controlled, or not interlocked with exhaust systems, it can depressurize your home and reverse the flow of combustion gases from furnaces, water heaters, and fireplaces.

Understanding the Backdrafting Risk

When you run a powerful range hood (400+ CFM) without adequate make-

Question 7

Does my Toronto home need make-up air if I have a bathroom exhaust fan over 150 CFM?

Accepted Answer

No, a single 150 CFM bathroom exhaust fan does not trigger Ontario's make-up air requirement. The Ontario Building Code requires make-up air systems only when total exhaust capacity exceeds 75 litres per second, which equals approximately 159 CFM.

However, you're very close to that threshold, and there are important considerations beyond just meeting code minimums. The 75 L/s rule applies to the total exhaust capacity of all mechanical exhaust in your home combined — not just one fan. If you ha

Question 8

How does make-up air affect my heating bill in a Toronto home during the winter?

Accepted Answer

Make-up air will increase your heating costs because you are bringing cold outdoor air into your home and heating it, but the increase is manageable with a properly tempered system and is the unavoidable cost of safely operating a high-CFM range hood in Toronto's winter climate. The real question is how much it adds and what you can do to minimize the impact.

The energy cost depends on three factors: how much air the system brings in (CFM), how cold it is outside, and how long the range hood ru

Question 9

Can I use an ERV or HRV as my make-up air solution in a Toronto home?

Accepted Answer

An ERV or HRV can serve as a make-up air solution in limited circumstances, but most residential units do not have enough capacity to match a high-CFM range hood, so they typically work as a supplement rather than a complete replacement for a dedicated make-up air system. Understanding the limitations is critical before relying on an ERV or HRV for this purpose.

An HRV (Heat Recovery Ventilator) exchanges stale indoor air for fresh outdoor air while recovering 70 to 80 percent of the heat from

Question 10

What is the difference between a passive air inlet and a powered make-up air unit in Toronto?

Accepted Answer

A passive air inlet is a simple wall opening that relies on negative pressure to draw outdoor air in, while a powered make-up air unit uses a fan and typically includes a heating element to actively deliver tempered air into your home. The difference in Toronto's climate is enormous — one leaves you with freezing drafts in winter, and the other provides controlled, comfortable air replacement.

A passive air inlet is essentially a hole in your exterior wall with a weather hood on the outside and

Question 11

Can a make-up air unit cause drafts or cold spots in my Toronto home during winter?

Accepted Answer

A properly installed and tempered make-up air unit should not cause uncomfortable drafts or cold spots in your Toronto home, but a poorly designed or improperly installed system absolutely can. The key difference is whether the incoming outdoor air is tempered — heated before it enters the living space — and whether the make-up air is delivered to the right location with appropriate diffusion.

During a Toronto winter, outdoor air temperatures regularly drop to -10 to -20 degrees Celsius. A make

Question 12

What are the different types of make-up air systems available for Toronto homes?

Accepted Answer

There are four main types of make-up air systems used in GTA residential applications: passive air inlets, motorized damper systems, powered make-up air units with tempering, and integrated ERV or HRV solutions. Each has different capabilities, costs, and suitability depending on your home's construction, the size of your exhaust system, and how well sealed your building envelope is.

Passive air inlets are the simplest and least expensive option. These are essentially controlled openings in the

Question 13

Does a make-up air unit need its own ductwork or can it tie into existing ducts in Toronto?

Accepted Answer

A make-up air unit can be connected to your existing duct system in some configurations, but many installations work better with dedicated ductwork — and which approach is right depends on your home's layout, furnace capacity, and the volume of make-up air required. There is no single correct answer, but understanding the options will help you have a productive conversation with your contractor.

The most common approach in GTA homes is to connect the make-up air unit to the return air plenum of

Question 14

Do I need make-up air if I install a powerful range hood in my Toronto home?

Accepted Answer

Yes — if your range hood is rated above approximately 400 CFM, the Ontario Building Code requires a make-up air system to replace the air being exhausted, and this is not optional. The specific threshold in the OBC is 75 litres per second of total exhaust capacity, which works out to roughly 159 CFM. In practice, because the OBC looks at the rated capacity of all exhaust equipment combined — not just the range hood — a powerful range hood in a home with bathroom fans and a dryer vent can trigger

Question 15

What is the Ontario Building Code requirement for make-up air with range hoods?

Accepted Answer

The Ontario Building Code (OBC) requires a make-up air system when the total exhaust capacity of all equipment in a dwelling exceeds 75 litres per second, which is approximately 159 CFM. This threshold is found in OBC Part 6 (Mechanical) and applies to all residential construction and major renovations in Ontario, including every municipality across the GTA. The requirement is designed to prevent dangerous negative pressure conditions that can cause backdrafting of combustion appliances — a pote

Question 16

At what CFM rating does a range hood require make-up air in an Ontario home?

Accepted Answer

Under the Ontario Building Code, a make-up air system is required when total exhaust capacity exceeds 75 litres per second, which works out to approximately 159 CFM. In practical terms, this means any range hood rated above roughly 400 CFM will almost certainly trigger the make-up air requirement, because kitchen exhaust is rarely the only exhaust in the home — bathroom fans, dryer vents, and other exhaust sources all contribute to that total. Most standard range hoods in the 200-300 CFM range w

Question 17

What happens if I do not have make-up air for my large range hood in Toronto?

Accepted Answer

Operating a high-CFM range hood without make-up air in a Toronto home creates a dangerous negative pressure situation that can backdraft gas appliances and pull carbon monoxide into your living space. This is the single most serious risk, and it is not hypothetical — it is a well-documented hazard in tightly sealed GTA homes, particularly newer construction built to modern energy codes and older homes that have been retrofitted with improved air sealing and insulation.

When a 600 or 900 CFM ran