Attic grow - Where to send my exhaust?

[BudSmoker]

I am building an insulated grow box to go in my attic. So far I have planned for the box to be about 40 ft3. My plans are to draw air in from a downstairs room with a huge fan and continuously replinish the box with fresh air. Maybe 6"-8"(400-600 cfm range) vortex. My main question for now is what to do with the exhaust.

Exhaust options

• Exhaust to attic - seems like a waste of air
• exhaust to outdoors - seems like a waste of air
• recirculate air back into house. - Will be scrubbing, but will my house stink?

What have you done and what do you recommend?

Bud

 

[Deviant420]

Two different setup under my belt. Both setups exhausted air outside the room 24/7 (but still in the house). Never had a problem with smell on the carbon filters.... could barely smell the fresh flowering while in the flowering room.

I would say scrub and recirculate into the house, especially with winter coming up.

 

[BudSmoker]

Thanks dev -
With the extreme temps in an attic, do you think keeping a fresh supply of air pumping through, will keep the box(well insulated) at an acceptable temp.

 

[Deviant420]

If you were matching intake/exhaust flows, I don't see why that wouldn't stay close to 'downstairs' ambient temp. I assume you mean extreme cold temps, so run the box during the night but be prepared to supplement with extra heat somehow. If extreme hot, just run intake/exhaust 24/7.

 

[BudSmoker]

Cool - During the winter months, I may be able to set the fan up on a thermostat and or use a speed controller to slow the fan down.

Also, what is meant by
"matching intake/exhaust flows"

 

[zappa66]

"seems like a waste of air"

lol

 

[BudSmoker]

"seems like a waste of air"

What is so funny about that?

If you pump 400 cfm out the window of 1500 ft2 house with 8' ceiling you are looking at 12000ft3 of conditioned air being pumped out in 30 minutes. That is emptying the entire house of air every 30 minutes 24/7. That does not seem very energy efficient for the heating/cooling system. However, my logic may be flawed.

Please enlighten me

 

[PeteWeedSeed]

my question is, how many watts are you cooling down?
after a certain amount, the grow room becomes more powerful then your furnance and you will have to blow the air outside.

it all really depends on have safe and efficient you want to be. which requires more details about your lighting, reflectors, and fans.

I understand what your trying to figure out in your calculations, but that's not exactly right.. once cold air meets heat, it becomes heat too. especially if your running the cold air over your lights..

 

[BudSmoker]

I plan on using a 250HPS.

 

[PeteWeedSeed]

LOL are you serious
a single 250 HPS?

You shouldn't worry about heat, I use a 400W in a 3x4 veg cab with a small 6" fan blowing air outside the cab.
Once you get past 400W then i'd worry about cooling and where the air goes. Just cycle the air around in the room, the A/C will overpower the heat processed.

 

[FreezerBoy]

Returning exhaust to the house is "wasted air" All that does is heat the air your cooling with.

Exhausting into the attic or outside is the effective use of air. It removes hot air from the operation. That's not a waste, it's the point.

 

[westinghouse]

LOL are you serious
a single 250 HPS?

You shouldn't worry about heat, I use a 400W in a 3x4 veg cab with a small 6" fan blowing air outside the cab.
Once you get past 400W then i'd worry about cooling and where the air goes. Just cycle the air around in the room, the A/C will overpower the heat processed.

werd, listen to this guy. A 250w hps will not produce enough heat to overpower the a/c you're going to be cycling through the grow box. So pulling the A/C'd air from the inside of the house, into the grow box, and exhausted into the attic or back into the house is a good idea.

However, if you're going to be using a carbon filter and an inline fan, and are wanting to exhaust the cycled air back into the house, you'll probably need to set it up the following way:

Inline vortex fan pulling air from the downstairs room, into the grow cab. Have the carbon scrubber inside the grow cab, and have it set up so that the scrubber has it's ducting end hooked up to the exhaust port on the cab, then the air still being pulled through the fan. This leaves the exhaust side of the fan to "push" air back into whatever room you want to push it into, using filtered air so there will be no smell. This may be easier to understand:

Going from intake to exhaust:

downstairs room -> ducting to intake of grow cab -> carbon scrubber that is hooked up to exhaust ducting to exit the cab -> vortex fan -> ducting that pushes air into whichever room in house you choose.

You just have to have the ducting port on the scrubber exiting the cab, so that when the vortex fan is pulling air through the scrubber, it's pulling air out of the cab, and it's filtering the air at the same time so that by the time the air gets to the fan, it's already been de-stinky-fied.


Hope that makes sense!

 

[BudSmoker]

Pete - Thanks. The insulated grow box will be in the attic surrounded by extreme temps. (Id say 30F-130F). My plan is to passively draw in 75F air into the grow box via a 6"-8" or even 10" if need be vortex exhaust fan. I am hoping to keep the grow box temp within 5 degrees of of inlet air temp. In essence the grow box will be a Cool tube!

FreezerBoy - Even with the volume and velocity of the air exchange, do you think the exhaust temp will be much more than the inlet temp??

 

[PeteWeedSeed]

If your using a bare bulb 250W in a ambient temp of 130, you will need to continously cycle cooled air in the cabinet and pass it outside since those are high temps, more then I thought.
Pulling air in at 75F will have to leave very soon since it's already warm, I would think a minium of 400CFM for such a small area. I would try and make more room for air.

 

[hoosierdaddy]

Growing in the attic means that the ambient temps are much greater than normal atmosphere in the summer. In the winter the temps are near the same as outside ambient if your house is insulated well.

If you truly have your box insulated properly, then the surrounding temp of the attic should not be a factor.
Taking the air from the house is always a BAD idea, in just about any situation. It may be all a grower has an option to do, but it should be avoided at all costs. Because it is a tremendous cost. You could buy herb cheaper than trying to keep up with both the house and the grow using just the house central air.
The AC wasn't designed to do that.

In summer, the air in the attic is simply too hot to use. So, the best alternative is to take it from outside. And getting air from outside when in the attic is one of the easiest, although it may seem very daunting. All you need to do is mount up a roof exhaust and you are in business.
They are cheap, come in any size and configuration you can think of, and all give detailed instructions on how to mount them. They also draw zero attention. You will need to cut a hole in the roof. For the roof man, this is no problemo, and is easy as pie. It's easy as pie for us too, we just need to get our heads right and do the deed.

You can also use the air flow items that the house has now, rather than cut a hole in the roof. At the edges of the attic, there may be flashing that has holes in it for air movement. You can fashion a way to connect a duct to suck air from there.
Or, the top of the roof may have a cap that allows air movement, and you could suck air from that space with some planning.
Also, there may be a gable vent that would be easy to get air from.

Now, when it comes to exhausting it...
I recommend exhausting right outside the box into the attic itself. In the summer, your air will create a big air exchange in the attic space, and this will allow the attic to be cooler than it would otherwise. This will increase the life of your roofs shingles dramatically.
In the winter, the exhausted air will keep the attic warmer than normal, which helps with the overall efficiency of your home system.

Don't take air from the house, and don't exhaust air into the house. The potential bad of doing that far outweighs any sort of good you may do.

 

[BudSmoker]

hoosier - I have two windows in the loft. I could easily draw air in fro the window.

How will cold outdoor temps affect the grow box temps? If i intake 30 degree air, will i just have to hook a thermostat to my fan and only vent bursts of air into the box when the grow lights heat the box to much?

Also how will the box stay warm when lights are out?

 

[FreezerBoy]

FreezerBoy - Even with the volume and velocity of the air exchange, do you think the exhaust temp will be much more than the inlet temp??

Maybe. I didn't do the math. FWIW, my cab's in a two car garage and I exhaust in same. I wish I could vent outdoors but, my architecture doesn't allow. My point was that removing air isn't wasteful, it's the idea.

This may interest you Insulated Attic Grow

 

[messn'n'gommin']

Although, these don't answer your questions directly, they may be points to consider.

• Try to locate the cab as near the leeward end of the house as possible. This will be limited by ease of attic access and what the living space below, is used for.
  
  Also, consider a thermostatically controlled attic fan. It will help to keep attic temps down which lessens overall A/C use.
  
  If you do decide to vent inside, try to locate the exhaust and intakes in separate rooms.
  
  Another option, is to vent the cab indoors and vent the lamp, via cool tube, to the outdoors (as venting to attic and venting outdoors is eventually the same thing.)
  
  As I said, just somebody's
  
  Namaste, mess

 

[BudSmoker]

My mind has been spinning today. So many options.

FreezerBoy If I vent to attic or outdoors, how much will this affect my light bill if I intake air from the house?

I have been thinking about what Hoosier said about using outdoors as intake. I thought about running a 250 or 400 HPS for flower chamber and 175 mh for veg chamber.

Check out pdf drawing here

I was thinking of staggering the lights so one is on at all times.

Notice the darkroom vents with computer fans. These will circulate are between the two chambers, so when one light is off the light from the other room can heat the unlit room.

I will have the fan set on a thermostat and draw in 40 degree air when the box temps reach 80-85 degrees or so. Have the room cool back down with the fresh air down to 70-75 degrees or so. I will use a damper on the intake so the computer fans will not draw in from outdoors.

Does this look like it would work?

 

[FreezerBoy]

FreezerBoy If I vent to attic or outdoors, how much will this affect my light bill if I intake air from the house?

An electric fan will raise your electric bill. Will a cooler bulb use less electricity? I don't know but, I doubt it would use more.