Hey, first I'd say go LED to keep the heat signature at zero. You can check my grow journal for ideas.
I have to use CFL supplementary lighting just to keep my plants warm.

Secondly, have a nice tent in the attic and place it between 2 rooms below the attic floor. Cut a 4 inch hole in each bedroom ceiling and place a vent cover on them to hide the hole. One 4 inch hole is your warm intake from downstairs bedroom 1. Pipe this into the top of the tent as your fresh air intake.
Then, from the bottom of the tent, pipe from the opposite side of the tent to the second bedroom (exhaust). So you now have fresh air coming from one bedroom and an exhaust into another bedroom. You will need a good extractor and a carbon scrubber. (detailed in my grow journal).

In the winter you will need to insulate the outside of the tent and the in-take/out-take pipes. If you use the 600w HID lighting you will be keeping most of the heat as it will be pumped into the bedroom. But some will be lost to the attic. At night you can leave the extractor on and this might keep the plants warm enough. If they freeze they will die and when cold they will be stunted in their growth.

In the summer you will have to keep the air moving at a high rate and have extra fans up there to keep good air movement and stop mould.This will increase the number of waterings though.

I was thinking of doing an attic grow sometime too. Need to move into a house first. But it is very safe when your gear is in the attic. No clues of what you are doing. Be careful of the heat signature in the winter.

Hope I was some help.

Take care
silent leprechaun Reviewed by silent leprechaun on . help needed for attic grow hi all this is my first post but i have spent a considerable amount of time reading around. i wish to have a small set up (6 plants) with a 600 watt hps in a grow hut (heavily insulated) approx 4x4x7ft and was thinking about growing in the attic. i live in the uk and my attic is hot in the summer (very hot!) and very cold in the winter. i have read alot of posts stating it is not a good idea to grow in the attic due to the police heicopter and due to the temp problems but it might Rating: 5