Hi guys,
I was just wondering.....
As im building a grow room in the attic and will have to run two ducting pipes to the outside world, are the fans i both need extraction and if so how do i get to suck up the air from the outside to go into my grow room

Get some roof vents put on your roof?

Napolean, there WILL be air flowing in and out of your attic, its required to keep down condensation and will have been designed in by the builder even for old houses. This venting may be as little as a 5 mm gap at the soffit board on both sides and not visable from the ground, eave venting can also be provided at the edge of the tiles above the gutter. For the the whole attic a thin strip adds up though. Ridge vents and tile vents may be present instead. Assuming you do have air flow you can vent the used air into the attic where it will just disperse, and extract the "fresh" air from the flat or house. Home air in winter will be warmer and cost less to heat (it may even have very slightly higher CO2 from your breath).

If in doubt about air flow, check for drafts in the attic especially at the bottom of the eaves

Have fun!

Oh and just so you know coz i may have taken your thread meaning wrong. Intake and extraction fans are 1 and the same, its just a matter of turning the fan the other way if ya want to blow or suck. On my RVK fans theres an arrow telling you which way the air flows