newbie neds venting help

[drambouie]

i have a 3" 50 cfm exhaust fan sucking hot air out the top of grow room and a 4" tube from the attic bringing cool air to the bottom of room for circulation, i was hoping the fan would suk* hot air out the top and negative pressure caused by the fan would suk* cool air from the tube. it seems to just suk* all the warm air from my house (verry little from the tube) and lower my temps in the house. the room isnt sealed, do i just need to add another fan to blow air into the tube from the attick or *suk it from the attick?

 

[Biffdoggie]

My guess would be the air resistance in the tube is more than your fan is pushing/pulling. If you really want to move some air get a bigger inline fan, make or buy a reducer and really push/pull it from one end of the tube or the other.

 

[drambouie]

in the tube i have no inline fan, i was wondering if i should add the exact size exhaust fan to it to blow some air through the tube. that way ill have 2 fans the same size, 1 blowing in 1 suking out. u think tha would help? this way im not creating negative pressure and sukin out all the heat from my house

 

[Hick]

the more efficient, my guesse would be to pull the air from the attic. Sealing the room would benefit too.

 

[KADE]

the more efficient, my guesse would be to pull the air from the attic. Sealing the room would benefit too.

Yup... easier to pull air then push it... it creates a vaccum in the tube and has to move through it.... this of course only works to a point... then u need a bigger, higher cfm fan...
On another note... I just bought a fantech 4" vortex fan.... gorgeous fan... soooo quiet... polished dust finish and moves air pretty damn well too.

 

[Biffdoggie]

A vortex is really what I was thinking of when I said "inline" fan too, I should have specified. Those things rock the air.

 

[drambouie]

home depot has a 4" inline fan about 40-80cmf for 24 bucks or a 3" exhaust fan 50cmf for 12 bucks. i already use a 3" one, should i get a second exhaust fan or an inline fan? which would work better? just the 3 incher now keeps temps at 85 steady. the 4" tube i have runs from the attick and would be able to bring down some cold air. venting hot air into the attick, would this throw off house temps?