How long will fresh air stay fresh?

[Dr. Manny Bowles]

So, I'm thinking of cutting off my vent fan a few times during my dark cycle to help regulate my night-time temps. The problem is I'm not sure how long a room full of air will sustain my girls without any problems.
My set-up is like this:
10x10 room with a table for flowering and 2 tents for vegging, fans everywhere running 24/7. Passive air intake, with 1 (or sometimes 2) 6" vortex exhaust. And a Cadet wall heater. On average I have 8-10 ladies in flower, 8-10 in veg and maybe some clones. During the day I'm good, my lights keep the room around 70 and the heater kicks on every now and then to keep things right.
At night when the lights go out, I think my temps are hitting around 60 and maybe even less on really cold nights. That's why I'm thinking of timing the fan to turn off to let the heater catch up.
My question is, how often should I exhaust the old air and bring in some new?
Thanks

 

[swiftgt]

you could try getting a domestic dimmer switch and connect it to your fan and just lower the fan speed.

 

[The Hemp Goddess]

If you have passive intake, that is enough during the dark period. Plants do not use CO2 when they are not photosynthesizing. Unless you need to run fans to keep things from getting too hot or too cold, you do not need to run them during dark.

 

[DirtySouthernAfficionado]

Or you can take you room dimensions and figure your square footage. Then you figure your CFM rating from your ventallation. CFM= Cubic feet per minute....
It's been awhile since I've done this...lol
You divide you sq footage by your cfm... I believe.
If it takes 30 minutes to completely circulate your room, you would run your vent 30 on 30 off.
I am a little high right now.... that sounds right.
I used to have to run my room every other 15 minutes.

 

[Dr. Manny Bowles]

Swift-Hmm, I can't run a dimmer because I need the fan to be at full strength when the lights kick on, and I don't want to have to be here when they do to turn it up.

THG- So the O2 in the room would be enough to last a 12 hour dark period?

 

[Dr. Manny Bowles]

Thanks to everyone so far, my thank you button is gone?

 

[DirtySouthernAfficionado]

I can't remember exactly but I thought it was something like you should cycle your air at least once every hour....
I wouldn't quote me on that though....

 

[The Hemp Goddess]

Swift-Hmm, I can't run a dimmer because I need the fan to be at full strength when the lights kick on, and I don't want to have to be here when they do to turn it up.

THG- So the O2 in the room would be enough to last a 12 hour dark period?

Yeah, you will be fine. You have a passive intake--it is not like it is a sealed room. I never run fans during dark and never have. I have a passive intake--that is sufficient.

 

[BBFan]

Well she's not called the Goddess for nothing folks.
Her advice solves your problem.
Good luck Doc (love that name!). Soon enough your problem will be reversed.

 

[Dr. Manny Bowles]

Thanks for all the replies everyone I had it timed to turn on twice last night and my temps were around 70 this morning. I will switch it off completely tonight, thanks again!

 

[swiftgt]

sorry i didnt get back to you sooner,
if you want to make your fan automated, not just control the speed
you can buy a thermostat and wire it in series with the fan,
this will allow the fan to turn on at your desired temp,
and not have to worry about the room temp again.
to do this you could use a domestic wall thermostat, an immersion thermostat or buy an expensive fan controler,
all these can be bought on ebay, or a plumbing wholesalers,
to wire it is straght forward,
connect the live wire from your power supply to the common connection on the stat, and bring a wire from the L1 connection to the fan,
and the neutral wire gos from your power supply straght to the fan,
easy!
make sure all your connections are good and tight,and tape it up so no water gets in,
also make sure you put it in a location where it wont get wet!
any questions?

 

[Dr. Manny Bowles]

Umm yeah... What?

I can do wood and glass, but electricity is way over my head. If it isn't pre-wired, I'm lost. Thanks for your help though :bong1:

 

[swiftgt]

well it may seem that electricity is complicated and scary, but its not that hard to understand, electronics is a whole other kettle of fish!
if you can wire a plug you will be able to manage to do this,
i did a little drawing to show you what i mean,

http://www.marijuanapassion.com/forum/attachment.php?attachmentid=101226&stc=1&d=1235220503

just remember electricity needs to flow to work,so imagine it flowing out on the live and returning back to source on the neutral,
if you need any help just ask.

 

[MindzEye]

Hi, Im a journeyman commercial HVAC mechanic, in my trade to become a journeyman you must master electrical, plumbing as well as HVAC...

Anyways heres a link fo a great thermostat that is accurate and will last for years, it has a remote probe and its pre wired so all you have to do is plug the fan into the thermostat set the thermostat for cooling, set your variance them set desired temp....

http://reptilebasics.com/Johnson-Controls-Thermostat-Pre-Wired-p-16178.html

Or if you want a proportional thermostat (doesnt shut off the equipment it adjust voltage going to equipment) so if it gets hot the fan will run fast and when it gets cold the fan will almost stop. This helps save electricity and is easier on equipment than your classic on/off style....
http://spyderrobotics.com/products/herpstat.html

 

[leafminer]

My little outdoor grow room had no ventilation at all for the first grow except for the leaks, and still did just fine.