hey guys nice thread. Room size 11x6x8 i will be running two solistek 600 watt lights with air cooled hoods but i dunno what duct size to go with as i may be converting to two 1000 watt bulbs as soon as i can get cash for a AC. Will a 6 inch duct work for two 1000 watt lights if theres a AC running? Im in northern Canada and usually only grow in the winter time indoors so im prety sure i can swing the two 600s with just air movement.

I have a 2x2x5 flowering chamber.
It has a 400 watt light m.h/hps.
It is in a cooltube with a 6" 381 cfm can fan on it.
I have a 60 pint dehumidifier (not running in winter) humidity already is below where i want it.
The mercury 4 multi mode fan controller takes care of all the thinking for me automatically.

I have a 1 gallon cool mist humidifier in the tent room that acts as a mini evaporative cooler. Lowers the room temp a few degrees while not incurring massive a/c electrical draw. & humidifying the dry winter air.

I have a 20" fan in the tent room on the floor pointing up to aid in making the air temp homogeneous from floor to ceiling. The cold air tends to settle, while the hot air tends to rise.
this averages out the temp. Which reduces large fluctuations in the temperature of the intake air.

last but not least there is a window ac unit nearby in the same room. I don't need it yet but it helps control the room temp quite well. I made sure to leave enough extra ducting on the exhaust end. So that during summer I can direct the concentrated hot air directly into the a/c unit intake. This ducting stays collapsed in a small pile during winter. This helps reduce pressure placed on the fan by keeping the ducting length shorter.

I have it set up in this order,
room air>intake filter>chamber>charcoal filter>can fan>cooltube>exhaust ducting>room air.

The reason I have the can fan after the charcoal filter but before the light fixture.

The fan drawing air through the charcoal filter.
Will create negative pressure in the chamber space. Ensuring that all air gets drawn through the charcoal filter for scrubbing.

Ahead of the fan it creates positive pressure through the cooltube then ducting into the room.

This does 3 things.

1.) It creates a higher mass of air flowing over the bulb since its positive pressure (more air density). This means the air will have a higher heat capacity.
Combined with the pressure of the air acting on the bulb to aid in heat transfer.
As well as being a denser charge of air
It will carry out more heat.

2.) If anything after the fan (cool tube/ducting) has air leaks. The already scrubbed air would leak back into the chamber to be re-filtered through the charcoal filter.

3.) The fan will be exposed to lower temperatures being before the light increasing its life expectancy.


If placed after the light fixture or at the end of the exhaust stream. It would work opposite to all 3 of those variables.

1.) The negative pressure would create a lower mass flow of air (lower density).
It would be lower pressure meaning lower heat capacity.
It would transfer less heat from the bulb due to lower force of air pressing onto the bulb.
And also due to a lower density of air flowing through.
All this would reduce the efficiency of drawing the heat outside.

2.) If there are any ducting leaks before the fan and after the charcoal filter(ducting/light fixture).
The negative pressure created by the fan will draw unfiltered air (bypassing the charcoal filter) out of the chamber and into the room. Leading to your neighbors finding out.

3.) The can-fan will be exposed to higher temperatures reducing its life expectancy.


During winter time/ cold days. The hot air venting into the room helps heat the house. But is just barely noticeable. It reduces the time between when the furnace kicks off and when it kicks back on.

Overall I'd like to say that a 400 watt light doesn't seem to put off much heat at all. So it is easy to control the temps.

3 rooms, 6 to 10 lights each. We used to use a DIY mini-split unit, that was real nice until it failed and we needed specialized help.

Currently we use hotel-style PTAC units. These run on 240V circuits, 12k-14k BTU cooling capacity, around $700 each. We have some running to the outside, and some on inside walls with ducting leading the hot air up and out of the building. I think we'll stick with these, due to low price and ease of removal for maintenance or replacement.

1. Size of room? 18'x22'
2. How well insulated is it? Very well
3. Total wattage in the room(s)? 10k
4. Burning gas for Co2? No
5. Ballast in the room? If so digital of magnetic? Digital
6. Dehu? What size? How often is it running? Yes, 100 pint, 24/7
7. What size, brand, and seer rating is your a/c or chiller system? Central AC
8. How often does it cycle (turn on and off)? Haven't needed
9. What is the highest and average outdoor temps? What the climate like? 67F, 63F, cold/wet
10. What is your grow room temps set at? 75F
11. Is the system able to maintain the temp setpoint through the entire light cycle? Yes

So I am pondering AC options for my new room. Eyeballing a 12,000 BTU window unit (1100w) but not sure if that's powerful enough to cool both the veg area and flower tent. Should I double the BTUs?

Assume fresh air to come from rest of house under door. Will pull ambient air from veg area into 6' insulated ducting through HID hoods and then out through window. Or maybe wiser to pull in outside air to cool hoods? Have not yet bought air filter to expel smelly/humid flowering tent air outside, but plan to. I want to make sure my HID ducting, flower room filter venting and AC are harmonized.

1. Size of room?
10' x 10' x 9' (L x W x H)

2. How well insulated is it?
Good... spare bedroom with 2 outside walls, one East-facing, one North

3. Total wattage in the room(s)?
two 1000w HPS in a 9x5 tent (flowering) and one 430w T5 in open room (vegging) + water chiller for DWC, fans, air pump, etc. which all add another 550w

4. Burning gas for Co2? no

5. Ballast in the room? If so digital of magnetic?
two digital Galaxy grow amps

6. Dehu? What size? How often is it running? not yet

7. What size, brand, and seer rating is your a/c or chiller system?
nothing yet -- gotta work that out!
I have 9.1 amps left on a 20a 240v circuit for this. Since I want to keep utilization at 80% or less, that works out to about 5.1 amps or 1224w for the ac. (If not enough, I can run an extension cord from another circuit but prefer to avoid this.)

8. How often does it cycle (turn on and off)?

9. What is the highest and average outdoor temps? What the climate like?
100+ in the Summer, warm to hot dry desert climate

10. What is your grow room temps set at?
i want to keep it stable at between 75 to 85.

11. Is the system able to maintain the temp setpoint through the entire light cycle?
i expect it to.

okay ill play
1. Size of room?
20x7x10 its in an "L" shape
2. How well insulated is it?
decent the whole building is made of masonry bricks essentially which seem to hold cold air very well in the winter although i havent had a run in full summer heat!
3. Total wattage in the room(s)?
from the lights 3k watts
4. Burning gas for Co2?
Not yet
5. Ballast in the room? If so digital of magnetic?
in my lung room, and digital
6. Dehu? What size? How often is it running?
in the mail had problem with PM last run cause of the unexpected rain in so cal
7. What size, brand, and seer rating is your a/c or chiller system?
i believe its some where around 15,000 btu i couldnt really find the ratings its huge and old AF, and
its an emerson, i only had to use it during veg back in october and it kept me under 80 degrees Fahrenheit for that month
8. How often does it cycle (turn on and off)?
it was at constant run on low kept my lung room around 70 degrees or so
9. What is the highest and average outdoor temps? What the climate like?
lately, its been cold AF and humid weird! but its socal so imma say hot, dry heat most of the summer months, and moderate all year around
10. What is your grow room temps set at? 75
11. Is the system able to maintain the temp setpoint through the entire light cycle?
ya it actually has gone up to 81 during october once but just cause i had an intake fan take a shit, which cut me from 900 cfm to 450 cfm and took me a couple day to realize it wasnt running. so far yes its done its job come 100 degree days we will have to find out. so far to cold has been my issue, so i just was running fresh air in and out, my room is like semi sealed only gettin air from cracks in the doors and windows, it vacuums quite well. i really need heat but idk if my breaker box can handle it!

Quick question....how many btu's (mini split) to cool 8 315 watt Sun System LEC's (cmh) fixtures in a 14 x 10 room with a quest 110 dehuey and using bottled co2 for gassing? One foot perimeter and a 2 foot "aisle" dowwn the middle of four 3x6 low tide dtw tables. Duhuey hung from 8 foot ceiling. Scrubber at the end of the aisle. Standard sealed growroom setup. Just ditching my hps lamps and relamping after rebuild of room with 8 cmh fixtures. I know it will be a small one...and i welcome that. HUGE ppwer bill savings is what iam after...i know i will take a hit on yields but not much compared to that dreaded monthly bill.

Check these out for controllers for fans, heaters, dehus, and humidifiers. Not gonna find a better deal. I use the itc-308 for my 10" qmax fan. Works excellent. Dehu controls nighttime humidity.

Keeps my temps between whatever I set it to. Right now, 22-26 celcius. No AC. 8x8' room, 8 foot ceiling one side, 10' the other. Probably going to install a wall banger AC for July and August this year. Just did outdoor for the summer last year.

Dirtbag said:

Check these out for controllers for fans, heaters, dehus, and humidifiers. Not gonna find a better deal. I use the itc-308 for my 10" qmax fan. Works excellent. Dehu controls nighttime humidity.

Keeps my temps between whatever I set it to. Right now, 22-26 celcius. No AC. 8x8' room, 8 foot ceiling one side, 10' the other. Probably going to install a wall banger AC for July and August this year. Just did outdoor for the summer last year.

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Better deal:

mojavegreen said:

Better deal:

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No it's not, not in Canada at least. That is $53 and the itc 308 is $46. Plus I recommended the package deal of temp AND humidity controller bought together.
Not to mention, that was 2 years ago, I wouldn't be surprised if something else has come along since