Dear *****, Thanks for prompt reply. Have made a Not - to scale picture of the area involved with the warm air heating. I do not know the route of the ducts.
1. The heater is serviced annually by BG, and they described the model as UT/RS 22-25 MA(?N)F It is about 15 years old, but still functioning very well
2 I do not know what the temperature reached inside the duct is, and don't know how to ascertain this information.
Sadly my husband, who planned the extension, is suffering from dementia, and cannot remember any details. I have found original details of every other appliance in the house, but not this one!!