Contradiction - extra exhaust fan increasing heat

Greetings! I have two variable-speed exhaust inline fans (And passive intakes down the bottom.)
I've just discovered that I get a higher temperature reading by 3 degrees C, 24.5 to 27.5, when I have my second exhaust fan running! What the!

The second one is on the wall of the grow tent, while the main/original is sucking out the ceiling.

I've got an indoor/outdoor remote thermometer with the sensor right in the middle of the plant canopy, among the flowers and getting direct light.
It's single plant in a large pot, with a spread out canopy from tying down.
The tent is approx 180cm high, and 80cm x 80cm wide.
The 400w open batwing reflector HPS is hanging halfway down the tent; as is a big but gentle non-oscillating circulation fan, hanging against the middle of the back at an angle pointing towards the front right corner. The HPS reflector is against it such that most air passes under, and a little air is blown across the top of the reflector wing.

... And yes, I've checked that the second fan isn't accidentally blowing in

I'm considering putting 50cm of duct so it draws air from a similar location as the top exhaust. Tomorrows experiment.

Can you remount the unit on the tent wall to outside the tent? Any motor is a heater.

hotrodharley said:

Can you remount the unit on the tent wall to outside the tent? Any motor is a heater.

Click to expand...

Oh fascinating idea!
Yes I'll give that a go - although I suspect that's not the problem, as the temperature changes really fast.
It's also really high, and pulls a lot of air, so I wouldn't expect warm air it produces to drift right down to the thermometer in a matter of seconds and warm it so much.
It seems more like turning it on greatly changes (or somehow reduces) air flow around the light.

Good thinking though! I'll experiment with that. Thanks!

Okay, I believe I've identified the problem as insufficient passive intake, or perhaps poorly arranged passive intake.
I unzipped the door a bit at the bottom and rolled it up, giving extra passive intake space on the front.
Finally, ramping up my second fan is correlating with lower rather than higher temperatures.

The tent has three rectangular patches with fly screens for passive intakes, one on each side and one on the back. They get dusty but I try to keep them clean.
It's also got two 6 inch duct holes, at the bottom near the front corners, which I've long kept propped open with short pieces of duct.

Perhaps turning on the second fan was shifting the flow of air from a general column, to a slip stream going mostly up the walls. This could also suggest insufficient or poorly arranged circulation.

Still much experimenting to do, but for now at least I can open the bottom of my tent and crank on my second exhaust fan when having heat issues.

(Hotrodharley, I didn't try your suggestion, after putting my hand on the fan and noticing no warmth)