Photon 55 warm air heaters take 100mm diameter flue. 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 size flue is required for a Photon55?
Information about Reznor's range of flue