Uncontrolled temp in tent

I am using a 48x96x70 tent with two HLG 260's. I have one 8" oscillating fan, one 6" fan and one 30pt dehumidifier within the tent plumed to drain to sewer. The tent is located in a basement that is 16x20x6 with temps that typically range 72-74* and humidity controlled with a second 30pt dehumidifier in the basement outside of the tent. The tent currently holds five plants in 7 gallon fabric pots. All plants are located in one half of the tent (4x4 area). These plants are nearing 8 weeks old and are ready to flip to flower as of now. I am venting tent with 6" passive inlet and an AC infinity T4 with a carbon filter vented to the basement general. Based on the formula that was recommended for exhaust fans, this fan (205 CFM) is "adequate". With the fan on high and the tent closed, I continue to experience temps 82-84*. Again, humidity is controlled with dehumidifier.

I don't want to purchase a 6" exhaust fan as I have already purchased a good-quality T4. Thoughts on why these temps are occurring with "adequate" exhaust and what I should do to decrease temps without purchasing another fan setup?

Thank you in advance for your helpful and respectful answers.

Depends on the formula used to calculate cfm. Most online guides are using air exchange rate for co2 levels, it requires a bit more math to work out the temp rise from ambient and you need to know all the wattage for every item.

If your venting back into the same basement your drawing air from then buying a bigger fan wouldn't make any difference anyway.

However the good news is 82-84 is considered a damn good range for LED growing so I wouldn't worry about that.

How are you keeping co2 from diminishing?

Yes sir... First off, there is a 60 gallon NatGas hot water heater in the basement. Also, during the winter, the NatGas furnace is down there. Beyond that, if it becomes super cold, I have installed a 12k BTU NatGas wall heater. All should help with the CO2 situation. AND THEN, I actually have an 8-burner CO2 generator that was gifted to me. It is entirely too big for my purposes and I hope to sell it someday but I could use it if needed.

I am thankful to hear that 82-84*F is appropriate. Incidentally, I can easily vent to the exterior if that becomes evident.

Sounds like everything will work out pretty good.

If your thermometer and rh meter are under the light thats your problem.

Sure sounds like it the way your describing.

Actually, Mr Kingrow1, you are completely correct! I thought that the thermometer needed to be at the level of your canopy. Where else is a good place for your thermometer/RH meter to but WITH your canopy!?! Man, I feel like an idiot for wasting Mr Webster's time.

So, the question is... where exactly should I place the meter probe so that it accurately reflects what is happening at the canopy level???

Simply put, you won't ever be able to actually regulate your grow tents environment, (the heat and the humidity), when your air exchange rate is less than (2) times a minute! And yours isn't even (1) time a minute! Yes, you have a good exhaust fan, the ACI(s) are great fans, but even so, a 205 CFM drawing fan hooked to typical 4" x 12" CF will drop the exhaust fans ability to maintain its actual CFM rating, so a 205CFM fan hooked to a typical 4" x 12" CF will only be able to pull 180.4CFM(s) @ the exit port of the exhaust fan. And as I said before at that rate you are about 10 CFM shy of even exchanging your grow tents environment (1) time minute. So you need a bigger CFM rated exhaust fan if you really want to control your grow tents environment!

Yes your details read like you had your thermometer in the light and pretty easy to tell. I teach the real science to tent set up here and we never want to know canopy temps so you can ditch all info or ideas on that.

Now to the actual 100% right way to read air temps - place thermometer away from all direct and indirect light. Light is radiation amd it dosent heat the air one bit but the surfaces it strikes.

Your reading the light and the closer you put the meter to the light the hotter it gets - this is NOT and in no way the air temperature of your tent.

Place thermometer in the coldest most shaded part of the tent away from all indirect and direct light and watch your lights on temps drop and thus saving you time effort and giving you the exact and correct answer as to where to place your meters.

Same for outside and the weather service, they use a stephenson screen to block all sunlight from their meters so they can read only air temp and not air plus a shit load of radiation that will heat the meter past the actual air temp.

Yes these basics must be used or everytime you turn your light on you need shot loads of cooling and your actually running much much colder than you thought or the plant likes.

You cannot create microclimates in a tent with a big ass exhaust - the tent will be and should be the same temp as the room air the tent is in. Try your self - place a heater in a room then open the window - heat is exhausted and cannot build - very simple science most get wrong because they read some clickbait info on canopy temps.

There are so called pros and then there is the actual pros - one will harp on about canopy temps and rubbish but the other just lays the simple science facts and truth out and then says "Get to it".

Let me know if you drop temps by placing the meter oit of the light in some shade

MountainMedic1206 said:

Actually, Mr Kingrow1, you are completely correct! I thought that the thermometer needed to be at the level of your canopy. Where else is a good place for your thermometer/RH meter to but WITH your canopy!?! Man, I feel like an idiot for wasting Mr Webster's time.

So, the question is... where exactly should I place the meter probe so that it accurately reflects what is happening at the canopy level???

Click to expand...

Well, here is the website where I found the formula I used to figure the fan size I needed. Their recommendation was to exhaust your tent every 3-5 minutes... not three times per minute. Soooo... that is why I have the fan I have. Bad advice on their part... bad research on my part. S'pose I'll pick up a six inch unit and move this four inch to my two 2x4x5 tents and try to see if it won't pull both of them Y'd together.

Okay... doing math... if my tent is 160 CuFt (4x8x5) with a carbon scrubber (+20%) equals 192. If I want to exhaust x2/min, than a 6" fan is minimally adequate at 351 CuFt/min... kinda. This fan is $150 and pulls 40w. The next step up is an 8" which will pull 740 which is clearly adequate but is $200 and pulls 180w!!! The filter for the 8 inch is another $100.

I understand that what is being said here is that I should get the 8". I am just uncomfortable with the wattage and the financial outlay for the purchase. Thoughts on wether I could get by with a 6"? OR... I could even get another 4" and run them both to exhaust with a cumulative output of 410cfm.

Mr Kingrow1... I am only using one half of the tent so I can put the probe in the unused half. Question is... should I put it high or down near the ground?

Air circulates in the tent so anywhere is fine, its not like the top of the tent is ten degrees cooler than the bottom. What we do need to is to shade it from the light, place it half way up on the wall of the unused side if thats away from the light.

It can be a hard principle to understand for newer growers but a hard and fast rule plus you can move it and find the coolest place as well as observe how light heats it up.

Exhausts are based on heat not air for the plants - your exhaust only needs to remove heat and at that point you will provide enough air and circulation for the plants. Some like a fan pointed up or away from the plants for extra circulation but any wind on the plants is bad so we never angle the fan at pla.ts.

There is a lot of info on fan size but if a smaller fan prevents heat build up your not gona need anything bigger.

Life and growing are a learning process - find your real air temps then you will know what size exhaust you need

MountainMedic1206 said:

Calculating CFM (Cubic Feet per Minute) for your Marijuana Grow Room Exhaust Fan

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Well, here is the website where I found the formula I used to figure the fan size I needed. Their recommendation was to exhaust your tent every 3-5 minutes... not three times per minute. Soooo... that is why I have the fan I have. Bad advice on their part... bad research on my part. S'pose I'll pick up a six inch unit and move this four inch to my two 2x4x5 tents and try to see if it won't pull both of them Y'd together.

Okay... doing math... if my tent is 160 CuFt (4x8x5) with a carbon scrubber (+20%) equals 192. If I want to exhaust x2/min, than a 6" fan is minimally adequate at 351 CuFt/min... kinda. This fan is $150 and pulls 40w. The next step up is an 8" which will pull 740 which is clearly adequate but is $200 and pulls 180w!!! The filter for the 8 inch is another $100.

I understand that what is being said here is that I should get the 8". I am just uncomfortable with the wattage and the financial outlay for the purchase. Thoughts on wether I could get by with a 6"? OR... I could even get another 4" and run them both to exhaust with a cumulative output of 410cfm.

Mr Kingrow1... I am only using one half of the tent so I can put the probe in the unused half. Question is... should I put it high or down near the ground?

Click to expand...

I will add this too - fans and exhausts dont cool tents they simply remove heat. If you want to make your tent colder (or hotter) you need to adjust the room temps the tent is in and not the tent itself.

Consider the tent uses the room air and thats what the tent will be . Heat is radiation conduction and convection - learn this well

Mr Kingrow1... Really good response and I think it addresses my question very well. Thank you. I do have a question about not directing fans on to the plants. Everything I read speaks to how an oscillating breeze helps to strengthen the roots and woody aspects of the plant and how it is just one more small thing that can help build buds. Help me to understand how these direct wind currents are actually a detriment? Thank you, sir.

Its just general knowledge but to save discussion you will find that transpiration or leaf cooling can be eithe free or forced and at wind speeds above 0.3 - 0.5m/s which is barely perceptable forced cooling takes over from free and leaf boundaries become so thin that the leaf cant keep up or simply looses too much water when opening stomata for transpiration.

We define this in simple terms in tents by saying to.make air exchange but not wind. You can have a good exhaust and it feel fresh in your tent with very little wind. You can check your exchange, go breath a puff of smoke in your tent and see if it travels up to the exhaust and clears quickly - good exchange no wind.

The bit about making thicker stems is wrong, you might stress the plant to be smaller and stockier but thicker stems really come from the need of more and more leaves as that requires a bigger thicker transport system and thus the healthiest happiest plants as in nature outside have the thickest stems and not those in a lot of wind which may look thick stemmed but are also smaller so not ideal for max yeild.

Stoners talk a lot of stuff, take it with a pinch of salt before you end up i. their led boveda canopy temp dreamland

MountainMedic1206 said:

Mr Kingrow1... Really good response and I think it addresses my question very well. Thank you. I do have a question about not directing fans on to the plants. Everything I read speaks to how an oscillating breeze helps to strengthen the roots and woody aspects of the plant and how it is just one more small thing that can help build buds. Help me to understand how these direct wind currents are actually a detriment? Thank you, sir.

Click to expand...

So, back to this thread....

The last few days, I am really starting to have problems with excessive humidity. I thought my 30pt dehumidifier was going to be up to the task for this tent but I am running into 95% humidity within an hour after watering including beads of water on the tent walls. Pots drain to collection plates and I am keeping those vacuumed out to prevent increased humidity from standing water. I know that it was decided that my exhaust fan was inadequate so I have ordered an S4 fan to go with the T4. That will give me 410cfm total although one fan will have a carbon filter for the time being. I will add a carbon filter in a couple weeks to the S4. I do know that filters reduce airflow. I am not terribly optimistic that these two fans will do the trick but the S4 was $85 and was what my budget could tolerate so that is what I am trying. If it fails, I will buy a 6" or 8" fan to replace the twin 4" system once I get paid again and use the 4's on a couple small tents I have.

I do not really understand everything about why my humidity cranks up after watering like it does. I know increased transpiration but to go from 50% or so to 95% seems excessive. I know that cooling the ROOM will cool the TENT and I have an AC that I can start using. Do you think that will really do what I need along with the increased airflow from the twin fans?

This humidity thing is crazy. I am desperately needing to flip to flower but I have gotten behind on the entire system and I can't seal up the tent and know that the temp and humidity will behave themselves.

Again, I am a little shocked that my dehumidifier is not controlling things.

I know I am rambling and I apologize. I feel at my wits end at the moment. My plants look fantastic but are getting HUGE from a veg standpoint.

Thoughts???

Basics are covered now and you have true readings or close enough so a link to your fan please as theres a gazillion with that name?

Sounds like a fan or fresh air problem in the basement.

What is the basement humidity too?

The basement humidity runs about 60% and seems to be well controlled by a second dehumidifier. Fresh air may be a problem... possibly. The central air system is down there and there is a small amount of air leakage from the ductwork but I would not say it is enough to keep things fresh. I will say, though, that the basement, although old, never smells musty or otherwise. I do have a few ways that I can make access to outdoor air, if needed. I am also really considering installing an A/C window unit I have to bring down the room temp to 68* or so as well as bring in some type of fresh air.

I should also mention again that I am exhausting the tent to the main room but the room temp and humidity seem reasonable. ~75* and ~60%

Fan I already have...

Filter...

Fan I will receive tomorrow. Pretty much an exact duplicate as the one above but "dumb".

I see no problems and cannot see how you got moisture on walks but are you using the fan control and its running too low or off or are the beads of water just round where the leaves touch the tent wall. I get a lot of moisture on tent walls where leaves touch sometimes and dont fret.

It should be impossible for your tent to get to 95% with basement at 60% unles the fan stops

MountainMedic1206 said:

The basement humidity runs about 60% and seems to be well controlled by a second dehumidifier. Fresh air may be a problem... possibly. The central air system is down there and there is a small amount of air leakage from the ductwork but I would not say it is enough to keep things fresh. I will say, though, that the basement, although old, never smells musty or otherwise. I do have a few ways that I can make access to outdoor air, if needed. I am also really considering installing an A/C window unit I have to bring down the room temp to 68* or so as well as bring in some type of fresh air.

I should also mention again that I am exhausting the tent to the main room but the room temp and humidity seem reasonable. ~75* and ~60%

Fan I already have...

https://www.amazon.com/gp/product/B06ZXWN3BG/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

Filter...

https://www.amazon.com/gp/product/B00E582DV2/ref=ppx_yo_dt_b_asin_title_o09_s03?ie=UTF8&psc=1

Fan I will receive tomorrow. Pretty much an exact duplicate as the one above but "dumb".

https://www.amazon.com/gp/product/B07JB292JC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Click to expand...