its a J&S johnson and starley but the filter is missing, the bottom front panel comes off and there should be a label on the inside telling you which model it is, its a very old unit and I would advise you to have it checked over before you use it, by an experienced engineer

Especially so if absent of a return air duct back to heater.if the vent is blocked or inadequate, it circulates toxic gases throughout the building and kills everyone inside.

That vent as you call it is part of the warm air system.its a J&S johnson and starley but the filter is missing, the bottom front panel comes off and there should be a label on the inside telling you which model it is, its a very old unit and I would advise you to have it checked over before you use it, by an experienced engineer
This is good advise as them vents are open/closable. So probably plenty of other things wrong with that also! Definitely worth getting it checked.
That is a Myson/Thorn warm air unit. Probably 30-40 model.
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