advice needed please

sorry, i posted this in general, but figure this is the better place for it.

Hi all, I'm growing in a 1mx1mx2m (3.2ftx3.2ftx6.5ft) tent and the tent is in a storage room under the house which is 3mx2.5m within the basement.

I am running 400w HPS with a cool hood with a fan blowing air from the storage room through the side of the tent, into coolhood and out the other side of the tent and then out of the room in to the basement.

My temps are running fine and I have no issues with that, but my humidity.......

I am running a 4inch fan/filter and with an older dehumidifier within the tent, I can only get humidity down to 65%. (im flowering at the moment) I just ran a test and the humidity within the storage area where the tent is in, is sitting at 75%. True outdoor humidity is around 70%.

When the light goes on over night the humidity drops down to 50%, so that's fine.

If I increase the exhaust fan to say a 6inch or even an 8inch, would that reduce my humidity further? does adding more air flow have a big impact?

I believe I understand what you are asking. You want to decrease your lights off humidity, but your external air(ventilation intake) is only 5% lower in humidity than your point of lights off equilibrium(what humidity raises to at night w/ lights off).

You will not be able to reduce your humidity via air exchange to less than the humidity of your ambient air reservoir...unless you add heat into the room. Maybe a small, high grade-fire safe, tipover auto shutoff, ceramic core heater(Hooked up to a humidostat).

If that makes sense, to reduce the humidity, we either have to use heat to drive off moisture, or pump in dryer air from outside via the ventilation system. (Or buy a more powerful electric dehumidifier)

Adding more airflow will have an impact, but no matter how much airflow you have, you will never get the air in the chamber dryer than the air you are pumping into it without adding heat. When the HID is on, it is adding heat.

thanks man, you got what i was meaning bang on