The rear clearance of all models of Photon warm air heater is 450mm. Please see the Photon Installation Manual (https://www.reznor.co.uk/wp-content/uploads/2025/05/Reznor-Photon-Installation-Manual-EN-2025-05-D301310-Iss-6.pdf) for more information.
What is the clearance to the rear of the heater on the Photon?
Information on Reznor's range of warm air heaters