They dont lie about the efficiency, I have a gas analiser, and can prove that some of these are up to 98% efficient in the winter.. sedbuk is a seasonal efficiency, not a constant... The criteria, in short, is that the savings made would be far less than the costs of installation, or if a condensing flue or drain cannot possibly be installed, this has to be applied for with the council, and very few are successful, if you live 20 storeys up, with no outside wall, you might just get away with it!
