I am giving myself a migraine trying to Figure out how to set up the carbon filter to the fan through the hooded light in a grow tent. I have 25 feet of ducting as well. I have a second fan too I suppose the other goes on the outside of the tent
Hang filter and run duct to lmap intake
Run duct from output side to fan. This will suck the hot smelly air through the lamp and out the exhaust port.
You need to control temperature in the big room, so when you refresh the air, you are getting the right temperature in the tent.
A 2nd fan can be set up to exhaust heat from the room if necessary.
Another way is: If you have a sealed room that contains your tent. You can set up you filter and fan in the room exhausating outside.
In the tent you run duct from an intake (low) port to the lamp, and duct from the lamp to an exhaust )high) port. This brings in cool air from outside the tent, and exhaust the hot air into the room. This method is a bit trickier due to the fact that you are counting on the air passing through the lamp allows the tent to be in a safe temperature range.
I also use a thermistata/humidistat switch to run my system
My charcoal filter is on the intake end. This works great. I am not too sure which is harder on the fan intake end or outgoing end.