2x2 Tent Ventilation cfm Help

[shoegal420]

Hello, I've decided to start my first grow in a 2x2x5 1/4' tent with 400w HID bulbs that I will dim with a ballast to 200w since 400 might be a bit much for such a small space.
Initially, I wanted to buy the 4" S & P TD-100x fan for my exhaust which is 137cfm on high and 100cfm on low. Using the Ventilation 101 thread, I calculated that I would need about 100cfm to exchange the air in my tent 5 times per minute and that's why I decided that fan would be adequate. Then, I read that having a carbon filter (which I will) decreases airflow and some other threads have suggested that I'd need 200cfm and higher to properly ventilate my tent.
My question is, will 137cfm be enough to vent my tent and keep the air pressure negative or do I need more?
I'm considering going for the 5" S & P TD-125 (197cfm on high,149cfm on low) but then I'd have to get a duct reducer because I can't find any 5" filters and I think the reducer would just create more noise.

If anyone has helpful input, I'd appreciate it.
Thanks

 

[messn'n'gommin']

(200w's x 3.2) divided by 5*F (temp differential between tent and room) = 128 cfm (10*F diff = 64cfm)

(400w's x 3.2) divided by 5*F (temp differential between tent and room) = 256 cfm (10*F diff = 128 cfm)

If you're exhausting into the room the tent is in, you'll need to keep an eye on room temps.

 

[qupee]

a TD-100 is enough fan for that tent.. but, 400w is too much light for that tent (50% power should be fine, though).

If you expect to have most of the ventilation inside the tent, forget the TD-125 as the reducers will be a pain in the rear taking up lots of space. If you think you need more fan than the TD-100, just get a 4" plastic-bodied centrifugal.

 

[messn'n'gommin']

Is it to late to change-out your switchable ballast for a 250w setup? It won't be much more difficult to ventilate the tent than with 200w's and it'll be easier to cool your tent than with 400w's. A 2'x2' tent is ideal size for a 250w'er and will give you 62.5w's per sqft, a good ratio! Either way, get the TD-100 and set it to high.

 

[qupee]

Is it to late to change-out your switchable ballast for a 250w setup? It won't be much more difficult to ventilate the tent than with 200w's and it'll be easier to cool your tent than with 400w's. A 2'x2' tent is ideal size for a 250w'er and will give you 62.5w's per sqft, a good ratio! Either way, get the TD-100 and set it to high.

Agreed. Running a 400w bulb at 200w will also skew the light spectrum and lower bulb life.

 

[shoegal420]

Thank you for the help everyone!

@messn'n'gommin' I found a ballast that works with both 400w & 250w bulbs and also can dim 400w down to 250w. Do you mean I should get the TD-100x which is 137cfm on high? because the TD-100 is only 101cfm on high..

@qupee I'm not too concerned about maximizing the bulb life I can just buy new ones when I need to but what does skewing the light spectrum do/mean?.

Would it be a good idea to just get 250w bulbs and run them on 100% or 400w and dim it to 250w or 250wSL?

(the Lumatek ballast I found can also run the bulbs on super lumens but I don't know what that does)

 

[qupee]

The colors shift, so you get more green light in lieu of more red light. Better to run a 250w bulb.

Super lumens is usually a 5 or 10% boost and that's usually over the ballast's highest wattage. So a 400w/250w I would assume the SL setting is 420w or 440w unless it specifically says there's a boosted 250w setting.

Get the TD-100x over the 100. Don't get too small of a filter either or it will restrict the flow too much, and frankly if you need to have a smaller filter or can't arrange a mostly straight duct run, or if the ambient room temp is high, I'd say going with a S&P MixVent is dicey. I didn't think they were really that quiet and a 4" plastic-bodied centrifugal inline fan is louder but will eliminate any doubt as to whether or not it will exchange enough air. The MixVent's fall flat quickly in the face of resistance. (I've owned the TD 125, 150 & 200 and a couple different 6" & 8" centrifugals).

 

[messn'n'gommin']

Thank you for the help everyone!

@messn'n'gommin' I found a ballast that works with both 400w & 250w bulbs and also can dim 400w down to 250w. Do you mean I should get the TD-100x which is 137cfm on high? because the TD-100 is only 101cfm on high..

@qupee I'm not too concerned about maximizing the bulb life I can just buy new ones when I need to but what does skewing the light spectrum do/mean?.

Would it be a good idea to just get 250w bulbs and run them on 100% or 400w and dim it to 250w or 250wSL?

(the Lumatek ballast I found can also run the bulbs on super lumens but I don't know what that does)

Yes ma'am! I meant the TD-100x! The 250w setting would be just about perfect for your tent!

My apologies for mixing up the fan model numbers and thanks to qupee for the correction!

 

[hush]

While I do agree that 250w is the ideal wattage for a 2x2 space, I am successfully using a 400 watter in my 2x2. I vent it with a 175cfm 4" centrifugal fan. Temps go up to 80*F max. When I open the tent for maintenance, the temp climbs up to 84, and that's just because the airflow at those times bypasses the thermometer.

The trick is using a cool tube. Oh, and it probably also matters that I don't have a carbon filter attached to it, because the tent is in a closet that has its own extraction fan and carbon filter.

 

[messn'n'gommin']

While I do agree that 250w is the ideal wattage for a 2x2 space, I am successfully using a 400 watter in my 2x2. I vent it with a 175cfm 4" centrifugal fan. Temps go up to 80*F max. When I open the tent for maintenance, the temp climbs up to 84, and that's just because the airflow at those times bypasses the thermometer.

The trick is using a cool tube. Oh, and it probably also matters that I don't have a carbon filter attached to it, because the tent is in a closet that has its own extraction fan and carbon filter.

Fully agreed! 400w'ers can certainly be used (and well!) in a 2x2 space and is more a testament to an individual's abilities. But, experience and understanding go hand-in-hand with success! The rub being, it tends to go past the experience of most just starting out. So...lol...I hedged my bets by advising simpler tactics! At the least, Shoegal420 still has the option of going higher wattage (or even an upgrade in footprint) at a later date as she gains more experience!

 

[shoegal420]

@hush I was going to use 400w bulbs but I decided since it's my first time I just didn't want to experiment too much until I get the hang of it.

A question for everyone, I read the carbon filters max cfm should always be higher than your fans cfm so since my fan has 137cfm, would a 4"x6" 140cfm Phresh filter suffice or should I get the 4"x8" 150cfm Phresh filter?

 

[Jnugg]

First and foremost what will be the hottest temperature the ambient/intake air will ever get.


C'mon guts,it's not as simple as x fan will work for y growroom/tent/cab with b lighting.

Variables people.

For simple ventilation 2x a minute is a good start as this helps keep humidity at bay.

If using one fan to both ventilate and cool the griw area you would take the cubic footage of your growroom/cab/tent and multiply by two.In the OP's case...

2x2x5.25 = 21 cubic feet

21 cubic feet x 2 = 42 cubic feet.So 42cfm (after pressure losses from ducting,bends in ducting,and carbon filter.

Now for cooling...look at this liadline/graph...note that 200cfm (after pressure losses from ducting,bends in ducting,aircooled hood,and carbon filter) keeps a 400w HPS about 6°F above ambient/intake air temps.

So...just add the two airflow/cfm ratings together...

200cfm + 42cfm = 242cfm

So,you would need an exhaust fan/carbon filter combo that is rated 242cfm after all pressure losses due to ducting,bends in ducting,aircooled hood,and carbon filter to keep a lights on temp of 6°F above ambient/intake air temperature.But keep in mind what your ambient/intake temps will be.If they are as high as say 78°F then a 6°F temp rise (lights on,in cab/tent) will give you a lights on temp (in the cab/tent) of 84°F which is not optimal unless going sealed and supplementing with c02 enrichment.


You and anyone that doesn't understand ventilation and cooling need to look at Ventilation 101 for a better understanding,and read the thread in it's entirety.

 

[messn'n'gommin']

Great post Jnugg, and I fully agree! The Ventilation 101 thread by Redgreenery should be a required read for everyone! His technical expertise on the subject has helped a lot of people, including me! But, I have seen more than a few first-timers come away from it a bit overwhelmed. Although, some of us have a bit more difficulty with the principles of ventilation, a working knowledge will get you by. So, without getting to in-depth, I try to explain in succinct and simpler terms that even I can understand.

Again, great post! Peace!

 

[qupee]

C'mon guts,it's not as simple as x fan will work for y growroom/tent/cab with b lighting.

Variables people.

Except that the, imho, most important variable - pressure loss - is consistently glossed over.

Every system has significant loss, and rarely do I see anyone calculate even a basic x # of feet of straight flexible ducting changes it by y, much less filters, hoods/tubes, 90° or 45° bends.

2x your volume or 3x or 5x your volume, and 5° or 6° or 2° over ambient is all pissing in the wind if you don't even attempt to estimate pressure loss.

 

[Jnugg]

Yes pressure loss is a huge variable.

 

[Bleed~green]

Yea I just got a TD 100x and I love it, definitely recommend it. My setup is a bit different, it's a 2x4x5 tent with 4 foot T5 HO. The fan works great. I clean the air up top and duct it back in thru the bottom. Temps stay between 70 and 75.