Any suggestions as to the best thing to fill around a balanced flue for a boiler? Its likely that the hole in the wall is not going to be exactle the same size as the flue and therefore needs something to fill up the gaps. As I understand it, the outer part is for fresh air with the inner part being the hot exhaust. If we used expanding foam would we need anything special due to the temperature (like Fire Foam), or is the outer part not very hot? Any other suggestions other than expanding foam?
Thanks
David