Iv been reading round the web and it suggests to increase air intake from outside to lower humidity, during the night periods yesterday it jumps from 50 to 70% in one day during the light off period 6am-6pm. The problem is, because the humidity outside tonight is going to be 75% ouside would that in effect make the situation worse, in effect introducing higher humidity from outside and making my tent 75% having drawn air from outside.

What im trying to ask is, would you only increase air intake from outside if the humidity outside is lower than your current grow room, or would you increase air flow to lower humidity and the outside humidity plays no part so to speak?

Been driving me nuts, not much information on this on the web would like to clear this up and avoid possible bud rot, I cannot find anyone who has asked this from mooching on various sites.

My intake incidently is drawing air from the loft, quite cold up there so would imagine it draws air from outside through little holes rather than from air rising through the house, can increase it, using about 40% of power, can also increase extraction which goes up a chimney but don't understand which one to raise or lower.

You can't compare humidity like that, because it is measured relative to the temperature - the warmer air is, the more water it can contain. It's bound to be higher at night because the air temperature is lower. If it's 50 during the day you have absolutely nothing to worry about, you're fine. If you draw the 75% rh air from outside into your grow room, you will find its rh drops dramatically as the light heats it up.

Always increase your extraction before you think about increasing your intake, you want negative pressure to prevent smell leaks.

Thanks mate, will increase exraction a little, humidity probably increased due to plant size increasing, was worried there for a min.

your extraction fan can only flow as much as your intake fan, unless you have passive vents also? if not increase both intake and exhaust proportionally