Choosing the right size boiler will determine heat efficiency. A boiler too small is not effective. One too large will waste energy.
Boiler size depends on a number of household factors. The type of house (attached, semi-attached, or detached), house size (square footage), external wall area, and windows (size and number) all affect heat usage. Without proper insulation, floors and roofs lose heat. Perhaps the most important household factor is consumption. If there are several occupants or your requirements are high for other reasons, this will affect the boiler size you need.
The Right Size
The size of a boiler is measured in terms of output (kilowatts), not its physical dimensions. A boiler should be selected on the output needed to meet the demands of your home. You can approximate space requirements by calculating the square footage of the home.
Measuring windows and exterior walls will consider potential heat loss. You can also add together the recommended heat output for every radiator. As buying a boiler can be a significant investment, engineers are available for home evaluations. They can give quotes on what size boiler you may need. Remember, proper boiler sizing leads to greater boiler efficiency and lower operating costs.