Quick thread for controlling VPD and heat control

I’m creating this thread because as a new grower I went through some troubles finding the perfect or close to perfect set up in order to control my Temps, Humidity and ultimately my VPD. It caused some stress on my auto and definitely on myself, so I’m here to try and relieve some of that stress for any beginners or anyone else struggling with high heat, low humidity. I know this will be a hefty thread but please feel free to skip towards the end where I’ll provide a short summary.

I’ve been struggling with high(er) temps at around 80-82 degrees whenever my lights were on and have to figure out how to use my humidifier with these high temps. Usually this puts me at having the humidity at around 70-75% at the moment in veg which is alright as long as you have good airflow. The problem with my grow was I had my tent in the closet with the air intake in the back closed off, if you’re like me and have the same set up or are lacking air intake, this is perfect advice for you. However do please take everything I say with a bit of salt as not everything will fit your grow set up and will differ on your indoor environment and outdoor environment.

Quick background, I live in a very dry environment with temps reaching 100 almost every day in the summer. You Cali people know what I’m talking about. Before we start here is a quick chart about VPD that I’ve found quite helpful. And before @Ickey starts lecturing us on Leaf Surface Temperature (LST) let’s pretend we’re focusing on our tent environment only and not the LST offset.

VPD Chart:

Recommended VPD:

If you do not have an AC Infinity or any other controller that automatically checks VPD in your environment here is a link to a website that can help you with that if you have the temps / humidity available.

Very worth read if you are just getting into VPD and are looking for a beginners guide + has the calculator to measure VPD.

1: First tip I’ll give you guys if you’re struggling with exhausting air is to REMOVE the carbon filter until it actually begins to smell. I’ve noticed that it helps with cooling down temps inside the grow tent.

2: Second tip I’ll give but I haven’t done so I can’t really comment on it is to put your carbon filter / inline fan on the outside of your tent. Someone told me it lowered their temps by 2-3 degrees, if you try this, please let me know if it helped at all.

3: HAVE PROPER AIRFLOW. This is a MUST for all growers. Be wary I am still a beginner grower but I’ve noticed that increasing my airflow has helped tremendously with VPD. I have a fan at the bottom and a fan at the top, there’s plenty of good YouTube videos that can help with airflow.

4: This is one I’ve recently done. I’ve purchased a 4" booster fan from AC Infinity and used it as my intake. It’s probably the best investment I have made. It is around 30 dollars, I’ll link it below. I’ll also drop some pics. It has helped me bring in cooler air and my temps are around 80 with no AC running.

5: This tip is for everyone using a humidifier, if you are using one and purchase a booster fan, put the humidifier right outside the booster fan, this will let the intake suck it in and throw it into the tent without straight on going near the tent walls, plants, or any other stuff you keep in your tent and want to take care of.

Here’s examples of before the intake fan earlier today vs later today with it installed.



Here is a link to the AC Infinity Booster Fan that is 4". They also have larger ones if you have a larger tent, but I’ve found that this helps produce the airflow that I need in my 3x5 tent.

I’ve written so much I mostly forgot what I was even planning on saying. Hopefully someone finds this useful and enjoys the read.

If you would like to check out some equipment I’m using or how I am using my intake fan vs exhaust, head over to my grow journal and scroll up a tiny bit and you can see the set up I’m working with.

To control your VPD all you need is good airflow. Using a booster fan from AC Infinity will be 100% beneficial and help you control your intake if you do not have a good place to intake air such as I, in a closet with the intake facing the wall. To help with temps remove your carbon filter until it begins to smell, put your carbon filter / inline fan on the outside of your tent, have proper airflow, use a booster fan for intake, and put your humidifier on the outside of your tent near your booster fan. Thanks for the read everyone, let me know your thoughts and comments! Peace.

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@Sammys, If I was of any help to you at was a pleasure, my friend. I figured out that you must be in a challenging climate.
I believe you will be a better grower after what you have been through. You are learning the parameters for your grow room and your techniques. You now know better what to look for in your plants also, (good or bad).
Let’s say that the VPD stars all aligned, and all went well from the beginning. All that you would had learned is what a healthy plant looks like.

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Doing the math & it looks like your sensor is giving you ‘Room VPD’, but your posted VPD chart & ‘Recommended Leaf VPD’ air temp & RH targets were both generated using a negative 5f (-5f) Leaf VPD offset.
You would want to be working off of this chart if you want to focus on your tent environment only, and not take the LST offset into account:

Just remember that the targets in the top right corner of the chart are really talking about your Leaf VPD, not your Room VPD.

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Have thw AC Infinity 4x2 200w tent

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Like it?

Great read man, my 2x4 is in a tight area closest with one side of the tents air intake holes blocked. I ordered 2 Ac infinity oscillating fans to help with the hear will go from there. Thanks

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You guys can also get flange kits from Jardin & install them if you need more intake area.