When it comes to choosing a new combi (combination) boiler, many homeowners struggle with the task. In the past, it was once common to choose boilers about 30 percent larger than actually needed, but this practice is now considered wasteful. In terms of sizing a new boiler, you must forget the notion that bigger homes require bigger boilers in terms of output power. All you need to know is that kilowatts (kW) is the foremost unit of measurement you must be acquainted with.
As a general boiler installation rule, certain home sizes require a specific kW range. For instance, most flats, apartments, and smaller homes with up to 10 conventional-sized radiators and a single bathroom requires a 24-27 kW boiler. Medium to large homes with 3-4 bedrooms, 15 radiators, and a bathroom would need 28-34 kW; and homes with at least 2 bathrooms and up to 20 radiators require 35-42 kW.
If you ask why sizing is very important, the answer is simple: you’d benefit greatly from the efficiency. An appropriately sized boiler will cost much less to run, which then produces a noticeable decrease in your electricity bills. This is because an appropriately sized unit will not turn on and off at irregular intervals to meet your heating needs.