Still too hot

runnung a 600watt HPS with a 420 cfm fan in a 4.5 x 2 x 7 closet with negative pressure system and a hooded sealed light. Outside the room is 74degrees and inside the room it hits 84-86
Why is there such a difference?
Should i try to get some cold air in there through my central AC by providing a small 4 inch tie in to my existing ductwork in the crawl? BUT, I was afraid the negative pressure in the room could mess with my central AC airflow but i dont know

ANY IDEAS??

ANYBODY ??

Is your thermometer sitting in direct light? 74f might just be too high of a starting point for a 600 in such a small area.

Don't know much about your AC ducting system but your 420cfm should be able to handle the pressure difference just fine. Is the room the tent is in climate controlled? It seems like an awful lot of effort if 86 is the worst you're worried about. A lot better than mine in this goddamn heatwave. I'm at 97 in a 2x2.5x7 w/ 250watt LEDs and a 400 something cfm and 3 computer fans, a D battery fan, bathroom fan and bigass ice packs hung up near the lights that I keep rotating. It isn't much cooler outside the tent. Tomorrow I'll probably have to dig out an AC unit. Your idea is certainly ambitious and I would go for it myself if I were in that position. Good luck.

If you've got central A/C have you considered using an inlet fan to push the cold air from your room into your tent

SPL hit the nail on the head. Where the thermometer is positioned would be key before doing anything else.

What do you have for intake? I assume its passive, but is it enough for the extractor to function to its full potential?

Do you have circulating fans in between the glass and canopy?

They can be positioned to help blow the trapped heat away and up to be picked up by the exhaust.

Where should the thermometer be positioned? I covered it with a small amount of dirt. I'm still getting readings in the 90s... Today will be hot again. The plant seems to be doing fine though. I don't see much new growth but the stalk is much thicker and the leaves got big.

Lighter404 said:

Where should the thermometer be positioned? I covered it with a small amount of dirt. I'm still getting readings in the 90s... Today will be hot again. The plant seems to be doing fine though. I don't see much new growth but the stalk is much thicker and the leaves got big.

Click to expand...

I keep the sensor to my temp/humidity gauges hanging right over the canopy under the lamp.

You can see the remote sensor hanging from the white wire.

Just took this before lights out in a minute.

SPLFreak808 said:

Is your thermometer sitting in direct light? 74f might just be too high of a starting point for a 600 in such a small area.

Click to expand...

That is an interesting subject
When you take a black plastic thermometer/ humidity reader and place it under the light at 20 inches it reads 92 degress. BUT I believe that is a false reading because all that is happening is the light is heating up the black plastic case of the thermometer and as you know black plastic will get very hot under a light.
So I took my digital instant read thermometer and placed it in the same position and i get readings of 79-81 degrees
At 14 inches from the light and placing the end of the probe under a leaf with the digital probe i get readings of 82
But i do leave one thermometer sitting on top of the light to read the hottest air at the top of the grow room and that is the one that gives me readings of 86 degrees

MichiganMedGrower said:

I keep the sensor to my temp/humidity gauges hanging right over the canopy under the lamp.

You can see the remote sensor hanging from the white wire.

Just took this before lights out in a minute.

View attachment 3960173

Click to expand...

Where did you get that sensor?

MichiganMedGrower said:

Do you have circulating fans in between the glass and canopy?

They can be positioned to help blow the trapped heat away and up to be picked up by the exhaust.

Click to expand...

I have 3 fans in there and one on the floor oscilates

oldcarp said:

That is an interesting subject
When you take a black plastic thermometer/ humidity reader and place it under the light at 20 inches it reads 92 degress. BUT I believe that is a false reading because all that is happening is the light is heating up the black plastic case of the thermometer and as you know black plastic will get very hot under a light.
So I took my digital instant read thermometer and placed it in the same position and i get readings of 79-81 degrees
At 14 inches from the light and placing the end of the probe under a leaf with the digital probe i get readings of 82
But i do leave one thermometer sitting on top of the light to read the hottest air at the top of the grow room and that is the one that gives me readings of 86 degrees

Click to expand...

Bang on. Your still getting a high reading with a thermometer on the light or just above, just the way heat rises. If your getting reading from 79-82 under the light then your not going to have a problem.
Isn't it crazy that some manufacturers make thermometers in black plastic I the first place!! '

http://cannabis.com/faqs/growing/growroom-how-do-i-measure-temperature-correctly.html

coreywebster said:

SPL hit the nail on the head. Where the thermometer is positioned would be key before doing anything else.

What do you have for intake? I assume its passive, but is it enough for the extractor to function to its full potential?

Click to expand...

my intake comes from the room the closet is in which is 74 degrees. I am using a 6 inch 420 CFM fan with one baffel at the end of the fan as it goes into the attic9 for stealthyness
I am using insulated ductwork to connect everthing because i am trying to be as stealthy as possible, but i am wondering if i might be getting too much restrictions when the light is all the way at the top of the closet because it is now two feet of compressed ductwork vs 4-5 feet when the light comes back down for the veg stage of growth. Would the smoother all metal non insulated duct be that much louder? I know that it would probably move more air but Stealth is a must!

coreywebster said:

Bang on. Your still getting a high reading with a thermometer on the light or just above, just the way heat rises. If your getting reading from 79-82 under the light then your not going to have a problem.
Isn't it crazy that some manufacturers make thermometers in black plastic I the first place!! '

http://cannabis.com/faqs/growing/growroom-how-do-i-measure-temperature-correctly.html

Click to expand...

Thats what i always thought and yet you still see plenty of other growers out there showing pictures of their black plastic thermometers! Thanks for the reply coreywebster!!

So what your saying is when in flower the light is raised and ducting compressed and when in Veg you fully extend the ducting so the light comes lower down. You could instead shorten the ducting and raise the plants to the light in veg. Keeping the ducting smooth. Rather than bring the light up and down. But in honesty I don't think your fan will struggle even if the ducting isn't pulled tight because its still relatively a short length.

oldcarp said:

Thats what i always thought and yet you still see plenty of other growers out there showing pictures of their black plastic thermometers! Thanks for the reply coreywebster!!

Click to expand...

First time I saw a black one was on here a year ago. I couldn't believe it. Some guy was panicking because he was hitting 90degrees C 6inch under a 600w hps.. He was going to give up trying to grow. Pulling his hair out.. I think it ended up about 78 degrees when he moved the thermometer above the light line.
No worries BTW, wish you all the best with this grow and the many that follow.

I've been moving mine all over the place trying to get a reading that doesn't freak me out. The plant is in veg and doesn't look like it will die, but I just can't seem to be able to lower the temps much. I have a 6in hyperfan and it's turned most of the way down cuz my small grow tent looks like it will implode, walls sucking in at least 3in. Also last night it was dead calm and I grew paranoid neighbors and people on the street might hear it if I turned it up higher. Would jacking it up make a difference? It's actually cooler in the tent than the room it's in and outside too. With the lights off. Yesterday w/ lights on it got up to 97 if I can believe that thermometer.

Lighter404 said:

I've been moving mine all over the place trying to get a reading that doesn't freak me out. The plant is in veg and doesn't look like it will die, but I just can't seem to be able to lower the temps much. I have a 6in hyperfan and it's turned most of the way down cuz my small grow tent looks like it will implode, walls sucking in at least 3in. Also last night it was dead calm and I grew paranoid neighbors and people on the street might hear it if I turned it up higher. Would jacking it up make a difference? It's actually cooler in the tent than the room it's in and outside too. With the lights off. Yesterday w/ lights on it got up to 97 if I can believe that thermometer.

Click to expand...

If you have a powerful fan but are worried about the noise you might want to consider getting a baffell They are a lot less restrictive than the old days and boy do they make a difference in sound! And make sure you have a fresh air vent coming into yout tent as well
Dont use a black plastic thermometer! Get one of those digital instant read cooking thermometers from walmart for about 12 bucks

I would like to have one of those thermos that Michigan medgrower is using in his picture, just because he has one and I dont ( its a man thing LOL )

oldcarp said:

If you have a powerful fan but are worried about the noise you might want to consider getting a baffell They are a lot less restrictive than the old days and boy do they make a difference in sound! And make sure you have a fresh air vent coming into yout tent as well
Dont use a black plastic thermometer! Get one of those digital instant read cooking thermometers from walmart for about 12 bucks

I would like to have one of those thermos that Michigan medgrower is using in his picture, just because he has one and I dont ( its a man thing LOL )

Click to expand...

Heh, I think that's the same one I have actually. A growbright? I've got a 4in intake from the outside, pulled in w/ a 50cfm bathroom fan just to boost it a little bit. While noise wouldn't be as much of an issue at the moment it does weird me out when the tent is buckling in. Like the walls suck in so much you can see a 360 outline of the support poles and that ain't even halfway. I have a feeling this summer will be a scorcher.