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What your system can do about smoke — and what it cannot
Three questions about what is installed, and a straight answer about what to change before the next bad week.
The guide
This is about equipment, not health. It describes what filtration and airflow do to particles in the air a system circulates — it is not medical advice, and it does not tell you whether the air in your house is safe. Public health guidance during a smoke event comes from the agencies, not from us.
What to do
A basic one-inch filter is there to protect the equipment, not to clean the air. It passes most of the fine particles that make smoke visible and smell.
- Move to a pleated MERV 13 filter if your system can carry one, or better, fit a deep media cabinet.
- Ask us to measure static pressure first — on some older blowers a tighter filter costs more airflow than it is worth.
- Keep spares. In a bad week a filter can load in days rather than months.
A MERV 13 filter removes a useful share of fine particles from the air that passes through it. The limit is how often that air passes through: a system that only runs when it is cooling filters for a fraction of the day.
- Set the fan to run continuously, or to a circulate mode, through a smoke event.
- Check the filter every few days during one — they load fast.
- A deep media cabinet would let you do the same with less pressure drop, if the system has room for one.
A deep media cabinet filters well and restricts airflow far less than a thin filter of the same rating. With the fan running, the house gets a lot of filtered air passes per day.
- Run the fan continuously during a smoke event, and change the media as soon as it looks grey.
- Seal what you reasonably can — the filter cannot catch what comes in around doors and windows.
- If one room matters most, a portable cleaner there still adds something.
Window units, baseboard heat and most ductless heads do not filter the room in any meaningful way — their filters are there to keep the coil clean.
- A portable air cleaner sized for the room you spend most time in is the practical answer here.
- Keep it running rather than switching it on when the smell gets bad.
- If you are considering ducted equipment anyway, this is one of the arguments for it.
Check the fan setting. If the thermostat has no continuous-fan option, the filter only works while the system is heating or cooling — which in mild smoky weather may be barely at all. On most systems this is a thermostat change rather than a new system.
Turn the fresh-air side down, not off. A ventilation system bringing outdoor air in is bringing smoke in with it. Reducing it during an event helps; switching it off indefinitely is a different problem, and in an occupied building there may be a ventilation requirement that comes first.
Portable cleaners work on one room. Put it where you sleep or where you spend the day, size it for that room, and leave it running. Moving it around all day gets you the worst of both.
Four things worth being honest about
- A filter does not seal a houseMost of what gets in during a smoke week comes through doors, windows and leaks, not through the ductwork.
- Filters catch particles, not gasesThe smell of smoke is partly gases, and a particle filter does little about those. Carbon media helps a little and is not a solution.
- Tighter is not always betterA filter the blower cannot pull through reduces airflow, which makes everything else worse. It is measured, not guessed.
- We make no health claimsWe can tell you what the equipment does. What that means for anyone's health is a question for a doctor and for public health guidance.
