Room temperatures for RDWC

[Royal T]

Hey everyone, I had a bit of a technical question I can’t seem to nail down by research.
how important is room temperature when growing in RDWC if I’ve got a chiller keeping water between 67-69 degrees? I recently got a dehumidifier to keep RH around 40 during late flower, but my room temps are in the high 80s sometimes low 90s.
Curious to know if I’m loosing out somewhere by having temps that high.

Second part to the question, if I do need to get those temps down a bit, would it be better to get an exhaust fan to vent to hot air? Or would a window AC unit be better to drop the temps?

thanks in advance!

 

[Arthur]

Depends on how important the terpenes are to you. Some terps will become volatile at just above 70* the number burnt off increase as the temps go up.

Also, temp/rH dictate how much and how fast your plant transpires fluids. It's a pressure difference, and getting the #s correct make a pretty large difference.
At 90* and 40% your in the danger area by VPD charts. Meaning too much pressure pushing fluids up and out. Increase rH, or drop temps move that # back in the right direction.
Edit: fluids moving too fast through the plant can cause her to take up more water, thus more nutes. Sometimes you can see overfeeding symptoms in a plant that's just off in VPD #s.

 

[Mañ'O'Green]

@Royal T Welcome to AFN When you talk about getting an exhaust fan does that mean you do not have one? Air exchange is critical for growing to keep heat down and provide Co² to the plants. The flip side of that is using an AC in a sealed space and add Co². I have tried the latter and it was just too much effort and does not pencil out cost-wise until you have about 20 plants. So yes get an exhaust system. Get bigger than you need with a speed controller. That way you can run it slower and it will be much quieter.

 

[Royal T]

Thank you Arthur that makes a lot of sense, especially the overfeeding in relation to VPD. I did notice what I thought was a feeding issue when I introduced the dehumidifier, I wonder if that was it.
I’ve read that CO2 supplementation changes viable temps as well. Have you used CO2 before by chance? I think my VPD and CO2 levels are probably my least in-check numbers I have. If I drop my room temps, would you think it’s suffice to just supplant CO2 during veg?

 

[Royal T]

@Royal T Welcome to AFN When you talk about getting an exhaust fan does that mean you do not have one? Air exchange is critical for growing to keep heat down and provide Co² to the plants. The flip side of that is using an AC in a sealed space and add Co². I have tried the latter and it was just too much effort and does not pencil out cost-wise until you have about 20 plants. So yes get an exhaust system. Get bigger than you need with a speed controller. That way you can run it slower and it will be much quieter.

Hey there! No, I’m currently running in a bedroom with no additional ventilation. I have a reciprocating fan that blows across the canopy, but that’s about it. I’m so stuck on the next move to make. If I just added an exhaust fan, and vented air outside, I’m not sure that I could get temps down to where I would need them (summer is going to be hot!) but then the other option would be window AC unit and supplemental C02. If I ran both AC and Exhaust fan, I think my energy consumption would be pretty astronomical

 

[Arthur]

Thank you Arthur that makes a lot of sense, especially the overfeeding in relation to VPD. I did notice what I thought was a feeding issue when I introduced the dehumidifier, I wonder if that was it.
I’ve read that CO2 supplementation changes viable temps as well. Have you used CO2 before by chance? I think my VPD and CO2 levels are probably my least in-check numbers I have. If I drop my room temps, would you think it’s suffice to just supplant CO2 during veg?

I ran it years back, C02 allows for higher temps, but brings a ton of other problems that then need to be dealt with. Plus the cost of refilling bottles etc. For me, it was not worth the added expense.

 

[Royal T]

I ran it years back, C02 allows for higher temps, but brings a ton of other problems that then need to be dealt with. Plus the cost of refilling bottles etc. For me, it was not worth the added expense.

Did you run the CO2 in veg? Or just opt out of it all together? I appreciate your help a bunch, thanks again!

 

[Mañ'O'Green]

Your plants can tollerate the high 90s without issues until the last couple of weeks when it should get "late Fall" conditions 64°F night and 74°F daytime to produce the best terpene profile. I live in the desert and fight 105°F days with ZERO RH. I have too run my lights opposite of the day to help with heat but sometimes it just cannot be in the good zone. I usually grow photoperiod plants in the summer because they seem to tolerate the heat better and take until the actual fall to finish blooming. By then I can get the temps into the desired range.

I am going to try some autos this summer as the strains available seem to be better for heat?

Get an exhaust system no matter what else you do. The ambient Co² is about 400ppm. It will be higher in your house depending on how many people live there as they exhale. Gas cooking appliances raise indoor Co² as well. 6 plants in my 4x6x8 - 192 cubic feet space will reduce the Co² level below 200 in less than 30 minutes without the exhast system on and this is a level that stops growth.

 

[Arthur]

Did you run the CO2 in veg? Or just opt out of it all together? I appreciate your help a bunch, thanks again!

Only ran in flower, was running photos then. Veg was done in another room.
With CO2, you run your tent sealed, no extraction to maintain high co2 levels, this makes things even hotter in the tent... if you have an extraction fan on, your tent C02 levels will be the room co2 levels, not wanted if supplementing CO2...
Next thing you need sensors monitoring temp that extracts to a certain temp, then C02 sensors to keep the level at the target ppm.
I think what you need to do is get your environment dialed, in the long run it will serve you better. AC, mini split, humidifier/ dehumidifier... even little by little.. a window ac unit like you said, would go a long way.
I see what your trying to do here, offset your heat by adding CO2. I think your asking for more issues than you'll get benefits.
Summer indoor with my AC set at 82, I'd have lights on at 9 pm, lights off 9am. Keeps the lights adding heat overnight during the coolest hours , and the AC doesn't have to work as hard through the heat of the day with the lights off. Running autos, I have my lights shut off 2pm and come on @ 8pm (18/6)

 

[Royal T]

Thank you both. Some of these environmental things are so confusing for me, but this has helped so much. I’ll definitely be setting up an exhaust system to start while I try and dial in the rest