I have two little rooms a grow room which is 3ft sq with a nice 400 HID Light.
My flower room about 4 / 8 ft sq with a 1000 HPS adjustable light and a 4inch extractor to bring fresh air in, a little 12 inch fan to circulate the air.
As am in my loft I’ve got 4 roof vents over my Flower Room to extract heat.