I have a temp sensor in the cabinet to control the fan above the chiller. The chiller really doesn't run very often yet. I have my lights turned down while im cycling the tank. I have slowly started to increase the intensity of the lights. I'm suspecting when i get the light to the intensity I want, it will start heating the water and the chiller will run more. The chiller I have actually blows the air towards the cabinet door. I don't think it will be an issue for me. If your chiller blows air towards the rear, may i suggest putting a fan on the back where the air blows to keep the temp down.I'm noticing you kept the thin boarding for the back of the cabinet. Are you having any heat related issues due to the chiller be enclosed in the space?