Smoke Season with an HRV or ERV: The 10-Minute Version

Why your ventilation system is the weak spot during smoke events, what a smoke filter bank is, and the one thing to check before you spend a dollar.

It's wildfire season, so keeping smoke out of your house is top of mind. If you have an ERV, HRV, or supply ventilation, you may have already disabled it to try to keep the smoke out. That can make the outdoor-air intake an important part of your indoor-air-quality strategy during a smoke event.

If your house has one of these systems, ventilation is an intentional part of its indoor-air-quality strategy. In a reasonably air-sealed house, turning ventilation off can reduce outdoor-air ventilation while other indoor pollutants continue to accumulate. During a smoke event, you have a tradeoff: bring in smoke-laden outdoor air, or reduce/stop outdoor-air ventilation and accept less dilution of CO₂ and other indoor pollutants. The first option works against you immediately; the second works against you by day two or three, which matters now that smoke events run for weeks in bad years.

With smoke days becoming less of an isolated incident, it makes sense to find an answer that avoids both. Enter the smoke filter bank.

What a smoke filter bank is

It's a set of filters that your incoming outdoor air passes through during smoke events, targeting both the particle phase of wildfire smoke and selected gas-phase pollutants. The goal is to keep some outdoor-air ventilation while substantially reducing the smoke load; no residential filter bank removes every smoke constituent. It can even switch itself on automatically when a local air quality sensor sees smoke coming.

Three stages do the work:

• A pre-filter to catch the bigger stuff and keep your more expensive layers cleaner, so they last longer.
• A carbon bed to adsorb some gas-phase pollutants — including many VOCs and some combustion products. Carbon performance depends strongly on the media, bed depth, airflow, humidity, and contaminant. (Not a thin carbon pad; those do roughly nothing. Here's why.)
• A high-efficiency particle filter — HEPA where the ventilation unit can support the added resistance, with lower-resistance alternatives where it cannot — to remove fine smoke particles.

All of this sits on a bypass loop beside your normal intake duct, with two motorized dampers switching between paths. The rest of the year, air takes the straight, unrestricted run and your ventilation system operates exactly as it always has. When smoke arrives, the dampers flip and incoming air routes through the filter bank instead. You're not putting the added filter resistance in the airflow path during normal operation. The damper control can also be arranged so loss of control power defaults the outdoor-air path toward filtration rather than the unrestricted bypass.

The one thing to check before you get excited

Every ventilation system has a "budget" of static pressure it can work with, and a filter bank spends some of it. Not every unit can afford the full HEPA-and-carbon stack — some can only support a lighter build, and the honest move is to find out before you buy anything.

Two ways to do that: the three-step self-check tool needs one number off your unit's spec sheet and does the rest, or read the static pressure explainer if you want to understand what's actually happening (spoiler: a filter can't damage your fan — but it can quietly starve your airflow).

One design tip that pays for itself

Wherever you have the choice, go bigger on the filter faces and the bypass ducting. Lower face velocity reduces pressure drop and increases the nominal residence time through a granular carbon bed, although actual gas removal still depends on the media and contaminant. Think of what your dirty car would look like if you drove it through the car wash at 50 mph versus the leisurely pace it actually takes you through. Bigger faces also mean less pressure drop and longer filter life — it's the rare upgrade with no downside except housing size.

Where to go from here

The full guide has everything: the duct layout, the damper wiring, three filtration tiers matched to what your system can handle, the sensor automation, a complete materials list with sizes and part numbers, and the operating playbook for before, during, and after a smoke event. Budget-wise, a manual-switch version starts around $350–500 in parts; a fully automated build with sensors runs more, and all of it is a fraction of what a premium filtration-ready ventilation system costs.

Start with the self-check, then read the guide. By the time the next smoke event rolls through, your house can be the one place it doesn't reach.