New Grow Cabinet - Heat Issues

Hey Everyone,

I just recently built a grow cabinet (4'x4'x2.5') and I am having some heat issues.

What I have done is finished the box but have not put anything in it as I am doing a "test run" to make sure that I get the temperature right before putting plants in it.

My cab consists of:

1 - 400w HPS
1 - 120cfm bath fan installed into the top of the box
1 - Normal fan mounted near the bottom that is just blowing air.
1 - 30" x 6" Return Air Grill (passive intake) mounted to the bottom of the back of the cab.

I am just exhausting the bath fan into the same room that the cab is in, not outside. I currently have the cab inside my garage which is much cooler than my house and I have not opened any windows because the temp. here is around 86 degrees F.

Anyways, sorry for rambling on... the cab temp is at around 92 degrees F. Any ideas on what I can/should do?

Thanks in advance!

Two suggestions:

1) Buy an intake fan, and hook it up an AC duct, or window unit
2) Buy a fan that can pull more CFM. At least double what you're using now.

Also, get that hot air away from you cab, it will help by at least 2-3 degrees.

dubwooze said:

Two suggestions:

1) Buy an intake fan, and hook it up an AC duct, or window unit
2) Buy a fan that can pull more CFM. At least double what you're using now.

Also, get that hot air away from you cab, it will help by at least 2-3 degrees.

Click to expand...

Thanks for the suggestions dubwooze! I can't hook an intake up to an AC because I don't have AC in my garage at the moment and buying an AC unit is just not within the budget. I guess I will have to buy another bath fan and give that a go.

Another quick question for you... I plan on doing a SOG grow and having between 36-48 plants in the cab. Will this increase the temperature dramatically or will it be minimal?

Thanks again!

That's a good question. I only have limited experience, but from the research I've done and what I know from observing friend's and room mate's grows, I'll attempt to answer. The temperature shouldn't be effected much at all, but when you flower the humidity will jump drastically. So, purchasing a dehumidifier may be in your future. Also, if you don't have access to AC, you might need an extremely strong fan, 300-400 CFM.

I almost forgot. If you vent your air outside, it could help with the temp too and you're garage won't get hot.

Check out my grow journal. I just started flowering tonight!

Yeah I was actually thinking the same thing about the dehumidifier.

I would love to exhaust outside but it doesn't really work in my situation. I am actually thinking about venting outside, through the window. The problem I'm having is that I'm trying to come up with a way to secretly vent the exhaust hood (or duct) out the window. I'm actually just in the midst of googling that topic right now.

BTW - I will definitely be following you thread. Subscribed! Everything is looking really good so far!!

a dehumidifier will make it ungodly hot... trust me.

your problem is your fan, you need at least 180 cfm to cool a 400w effectively.

passive intakes on the bottom of the cab, or as close to the bottom of the cab will pick up cool air from the floor...

putting the fan at the top, blowing out, with a passive intake at the bottom,is the most effective way to remove the heat.

and a little a/c goes a long way.

Yourztruly said:

Yeah I was actually thinking the same thing about the dehumidifier.

I would love to exhaust outside but it doesn't really work in my situation. I am actually thinking about venting outside, through the window. The problem I'm having is that I'm trying to come up with a way to secretly vent the exhaust hood (or duct) out the window. I'm actually just in the midst of googling that topic right now.

BTW - I will definitely be following you thread. Subscribed! Everything is looking really good so far!!

Click to expand...

dryer flex duct..... slilver metallic duct tape... and some good carboard (for flanges)

Yourz, what are temps inside the garage? You don't say that the lamp is air cooled so I assume that it is not. Is that an option or do you have one of those batwings? I find that the dehumidifier pushes the room temps about 7 deg, if you run it in the garage on an opposite 12/12 when you are in flower it's not that bad just run the machine when the lights are off. You will need a better fan to exchange the box air with room air, lots of it. Last, 40 plants in 16 sq feet? I would re think that, 2.5 plants per sq foot?

IAm5toned said:

a dehumidifier will make it ungodly hot... trust me.

your problem is your fan, you need at least 180 cfm to cool a 400w effectively.

passive intakes on the bottom of the cab, or as close to the bottom of the cab will pick up cool air from the floor...

putting the fan at the top, blowing out, with a passive intake at the bottom,is the most effective way to remove the heat.

and a little a/c goes a long way.

Click to expand...

Thanks IAm5toned,

I do have the bath fan in the top of the cab and the passive intake at the very bottom of the back wall. So, I'm sure you are right about needing a more powerful fan which is what I'm going to go get. Well, actually I'm just going to add another 100 or 120 cfm fan.

ow.douglas said:

Yourz, what are temps inside the garage? You don't say that the lamp is air cooled so I assume that it is not. Is that an option or do you have one of those batwings? I find that the dehumidifier pushes the room temps about 7 deg, if you run it in the garage on an opposite 12/12 when you are in flower it's not that bad just run the machine when the lights are off. You will need a better fan to exchange the box air with room air, lots of it. Last, 40 plants in 16 sq feet? I would re think that, 2.5 plants per sq foot?

Click to expand...

ow.douglas,

The temp in my garage is about 68 degrees F. No, I don't have a cool tube, but believe me I would love one! I currently am using an old light and ballast from our old Greenhouse. It is quite big (and ugly) and has the ballast and light all connected in the same enclosure. I actually planned on taking it apart and separating the ballast from it and making a DIY Cool Tube but came to realize that the ballast is WAY too complicated to take apart.

Actually, my cab is only 10 sq/ft, not 16. I am planning on going with 3.5-4 plants per sq/ft ONLY because I seen someone who was VERY successful with this. Here's the link:

http://www.icmag.com/ic/showthread.php?t=27982

If you click on the links at the top of his thread it actually shows the box in action, not just the building of the box.


Thanks for the reply and help.

That is a lot of plants, it will definitely be a sea of green. What type of genetics are you using, clones, seeds, bag seed? I wonder if a thick canopy, produced by that many plants would slow, or prevent circulation. Another thing, you have to consider the differences in equipment between you and the grower in the thread. Did he have AC, what CFM was he moving out? I'd suggest, though they're pricey a good squirrel cage fan that can push some serious air, especially if you hook up a carbon filter to it, which you should definitely do if you move the air outside. Check out my journal to see how I hid my ducting that went outside.https://www.rollitup.org/grow-journals/349121-bit-late-but-finally-made.html

Also, you're right, you need to get that ballast out of your box, it'll help decrease the temps a little.

Yourztruly said:

ow.douglas,

The temp in my garage is about 68 degrees F. No, I don't have a cool tube, but believe me I would love one! I currently am using an old light and ballast from our old Greenhouse. It is quite big (and ugly) and has the ballast and light all connected in the same enclosure. I actually planned on taking it apart and separating the ballast from it and making a DIY Cool Tube but came to realize that the ballast is WAY too complicated to take apart.

Actually, my cab is only 10 sq/ft, not 16. I am planning on going with 3.5-4 plants per sq/ft ONLY because I seen someone who was VERY successful with this. Here's the link:

http://www.icmag.com/ic/showthread.php?t=27982

If you click on the links at the top of his thread it actually shows the box in action, not just the building of the box.


Thanks for the reply and help.

Click to expand...

not really... theres 3, maybe 4 parts. a ballast core (the heavy one) a capacitor(and on an HPS light there is also an ignitor) and a lamp socket.
number any wires you have to cut with a sharpie; on both sides of the cut, to avoid confusion later on....

Hi guys,

I doubt any of you will read this anymore but I just wanted to thank-you for your interest and your help. I have been away for about a week and haven't really had time to post anything on RIU until today.

Thanks again and sorry to just leave you hanging!

Yourztruly said:

ow.douglas,

The temp in my garage is about 68 degrees F. No, I don't have a cool tube, but believe me I would love one! I currently am using an old light and ballast from our old Greenhouse. It is quite big (and ugly) and has the ballast and light all connected in the same enclosure. I actually planned on taking it apart and separating the ballast from it and making a DIY Cool Tube but came to realize that the ballast is WAY too complicated to take apart.

Actually, my cab is only 10 sq/ft, not 16. I am planning on going with 3.5-4 plants per sq/ft ONLY because I seen someone who was VERY successful with this. Here's the link:

http://www.icmag.com/ic/showthread.php?t=27982

If you click on the links at the top of his thread it actually shows the box in action, not just the building of the box.


Thanks for the reply and help.

Click to expand...

I believe that is too many plants per SQ ft, unless you are going to grow one cola per plant on a stake support and use (4) 6" square pots per sq'. You maybe able to grow 2 colas per plant if topping, since you have 400w of light in that small space. You have to get rid of the heat or got with a smaller light.

Good luck and let's see some pics!