I have a 2 foot, 4 tube t-5. They sit in a closet in a 3'x2.5' area. I can keep them 1 inch or closer (I'm around a lot). With my house temp ranging from low 60s - mid 70s, I can pretty steadily keep it 74-78F with a 44 cfm fan (120mm comp fan) on each side of the light.