Your Range Hood Isn't Broken: Kitchen Makeup Air Systems in Airtight BC Homes

The range hood is on high, dinner ended an hour ago, and the kitchen still smells like the middle of the sauté. Someone finally cracks a window and the fan seems to find a second gear: the air clears, the smell lifts, and the whole room breathes out. Congratulations, you have just diagnosed your house.

That window trick is not a quirk of your kitchen. It is the classic sign of a home built, or renovated, so airtight that the exhaust fan is starving for air. Nothing is broken and nobody did anything wrong. The fix has a real name, and it is one of the least glamorous, most useful pieces of equipment in modern home ventilation: the kitchen makeup air system.

Modern homes are sealed like thermoses, and that is mostly great

Building codes in BC keep pushing new homes toward better energy performance, and the biggest lever is airtightness. Less air leaking through the walls means less heat escaping in January and less heat sneaking in during the kind of July heat wave that pushes local houses past comfortable. A tight envelope makes a home cheaper to run and more comfortable in every season, so on that front the codes have it right, and we would not wind them back.

Here is the catch. A very tight home behaves less like a breathing building and more like a sealed bag. Every litre of air a fan pushes out has to be replaced from somewhere, and in a tight house there is no somewhere. The physics play out the same in a new build in Valleycliffe, a tightened-up 1990s home in Brackendale, or a freshly renovated place in Lynn Valley: tight envelope, big fan, same conversation.

What happens when a big fan meets a tight house

A serious range hood moves a lot of air out of your kitchen in a hurry. In a leaky older home, replacement air seeps in through a thousand small gaps and the fan never notices. In a tight home, the fan pulls the whole house into negative pressure: a slight vacuum, with the fan on one side and every sealed surface on the other.

Negative pressure does two unhelpful things at once. It fights the fan, so the motor keeps spinning while the air barely moves (the technical crowd calls this cavitation). It also invites air to sneak back in through any path it can find, which in some homes means air pulling backwards through vents and flues that were designed to flow the other way.

The lived result is a kitchen that never fully clears. Smells hang around, moisture lingers after cooking, and over the months a fine film of grease builds up on the ceiling and the upper cabinet doors.

Five signs your kitchen is asking for makeup air

• Cooking smells stick around long after the fan should have cleared them.

• The kitchen feels humid, and condensation shows up after a big cook.

• A thin grease film keeps returning to the ceiling and upper cabinets no matter how often you clean.

• You feel a rush of air when someone opens an exterior door while the fan is running.

• The range hood noticeably improves the moment you open a window.

One of these on its own can have a simpler explanation, and sometimes the boring fix (a clogged filter, a duct issue) is genuinely the right one. Two or three together, in a newer or recently tightened home, point at pressure.

Makeup air is not an HRV

We hear it all the time that a home with an HRV has ventilation covered, so a struggling range hood must mean a defective fan. An HRV is doing a real and valuable job: continuously exchanging modest, balanced amounts of stale indoor air for fresh outdoor air. A range hood on high is a different animal, moving a large volume in one direction in a short burst, and a balanced ventilator was never designed to backfill that. Makeup air is the answer built for the job: a deliberate path for outside air to enter the house while the exhaust fan runs, so the fan can actually do what you bought it for.

The right-sized fix, from simple to serious

There is no default answer here, only the answer your kitchen needs, and in our service area that answer shifts with the weather. We work the full corridor from North Vancouver to Squamish to Whistler, which spans everything from mild North Shore shoulder seasons to real alpine winters, so the first question most people ask is a fair one: if this system deliberately lets outside air in, what happens in January?

A properly designed system never just dumps raw winter air into your kitchen. For smaller exhaust needs, a passive setup introduces outside air into the return duct of the furnace or air handler, where it mixes into the airstream before it ever reaches a room, so the cold arrives diluted and nobody feels a draft crossing the kitchen floor.

Bigger appetites and colder settings need more. A large range, say a 48-inch gas cooktop, wants somewhere in the range of 600 to 1000 CFM of exhaust to actually capture what serious cooking throws at it, well past the point (roughly 400 CFM) where BC code expects makeup air to be part of the plan. At that scale, or the further you head up the corridor into colder winters, an active makeup air system earns its keep: a supply fan pushing air into the house, with a tempering element, gas or electric, warming the incoming air so a February stir-fry does not arrive with an arctic side draft.

The specific hardware matters less than the principle. Exhaust and supply get planned as one system, sized to your range, your envelope, and your climate, with real numbers measured from your actual home rather than read off a chart.

A word for anyone air-sealing an older home

Air-sealing an older home is one of the best efficiency upgrades available, and in most cases we would cheer you on. It also changes how your house breathes, all at once. A house that never had this problem before can start showing every symptom above within a season of the envelope getting tightened, and moisture that used to escape through the leaks now stays inside, where over time it can feed mold and drag down the air your family breathes.

None of that is a reason to skip the upgrade. It is a reason to plan ventilation and makeup air in the same conversation as the sealing, so the energy savings arrive without trade-offs nobody mentioned. If the bigger picture of what you are breathing at home is on your mind, we wrote a full Sea-to-Sky guide on how to improve your home's indoor air quality.

FAQ

Do I need a makeup air system for my range hood in BC?

It depends on the size of your exhaust fan and how tight your home is. Larger hoods generally need a purpose-built makeup air path (BC code starts expecting one around the 400 CFM mark), and even a smaller fan can struggle in a very airtight house. The five signs above are a good first check, and a proper assessment settles it.

Is a makeup air system the same as an HRV?

No. An HRV continuously exchanges small, balanced amounts of air to keep a home fresh. A makeup air system supplies replacement air on demand for high-volume exhaust like a range hood, so the two solve different problems and many tight homes eventually want both.

Will a makeup air system make my house cold in winter?

Not when it is designed for the climate it lives in. Smaller passive systems dilute incoming air into the furnace airstream so you never feel it, and active systems warm the incoming air with a gas or electric tempering element before it enters the house. The colder your winters, think Whistler in January, the more the tempered active approach earns its place.

Can an airtight house cause mold?

Airtightness alone does not cause mold; trapped moisture does. In a tight home without planned ventilation, the moisture from cooking and daily life stays inside and can condense where you cannot see it, which is why sealing work and ventilation planning belong in the same conversation.

Where to go from here

If your kitchen has been failing the window test, you do not have to guess at the cause or live with the grease film. The easiest next step is to book an in-home consult: we look at the actual house, the actual fan, and the actual airflow, your questions get answered in plain language, and you get options to consider with what we would recommend and why. You stay in the driver's seat the whole way, and consults are bookable five days a week.

If a heat pump or a bigger comfort project is also somewhere on your horizon, our guide Thinking About a Heat Pump? READ THIS FIRST is the place to start before you commit to anything.

We are Porcupine Mechanical, a Squamish-based mechanical contractor working from the North Shore up through the Sea-to-Sky, from North Vancouver to Squamish to Whistler, on residential heating, cooling, and ventilation. Our whole thing is doing it efficiently and doing it right the first time.