To GWE Braintrust...Your thoughts on controlling Relative Humidity during flowering

[Insight]

This RH stuff is driving me crazy. I've entered the flowering stage and trying to keep temperature and humidity within range.

My tent is 4'x4'x7' and using a can max 6" 334 CFM fan sucking air through a phresh filter...through the HPS hood ...and vented to the outside.

Vegetation with 600 watt MH was no real problem, had to add a small humidifier and kept temps around 75°F and RH around 45-50%.

With the 600 watt HPS on, the canopy temperature is never higher than 82°F with RH of 44%. When the lights go off, the temp drops down to 68°-72°F, but the RH increases to the low 50% - low 60%. The lower I get the temperature in the tent...opening the AC vents in the room and flaps at the bottom of the tent....the higher the RH gets (which is the laws of physics).

I can put a dehumidifier in the tent and run it when the lights are off...would need a compressor type to achieve RH around 40-50% at temps around mid 60's to low 70's...but that would raise the temp in the tent to around 78°F (based on experimenting with my current dehumidifier). GWE tutorials suggest low temps (65°F) at night with humidity around 40-50%.

I thought of using one of those small peltier dehumidifiers but everything I read about them says they don't really do anything, especially at temps lower than the mid 80's°F. Anybody using one successfully in a tent?

How are you controlling humidity?......or is low 60% RH at night not really a problem, I've got plenty of air blowing around the inside of the tent. I'll be able to check the inside of the tent in a few more hours...I'll feel the surfaces of objects in the tent and see if they feel "wet"?

TIA

[Weed Pharma]

If you have good airflow on/around the plants and strong ventilation bringing in fresh air, you will be fine.
There can be problems with low temps (<-68f) and increased humidity- WPM, pests etc.

Consider-defoliation to help manage this as well.


Having the RH between 40-60% will work for all grow phases with proper airflow/ventilation.
If you did nothing , you would still be fine!

[Insight]

Thank you....that is both helpful and a bit comforting. I've got 4 fans blowing away in the tent and the girls seem to love the wind.

[LuckyAcres]

The a/c doesn't help with rh?
Keeping my girls at 77F all day all night, using a 70pint dehumidifier but the heat generated is killing me, gonna need an a/c soon.

[Insight]

I thought the AC would help...even have a vent in the room where the tent is located....but the lower I get the temperature....the higher the humidity..and after some research....that's what does happen....Basically, if the moisture in the air stays stable...as you lower the temp...it can hold less water so it is more saturated therefore higher RH..

"TEMPERATURE LIMITS HUMIDITY
The temperature of a parcel of air puts a limit on how much water vapor (humidity) the parcel of air can hold. The warmer the air, the more water vapor it can hold. By the same token, cold air can hold significantly less water vapor than warm air.

HUMIDITY RESPONDS TO TEMPERATURE
Humidity is water vapor contained in air. At higher temperatures, air can hold more water vapor than the same amount of air at lower temperatures. For example, if a sealed parcel of air experiences a rise in temperature with no addition of water vapor, the relative humidity of the parcel of air decreases because the warmer air is capable of holding more water.

RELATIVE HUMIDITY IS BASED ON TEMPERATURE
The relationship between temperature and humidity is often expressed by a percentage called relative humidity. Relative humidity is the ratio of water vapor present in air at a given temperature relative to the maximum amount of water vapor the air at that temperature could hold."

[Beach_Town_Brit]

I'll admit I have the opposite problem, with the Santa Ana winds blowing right now my tent is down to the teens of RH! And I have both flowering and vegging plants in there.
It's not much in the way of advice, but I've come around to not worrying about temps and RH too much. I feel like we have all this knowledge, all these best practices, that have been developed by large scale commercial growers and trying to live up to those standards in a small grow can drive you crazy. As long as you're not having any mold issues, and you have a good oscillating fan in the tent then I'd be tempted not to "sweat" it : ) These plants will put up with a lot of "less than ideal" and still produce wonderful powerful weed.

[9fingerleafs]

Woooooooord. Great way to put it

[9fingerleafs]

You are entering the realm of uncertainty. Hahaha rh is a very complicated relationship between temperature. Moisture content. And most importantly the dew point. I don't really understand what sets the dew point.
i agree with pharma. With good airflow you will be fine. I'll add a chart to calculate how low of high the humidity can get taking in consideration the starting humidity and temperature

[Beach_Town_Brit]

And I think altitude and barometric pressure influence RH too. Probably the tides and moonphase as well!