Heat energy in buildings is often provided by combustion of solid, oil or gas fuels. This chapter is not concerned with the detailed design, construction and operation of combustion equipment, but only with some of the problems that may be encountered with normal types of equipment. Installations in large commercial and industrial buildings are usually designed and installed by experienced specialists and give fewer problems than normal domestic systems. Although architects are interested in the appearance of fittings such as radiators and fireplaces, they seldom have any knowledge of combustion technology, relying on the general contractor to supply and install suitable fireplaces, and the plumber and heating engineer to provide suitable boilers. Appropriately qualified and experienced plumbing and heating engineers can provide an efficient and reliable installation, but the incidence of defects suggest that many firms lack qualifications and experience, or even common sense in some instances.