Is there any way I could obtain the proper Kw output rating for this 30 year old Windsor 3 Radiant gas fire, which does not have a specification or an ID plate.

AL, February 2010

you need to gas rate the appliance ! That will gas rate it in kw !
What gas meter do you have, dial or numbers ?
If you have a dial (looks like a clock with one hand) put your gas fire on full and time the dial to do one full rotation! if you have numbers in a row put the fire on full, write down the numbers, time 2 mins then write down numbers again!
Add that info and I will work it out in KW for you !

kye, February 2010