Yes there will definitely be some contamination when I open the door or take the plants out. I’m hoping it’s a matter of concentration and the odd spores won’t be as bad as the plants bathing in them 24/7 lol. I really don’t know though tbh, only one way to find out I guess 🤷
I also don’t know how much this fabric will choke my fans. I don’t assume it will be very drastic but time will tell. If it’s bad I’ll add more intakes to each box to compensate.
The hydrostatic filter material I used to line the passive intakes on my new breeding tents was rated with a max CFM, too medicated to remember or walk down to check lol but it was in the 4-600 CFM on the 3M stuff I bought. A lot of these sheet style filters are designed to be used with other filters so the reduction in flow is negligible as long as you aren’t tripling it up 
Sweet, good to know thanks 
Got a link to your filter or something similar for posterity? Maybe someone else will find it useful…and I’m curious as well
MERV 13 should be enough to handle what you need - and will be cheaper than HEPA.
The other consideration is the pressure drop across HEPA filters… the flow of your fan may be significantly reduced (if that’s an issue).
Commercially a 12 x 12 panel is probably the smallest common size you’ll find. If you can work with that using some sort of transition to your intake that may be the most cost effective buy.
Good info. I saw some of those 12x12s and thought I could rig a filter box that had two intakes going out of it but that would have required some serious redesign and cost me more than this fabric. Time will tell!
Return air grilles come in many sizes. The larger the opening the lower the pressure drop across the filter. This one takes a standard 14x20 filter. Running pleated filters allows larger surface area and smaller openings in the mesh for better filtration at lower energy(pressure drop)
Ya building intakes to standard sizes is definitely a good idea to make life easier
As I mentioned these are supposed to be used in conjunction of your typical panel furnace filter but are not MERV rated ( as it is a 3M product) so they rate with MPR, these are rated at 1000 MPR, locally available, fairly reasonably priced (did the intakes on 3 tents with less than one $18 pack)
Very nice. In the future I will definitely build my intakes to standard sizes so I can use things like these.
I didn’t, I just cut to size, silver taped directly to the inside of the tent over the intakes, have some smaller pleated filters that will be in front of the materials and again silver taped to the inside of my tents, there is always a way!
Freaking MacGyver over here! Do they block light?
Don’t know yet but I use the passive intake covers that come with my tents and they do. In the past I have used cut straws directly in the Velcro for the closure of the intake going perpendicular to the strip of Velcro, on the outside of the tent, every few inches and sealed the Velcro around each one (10-20 of them per intake) and this is the only way to keep passive ventilation without leaking light IME.
There is only one vent that I need to worry about in my setup ( veg tent inside the flower compartment) whereas the pollen mitigation system is for my auto breeders in my lung room - not worried about light pollution there as everything in that room is on the same cycle
Just gotta point out merv 17 to be n95 territory, think it was 19 to hit HEPA.
So if you’re really looking for HEPA like filtration you’re going to need a bit more material inline.
How did your lightproof passive vent project go @Hephaestus ? When you started that I thought maybe I won’t have to use black straws in my intakes anymore 
Haven’t had any noticeable light leaks… Just a 180° reversal. Haven’t tried a million candella and sensitive light detectors… Flat black inside was enough to take it down to good enough for the girls I go with.
I’m a little late to this but a vacuum hepa filter isn’t very big and allow high air flow. May have to MacGyver a way to attach tho. I built my boxes with osb so I’m just gonna a quick mount to place over air intake on top of box
thats what i bought from amazon 2 years ago, they were very inexpensive then there spendy now and not on amazon
Nice unit. This whole thread gives me a business idea, I’m sure you can guess what it is lol
Idea train.
Noticed this pic in my files and had to share. Some day I will cobble one similar. Wish I could credit the builder. Found here or interwebs.
28x18x6" add flanges to bottom, drill intake holes in the lid… Then it’s just a flange to fit some 16x25 filters…
