, whereby the heating circuit is pressurised using a high level cold water tank usually located in the loft. The open vented boilers, whilst being very traditional in the plumbing arrangement, are however usually wall-hung boilers which help to save large amounts of space.
Industrial and commercial boilers are also highly efficient but tend to have cast iron heat exchangers. They are often referred to as 'gas atmospheric boilers' and can produce outputs of 46Kw to in excess of 338Kw. A modern boiler would need to meet European Standards on emissions of Low Nox (Class 5) and Building Regulations Part L2A and Part L2B.
Most natural gas boilers are suitable for Propane LPG fuel options and require only a change of burner nozzle. Many boilers are now able to run in conjunction with solar panels where gas forms the secondary top up, heat source. Solar smart combi boilers are now being produced by many boiler manufacturers. Other new features available are economisers, or top box gas savers, where even more heat is recovered from flue gases by incorporation of a secondary heat exchanger.
In recent years hybrid versions of combination boilers have evolved whereby a small amount of water storage is provided within the casing of the boiler. These are known as storage combination boilers.
The heat provided is a radiant heat and thus creates very few convection air currents or draughts. The whole electric under floor heating system is controlled by room thermostats.
Traditional solid fuel boilers tend to have twin wall fluing systems due to the extremely high temperature of the flue gases.