What Size Boiler Do I Need?

Boiler size is usually described by output in kilowatts, but choosing an output from radiator count alone can be misleading. Construction, insulation, room dimensions, glazing and how the property is used all affect heating demand.

Extensions and improvements may mean the old boiler output is no longer the correct reference point. A home survey should assess the current property rather than automatically replacing like for like.

The boiler must meet the building's heating requirement, while combi selection must also consider the hot water flow expected at taps and showers. A property can have a modest heating load but still need strong hot water performance.

For homes with several bathrooms or frequent simultaneous use, a system boiler and correctly sized cylinder may be more appropriate than an oversized combi.

An unnecessarily large boiler can cycle on and off more often instead of running steadily at an efficient output. An undersized boiler may struggle to meet demand in colder weather or provide the expected hot water performance.

Modern boilers can modulate their output, so both the maximum requirement and the boiler's lower operating range matter when specifying the system.

APS reviews the property, current boiler, emitters, pipework, controls, fuel and hot water use before recommending an appropriate model. The quotation then sets out the proposed boiler, controls and any system alterations required.