When wildfire smoke settles over the Fraser Valley, the single most effective thing you can do is close the house up and filter the air inside it. That means windows shut, mechanical ventilation managed carefully, and a filter good enough to actually catch smoke particles - MERV 13 or higher, ideally paired with a portable HEPA unit in the rooms you use most.
Smoke season is now a recurring part of Fraser Valley summers, not a freak event. Chilliwack, Abbotsford, and Langley have all sat under smoke advisories for stretches of July and August in recent years, with air quality readings that make going outside genuinely unhealthy. The good news is that a well-set-up home stays livable through it. Here is how to think about indoor air quality when the smoke rolls in, and where a heat pump and the right filtration make a real difference.
Why indoor air quality drops during smoke events
Wildfire smoke is dominated by fine particulate matter, called PM2.5 - particles small enough to travel deep into your lungs. These particles do not respect walls. On a smoky day, every time a door opens, every gap around a window, and every run of your ventilation system pulls some of that outdoor air inside.
Homes are not sealed boxes. Even with everything shut, outdoor air leaks in through the building envelope, and indoor PM2.5 levels climb over a smoke event unless you are actively filtering. For anyone with asthma, allergies, heart conditions, or young kids and older parents in the house, that indoor buildup is the part you can control.
The valley makes it worse. Our geography traps air against the mountains, so once smoke moves in, it can sit for days. That is why a closed-window, filter-forward strategy matters more here than in a breezier coastal spot.
The closed-window strategy
The instinct on a hot summer day is to open windows overnight to cool the house down. During a smoke event, resist it. Opening up to cool off just fills the house with the particles you are trying to keep out.
The better approach:
Keep windows and exterior doors closed for the duration of the advisory.
Run your central system’s fan so indoor air keeps cycling through the filter rather than sitting still.
Cool the house mechanically instead of with outside air - this is where a heat pump earns its keep, because it cools and filters at the same time.
Create at least one clean-air room - typically a bedroom - with a portable HEPA purifier running, so there is always a low-smoke space to retreat to and sleep in.
Closing up and cooling mechanically is only comfortable if you already have cooling. Homes that rely on open windows for summer relief are stuck choosing between heat and smoke. A heat pump that cools all summer removes that trade-off entirely.
Filtration: MERV 13, HEPA, and whole-home purifiers
Not all filters catch smoke. The rating that matters is MERV, and for wildfire particulate you want MERV 13 or higher. Lower-rated filters are built to protect the equipment, not your lungs - they let most fine smoke particles pass straight through.
Here is how the common options compare during a smoke event:
Option | What it does | Best for |
|---|---|---|
MERV 8 filter | Catches dust and large debris | Protecting the equipment, not smoke |
MERV 13+ filter | Captures a high share of PM2.5 | Whole-home smoke filtration |
Portable HEPA unit | Near-total fine-particle capture in one room | A dedicated clean-air room |
Whole-home air purifier | High-efficiency filtration built into the ductwork | Continuous, house-wide protection |
A few practical notes. Before jumping to MERV 13, the system has to be able to handle the tighter filter - a denser filter restricts airflow, and not every older furnace or air handler is built for it. That is a quick thing to confirm during an assessment. A whole-home air purifier integrated into the ducting is the strongest option because it filters continuously without you managing a portable unit in every room. And whatever you run, change filters more often during smoke season - they load up with particulate fast and stop working well once they are clogged.
Why a heat pump filters air better than a furnace
This is the part most homeowners do not know. A heat pump’s blower runs continuously on a low speed, where a traditional furnace fires in short, full-blast bursts and then shuts off.
That difference matters a lot for air quality. A furnace only filters your air while it is actively heating - on a smoky summer day when there is no call for heat, the fan barely runs, and the air just sits. A heat pump running in cooling or fan mode keeps air moving through the filter all day. More passes through the filter per day means more particulate removed.
It is the same reason we flag cleaner indoor air as a real benefit of the technology in our heat pump benefits guide. The continuous low-speed airflow is quieter, more even, and, during smoke season, meaningfully better at scrubbing the air. Pair that blower with a MERV 13 or whole-home purifier and you have a system that filters the whole house every hour, not just when the thermostat calls.
You can read more about how the equipment itself works on our heat pump installations page.
HRV and ventilation during smoke
Heat recovery ventilators and other fresh-air systems are a good thing most of the year - they bring in outdoor air and exhaust stale indoor air to keep the home healthy. During a smoke event, that same fresh-air intake is working against you, pulling smoke inside.
The right move depends on your unit:
If your HRV has a recirculation or high-filtration mode, switch to it so it moves air through a filter without drawing in fresh outdoor air.
If it only runs in fresh-air mode, consider reducing its runtime during the worst of an advisory, then returning it to normal once the air clears.
Do not shut off ventilation and forget it - homes still need air exchange, and moisture and indoor pollutants build up without it. The goal is to manage ventilation through the smoke, not abandon it.
If you are unsure how your specific system behaves in smoke conditions, that is worth a conversation before the next advisory hits.
Practical homeowner steps
A few things you can do yourself before smoke season starts:
Buy the right filter for your system - MERV 13 if it can handle it - and keep spares on hand.
Set your thermostat fan to “on” rather than “auto” so air filters continuously.
Set up a clean-air room with a portable HEPA purifier.
Watch local air quality readings so you know when to seal up.
What a pro can add
Some of it is not a DIY job. During a no-charge Home Energy Assessment, we check whether your system can handle a higher-MERV filter, look at your ductwork for a whole-home purifier, review how your ventilation behaves in smoke conditions, and, where cooling is the missing piece, size a heat pump that keeps the house comfortable with the windows shut.
Cohesive Mechanical is HPSC-registered and installs ENERGY STAR certified equipment. Whether it is a filtration upgrade on your existing setup or a full heat pump that cools and filters in one system, the aim is the same - a home that stays clean and comfortable through the smoke. Book a free quote and we will walk through what your home needs.
FAQ
What MERV rating do I need for wildfire smoke?
Aim for MERV 13 or higher. That rating captures a high share of the fine PM2.5 particles that make up wildfire smoke. Lower ratings like MERV 8 mainly protect the equipment and let most smoke particles through. Confirm your system can handle the tighter filter first, since a denser filter restricts airflow.
Does a heat pump help with wildfire smoke?
Yes. A heat pump’s blower runs continuously on low speed, so air passes through the filter far more often than with a furnace that only fires in short bursts. On a smoky summer day with no call for heat, a furnace fan barely runs, while a heat pump keeps filtering and cooling. More passes through the filter means more smoke removed from your air.
Should I keep windows open to cool down during smoke?
No. Opening windows fills the house with the exact particles you are trying to keep out. Keep windows and doors closed and cool the house mechanically with a heat pump or air conditioner. Set up at least one clean-air room with a portable HEPA purifier for a low-smoke space to sleep in.
Should I run my HRV during a smoke event?
It depends on the unit. If your HRV has a recirculation or high-filtration mode, use it so it filters air without drawing in fresh outdoor air. If it only runs in fresh-air mode, consider reducing its runtime during the worst of an advisory. Do not shut ventilation off entirely, since homes still need air exchange.
How often should I change my filter during smoke season?
More often than usual. Filters load up with particulate quickly during smoke events and stop working well once they are clogged. Keep spare filters on hand and check yours regularly through the advisory rather than waiting for your normal replacement schedule.
Is a whole-home air purifier worth it in the Fraser Valley?
For homes that face recurring smoke summers, it often is. A whole-home purifier is integrated into your ductwork and filters continuously across the whole house, so you are not managing a portable unit in every room. We can tell you whether your ducting and system are a good fit during the Home Energy Assessment.
Cohesive Mechanical is the Fraser Valley’s trusted HVAC and plumbing experts - based in Chilliwack, serving Abbotsford, Langley, and the Lower Mainland since 2017. HPSC-registered. ENERGY STAR certified equipment. Clean installs. Clear communication.
Book a free quote and we’ll walk through the right filtration setup for your home. Learn more about our heat pump installations.
Related: 7 Real Benefits of a Heat Pump for Fraser Valley Homeowners · How Your Heat Pump Keeps You Cool All Summer
