Workshop
Workshop Air Exchange Calculator
Estimate CFM of fresh-air ventilation needed for your shop, plus recommended filter change schedule.
Calculator
4 = hobby, 6 = active, 10 = finishing.
What makes this different
Most woodshop air calculators focus on dust collection, not general ventilation. This one uses ACH (air changes per hour) targets (4–8 for a hobby shop, 10+ for finishing), factors in the volume of the room, and shows what size exhaust fan you need.
Who it's for & when to use it
Sizing an inline fan for finishing work, deciding if a window fan is enough, balancing make-up air with dust collection.
How to use
- Enter the dimensions of your material or the parameters of your project.
- Adjust the optional knobs (waste factor, kerf, planer allowance) to match your shop practice.
- Click Calculate and read the output. Use the per-item breakdown for ordering, the totals for budgeting.
- Compare the result to your lumber yard's quote — the effective $/BF column is the apples-to-apples number.
Formula: CFM = (Volume × ACH) / 60. Volume = L × W × H.
Notes & tips from the shop
- Make-up air is as important as exhaust. A 600 CFM exhaust fan in a tight shop will starve a 1,200 CFM dust collector.
- VOCs from finishes linger for hours. Schedule finishing for end-of-day or run an inline fan for 4 hours after.
- Carbon filters extend the time before exhausting solvent fumes but don't replace ventilation.
Frequently asked questions
How do I know if my fan is big enough?
Hold a tissue near the intake — it should pull strongly. If it flutters, you need more CFM.
Can I just open a door and window?
Yes in summer; in winter the heat loss is brutal. A balanced inline system is cheaper to run long-term.
What about HEPA filters?
HEPA captures fine dust and some VOCs. They reduce the required ACH for fine-dust work but not for solvent finishing.
Limitations
Single-room model. Multi-room shops with shared ventilation need zone-by-zone sizing.
All calculations happen in your browser — nothing you type is sent to a server.