Time to hook up dehumidifier

I am in the 4th week of 12/12 and I do believe it's time to get the dehumidifier up and running. Temps fluctuate between 70 and 86° Humidity fluctuates between 55 and 81% per my guage. That said, the 81% comes from a very short time while I'm in the shower and then drops back down just as quick. In reality, it probably gets up to around 70% without the shower. I have a 6" inline fan and charcoal filter that runs on low 24 hours a day. What is the target humidity that I should be aiming for in flower?

Edited to add:
3x3 tent
3 plants
3 gallon fabric pots
FFOF soil
Handwatered/fed
2 150w linkind led panels about 14-18" above canopy

I try to keep it under 50% late flower. Costco has a great deal on Dehumidifiers right now if you need one

TiresMakeContactwRoad said:

I try to keep it under 50% late flower. Costco has a great deal on Dehumidifiers right now if you need one

Click to expand...

I have one. I just dug it out and am cleaning up the corner of the bathroom my 3x3 tent is in. Gotta prep it for the dehumidifier and the 4x4 tent I've gotta pick up to replace the 3x3 so the phlizosun light I won will fit.

Hooked up the dehumidifier today. Started it about 1:30pm. Lights out, humidity was at about 72%. It is currently hanging out at about 50% now with lights on and temp has climbed to 88° with it running. It was about 52% humidity right when the lights came on. So, it is working at the cost of raising the temp a couple degrees. I have it set to 35% and that should hopefully keep up and keep it at or around the 50% mark in the tent. It also rained here all day today so I'm sure that helped keep it up a bit as well.

TCH said:

Hooked up the dehumidifier today. Started it about 1:30pm. Lights out, humidity was at about 72%. It is currently hanging out at about 50% now with lights on and temp has climbed to 88° with it running. It was about 52% humidity right when the lights came on. So, it is working at the cost of raising the temp a couple degrees. I have it set to 35% and that should hopefully keep up and keep it at or around the 50% mark in the tent. It also rained here all day today so I'm sure that helped keep it up a bit as well.

View attachment 5196381

Click to expand...

Is your dehumidfier inside the tent or outside in the bathroom? What size Liter dehumidifier is it?

strongbow19 said:

Is your dehumidfier inside the tent or outside in the bathroom? What size Liter dehumidifier is it?

Click to expand...

It is outside the tent in the bathroom. It is a 25 pint (so if my math is right, about a 14 liter) dehumidifier.

Well, it was 90+ degrees in my bathroom and 100° in the tent this morning after dehumidifier was running all night. It pulled out 84 oz of water over the course of 9 hours overnight. The good news is that the rh was 47%. Plants were looking just fine this morning before lights out. Did not seem to have any issue with the additional heat. This will be a rough way of doing things while the weather is hot out. It will be nice over the winter months though.

It's way too hot. Your VPD is all screwed up at that temperature.

ismann said:

It's way too hot. Your VPD is all screwed up at that temperature.

Click to expand...

My deodorant agrees. It fucking fell apart this morning. Haha. Luckily there wasn't much left. Now that the rh has dropped down to a tolerable level, I dialed the dehumidifier back from 35% to 50% to see if it just maintains throughout the day and hopefully doesn't run as constant and actually takes a break. We shall see. Hopefully that will help the temps come down. I dont have an option to add an ac unit. Worst case scenario, I could probably hook up an intake that draws from my bedroom through the wall and just cover that with a register vent so it just looks like an air return.

Run bathroom vent fan?

buckaclark said:

Run bathroom vent fan?

Click to expand...

It is on 24 hours a day. I may have to look into a heavier duty unit.

This morning, I set the dehumidifier to 50% so ideally once it is under 50% the dehumidfier will shut off. Lights went off at 6am and temp immediately fell a couple degrees. From 7am to 530pm it only collected about 8oz of water and the temperature is currently 75° and rh about 49%. I feel like this is an acceptable range, yes? Hopefully now that I have the initial spike taken care of, the dehu doesn't need to run constantly and heat up the room. If I'm not mistaken, doesn't the humidity actually drop a bit when lights are on and temp goes up?

I have one about the same size and I run it during fall/winter/spring pretty much 24/7. It's such an essential piece of equipment for me during the winter that I keep a backup around (same with AC).

TCH said:

This morning, I set the dehumidifier to 50% so ideally once it is under 50% the dehumidfier will shut off. Lights went off at 6am and temp immediately fell a couple degrees. From 7am to 530pm it only collected about 8oz of water and the temperature is currently 75° and rh about 49%. I feel like this is an acceptable range, yes? Hopefully now that I have the initial spike taken care of, the dehu doesn't need to run constantly and heat up the room. If I'm not mistaken, doesn't the humidity actually drop a bit when lights are on and temp goes up?

View attachment 5196862View attachment 5196863

Click to expand...

When temperature goes up, relative humidity goes down, yes. Hotter air can hold more water than cooler air.

At 75F, ideally you want to be at 40% humidity and you ideally need to check leaf temperature, but it's way better than 100F.

I run my dehu pretty much 24/7 and use ac to combat the heat it puts off. It's a constant battle between the dehu and the ac for me. I ended up having to get a timer for my ac unit, so it will shut off at the same time as the lights. Even at night with the lights off if I only run the dehu it'll bake my tent. To save money I can get away with running a fan at the dehu to control nighttime temps. During the day I have to set the window ac on exactly at 6.5 and low to maintain proper temp. But it's a dance for sure. Mine took me a while to get right. On my days off I'd watch it through the ac infinity app to see where it was at all day and adjust accordingly. One thing that helped a little was my intake vents have 4 inch duct hooked up to it, so light doesn't come in. Depending on how humid or hot it is that day I'll either swing them over to the dehu or ac side. It'll makes a few degree difference inside the tent. It's mostly just to save money by not turning the ac up higher. I've spent so much time and effort getting my vpd right, it's the one area I can speak with at least a little confidence.

Got a Govee Bluetooth thermometer/hygrometer yesterday to be able to actually see what is going on and when throughout the course of the day with temp and humidity. For $25 for 2 units, I am a big fan. That said,we will see how they hold up in the long run. The app shows temp, humidity, dew point, and vpd. You can see on the chart where lights went off this morning and temps dropped quickly. The humidity started to spike, but I kicked on the dehumidifier and you can see where that dropped down as well.

I've had one of the WIFI Govee units in my tent for about a year and a half and they work fine, you won't have them fall apart quickly. Note that the VPD won't be correct since it doesn't account for leaf surface temperature, but is based upon air temperature instead and has no offset. It's nice to see the graph, but know that you're not where it says you are.

On the humidity, I think you're on track to aim at 50% on your humidifier, or if it's cooler, aim at 45% and use the extra heat to your advantage. If you're keeping in that 45-55% range and maybe tipping a bit higher for a few moments at lights out, you're doing pretty good, make sure you have good circulation in your tent so you're less likely to have PM issues.

I further control tent humidity and temps by using the AC Infinity controller to goose my intake and exhaust fans up and down according to temperature and humidity triggers. So, humidity goes up, fans turn faster, drier cooler air comes in the tent and the hotter wetter air goes outside. The AC-I controllers also give VPD graphs but allow for offset, so they're more accurate.

Good to know on the vpd. I brought home a laser thermometer last night to check leaf temps. If I remember correctly, they were between 70 and 75 or so when it was 80-85 in the tent. I will do some more checking this evening and get more exact numbers so I know the actual difference between air and leaf temps.

TCH said:

Good to know on the vpd. I brought home a laser thermometer last night to check leaf temps. If I remember correctly, they were between 70 and 75 or so when it was 80-85 in the tent. I will do some more checking this evening and get more exact numbers so I know the actual difference between air and leaf temps.

Click to expand...

If you're using LEDs, I'd expect that difference to be much much smaller. I know that my LST measures at ~2.5f degrees less than the ambient tent temperature which is fairly well in line with what others using LEDs are getting, so I'd definitely try that again. I generally aim for my daytime tent temps to be 80-86 with it mostly staying in the 81-84 range and my lights-out time to be no lower than 76. I use a small 400w oil-filled flat panel heater in the tent for lights out (triggered by an Inkbird) and set for 77 to make sure it doesn't dip too low. Then during lights on I use my tent's intake/exhaust fans to try to keep temps below 86.

For humidity, I run dehumidfiers outside the tent set for 45%-50% while in veg, and then I back that down to about 40% during flower. I also have taken to taking mid-July to the end of August off from growing since that's the most humid/hottest part of our year and it's just difficult to keep temps & humidity reasonable. I have a small humidifier in-tent (triggered by another Inkbird) to raise the humidity if needed during the driest part of the winter.

With any setup that's not a sealed/AC'ed space you have to sort of 'balance' your temps & humidity the best you can, and finding a 'perfect' point is close to impossible, so it's a case of getting somewhat close.

Lights were on for about 30 minutes and the temp at the top of the canopy was 84° and the leaf temperature was pretty much between 72 and 75°. I will check again before bed after lights have been on a couple hours and see if the leaves warm up a bit.