Shop air quality
Dust collection captures the heavy chips; air filtration captures the fine particles that cause respiratory problems and damage your tools. This calculator tells you your shop's air changes per hour and whether your air filter is sized to clear the dust load.
Calculator
Why dust collection isn't enough
Even a perfect dust collection system at the tool captures only 80–95% of dust. The rest — the fine particles below 10 microns — escapes into the shop air. These are the particles that stay suspended for hours, get into your lungs, and settle on every surface in your house. An air filter (the kind that hangs on the wall or ceiling and pulls air through a fine filter) catches what dust collection misses.
The 6 ACH rule
ASHRAE's standard for residential workshops is 4–6 ACH. For a wood shop with significant dust production, 8+ ACH is better. The calculator gives your shop's actual ACH based on air filter CFM and shop volume. If the result is below 6, you need either a larger filter or to run multiple filters.
MDF and plywood are special
MDF dust is finer and more hazardous than solid wood dust. The urea-formaldehyde binder is a respiratory irritant. If you cut MDF or plywood regularly, double the calculator's recommended filter size — or run it outside if possible. MDF is the most common cause of "shop cough" in hobbyists.
Limitations
- ACH is a steady-state calculation. Real air filtration ramps up over time as the filter loads.
- Doesn't account for open doors / windows — they change ACH dramatically.
- Doesn't model filter degradation; replace filters per manufacturer schedule.
- Doesn't replace a respirator for direct exposure to dust.
Frequently asked questions
Air filter or dust collector?
Different jobs. Dust collector captures chips at the source; air filter captures fine dust in the air. You need both. Skip one and you're either dealing with piles of chips or breathing fine dust.
Is a ceiling-mount filter better than a wall-mount?
Ceiling-mount drops clean air downward (pushes dust down toward the floor); wall-mount pulls air across the room. For shop dust, ceiling-mount is generally better because fine dust settles slowly and benefits from being pushed toward the floor. Either works if sized correctly.
How often should I change the filter?
HEPA filters last 2–4 years in a hobbyist shop; pleated pre-filters need cleaning or replacement every 6–12 months. Watch for reduced CFM (filter cycling time) as a sign the filter needs attention.