Glossary

Kitchen/Utility Boiler - a standard white cased boiler without circulating pump or expansion vessel. Some manufacturers (like Firebird) produce a kitchen and utility version - the utility will be more cost sensitive and may not have all the features of a kitchen variant.
Combi or combination boilers feature a thermal store and provide instantaneous domestic hot water. They are sometimes more straightforward to install than a standard boiler combined with a hot water tank but are mechanically more complex and can have limited hot flow rates.
System Boilers are similar to kitchen/utility models but have integrated circulating pump and expansion vessel.
Boiler House models are designed to be fitted indoors but normally out of sight. They often feature a 'closed case' design with the burner exposed on the front of the boiler - this can make servicing easier.
Wall Mounted oil boilers are not as common as wall mounted gas boilers because of their weight and bulk however, Grandee & Thermecon both produce them at the lower end of the output range.
External boilers are specifically designed to be sited in the open air. They are available in standard, system and combi variations and feature weather resistant cases and integrated balanced flues.
Balanced Flues consist of two concentric tubes. The exhaust gases are ejected from the inner tube and the intake gases through the outer tube. This type of flue is used on a room sealed or external boiler.
Conventional Flues are connected only to the exhaust of the boiler and therefore fresh air must be allowed to enter the boiler room to enable combustion to take place.
Condensing or High Efficiency Boilers are now a legal requirement in UK except in certain regulated situations. The exhaust gases in these devices are so cool that they condense in the flue producing a slightly acidic 'water'.

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