Hopefully everyone is aware how important filtering fine dust out the air in your shop is. You can find numerous articles detailing the dangers of breathing very fine saw dust particles, that can work their way deep in to your lungs and cause long-term cumulative damage. The most dangerous particles are the smallest ones that are hard to see and stay suspended in the air for long periods of time, vs. large particles/saw dust which quickly falls to the shop floor.
There are many available commercial air filters designed for shop use, but a few years back I built my own. In my case, it’s a three-stage filter with a 460 CFM blower which turns over the air in my shop about every 20 min.
The pre-filter removes relatively large dust particles, significantly extending the life of stage 2 and 3 filters which are working hard to filter out the most dangerous dust particles.
- Pre-filter (stage 1): Protects stage 2 & 3 filters from “large” particles.
- MERV 8 / FPR 5 (20″ x20″ x 1″)
- Non-Electrostatic, filters Dust Mites, Dust/Lint, Pet Dander, Pollen
- MERV 8 / FPR 5 (20″ x20″ x 1″)
- Primary filter (stage 2):
- MERV 11 / FPR 7 (20″ x 20″ x 4″)
- Electrostatic, filters Bacteria, Dust Mites, Dust/Lint, Mold Spores, Pet Dander, Pollen (95% of airborne particles from 0.3 microns to 10.0 microns).
- MERV 11 / FPR 7 (20″ x 20″ x 4″)
- Fine filter (stage 3):
- MERV 13 / FPR 9 (20″ x 20″ x 4″)
- Electrostatic, filters Allergens, Bacteria, Dust Mites, Dust/Lint, Mold Spores, Most Smoke, Pet Dander, Pollen, Virus Carriers (95% of airborne particles from 0.3 to 10.0 microns).
- MERV 13 / FPR 9 (20″ x 20″ x 4″)
Pre-filter at six months
Below you can see an example of the difference between an unused/new pre-filter (left) and an identical filter after six months of use (right). The change in appearance is slow, so you may not realize how dirty your filter is getting until you compare it to a new one. Right now I change the pre-filter every six months, but comparing the two, I may consider changing the schedule and start replacing it every four months.
Resources
- Articles
- US EPA – What is a MERV rating?
- Filter media
- Orange big box store – MERV 8 filter
- Blue big box store – MERV 11 filter
- Orange big box store – MERV 13 filter