Short answer
Commercial gas boilers are usually condensing modules (wall-hung or floor-standing) arranged singly or in cascades, or larger floor-standing boilers fitted with forced-draught burners. Choice depends on heat load, plant room space, flue route and redundancy needs.
Cascades
Several smaller boilers on a common header give redundancy and good part-load efficiency. Gas pipework must be sized for all boilers firing together — a common cause of lockouts at full fire.
Servicing and certification
Commercial boilers need annual servicing, combustion analysis at high and low fire, and a CP15 commissioning record when new.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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