New cab reaching 90+ degrees w/ low humidity

Hey all,

I just got my homemade cab up and running, two seedlings in DWC. The interior of my cab is 23"x27"x63". I have an S360 Advance Spectrum MAX LED with a 4" fan/filter combo. I've put in two 4" passive intake holes at the bottom of the cabinet. Unfortunately, the best place for this is upstairs in my spare bedroom, where traffic is rarely anyone but me. The room itself sits in the mid 70's with 30-40% humidity range. However, with the light running in the cab the temp is peaking past 90 degrees and the humidity is dropping to around the 20% area.

I was thinking of getting a swamp cooler for the room, but from what I've read the higher humidity outside the box would make it less effective. I'm dreading the idea of having to install a window unit, but it may come to that... The LED puts off a surprising amount of heat, should I bring my carbon filter down next to it to help pull that heat away from the plants? I have a small 6" fan blowing air up at the light in an attempt to help it get to the filter at the top of the box. There's no room for an A/C unit or anything inside the cab.

Any help would be greatly appreciated!

journalreader said:

but from what I've read the higher humidity outside the box would make it less effective.

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A swamp cooler is definitely more effective with dry air, this is why you only really see them in arid climates. An AC unit is best for cooling, a swamp cooler is best as a humidifier.

get a bigger fan and a reducing coupler to fit to your 4" exhaust.

where are you venting to?

filter>>extraction ducting>>extraction fan>>vent ducting, is this a rough diagram of your setup?

A LED light shouldn't make that much heat, is that one of those blurples?

Dr.J20 said:

get a bigger fan and a reducing coupler to fit to your 4" exhaust.

where are you venting to?

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Venting out the top into the room. I know its definitley compounding the problem, but Im trying to still keep it somewhat stealth in case random company stays the night. Wouldn't using a reducing coupler make it so that it can only pull as much air through thr ducting as the previous fan since its the same diameter? Do you have any recommendations for 6"?

Dr.J20 said:

filter>>extraction ducting>>extraction fan>>vent ducting, is this a rough diagram of your setup?

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That's correct

Renfro said:

A LED light shouldn't make that much heat, is that one of those blurples?

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It does have a slight purple light, but not sure about the blurple you're talking about. Here is the product link.

Thanks again for your replies!!

Really without pictures it's difficult to see a problem.

journalreader said:

Wouldn't using a reducing coupler make it so that it can only pull as much air through thr ducting as the previous fan since its the same diameter? Do you have any recommendations for 6"?

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Reducing is definitely going to kill flow. If anything you want to oversize a duct run to make up for length / bends. A single bend will kill 15% of the CFM. Four or five bends and you have a dead end lol.

A larger exhaust fan would increase the flow through the cab. If it is 75 outside the cab and 90 inside the cab we are lacking enough flow to equalize the temperatures better. With intake air at 75 and LED lighting you should be able to get temperatures down to 83 - 85 if you have enough flow. I would first see if there is something killing flow. Perhaps add a third passive intake as we like to size a passive intake with 2.5x the area of the exhaust.

How many CFM is the fan rated for? Is it centrifugal? Axial and mixed flow types don't cope with static pressure loss as well as centrifugal.

journalreader said:

It does have a slight purple light, but not sure about the blurple you're talking about. Here is the product link.

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Just trying to figure out why it makes so much heat. Blurples are the nickname we gave the LED lights that have the red and blue diodes. The efficiency isn't that great on many of those and therefore they make more heat per watt than a higher quality LED. I have noted that many users with such lights have heat problems.

Its a 270w light, so its going to heat up a small space.
You could of spent half that money on a light twice as good and ran with 120-150w light , if it were more efficient.

End of the day you need to use a fan that does what its supposed to. Some fans wont pull air through a piss flap
Lots of silly fans that don't perform on the market these days.

You want a good fan and you want to vent outside.
You want to shade your thermometer from direct light, especially if the LED has ir diodes

Post a link to the fan you have currently please.

coreywebster said:

Some fans wont pull air through a piss flap

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Love it! So true. Piss flap... lol

Changing to a 120w-140W light would reduce temps and increase humidity. You could ask for suggestions in the LED/lighting forum.

coreywebster said:

Its a 270w light, so its going to heat up a small space.
You could of spent half that money on a light twice as good and ran with 120-150w light , if it were more efficient.

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It claims a 9 sqft flowering footprint, that means only 30 watts per sqft. I would say that might be good if the light was a HLG diablo board or equivalent light. I suspect that with that particular lights lower efficiency (putting out heat instead of light) a 40 - 45 watt per sqft number would make for better flower, of course cooling the excess heat would be required.

I am getting 4.3 sqft when I run the math on his cab dimensions. With his light thats about 62 watts per sqft. I would think he could dim the light down to the 40 watt per sqft level and have less heat.

Renfro said:

Perhaps add a third passive intake as we like to size a passive intake with 2.5x the area of the exhaust.

How many CFM is the fan rated for? Is it centrifugal? Axial and mixed flow types don't cope with static pressure loss as well as centrifugal.

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coreywebster said:

Its a 270w light, so its going to heat up a small space.
You could of spent half that money on a light twice as good and ran with 120-150w light , if it were more efficient.

End of the day you need to use a fan that does what its supposed to. Some fans wont pull air through a piss flap
Lots of silly fans that don't perform on the market these days.

You want a good fan and you want to vent outside.
You want to shade your thermometer from direct light, especially if the LED has ir diodes

Post a link to the fan you have currently please.

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I have a 4" passive intake on the back wall connected to ducting, a 4" passive on the floor running power, and two 3/4" passive intakes near the doors.

Fan is rated at 190cfm, heres the link: https://growace.com/fan-filters-co2/fan-filters/yield-lab-4-inch-190-cfm-duct-inline-fan-with-6-carbon-filter-ducting-and-clamps.html

The light is definitley the problem, I can feel the heat radiating off of it. Fan works pretty well, can feel it blowing out hot air but doesn't seem to make a difference. Maybe if I attached my filter to a pulley system to lift/drop so it stays close to light? Here's some pics.

journalreader said:

Maybe if I attached my filter to a pulley system to lift/drop so it stays close to light?

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Leave the filter up high where the hottest air is located. Hot air rises.

That power strip on the floor is an accident waiting to happen.

Just Be said:

That power strip on the floor is an accident waiting to happen.

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Lol you're telling me. Temporary measure until my new one comes in!! Hanging on the wall.

Fan seems legit, not what I was expecting to see.

However you shouldn't have the thermometer in direct light. Same reason weather stations don't, light radiation heats up the thermometer. Throws off the reading.

You may be able to remove the air pump and place it remotely outside the space too?

Lights like that are made with minimal heat sink so they have to run active cooling which means they blow hot air out which is very easy to notice.

I don't suppose you can return the light?

If you have access to a handheld anemometer, you can measure the velocity of the air exiting the exhaust duct. Convert whatever number you get into feet per minute.

Do a little math and we get an area of 12.5 square inches on the 4 inch duct, lets just call it 12 square inches since it's accordion duct. Thats one square foot.

So if we take the linear speed of the air exiting the 4 inch duct and its 60 feet per minute, x 1 square foot, we get 60 CFM.

In this manner we can determine exactly how well the system in performing.

coreywebster said:

However you shouldn't have the thermometer in direct light. Same reason weather stations don't, light radiation heats up the thermometer. Throws off the reading.

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Indeed. If he makes a little shield, like a small circle of cardboard that will shade the probe from the direct light then he can hang it off to the side but still have it at canopy level.

Renfro said:

Indeed. If he makes a little shield, like a small circle of cardboard that will shade the probe from the direct light then he can hang it off to the side but still have it at canopy level.

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I popped mine into a discarded spark plug box.

Just Be said:

I popped mine into a discarded spark plug box.

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As long as it's open, the IR light heats up the box (like a car in the sun).