[green54321]

Hi all.

This is the basic design I'm thinking of.

-Planning to vent two 3'x3' flower spaces into it (315 watts each).
-1/4" plywood for the box.
-Metal brackets to attach the sides of the box and then glue the bejesus out of them to keep it air tight
-Want to keep the outlet side unglued so I can remove it to put in fresh carbon as needed

Couple q's:

-Would bumping the outlet up to 8" be sensible?

-How long should I make it to manage two 3'x3' spaces?

-How thick should the layer of carbon be?

-Does this seem like a good price for carbon? (in the US)
https://www.thatpetplace.com/filter-carbon-pellets-52lb

Any other suggestions?

[queequeg152]

a few things.

make a V shape at 30-45 degrees.

carbon tray thickness should be based on that static pressure capacity of your fan.

generally the tray thicknesses are around 1", but this will generate a good amount of static pressure unless you have very large trays.

google vapor phase acivated carbon. make sure you get the larger pellets, not the smaller pellets. get the manufacturer specs on the carbon... they will usually give you reccomended thicknesses.

mark the weigh of the trays with a paint pen when empty, then mark the weight of the the carbon + tray when the carbon is brand new and dry.

the carbon weight is how you determine when its ultimatly exhausted.

put static pressure probes on your box and install a magnehelic 0-2 inch gauge or a mark 2 inclined manometer.

this will help you determine when to agitate the carbon and when to change the prefilter.

MDF is very heavy if you dont already know... you might consider plywood as an alternative. galvanized sheet metal would be even better, but im assuming you dont have sheet metal tools.

make absolutly sure you have enough filter area to yeild a decent static pressure. dont worry about how much carbon you need for the rooms, worry about whether or not your fan will work properly.

for an 8" collar the max you really want is 250-300 cfm. any more and you are pushing up into 900 FPM territory which is noisy and turbulant. slower is always better with respect to static pressure.

[queequeg152]

this is a filter bank.

https://www.aafintl.com/en/power-and-industrial/browse-products/ep/side-access-filter-housings/side-access-vee-bank

just imagine a single 'V' instead of a 'W' shape.

to retain the filters, just buy some aluminum angle and tape down some closed cell neoprene gasket to the housing for air sealing.

[WaterFarmFan]

I think it would be much easier to use an existing filter and build a box around it. Your two spaces vent straight to the top of your box, and then you cut a hole in the bottom of your box for the filter. Use spray foam to secure filter to box and let cure. It will be air tight and wont move. Then COMPLETELY SEAL every corner of your box absolutely air tight with low-vox epoxy. You will have to cut the epoxy to open box later, but filter will last 9+ months with moderate humidity.


https://growershouse.com/growers-house-carbon-filter-4-x-12-200-cfm

WFF

[WaterFarmFan]

I make similar boxes with thick HEPA filters as the walls and a just a duct fan spray foam attached to the back. I suspend these in growing area from the ceiling and it is a budget but high-quality hepa filter that cleans the air 24/7.

WFF

[Ununionized]

I might want to construct one. I'm gonna be in the woods but still, people driving up to a property with the right wind, can discover inconvenient truths about my lifestyle.

I'm a security freak since I spent my life in illegal pot country. Just because pot's legal doesn't mean I want everyone knowing I have some.

I never realized a hepa filter can block terpenes. Thank you for saying something because I loathe and despise buying and making charcoal filters.

Originally Posted by WaterFarmFan

I make similar boxes with thick HEPA filters as the walls and a just a duct fan spray foam attached to the back. I suspend these in growing area from the ceiling and it is a budget but high-quality hepa filter that cleans the air 24/7.

WFF

[DocTim420]

Instead of plywood, investigate those thick styrofoam "rigid insulation sheets" (plywood can attract mold--styrofoam not as much). Home Depot has 4' x 8' sheets that 2" thick (I used 1 1/2" thick ones), like this...



You will need a special foamboard adhesive like the one made by Loctite https://www.homedepot.com/p/Loctite-...1941/202020476.

And if you design it right, standard $3 filters (12"x12"x1") can be used. That is what I did, I built filter boxes to filter the air cooling my lamps. I change filters every 90 days or so...and they are almost all "black" by that time.

[WaterFarmFan]

Originally Posted by Ununionized

I might want to construct one. I'm gonna be in the woods but still, people driving up to a property with the right wind, can discover inconvenient truths about my lifestyle.

I'm a security freak since I spent my life in illegal pot country. Just because pot's legal doesn't mean I want everyone knowing I have some.

I never realized a hepa filter can block terpenes. Thank you for saying something because I loathe and despise buying and making charcoal filters.

Hey there. I actually use Phresh charcoal can filters for my smell and the hepa filter cleans out nasties from the air like mold and powdery mildew spores. I absolutely love to diy just about everything, but unless you have a micro-box with very small fan, it just seems easier to use pre-made carbon filters. The trick about the longevity of carbon filters is keeping the humidity to reasonable level. If you have +70-80% humidity at night in sealed or semi-vented room, the charcoal can become ineffective quite fast.

As to building the hepa box, it is really simple. Just buy the hepa filters, which are typically insert replacements for stand alone machines, in a size that makes a good wall like 10x12 or 12x18. You can use 2 or more to redirect airflow to the side and down. Cut your sheets for all the non-hepa walls, including the back. Use the appropriate duct fan for the surface area of the hepa filters (ie dont use a 8" duct fan for a single small hepa filter). Cut the hole for your fan in the back and assemble box using a 1x1 down each side (on inside of box) so that you screw it together and provide support. Screw the box so that hepa filter fits snug with the walls. Use low-vox epoxy and seal all corners of box. Once epoxy is cured and you have a completely sealed box, flip up side down and slide duct fan directly into hole with cord on outside of box. While holding and being careful to not drip on hepa filter, use spray foam to seal gap between wood and fan. Let dry and turn on to test. Air should only be coming out of the hepa and no where else. I then screw in a eye bolt in the center of box and hang from the sealing.

WFF