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.
Boilers in steam locomotives work this way. Plate/fin heat exchangers have lots of thin metal plates or fins with a large surface area (because that exchanges more heat more quickly); heat exchangers in gas furnaces (gas boilers) work this way. Photo: Two types of heat exchanger.