Grow room too hot, humidity too low

putyourlightson

putyourlightson

Member
Hey guys,
I'm getting ready for my first grow and everything is set. But as I turned on lights and exhaust, I get high temps and low humidity. The tent sucks in, so negative pressure is ok. No plants yet, but constant readings inside the tent are: 27.5 C and 37% RH.
Mention is I am unable (totally out of the question) to vent the tent outside the house or to get air inside. So I get air from inside the house and vent it back into the house.

I understood that if i am too rise humidity, temperature also rises.
If I open more of the intake, humidity drops. Same for connecting the small clip fan.
If there will be plants, humidity will rise, but also will temperature, right? Thing is that I cannot even germinate well in these conditions - 37% RH.
One thing that's hindering me would be the curved ducting. I thought about getting the carbon filter and the exhaust vertically, to prevent the first curving. But there will be longer ducting - some 1.5 in total, i guess.
Would a combination between a large oscillating fan (to lower temp), a humidifier (to grow RH) and a dehumidifier (to keep the balance) work?

Specs are:
Tent: Mammoth Lite100 (100x100x180cm)
HPS 400w (Sylvania Grolux Dual spectrum) with ETI Duo 400w ballast
Vents Extractor VK150 - 495m3 / 64w
Carbon filter: Pure Filter 400 - 680m3
1 meter of ducting, curved to go through the roof of the tent, then curved again on top of the tent.
Small clip fan
Passive intake (low left)
(pictures attached)

What can I do and how can I start growing? I would appreciate your inputs.
Thanks a lot.
 

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why cant you germinate in those temps / rh?....i germinated and got all my seeds to sprout sitting above baseboard heater, 82f/21%rh

Mist the newly sprouted babies and cover them with ziploc bags or clear cups or something to create a humidity dome. once they grow a little you can remove the dome and let them grow normally.

some growers around here never get up to 30-40% rh during our winter months, we all still grow.

Your temps while a little high are still within range. Definitely not too high that plants wont grow.

As your plants get bigger they will begin raising the RH themselves.

Keep your flaps opened a little on the bottom of tent for passive air flow while lights are on. Close them up when lights are off and you dont want to let any light in the tent.
 
to add to my above post.

Adding humidity will drop your temps , adding a small humidifer will increase your rh and drop temps 2-4f. it does for me anyway.

you will also notice, when the lights go out and the temps drop in your tent, you will always see a rise in your rh.
 
Right now i have 12 seedlings under t5. 29.5c and 25%rh. Doin fine... its -30c here right now. I germinated the seeds in the same room. Without the light. Used a space heater to keep the temp at 28c ish.

Once those seedlings get bigger and transpire more they will provide more humidity, as will the wet promix.

Bigger concern is... your exhaust / intake.

Once the plants get bigger the O2 they transpire will be exhausted in your house and it will choke off the co2 levels, which will be needed by your plants. If the co2 levels are low on your intake of air then your plants will suffer. They will develop brown spots, which is them eating themselves looking for co2.

Ask me how i know. Lol

Hopefully you can exhaust from your space to several rooms away, where the O2 will mix well with other household air that is richer in co2 (which humans expel from their lungs) before it gets drawn into your grow space.

Or... draw air from several rooms away into your grow space.
 
diggs99 said:
why cant you germinate in those temps / rh?....i germinated and got all my seeds to sprout sitting above baseboard heater, 82f/21%rh

Mist the newly sprouted babies and cover them with ziploc bags or clear cups or something to create a humidity dome. once they grow a little you can remove the dome and let them grow normally.

some growers around here never get up to 30-40% rh during our winter months, we all still grow.

Your temps while a little high are still within range. Definitely not too high that plants wont grow.

As your plants get bigger they will begin raising the RH themselves.

Keep your flaps opened a little on the bottom of tent for passive air flow while lights are on. Close them up when lights are off and you dont want to let any light in the tent.
Click to expand...

Hey man, thanks a lot for your advice, my heart's more at peace now :D
Been reading your journal for the past hour or so. Looks amazing, congrats! And it's great to you updated it frequently.
I've also researched a lot (like for the past 4 years lol) but i know it doesn't compare to practice :)) I think I'll make a journal like that too, for I'm a newbie, got a lot to learn and i think growing might get a little lonely without me sharing it with you guys.

I am waiting to germ my first ones. Going for Northern Lights AutoFem (Green House) and Amnesia XXL AutoFem (Dinafem). Lol, i've read that the Amnesia can be quite a challenge, but it was one of the few strains available. Lucky I've found those Auto NL, as they don't stretch much and are low on smell. Got an Ona Block and if smell shows up, I might get some gel too.

One question: would it be wise to germinate inside the tent with lights on and far away (but after I sink seeds into water for some 24h)??
 
putyourlightson said:
Hey guys,
I'm getting ready for my first grow and everything is set. But as I turned on lights and exhaust, I get high temps and low humidity. The tent sucks in, so negative pressure is ok. No plants yet, but constant readings inside the tent are: 27.5 C and 37% RH.
Mention is I am unable (totally out of the question) to vent the tent outside the house or to get air inside. So I get air from inside the house and vent it back into the house.

I understood that if i am too rise humidity, temperature also rises.
If I open more of the intake, humidity drops. Same for connecting the small clip fan.
If there will be plants, humidity will rise, but also will temperature, right? Thing is that I cannot even germinate well in these conditions - 37% RH.
One thing that's hindering me would be the curved ducting. I thought about getting the carbon filter and the exhaust vertically, to prevent the first curving. But there will be longer ducting - some 1.5 in total, i guess.
Would a combination between a large oscillating fan (to lower temp), a humidifier (to grow RH) and a dehumidifier (to keep the balance) work?

Specs are:
Tent: Mammoth Lite100 (100x100x180cm)
HPS 400w (Sylvania Grolux Dual spectrum) with ETI Duo 400w ballast
Vents Extractor VK150 - 495m3 / 64w
Carbon filter: Pure Filter 400 - 680m3
1 meter of ducting, curved to go through the roof of the tent, then curved again on top of the tent.
Small clip fan
Passive intake (low left)
(pictures attached)

What can I do and how can I start growing? I would appreciate your inputs.
Thanks a lot.
Click to expand...
Heat management ideas:
- cool tube HPS reflector
- switching to LED
- pumping room air out
- AC unit

RH management ideas:
- humidifier
- house plants
- switch to hydro



I use an inline duct fan + register boot + flexible ducting to pump the room air (and excess RH) back into the HVAC. This draws house air into the room and allows me to pump hot humid air away and treat my house like a heat sink.

Hydro is going to add RH. Airstones in reservoirs or DWC add RH.

Once your plants are growing good you'll probably have too much RH if you're in an enclosed environment.

Cool tubes are great for HPS and really help cool tents down. Adding the inline duct fan to exhaust the hot air filling the grow room coming from the cool tube exhaust would be recommended.

I notice my tent can only heat up about 7°-8° more than the ambient room temp before it reaches a point of equilibrium where it dissipates it as fast as it's absorbing. Exhaustig my grow room using the inline duct fan + the register boot through the house HVAC to keep it 7°f cooler than my target internal tent temp, makes the internal temp of the tent right on the money during lights on, and 7°-8° cooler during lights off (my 2'x4' tent uses a 400cfm exhaust fan for gas exchange).

If you can't vent, or exhaust, or open windows or doors, I'd say ditch the HPS and get a few QBs. That way you have one less issue to worry about (heat) because they run so much cooler.

The higher the RH the less the plants will suck up nutes. The lower the RH the more they'll suck up. If you're running lower RH then what's recomended for the current stage of growth that your in, you'll want to dilute your nutes so that your plant doesn't take up more than it can handle. Look up VPD. I'm just learning about it myself.
 
Last edited:
Gquebed said:
Right now i have 12 seedlings under t5. 29.5c and 25%rh. Doin fine... its -30c here right now. I germinated the seeds in the same room. Without the light. Used a space heater to keep the temp at 28c ish.

Once those seedlings get bigger and transpire more they will provide more humidity, as will the wet promix.

Bigger concern is... your exhaust / intake.

Once the plants get bigger the O2 they transpire will be exhausted in your house and it will choke off the co2 levels, which will be needed by your plants. If the co2 levels are low on your intake of air then your plants will suffer. They will develop brown spots, which is them eating themselves looking for co2.

Ask me how i know. Lol

Hopefully you can exhaust from your space to several rooms away, where the O2 will mix well with other household air that is richer in co2 (which humans expel from their lungs) before it gets drawn into your grow space.

Or... draw air from several rooms away into your grow space.
Click to expand...

Hey Gquebed.
First, congrats on your seedlings, waiting to hear more about them.
Ok, thanks about your exhaust/intake and CO2 input. I was just thinking about that last night, trying to solve the problem.
First of all, I live in the same space where my grow room is. Lol, don't have a lot of space. So I am breathing and expel CO2 (me and my dog, too). Will that help? And if not enough, would some CO2 tablets work the magic?
Aside of that, I can open the window at times, to bring fresh air in. Temps will drop, yea, but I hope it will help. I really cannot exhaust outside the room I'm living in.
Thanks again. And waiting for your feedback
 
Room exhaust back into HVAC...
USER_SCOPED_TEMP_DATA_orca-image--1266968089.jpeg_1549219446434.jpeg USER_SCOPED_TEMP_DATA_orca-image-694533633.jpeg_1549219637272.jpeg

Shut the room door and crack the window for negative pressure and to draw cool outside CO2 & air into room.
 
Last edited:
ChiefRunningPhist said:
Heat management ideas:
- cool tube HPS reflector
- switching to LED
- pumping room air out
- AC unit

RH management ideas:
- humidifier
- house plants
- switch to hydro



I use an inline duct fan + register boot + flexible ducting to pump the room air (and excess RH) back into the HVAC. This draws house air into the room and allows me to pump hot humid air away and treat my house like a heat sink.

Hydro is going to add RH. Airstones in reservoirs or DWC add RH.

Once your plants are growing good you'll probably have too much RH if you're in an enclosed environment.

QBs are awesome and can run at very cool temperatures.

Cool tubes are great for HPS and really help cool tents down. Adding the inline duct fan to exhaust the hot air filling the grow room coming from the cool tube exhaust would be recommended.

I notice my tent can only heat up about 7°-8° more than the ambient room temp before it reaches a point of equilibrium where it dissipates it as fast as it's absorbing. Exhaustig my grow room using the inline duct fan + the register boot through the house HVAC to keep it 7°f cooler than my target internal tent temp, makes the internal temp of the tent right on the money during lights on, and 7°-8° cooler during lights off (my 2'x4' tent uses a 400cfm exhaust fan for gas exchange).

If you can't vent, or exhaust, or open windows or doors, I'd say ditch the HPS and get a few QBs. That way you have one less issue to worry about (heat) because they run so much cooler.

The higher the RH the less the plants will suck up nutes. The lower the RH the more they'll suck up. If you're running lower RH then what's recomended for the current stage of growth that your in, you'll want to dilute your nutes so that your plant doesn't take up more than it can handle. Look up VPD. I'm just learning about it myself.
Click to expand...

Hey. Thanks a lot for your detailed input.

Thing is I cannot change the setup right now, as I've already spent more than 600$ on it. It may not seem a lot, but it was a burst.
Well, I might go for the cooltube in some months, yea, that wouldn't add much to costs and I know it will lower tent temp. But for the time being, I will go for a small 30$ humidifier and a larger (some 100+$) dehumidifier, to manage RH.
I've read that in vegetative stage, I should go for a higher RH, and lower it in flowering.

About the nutes, I don't plan to give any Nitrogen based ones in the first place, as I've understood that the soil can provide it for some time. I got the Plagron Seedling & cutting soil for start, than a Biobizz Allmix, after transplant.
For flowering, I got the BudXL + Top Booster from House & Garden. But anyway, still a long way 'till I get there :)

Will be looking forward on your posts, man.
 
putyourlightson said:
Hey Gquebed.
First, congrats on your seedlings, waiting to hear more about them.
Ok, thanks about your exhaust/intake and CO2 input. I was just thinking about that last night, trying to solve the problem.
First of all, I live in the same space where my grow room is. Lol, don't have a lot of space. So I am breathing and expel CO2 (me and my dog, too). Will that help? And if not enough, would some CO2 tablets work the magic?
Aside of that, I can open the window at times, to bring fresh air in. Temps will drop, yea, but I hope it will help. I really cannot exhaust outside the room I'm living in.
Thanks again. And waiting for your feedback
Click to expand...
Co2 additives dont seem to work in my experience.

Opening the window is an option. Can you run exhaust ducting well away from the tent? The exhaust will need to mix well with the fresh air before negative pressure sucks it back to the tent... which will help with cooling...
 
Gquebed said:
Co2 additives dont seem to work in my experience.

Opening the window is an option. Can you run exhaust ducting well away from the tent? The exhaust will need to mix well with the fresh air before negative pressure sucks it back to the tent... which will help with cooling...
Click to expand...

I think I may be able to get some more ducting - to get to the window. It would be best to move the tent near the window, but cannot do that right now, as the room's heater stands just below it. And I need the heat - as it gets really cold around here these months - but the tent wouldn't like it. In the summer, maybe. Don't know, guess I will start with this, get a humidifier and try to keep things balanced.
Will keep you posted.
 
putyourlightson said:
Heard about that, but didn't research it yet. I shall. Thanks, man.
Click to expand...
The more humid the air is the less they can cool.

I live in a dry climate. I use large swamp coolers in my rooms, not so much for cooling but for the humidity addition. They are basically giant humidifiers. I plug them into the humidity output of my autopilot controller. They do some cooling and that takes a little load off the AC. The AC is constantly dehumidifying and the swamp cooler is adding humidity to keep the RH% where I want it.

I hope this helps you. The swamp coolers that have the float valve are best as you can hook them up and never have to refill the tank.
 
Hot air holds more water than cold air. That's why your windows "sweat." The warm humid air comes into contact with the cold window and as the air cools it loses energy and can't hold onto as much water and so the water is condensed.

When adding moisture to hot air watch for temp swings (during lights off) as that moisture will have nowhere to go but condense if your room temp gets too cool.
 
ChiefRunningPhist said:
Hot air holds more water than cold air. That's why your windows "sweat." The warm humid air comes into contact with the cold window and as the air cools it loses energy and can't hold onto as much water and so the water is condensed.

When adding moisture to hot air watch for temp swings (during lights off) as that moisture will have nowhere to go but condense if your room temp gets too cool.
Click to expand...

Hello again.
Thanks for the advice. I've germinated. Posted here: https://www.rollitup.org/t/first-grow-from-day-0.984363/
 
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