Grow Tent Heat Issues - Any input would be appreciated!

Hello everyone!

I'm not new to growing, but I am new to grow tents...

Here are the specs:
5 x 10 x 6.5 foot grow tent
2 1000 w MH/HPS air cooled reflectors
6 x 16 black ops carbon filter
435 cfm hurricane fan

When the tent is closed, my temps are getting into the mid to high 80s...which I know isn't ideal. I'm restricted with space, so there are multiple 90 degree bends in the exhaust line.

Can anyone offer some suggestions on how to decrease my temps without getting an ac unit? I was thinking I could separate the carbon filter and light exhausts...or maybe adding a higher cfm fan to push air though faster...

Seeds germinating now.

Any help would be greatly appreciated!

Are you pulling in fresh air from the outside and exhaust to the outside too? If not, that would be the first thing to do. Second thing is a stronger fan as you mentioned. Also, it's best to place the filter or exhaust air at the highest possible point as heat moves upwards. If you are sucking the air from a neighbour room, place the hose on the floor of that room as cold air is located at the bottom.

Hello,

I'm pulling in air from this crawlspace (it's received heated and air conditioned air) and venting to the outside of the house. I do have the scrubber strapped as high up in the tent as possible. I have good negative pressure when the tent is sealed.

Instead of separating the exhausts, maybe I just need a higher cfm fan, correct?

Just from a quick glance of your setup the fan needs to be a 8" and your carbon filter is too small in my opinion. I'd try a 8x24 phresh filter with 8" exhaust fan. Try for testing purposes running a single 1k and see how your temps are because i feel thats what your fan/filter you have now are limited too. Another test would be to unhook the filter and run both lights and see how high temps get without the filter restricting.

This is all inside my crawlspace...which is usually around 65 degrees year round. It gets pretty cold where I live during the winter, so I can't bring outside air into the tent.

Some options:

1. Add a second fan on the circuit to help move the air after the second reflector

2. Separate the carbon filter/fan and reflectors, adding another fan dedicated to the reflectors. The scrubbed air could exit the tent into the crawlspace and the hot air could be vented outside

3. Get a higher cfm fan and replace the 435 cfm fan that is attached to the scrubber (maybe another 435?). I'd like to use the 6 inch ducting I have instead of using reducers on my hoods, if possible.

Just some thoughts, but I'm looking for any advice I can get at the moment...I have a few days before the seedlings go in!

Gday mate! Welcome to ICmag.


I have had similar issues. In my experience having the reflectors in series like that significantly reduces the air flow of the fan due to restriction. I'd put in a second fan and consider the first one just as a reflector cooler. Without active cooling the only way is to move more air.

Much appreciated!

In my setup, where would you install the second fan?

It looks like you have other duct inlets near the ceiling in your tent. I'd hang another fan (with a scrubber mounted direct to the inlet) as close to the top of the tent as possible. a 10 x 5 tent with 2 1000w lights has a fair amount of heat to get rid of. In winter you may be able to shut down the second fan if temps are too low. 6 inch ducting is what I use in my 4x4 tent so that's another reason I'd add more air flow.


Edit: I was just doing some calculations. I have a 4x4 tent with a 600W HPS and I have an extraction fan that I run on the second speed which produces about 200cfm of air flow. The distance from the inlet of my fan and the outlet of the duct in the roof would be no more than a few metres. The longer the duct the more the air flow is reduced.

You have about 3-4 times the heat load so it makes sense you would need at least that much more air flow. I doubt you'll be getting near the stated air flow of the fan the way you have it set up.
What I'm getting at is doubling the air flow you have may not even be enough. I would try and get a larger fan and larger ducting for the second fan.

It's winter here now...quite cold outside actually...so maybe I need to rethink the entire setup.

You can add a second fan as an intake fan blowing outside air into the tent (two similar fans in series).

Alternatively you can try mounting the carbon filter to one of the hoods (with a short piece of duct) and move the fan to the tent's exhaust port so that the restriction is only on the fan's intake side.

Filters have many advantages but if you remove the filter say using a roof vent or replace it with a larger filter that will likely increase flow.

The way it's set up now the fan is taking the warmest air in the tent and moving it through uninsulated duct and hoods before leaving.

You may be able to lower the height of the intake to canopy or floor level. I'm not sure if or how this might affect the temperature.

Keep the duct as short as possible. Each length and turn causes restriction. A 435 cfm rated fan may flow less once installed.

bhodi said:

It's winter here now...quite cold outside actually...so maybe I need to rethink the entire setup.

Click to expand...

Shit! You're going to be in a world of hurt in summer. Definitely need to do something.

Where I have my 2x4 ft tent with 500 watts of light, it will maintain temperature with the fan recirculating the vented hood's air. One bottom flap is slightly open and the 4" fan is pointing toward an exit port on the tent about 1 ft away which is slightly open.

Maintaining temperature will be a challenge without a larger fan and thermostat and/or another fan. I don't imagine you'd need A/C for most places when it's cold but for indoor growing during the outdoor season yes maybe A/C and/or dehumidifiers are necessary or beneficial or worthwhile.

Without going off on a tangent the climate is different everywhere and this plays a big part in how much effort is required to find ideal growing conditions. For two 1000w lights in an average residential dwelling I'm willing to bet that outside air can easily provide all the cooling and CO2 you require. For 10-20 lights in a basement or industrial concentrated setting you'd need much larger fans and/or a taller ceiling to let heat escape/dissipate.

Some indoor growers get into climate control with sealed rooms and (de)humidifiers, CO2, A/C, other chillers/heaters, to create or maintain an environment inside. That might allow the definition of a dialed in room but I wonder about the equipment and power cost at that point. There is an assumption that it is financially viable to use climate control (which by definition goes against reducing climate change since it requires energy). Perhaps in some cases or maybe in some places it is (viewed) necessary to use climate control.

At this point politics rears its ugly head in an unavoidable way. Any gas, oil, or power, electricity subsidy or incentive or differential price for different people, affects everyone both directly (benefit) and indirectly (detriment). The power (oil and electricity) cost can be set to a different number benefiting whomever is buying/supplying all of that energy to the detriment of the environment and the surrounding population. In other words everyone else, in real everyday terms of cash, wealth, employment, the price for abc etc. Gas and oil being burned to convert into paper currency, these are two things which I would vote against given a choice. At least an open discussion.

What about all of that equipment cost though? It is pretty easy to see how an indoor grower looking to make a living at it can easily accrue a large overhead that translates essentially into a heavy debt pre-tax, before any flowers are produced. Compared to passive geothermal or simple exhaust fans, cooled hoods etc.

Shame to waste 6000+ btus of heat to outside in the winter, i would run the hoods on a closed loop (from one side of tent to the other, in a straighter line) and pump the heat into the house.

Then set the carbon filter with another fan as your main exhaust where ever you want, inside or even outside the tent. A cheap temp controller could keep the temps in check, making the fan only come on when you hit a certain temp, and back off when it gos back down.

The current filter setup would work better because the other fan will take away most the heat through the hoods. Just make sure to seal them up well so the smell doesnt get sucked into the hoods. You could even hook that fan into the light timer so it shuts off with the lights...

8 inch would do, but thats a lot of upgrades, new fan, new ducting, new filter, 2 new 8 inch hoods.

Four 6 inch to 8 inch reducing duct fittings could cost $50-60 alone, and kinda defeats the option of just buying an 8 inch fan that will be restricted by the hoods.

Thats the reason i would just get another 6 inch inline..

+1 Drop That Sound's first idea sounds like a great plan. One fan is only for moving outside air through the hoods (outside of tent -> lights -> outside of tent, all sealed). Then your second fan can use a thermostat so it only turns on when needed. Finer adjustment that way.

Increase the size of your air intake - use an 8” intake with a reduced to the 6” hood, then use 6” ducting and vent fan. The size of the intake is likely the limiter. This is a relatively inexpensive option to try.

GB

Light cooling should be seperate from exhaust of tent. Upgrate to 8" fan for lights pull air for outside thru. If you pulling air from tent through lights the cooling will ve limited to the tent temo which is high already no exchange.

Hello everyone,

Happy to say that after adding a second fan (separating carbon filter and reflectors into two circuits), the temperature has dropped 8-9 degrees...

Seedlings in now...will report back in a few weeks.

Thank you so much for the help!

Its all already been mentioned.
1)your exhaust filter is way too small. You should have a larger 6" compatible filter. An 8" fan might be overkill usually, but in that small of a space, its nice to exchange air frequently.
2)You need more/larger intakes. Once your intake allows twice the air as the exhaust, you should see temps drop. (for example, 2-6" intakes and 1-6" exhaust). With tents, I'll increase the amount of intake area until I lose negative pressure.
3)You can run your lights so they're flipping back and forth and only one is on at a time. That, or run them with an overlap during the middle of the day. This will drop down heat and not cut your growth too much, especially during early veg.
4)Pull air in from outside, if you live in a cold climate. That way you run cooler, can have both lights going at once, and not have to move as much air. The humidity could mess with your filter's effectiveness if you're not in a dry climate.

good luck, and welcome!

A 6” fan is barely adequate for my single 600w hood. If I was going to run 2 1ks I’d be looking at 10” fans.