The CE mark, or formerly EC mark, is a mandatory conformity marking for certain products sold within the European Economic Area (EEA) since 1985. The CE marking is also found on products sold outside the EEA that are manufactured in, or designed to be sold in, the EEA.
Condensing boilers are water heaters fueled by gas or oil. They achieve high efficiency (typically greater than 90% on the higher heating value) by condensing water vapour in the exhaust gases and so recovering its latent heat of vaporisation, which would otherwise have been wasted.
A gas boiler is similar to a gas furnace in that it is a system that uses natural gas -- like propane -- to heat your home. However, a furnace provides heat by using air, while a boiler uses water. This water can be sent through pipes to provide heat to fan coil units to provide warm air, but it can also be used for heating swimming pools, baseboard heaters, radiant floor heaters, snowmelt systems, or even as steam to radiators.