How much does the size of the exhaust hole matter?

I am on 18/6 in a 12' by 12' upstairs room. Recently I've been buying larger fans to accommodate the heat but I'm having problems with ducting/exhaust sizes. All my old fans have 4" openings for exhaust and I bought hoods with 4" exhaust holes. I've started been buying inline fans with higher cfm, recently bought one around 700cfm with 8" exhaust holes, but all my hoods only have 4" openings. Right now I use downsizing connectors to exhaust heat from my hoods which are 4" to my 8" fan. Even with this more powerful fan the temps are still way too high in this small room. The inline fan exhausts 2 hoods with 1000w bulbs (one MH and one HPS right now). In addition, I also have 2 smaller fans (not inline, 300 - 400cfm i think), one which exhausts only one other hood and one which just exhausts from the room in general. The air in comes from outside (a problem on 80 degree days like yesterday...) and vents out into the house and/or attic space. With summer here, even with these 3 fans there is no way I can run all 3 lights without the temps getting up to 100 degrees F. I can't even really run 2 when it's up to high 80s or 90s. Would new hoods with 8" or even 6" exhaust openings help at all? Does anybody have any ideas how I can get the heat down? Any ideas would be greatly appreciated

I have thought about using AC, and I might, but I'm way too high on my power load for that circuit. Plus, I'm trying to keep the power bill down for money reasons and also not too look to conspicuous. But it might just come to that....

Here is the problem. If the fresh air temperatures are 80-90 degrees you are not going to get the temp any lower no matter how much air you move through the room.

Agreed. Are you in a situation where evaporative cooling might be useful? I think that if your airflow is sufficient the plants shouldn't mind higher temperatures too much, should they? The other issue is humidity, and again, if you've got good airflow that shouldn't be too much of a problem. I've noticed a marked difference in behavior of my outdoor plants if there's too much humidity (the leaves curled under).

Seamaiden said:

Agreed. Are you in a situation where evaporative cooling might be useful? I think that if your airflow is sufficient the plants shouldn't mind higher temperatures too much, should they? The other issue is humidity, and again, if you've got good airflow that shouldn't be too much of a problem. I've noticed a marked difference in behavior of my outdoor plants if there's too much humidity (the leaves curled under).

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whats evap cooling........i am intersted....

Go with a portable A/C something under 10,000 btu--they use 5.5 to 8 amps--the delogh. line is pretty good.
Dr. VonDankenstine

nickfury510 said:

whats evap cooling........i am intersted....

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Do you know what a swamp cooler is? It's air being passed over water (in a swamp cooler the water flows over lots of fins, something like a radiator), and in a DRY environment the water evaporating provides a heat exchange. It's why we sweat -- evaporative cooling. In this case I'm thinking that passing the air flow over the water (if we're talking about a hydroponic design) could help to cool the whole room, rather like aquarists do when they install muffin fans in aquarium hoods. Otherwise something like a chiller would be necessary, and that's as cost-effective as an air conditioner.

A trick I used to sleep at nights may work. This was back before I had no AC.

Take 3 one gallion milk jugs and freeze them get a pan large enough for 1 jug put the jug in the pan and the pan in front of a fan.

When that jug melts put it back in freezer and put froozen jug in it's place.

Then keep rotating them as they melt. If it's really hot you may need more then 3 jugs. This trick can keep an avg. size room nice and cool. But a grow room does start with more heat. Good luck hope this helps.

Have you considered locting the ballasts remotely ? Might be esier to deal with the heat. They say dont run more than 25ft of wire to the lamp to avoid starting problems but it has a lot to do with the condition of the ignitor.

RandyRocket said:

A trick I used to sleep at nights may work. This was back before I had no AC.

Take 3 one gallion milk jugs and freeze them get a pan large enough for 1 jug put the jug in the pan and the pan in front of a fan.

When that jug melts put it back in freezer and put froozen jug in it's place.

Then keep rotating them as they melt. If it's really hot you may need more then 3 jugs. This trick can keep an avg. size room nice and cool. But a grow room does start with more heat. Good luck hope this helps.

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Thanks for all your responses so far... I could try evaporative cooling since I don't live in a very humid area. The temps get cool at night too, so maybe I wouldn't even need to be replacing the jugs in the middle of the night anyway since the air coming in would be around 60 F. The ballasts are enclosed on a closet shelf and drywalled in so as not to introduce that heat to the area. I think the AC might be my only option during the days since I think the frozen jugs would melt in about 10 minutes in the 90 degree heat. The evaporative cooling would be cheaper than AC and it's supposed to get cooler here soon so I will try that and use AC as a last resort. Nobody has commented in the exhaust hole sizes in the hoods; does everybody think that's a more minimal problem that won't really make much of a difference?

run your lights at night, and yes of course a bigger exhaust hole will give you better airflow for the 8 inch exhaust fan you have...

lylastarr said:

Thanks for all your responses so far... I could try evaporative cooling since I don't live in a very humid area. The temps get cool at night too, so maybe I wouldn't even need to be replacing the jugs in the middle of the night anyway since the air coming in would be around 60 F. The ballasts are enclosed on a closet shelf and drywalled in so as not to introduce that heat to the area. I think the AC might be my only option during the days since I think the frozen jugs would melt in about 10 minutes in the 90 degree heat. The evaporative cooling would be cheaper than AC and it's supposed to get cooler here soon so I will try that and use AC as a last resort. Nobody has commented in the exhaust hole sizes in the hoods; does everybody think that's a more minimal problem that won't really make much of a difference?

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Again, unless you get the temperature of the ambient air down through A/C and/or evaporative cooling it really does not matter what ducts sizes your lights have.

Once you have cooler fresh air flow you will likely have to test the setup for a while to see how effective it is.

Lowes sells a 10,000 btu energy efficient A/c unit for 535.00 out the door-I have one and the thing runs great(comes with a 6" intake and 6" exhaust) it also has a zero condensation--all the water goes out the exhaust with the hot air------Delohgi penguin. Says it will cover up to 700 sq ft---(i always go by the 1/3 rule) so it will efficiently cool 200-300 sq ft.

You can find 8000 BTU units for the low $300's on the internet. All you need is an plact for the hot air output and that will easily cool any small closet or room.

If you remember, amount of amps is the issue with A/C.I had to run a separate circuit to run my A/C. It solved my summer temp problems well.

Yeah, I am aware of the amp issue. I have been comparing AC amps with my current fans and I'm deffinitly going to need to get some more power from a different circuit. I wanted to try all these ideas but now it's gotten cooler so I'll have to wait until it gets hot again to try out the AC and/or evaporative cooling (have already started freezing milk jugs)