Originally, I though this was going to be a straight forward question and then just now I checked something. To cut a lengthy explaination short...a friend has what we thought was a living flame fire, which sits within a brick chimney breast. Work is being done on the chimney on the roof and it was recommended that the existing square chimney pot connecting to this particular fire be replaced with a gas terminal. I rang a friend who is a gas registered plumber, who back in the day of Corgi, used to be a trainer. He said that a 5" GC1 would meet regulations, however a 7" one would be better. He said there would be less chance of restricting the, well something. I can quite remember what he said. He described the 7" cowl as looking like a cheffs hat. Anyway, the gas fitter who actually came to check the fire (another person, not my mate) said that a 5" terminal is sufficient and that a 7" may restrict the flue more. Something to do with wind blowing. Who is correct? To complicate things further, I now wonder if I have given an accurate description to my mate. I now think the fire is actually a DFE fire not a LFE. I think Ive just found out they are two distinctly different fires. I can tell you that the fire in question has, simulated coals and you can clearly see right up the chimney flue, if you peer upwards. It is in no way sealed to the chimney breast. Would this change the requirements? What type of gas terminal is needed? Also, should the plumber have swept the flueflu part of 'signing off' the fire. It was not a new installation, just a service. Many thanks for your patience reading this.