Better to Force in More Cool Air or Crank up the Exhaust Fan

bigboerboel

bigboerboel

Well-Known Member
After multiple outdoor grows, I finally tired of budrot, catapillars, and a thieving gardener. I bit the bullet, opened my wallet, and thanks to all of your good information, set up a dialed-in grow tent. Just popped some seeds in the tent yesterday.

I want to bring my lights-on temp down a few degrees from 85 to 75ish, but keep my RH between 55% and 65% (for seedlings). When I turn the exhaust fan up, the temps drop nicely, but the RH drops to 50%. If I drop the exhaust fan and turn up the active inflow fan the RH stays around 60%, and the temp drops to 76, but the tent pressure is just barely negative. I'm already running my humidifier full blast.

So, what's better, force in more cool air and keep RH up, or draw out more warm air and settle for lower RH?
 
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Sfpyro420

Well-Known Member
Me personally I go for lower rh so I don’t get mold issues in my tent, negative pressure for me is only important during flower when I have visitors for smell reasons
 
HydroKid239

HydroKid239

Well-Known Member
I would guess that blowing in the cooler air would be the better option if you have a humidifier to add moisture to incoming dry air. You should be able to tune in the inflow & exhaust to where your comfortable on the hygrometer. Nothing wrong with warmer temps tho.
 
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NewGrower2011

Well-Known Member
If you blow in too much air, you'd lose the "negative pressure" you're trying to achieve - primarily for odor control reasons (if that matters to you) but also to govern the general air flow. i.e. people use a 6" exhaust fan with a 4" intake fan, etc.
 
ChemDogLover

ChemDogLover

Well-Known Member
NewGrower2011 said:
If you blow in too much air, you'd lose the "negative pressure" you're trying to achieve - primarily for odor control reasons (if that matters to you) but also to govern the general air flow. i.e. people use a 6" exhaust fan with a 4" intake fan, etc.
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I was just gonna say that you don’t wanna lose your negative pressure
 
bigboerboel

bigboerboel

Well-Known Member
Is negative pressure necessary? If odor control is not important in this location, is it OK to just blow in fresh fresh air and let it escape passively? With the extraction fan off, I maintain 72 degrees and 60% RH with the humidifier set at 60%.

The seedlings are 7 days old now.
 
Comnconnection

Comnconnection

Member
I
bigboerboel said:
After multiple outdoor grows, I finally tired of budrot, catapillars, and a thieving gardener. I bit the bullet, opened my wallet, and thanks to all of your good information, set up a dialed-in grow tent. Just popped some seeds in the tent yesterday.

I want to bring my lights-on temp down a few degrees from 85 to 75ish, but keep my RH between 55% and 65% (for seedlings). When I turn the exhaust fan up, the temps drop nicely, but the RH drops to 50%. If I drop the exhaust fan and turn up the active inflow fan the RH stays around 60%, and the temp drops to 76, but the tent pressure is just barely negative. I'm already running my humidifier full blast.

So, what's better, force in more cool air and keep RH up, or draw out more warm air and settle for lower RH?
Click to expand...
Positive pressure is better except for smell like others said. I think you got it right on. Turn down the exhaust and turn up the intake. The positive pressure helps with temp and humidity like your finding out and also can help keep air borne stuff out. I’d recommend also putting a carbon filter and hepa combo on one fan and let it scrub the air in the room around the tent as an extra precaution for pathogens. Any clean room uses hepa filtered air to keep rooms at positive pressure.
 
ChemDogLover

ChemDogLover

Well-Known Member
bigboerboel said:
Is negative pressure necessary? If odor control is not important in this location, is it OK to just blow in fresh fresh air and let it escape passively? With the extraction fan off, I maintain 72 degrees and 60% RH with the humidifier set at 60%.

The seedlings are 7 days old now.
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It’s Not bad, but that carbon scrubber won’t get all the exhaust.
 
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SBNDB

Well-Known Member
Can u dim your lights to help bring temp down? If u just popped seeds you don’t need much light anyways. A smaller light for seedling/ early veg is a good option to keep temps and wear n tear on your “good” light.
 
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