CFM / Ventilation Question

Just split up my old setup to have grow/veg tents, not sure if I need bigger intake fan & filter.

I have vivosun 6" inline fan attached to "6 carbon filter. This is attached to a Wye and ducted to 2 tents (one for veg and one for flower). See pictures below





VEG tent - 4x4x6.6 ft
FLOWER tent - 4x8x6.6 ft

CFM -
4x4x6.6 = 105
4x8x6.6 = 211

My understanding is that to consider for fan and filter, you have to multiple tent CFM by 3. That puts me at needing around 950 CFM through fan if I want to exchange fresh air into the tent every minute, right? If my current fan only can push 440 at max, do you think that its sufficient to cycle fresh air in there every 2 mins?

Also, does this kind of setup make it so it is no longer necessary to vent out of window/roof? Thanks for all your input team!

Anyone here vent 2 tents in a similar fashion?

I would run an 8” exhaust vs a 6”. 8” to me is an overkill in 1 tent, just right with 2. Having a fan controller will be extremely useful. That way you can control the air flow vs the fan running at max the whole time.

MidwestTentGrowerDude said:

Just split up my old setup to have grow/veg tents, not sure if I need bigger intake fan & filter.

I have vivosun 6" inline fan attached to "6 carbon filter. This is attached to a Wye and ducted to 2 tents (one for veg and one for flower). See pictures below

View attachment 4588413

View attachment 4588414

VEG tent - 4x4x6.6 ft
FLOWER tent - 4x8x6.6 ft

CFM -
4x4x6.6 = 105
4x8x6.6 = 211

My understanding is that to consider for fan and filter, you have to multiple tent CFM by 3. That puts me at needing around 950 CFM through fan if I want to exchange fresh air into the tent every minute, right? If my current fan only can push 440 at max, do you think that its sufficient to cycle fresh air in there every 2 mins?

Also, does this kind of setup make it so it is no longer necessary to vent out of window/roof? Thanks for all your input team!

Click to expand...

I also forgot to mention that running your veg tent through the filter isn’t necessary. You go could get more air flow by exhausting your veg tent to your flower tent to the filter, that would eliminate your Y connection. Food for thought.

I appreciate the feedback. I considered running veg tent straight through flower tent - but I thought I would have odor issues, and temp/rh control per-student issues. Now you have me thinking...

Most likely scenario is just buying a 12" vortex fan, bigger carbon filter and venting through there.

It's not absolutely necessary to vent outside, is it? I'm trying to avoid a larger project ducting out of my basement to the outside. Thanks again for your feedback.

MidwestTentGrowerDude said:

I appreciate the feedback. I considered running veg tent straight through flower tent - but I thought I would have odor issues, and temp/rh control per-student issues. Now you have me thinking...

Most likely scenario is just buying a 12" vortex fan, bigger carbon filter and venting through there.

It's not absolutely necessary to vent outside, is it? I'm trying to avoid a larger project ducting out of my basement to the outside. Thanks again for your feedback.

Click to expand...

To some degree it is necessary to vent out of the room your tents are in, reason being, it just becomes recycled air that you just put back into a tent you exhausted out of. Unless you are dealing with excessive heat issues, exhausting out of the room is the quick fix by keeping that hot air out of the grow area. If heat isn’t an issue, venting outside isn’t that crucial.

If you have a single fan venting two tents then the cfm is split equally, as a result the smaller tent is exchanging air twice as much as the bigger tent and as a result of that the temps will be cooler in the smaller tent than the bigger one.

When you have the two tents full then they are going to be transpiring a lot more and by not venting outside your just recirculating the same humid air which will raise humidity and when it raises too much you will have problems, mould all over your room, condensation in your duct work which will run into your fan, your filter wont work at high humidity.
Obviously this also affects air temp, if you recycle the air over and over it gets warmer, it also loses co2 because no new air is coming in.

You could run the basement as a sealed room and add AC, dehu and co2.

and as far as the cfm needed for a space, its a massive generalisation which mostly related to the co2 been refreshed because that calculation doesn't involve wattage of everything in the tent and its the wattage that adds the heat.
The wattage will determine the rise above ambient. Since we all have different climates with difference ambient temps the cfm required to keep a certain space X degrees above ambient with Y wattage will be different.