Added an A/C to HPS ventilation, is this set up right?

Just got an A/C to bring down the room temp. Is this set up right as I have it?

Six inch inline fan sucks air from the top of the room and blows across the 1000 watt HPS bulb, the exhaust connects to the A/C exhaust with a three way 6" duct adapter and exits the room into the attic.

Not sure if the A/C should point towards the plants or not, two fans blow across the canopy.

I know everyone says use a tent, but I like it this way. :person_shrugging::v::v:


i wouldn’t blow it on the plants, should be fine where it sits as long as the room is staying at the right temp and the ac not putting off heat towards the plants


Hey @spacey. I’m seeing you have the air intact on top to the right going through the HPS then the hot air goes out to the T. From the T you are going out to the top left and down to the bottom left behind the A/C.
I’d move the intact to the end of the line upper left so you are sucking air from the HPS and A/C.


Seems fine the way you have it. I have a fan blowing through 2 cool tubes with hid lights. I think pushing air through lights is better so fan isnt subjected to the heat and will last longer. Youre doing what works for you awsome


Looks more like you’re cooling bulb heat with ac than cooling room? I don’t really understand the air circuit from picture, but running ac in a ventilated room is least efficient way to do it. You’re basically exhausting your conditioned air, or not exhausting and also not replenishing co2. You can’t really do both unless you have properly setup sealed room with ac and co2 generator.

You have an air cooled hood. If this is setup properly in that large of room you shouldn’t need ac. Is glass installed on hood? Where does exhaust go? What is temp of intake air? Without knowing any of that i can tell you have way too much duct and it’s not straight enough. You should have as little amount of duct as possible, and it should be as straight as possible. Length and bends botj add static pressure and reduce amount of air moved.

Worst case scenario, run light cooling on separate air circuit. Bring air in from outside of the room and exhaust it outside of the room for light. Then use separate fan for air exchange in the grow room. Running 2 fans is way cheaper than running a fan and ac unit.

People use tents to have a light tight space when they don’t have an entire room to dedicate to growing a full cycle. Anyone that knows what they’re doing would much rather not have to deal with a tent, i promise!


I think you may be right, the heat exhaust from the A/C could be flowing back into the light and maybe even out the intake fan. The room is not cooling like it should.

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The A/C is attempting to cool the room, not the bulb. The ducting from the A/C is the heat exhaust, not the cool air output.

I think the problem is that the A/C heat exhaust is connected to bulb heat exhaust but not separated, so when the six inch inline fan is off or running at a low speed, the A/C heat exhaust could be flowing both upwards into the attic and backwards through the hood across the bulb and out the inline fan, which heats the room up.

The room isn’t cooling like it should, I’m thinking a second hole in the ceiling is necessary to separate the ducting, or installing a second inline fan at the ceiling hole to suck air from both ducting lines at the same time to pull more heat from both lines.

What do you think? :person_shrugging:

Hey @spacey Yes, you could run two separate ducting one from light and one from A/C.
I would move your inline fan to the top left so it is sucking out at the top left. Keep the inline fan running whenever your light is on. Pulling the air from the top will pull air from both light and A/C. Keep the fan running when light is on.

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Where is the air intake thats feeding this room and how large is it?

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You might also want to consider having the intake near the floor so it will bring in cool air that will then move across you light and then into the splitter.

Also moving the exhaust fan on the other side of the Y like mentioned above would benefit pulling the air out of the AC and light.

Problem is like db said, you’re gonna kill your house central air.
How are you draining the AC?

A dual AC would be good in your case so you could bring fresh air into the AC and exhaust outside. Good luck! :+1:t2::v::sunglasses:


so my question/questions is whats the temp in the room and possible temp where the lights are?

I ended up running a separate duct line into a separate ceiling hole. I finally realized the AC was pushing hot air back through the light and out of the six inch inline fan. Moved the fan lower to pick up cooler air. Room temp dropped 8 degrees.


Thanks. I lowered the inline fan and shortened the length of the ducting, The heat issue was resolved by taking out the Y adapter and keeping the lines separate. Room temp lowered 8 degrees.


Do you have any way to measure the humidity and temp right in the middle of all your plants canopy?:v::sunglasses:


The black wire has a sensor on it that turns the fan off and on, and there’s a small battery gauge…


Can you just leave fan on and turn it down some? I would rather see you in 78-80f range and using less energy. Your leaf surface temp will be better there. You shouldn’t ever stop your air exchange while lights are on. And usually not a great idea to do while lights are off.

You also never answered my question about your intake air?

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The intake air diameter is six inches, as is the ducting. I can turn down the AC some, the inline fan blowing across the bulb turns on at 77 right now, so it should just always be on?

The other two fans blowing across the canopy already stay on 24/7

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I would leave your exhaust on so it’s continually bringing more co2 into your grow room. Then try to tweak fan speed to stay around 78f while lights are on.

Your 6" intake is passive then? Where is at, and what is temp of air coming through intake?

You are on same page as me asking about the intake air for your grow room right? Not the size of your exhaust fan.


Okay thanks. The 6" inline fan was passive, but now I have changed it to be on 24/7 on half speed (5 out of 10). Temps are stabalized now within an 11 F degree range.

The portable A/C temp is now set at 71 F, it turns itself off and on and keeps the canopy at a 70F to 81F range daily with the new ducting setup.

The intake inline fan diameter is 6", the fan blades are probably 8" in diameter when looking at the housing of the fan compared to the diameter of the ducting that it fits. All of the ducting lines are 6".

In the new images, the 6" intake sucks up A/C colder air from the canopy top to blow across the hot HPS bulb and then into the attic, while the A/C exhaust is a separate duct line which also exits into the attic.

There are two oscillating fans that are on 24/7 blowing in opposite directions. A small space heater is connected in case the room temp drops below 70 F.

The ceiling fan is not on now, but should it be? I don’t know.

Any suggestions?



By passive you mean you have somewhere in your grow room that enough air is allowed to come in from a different part of the house? Your exhaust fan is displacing air into another room, so you need bring in air to replace this. I don’t have exact math memorized, but if passive needs to be something 2-3 times the size of your fan. I feel like if you had this right, you wouldn’t need the air conditioner at all. As long as you keep rest of your house at comfortable temperature anyway.

The way you have setup now looks like it will work, but you’re probably spending more than is necessary and may not be getting mostvout of your plants.