??? about light burn & my vent fan

Hello, i searched through some threads but my questions are kinda specific. I have the Jorge Cervantes bible and it's great but i can't find much in it about my situation and this site seems to have some knowledgable people.

First off, i'm not positive of my girls exact age but i got the clones 2 weeks ago. I decided to veg. only the first week so they've been flowering for 1 week now. When reaching for the light, the tallest plants are about 14in. For the most part, they seem very healthy. The only major issue right now is light burn (knock on wood).

I have 2 - 1,000W hps. Right now i'm only running 1 of them because the girls are still so young. My room temp. usually stays around 70 during the day and 60 at night. I have a intake fan bringing fresh air in constantly but i haven't started running the vent fan continuously yet because i don't have an odor problem yet and the vent fan sucks air through my carbon filter. I'll get back to that later.

Anyway, my girls have been getting a little bit of light burn on the upper leaves. So, i've been raising the light to compensate for their growth but i feel like the light is already kinda far away. I realise how hot 1,000s get but right now the light is 4ft. 7in. from the top leaves. Is this typical???

The one other factor which i've been scratching my head over is my vent fan. Obviously i'm kinda new to this, but i did buy good equipment, so i got that goin for me. My room is approx. 960 cf. and my vent fan is rated at 1,050 cfm. A couple times a day, i will run the vent fan to cycle the stale air out of the room. Once i have an odor problem, i was planning on running it constantly.

The thing is, after running the vent fan for about an hour, the leaves seem to droop. Like they're not reaching for the light anymore. When i shut the vent fan off, the leaves start reaching for the light again. I know the filter should be hung from the ceiling but i have a bad back so mine is just standing with the vent fan a few feet above it on the wall (connected by ducting of course). Some people say it's ok as long as the vent fan is powerful.

Any opinions or advise is greatly appreciated and i'm sorry that my first post here is so long winded. Thanks in advance!!!!!!!!!

Dude, something's not right there. a 1000 watt light at 55" away! You say your temp is 70F during the day??? Those plants are going to stretch for sure, looking for some light. That light should be anywhere from 14" to 24" away. That 1000 HPS generates approx. 3420 btuh (heat).
Moving 750cfm constantly would raise your room temp about 4 degrees over the ambient temp.

Thanks for the quick response. OK, are you saying that if i run the vent fan, it will raise the temp of the room? I thought running the vent (exhaust) fan would drop the temp by venting hot stale air.

Edit: The leaves droop when i run the vent fan. So if it gets rid of the hot air around the HID, i guess i can drop the light without burning leaves? Sorry if i'm being redundant.

I am saying, that if you have a vent(s) as an inlet, and exhaust with a fan, exhausting the air at 750cfm, it'll only raise the temp about 4 degrees. Your inlet vent needs to be atleast 1.5 times the size of the exhaust.
You also may want to consider air cooling that light.
Peace

Absorb_intel said:

Thanks for the quick response. OK, are you saying that if i run the vent fan, it will raise the temp of the room? I thought running the vent (exhaust) fan would drop the temp by venting hot stale air.

Edit: The leaves droop when i run the vent fan. So if it gets rid of the hot air around the HID, i guess i can drop the light without burning leaves? Sorry if i'm being redundant.

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How are measuring the temp? Do you have a sensor that you place at the highest point or tallest part of your plant? That is how to tell how your plants feel. Just because the room is 70 doesn't mean that the plants are 70. My thermometer has a remote sensor that I place on a stick that I can raise of lower depending on my plants height. That way I know their temp. not the temp of the room. Also you could have heat leakage around your hood unless you have one that has a gasket or other type of air proof seal.

Thanks for the replys. I may just have some heat leakage because i don't believe there is a seal. The hoods are "sun systems". Pock marked aluminum rectangle. They have a hole for the bulb to slide threw.

I guess i should go to the store and talk with the guy who sold me everything and find out what i'm doing wrong..

Edit: The guy who sold me the equipment said i should be continuously running the vent fan and that it would cool down the room by venting the hot air around the light. He also said clones that were originally grown under fluorescent lights, will often get leaf burn while adjusting to the HIDs. Raise and lower them accordingly.

This edit is mostly for future readers with similar questions.

They're sleeping now but i'm definatly moving it closer when they wake.
BTW VideoMan, i think i understand what you meant now after reading another thread.

If i have 2,000w of light multiplied by 3.2 = 6,400. Now, 6,400 divided by my fans cfm which is 1,050 = 6 remainder 100. Therefore i can determine that the 2,000w of light i plan on using will raise the temp by 6 degrees. Is that right?

Yeah dude, you did good. I get 6.09 as the answer. So basically your temp should rise 6 degrees from the temperature of the air you are bringing in the room.
Peace

I am not sure why, but the formula never has worked for me. I have 800w and about 650 CFM of venilation (at least accoording to the info on the fans) and I get a 28(f) difference in temp. Any thougths? I run at about 95 when eveything is on.

I would agree. I have three fans. One large 500CFM, and two smaller ones.

littlepuppet2002 said:

Dude, your vent fan is killer for your room size. Now I can't remember the formula, but with the cfm's your fan has, you should have it on for about 4 minutes!!! Is your 1000w light tied into your vent fan and carbon setup? Anyways, your fan is sucking all the air out of the room choking the plants. So several minutes of running your fan will completely clear the air out of the room.

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Thats what i thought (the vent fan is sucking air out to fast and choking the plants). The guy who i buy equipment from said i should run it all the time though. Hes really experienced but i have my doubts.

I started running an oscillating fan tonight and it's helping with the light burn factor. I also moved my light closer. I think the 1,000s just get to damn hot. I need to air cool them, just not sure how i'm gonna do it yet. Any opinions.