What your engineer told you is true abeit in the right context.You no have to fit a condensing gas boiler if possible.There are certai criteria that would allow you to fit a backboiler such as if the hous is terraced,if the flue has to be extended by more than 2mtrs or if i was just not possible to install a condensing boiler without causing t much extra cost. To determine requirements your corgi installer will carry out a assesmen
-- gasgard