Back Boiler Units are the same as Conventional Boilers but are fitted in the fireplace behind a gas fire.  The main advantage of this type of boiler is that it saves space and is unseen.  A range of boilers can be chosen with very attractive gas fire fronts, including living flame fires.  This type of boiler requires a flue liner fitting and additional ventilation may have to befitted in to the room in which the boiler is fitted.  A Back Boiler system may cost more to install than a conventional wall mounted boiler.