Newbie ventilation question

[jimbro]

Hi folks,
I've just about got my room ready to go. The main problem I've found is wading through all the info concerning ventilation. The basic formula is understood, but the many variables to consider seem to sometimes be contradictory or incomplete (ha, I know, imagine that from a bunch of cannabis growers!).

If someone could please give my some guidance, I'd sure appreciate it, and I'll certainly pay it forward as time goes by and I get some experience under my belt.

Here are the facts:

I live in Norht Central Texas;

my room in in the attic. It's fully insulated, top, bottom and sides, it has no windows;

Total cubic ft. is 920;

I'll be using (2) 1000 watt HID lamps, using reflectors only, non-cooled;

The ballasts will be located outside the room;

I'm going with (2) 20 plant aeroponic systems;

Strain will be Indica, type yet to be determined (any suggestions on this would be greatly appreciated as well!);

Once again, I understand the basic formula for CFM based on cu. ft. and #/wattage of lights, and that I need to bring fresh cooler air in, and exhaust the old air out. But I've read you can deduct 10% per ballast if they're outside the grow room. I've also read you add 20% per non cooled HID light. Then there's the addition of percentage based on where you live temperature wise. Finally, the air exchange rate varies a lot, anywhere from 1-5 minutes.

Can anyone help clarify a formula, or just give me some simple guidance.

I've put 136 hours of labor into building my room, and a LOT of money in equipment so obviously I want to get the ventilation part right, I know it's hugely important.

Please let me know if you need more info, I'll be happy to provide it.

Thanks so much for anyone's help on this,

I look forward to being a part of this forum and sharing what experience I glean from my first grow, and hopefully the many to come.

Jimbro

 

[bigjack]

Whatever you do you're going to need a lot of cooling to deal with summer Texas heat in the attic.

 

[jimbro]

You're right Jack, its hotter than hell here in the summer! I plan to bring in air from an air conditioned room, and supplement with a small portable a/c unit during those "hellish" months.

 

[c526]

hey jimbro-

any reason to use the parabolic shades instead of vented hoods??
attic growing is tough,shades would be ok in the winter

im north of you, we set a friend up in the attic,his ac cost this summer were out of control,12btu running for 16 hrs a day min
hard to keep a room in the 70;s when is 110 outside, we did plumb into his central ac,lowered cost some
he runs 8 inch fans with a speed controller set about 60% speed, quiet as a mouse when they come on

 

[jimbro]

C, no, other than they seem to provide more coverage. I can imagine what my costs will be. I may just pass on growing during the summer months and focus on fall, spring and winter! I'm hoping the insulation and keeping the ballasts outside the room will help (somewhat) offset the cost of elec. But I do realize it's gonna cost me!

Oh, also, I just didnt want to mess with one more ventilation hassle, though I might regret it later on.

Thanks for the input C!

 

[KingJohnC]

Your grow area should have the air exchanged every 5 minutes. I can not advise you on how large of CFM fan to purchase as your ambient room temperature and room temperature with the lights on can be hard to overcome. I would advise you to use cooltubes or a air cooled shade to reduce the amount of heat added to your grow room. You want from 70°-90° Fahrenheit and 50%-70% humidity for vegetative growth and 30%-50% humidity for flowering. I suspect you may need a 10" or 12" inline fan to cool your grow area.

 

[BudBGrowin]

If I was to run in this situation I would use two 10 inch cool tube reflectors with a powerful inline fan and carbon filter and use that to directly exhaust the cool tube air outside. That would be the best way to get the hottest air from your grow outside without having to fight your a/c and you still wouldn't have to worry about any smell issues with the carbon filter. You could use one of those little spinning vents to keep it from looking odd and out of place. Other than that I would try to get as much cool air from a/c rooms vented into the attic also.

 

[jimbro]

Thanks so much for the input folks. I've already bought and installed the adjust a wing reflectors, so cool tubes are out of the question. I'll just deal with all the heat and ventilation issues as best I can. I'll certainly have some invaluable experience to share within the coming months, and I plan on keeping a detailed journal, I'm kinda anal like that!

 

[BudBGrowin]

Cool deal good luck! But if it is a cost thing just remember the initial investment for 2 cool tubes might pay for itself in 2 months worth of power bills. If you run just the hoods make sure your exhausting the hottest air from near the top of the room and bringing in cool air down near the bottom.

 

[jimbro]

Thanks Bud! Well, I also have an 8' light rail, so the wings are the best bet for using on the rail, though I"m sure I can rig anything for a cool tube or ventilated light given enough time and thought!

That's exactly how I have it planned, bottom in, top out! and the air strean will go directly across the entire canopy, so that should get that a lot of the hot air out.

 

[BudBGrowin]

If you haven't bought a fan yet look into getting one with the max cfm rating you can get because you will need it for a room that big. Then you can get a fan speed controller and you will be able to adjust the ventilation based on your temps. Maybe something like a can fan max 12 inch if you can do it. Ventilation will be key to overcoming your heat. And don't forget to cover your smell, it wont dissipate completely being directly exhausted outside especially with a room that big.

The whole 1-5x a minute thing is a range meant to help determine what size fan to get for your room, but with speed controllers it is better IMO to get the best fan you can get (within reason) and just dial it back to what you need. So with 1x exchange a minute being a general maximum exchange rate necessary and 5x a minute being in general the minimum requirement, I would prefer to have too much and not need it all then not enough and come up short. If that make sense.

If I were buying a fan to cool that room I would look at something like a can fan 12" high output model at 975cfm with no load (ducting or filters) or a can fan maxfan 10" that will do 1019cfm at no load and has a built in speed controller (3 position if like my 6" model). Any ducting and carbon filters attached will reduce the cfm rating slightly allowing you plenty of range to get your temperatures right during different times of year and such! good luck!

 

[jimbro]

Bud, are the fans for input and exhaust the same size?

 

[c526]

budbgrowin has some solid advice in there---I really agree with the roof top turbine

light rails will work on anything,I have 2 600 in air cooled hoods, swinging away

keep an eye on ebay or craigslist,ive picked up cool tubes for 30 bucks,and hoods for under 50
you will save this money on a electric bill,maybe first month, for sure by second month--making money by the 3rd month

my buddy in north texas does not flower in the summer,he spends that time vegging and making trees

 

[BudBGrowin]

The exhaust should be your biggest fan if you have the more powerful fan on the input side you will hove positive interior pressure and may have smell leaks. Big fans on the way out to create negative pressure will help a lower power fan move air in.

 

[jimbro]

Thanks bud, got a 10" and 8", both 3 speeds, on the way

 

[jimbro]

Hi bud,
you've been extremely helpful with my ventilation question and I greatly appreciate it. I have the fans installed, and have one more question. Can you recommend a timer for the fans?

 

[BudBGrowin]

Get a digital one for sure. If you get a push pin style timer they will wear out and lose time eventually. I just look at any home improvement store and find one that would cover the fewest outlets on a surge protector because they are usually bulky. I have a two outlet digital timer I love using for a fan and the other for the hid light. That way my cool tube runs when the light comes on. Or you could use it to synchronize fans or use it for air or water pumps the possibilities are endless!

Either way digital timers also usually come with a battery backup and time display screen for accuracy.

 

[BudBGrowin]

Also make sure your timers work for grounded three pin style outlets.

 

[escape]

Hello people, I built a nice grow cabinet and have 2 Purple Haze and 2 #1 Skunks growing for 1 week, they seem to be doing great. I am new at this and this is my first indoor cabinet grow, I will share as much as possible, maybe I can be some help........

 

[KingJohnC]

Escape if you have a look at my KingJohnC 400 Watt LA Confidential Seed Cabinet Soil Indoor Grow Journal you can see how I have my equipment hooked up.


KingJohnC's 400 Watt LA Confidential Seed Cabinet Soil Indoor Grow Journal