Closet Temps and Ventilation

Hi all. I have a small closet that's 2ft by 3.5ft and 8ft tall. I have a 4in 205CFM extraction fan mounted to the top of the closet that sucks air out. I cut a hole in the wall and ran 4in ducting to a window in the room the closet is in. At the bottom of the closet door I have cut 2 4in holes to provide passive intake. For lights I have 2 Vero 29 cobs being driven by a 250w meanwell driver.

But no matter what I struggle to keep the temps under 80f. I end up dimming the lights 50% and opening the closet door. The temperature in the room outside the closet stays around 70F.

How much passive intake do I need? Will cutting more holes in the door help? The closet is less than 80 cubic feet and the fan does 205cfm so it seems like that is enough?

To get say for example a 7 degree rise from ambient you need about 75-100 cfm extraction ( that's taking into account a filter too) . Your 2x 4" passive intake should be fine to keep up with extraction.

There must be something wrong with your set up.

Can you take some pictures and link the fan you are using.
Where is the thermometer? How many circulation fans and where? Filter?

BTW low 80s is fine with cobs.

Thanks for the response!

coreywebster said:

Your 2x 4" passive intake should be fine to keep up with extraction

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That's what I thought... seriously starting to feel like I took crazy pills haha.

The fan I'm using I bought off Amazon https://www.amazon.com/gp/product/B00D7M6692/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 , I *swear* when I bought the fan it claimed 205CFM where it's only saying 190CFM now... but either one should be enough for my closet I'd think. I'm running the fan with NO filter so I'm not loosing CFM from that.

If you notice in the ceiling there's some holes(2 4in holes) that I've covered up. They go into the attic which is hot. Can hot attic air "fall" down? I just covered the ceiling with in some reflectx reflective bubble stuff that's supposed to offer some insulation, but I don't have much confidence in it doing much.

Here's some pics:

The heat coming down will only happen if your passive intake cant pull from anywhere else.

You need that ducting connecting to one of those holes. The heat needs to leave your grow space or it will be recycled and get warmer by every pass through your tent.

Extracting to the loft is not ideal due to humidity but if its your only option then do that.

In a rush pre work, will check back in for a better look later.

Wicked0ne said:

Thanks for the response!


That's what I thought... seriously starting to feel like I took crazy pills haha.

The fan I'm using I bought off Amazon https://www.amazon.com/gp/product/B00D7M6692/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 , I *swear* when I bought the fan it claimed 205CFM where it's only saying 190CFM now... but either one should be enough for my closet I'd think. I'm running the fan with NO filter so I'm not loosing CFM from that.

If you notice in the ceiling there's some holes(2 4in holes) that I've covered up. They go into the attic which is hot. Can hot attic air "fall" down? I just covered the ceiling with in some reflectx reflective bubble stuff that's supposed to offer some insulation, but I don't have much confidence in it doing much.

Here's some pics:

Click to expand...

Your thermometer is in the wrong place.

I will explain why.

Light heats the surface of everything it falls on, but it doesn't (to any major degree) heat air.
Its the air temp you want to be measuring, you will get false readings placing a thermometer in direct light.
It should be above the light line, in shade, air circulating. Not directly below the light, not directly above the light, Level with your light on the wall.
Plants can tolerate much higher radiant temps.

PS, ignore my last post, I misunderstood how your duct was set up, had just woke up. So I gather you are removing the heat via the window.

Move the thermometer to the correct place, see how it looks then.

I'm reading temps from both that thermometer and a raspberry pi(you can see it hanging in the middle pic. I'll try to move the sensors out of the light, I always assumed temps should be measured around canopy height.

When the lights come in a few hours I'm going to move the thermometers and hope for the best. I just hate having to turn the lights down and leave the door open in order to maintain under 80...

Thanks again and I'll report back what the temps read in the new positions.

Wicked0ne said:

I'm reading temps from both that thermometer and a raspberry pi(you can see it hanging in the middle pic. I'll try to move the sensors out of the light, I always assumed temps should be measured around canopy height.

When the lights come in a few hours I'm going to move the thermometers and hope for the best. I just hate having to turn the lights down and leave the door open in order to maintain under 80...

Thanks again and I'll report back what the temps read in the new positions.

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I like to put a sensor just under canopy level occasionally, too. Other poster is right, you will get false high temps from radiant heat when they are right under the light, whereas ambient temps are significantly cooler.

The acceptable ambient temperature range depends on your RH, too. High relative humidity will allow plants to tolerate and even prefer higher temperatures, check out Vapor Pressure Differential, VPD, when you want to take it to the next level. I should manage my vpd a little better, but I am not Mr. Min-Max Everything.

After moving the sensor about halfway up my temps are still high. The sensor on the wall reads 81F, floor sensor is 85F and it's currently night and 60F outside with my ac running at 66F. The exhaust fan is running at 100% and the door is closed.

I really have no idea where the heat is coming from or why it's so hot in there. This house sucks and has super thin walls, but I lined the closet with foam insulation board. The ceiling has reflective bubble insulation stapled to it and the floor of the closet has a unfurnished rootcellar under it that stays cool during the day. Though... I don't recall if there is insulation under the floor/on the cellar ceiling. Even if the cellar remains cool, could there still be heat rising into the closet if there is no insulation in place?

Just a thought. Add a intake fan to bring more cool air into the closet.

CAPT CHESAPEAKE said:

Just a thought. Add a intake fan to bring more cool air into the closet.

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At one point I had two of these https://www.amazon.com/gp/product/B009P0R6VC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 on the intake's and back then, they did not make too much of a difference. I'll try to stick a little desk fan I have aiming at the intake holes and see if it helps push more air in.

CAPT CHESAPEAKE said:

Just a thought. Add a intake fan to bring more cool air into the closet.

Click to expand...

Exactly what I was going to suggest if the heat continues to be an issue. Cooling is a combo of extracting hot air and replacing hot air with cooler air, since the temps outside the room are 70F, an active intake should provide some options, with a variable controller even better, you can use one or both to "dial" the space in.

GroErr said:

Exactly what I was going to suggest if the heat continues to be an issue. Cooling is a combo of extracting hot air and replacing hot air with cooler air, since the temps outside the room are 70F, an active intake should provide some options, with a variable controller even better, you can use one or both to "dial" the space in.

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X 2 @ GroErr. You just have to get more of that 70 degree air into the grow area.

Wicked0ne said:

I really have no idea where the heat is coming from or why it's so hot in there. This house sucks and has super thin walls, but I lined the closet with foam insulation board.

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The insulation board could be the problem, it's retaining heat therefore insulating and trapping heat.

CAPT CHESAPEAKE said:

Just a thought. Add a intake fan to bring more cool air into the closet.

Click to expand...

It's all about air exchange.

Wicked0ne said:

But no matter what I struggle to keep the temps under 80f.

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coreywebster said:

BTW low 80s is fine with cobs.

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Recommended air temps under LED are low to mid 80's. LEDs don't produce infrared like HPS etc, so leaf temps are lower under LED.
https://www.blackdogled.com/lst
http://www.just4growers.com/stream/temperature-humidity-and-c02/vapor-pressure-deficit-the-hidden-force-on-your-plants.aspx
https://www.rollitup.org/t/leaf-temps-under-led-lec-hps.965610/

I kinda have/had the same problem as you do.

Do you have any circulation fan inside the closet? I cut like 3-4f by putting a fan circulating the air coming in from the passive intake.