Novice needs advice on ventilation

[mike54]

Greetings from U.K.My first grow last year was reasonable but had problems with temperature and humidity.My growing room is 6ft x 4ft x 5ft high. I grew about 8 plants in this space under 4 250watt cfl's ,6400k and 2700k.There are four 1" holes drilled each end of the floor to draw in fresh air.
I fitted an old cooker hood fan for extraction but nothing to tell me the cfm. Without the fan, the temperature rose to around 78 and humidity shot up .The fan, on its lowest setting (3 in all), brought the humidity down but pulled all the heat out down to about 60.Is the fan the problem.? The lights don't give off much heat as opposed to other sorts of lighting .Thought I might get one of those small bathroom fans 4" ,would that do.? Would really appreciate some advice.

 

[Spimp]

So the issue is too much ventilation?
What is the ambient air temp of the room where the "intake air" is coming from?

 

[mike54]

Hi their,thanks for replying. If you look through the holes I have in the floor,you can see grass.It's U.K.weather which says it all.Is the fan pulling in too much air from outside?

 

[Spimp]

Well, yes. But the issue is intake air temp. Wheather you get a smaller fan or not isnt gonna matter. 60 f is 60 f. Entering slowly or rapidly isnt gonna matter.
The only benifit I can think of a smaller fan would be keeping the Bulb heat in more. But if the heat is minute, I dont see it making much difference. 78 is a good temp for MJ. Maybe dont run an exhaust fan and makeit a passive exhaust? Is there any air movement from the holes if the exhaust is off?

 

[mike54]

Very little air movement from outside,when the wind blows there must be a bit,not very helpful ,am I ?What do you mean by passive exhaust ,just a hole where I have removed the fan ?
Thanks for taking an interest

 

[Spimp]

Yes. Passive meaning no forced air. Can you put a small desk fan in there for air movement and not freeze out the girls?
Happy 4th btw.

 

[mike54]

I will try a small desk fan to move the air.Would that be continuous or timed to come on and off ?

 

[Spimp]

Continous. I mean you can turn it off its it loud or whateveer, but keeping it on will make those ladies strong and able to hold up heavy buds. We all ike heavy buds!

 

[mike54]

what happens when lights are off,will it get too cold for them.?

 

[Apelles]

In those conditions HID lighting seems ideal!

 

[Apelles]

Put a bunch of rocks in there to hold on to the heat when it's lights out?... and a speed control on the fan and set lower, just to keep some movement.

 

[Farscape]

Hi dude, Imho You should be fine atm with UK weather (depending where you are).
I am on the South coast UK and have my plants in a shed with cold stone floor. My cabinet is built around an open chimney flue which is open atm, when it starts to get cold i cover over the flue and put in an electric fan heater to keep my girls warm controlled by a thermostat.
Cant talk more my missus is shouting at me to move my arse

 

[Apelles]

Hey there, I was just reading that if the roots are kept within range the rest of the plant can stand up to most anything within reason. So a solution may be to get a fish tank heater and adjust to the reach ideal root temp. After that... your likely in fine shape unless it gets' under 40*F or over 100*F. Just speculation on my part. Run this by someone with experience to be sure.