Originally Posted by Landragon

8 x 54 = really happy plants
4 x 54 = happy plants

They make plenty of heat, as watts are watts for the most part. They just feel cooler to the touch as their heat is spread over more surface area than a single HID. Ventilation will be needed and must be adequate. Somewhere between 200-400 cfm in 2x4x6 area if intake air is 70-75•F.