How to choose a central heating boiler

Updated February 21, 2017

A central heating boiler can provide warmth to your whole house, warming everything from the water to the rooms, and ultimately the people inside. Unlike localised heating, central heating occurs in one place (usually a boiler or mechanical room) and then the heat is spread out via a system of pipes and duct work. A boiler generates heat via the process of fuel combustion-- here a chosen fuel (gas, oil or wood) is burnt and transformed into heat, making it one of the cleanest heating systems around, as far as indoor air quality is concerned. There are several factors to consider when updating and replacing your central heating boiler.

Decide which type of fuel you want to operate your boiler. Gas or oil are most common, and many prefer the convenience of gas since you can connect your unit up to a main gas supply and avoid having to replenish when empty. Wood burning boilers are more labour intensive, since the ashes must be regularly cleaned out. Also consider that the type of fuel can greatly determine the cost of the service and maintenance your system will require. It is more expensive to service an oil-burning boiler system, for instance, than a gas or wood-burning unit.

Calculate the size or capacity of the central heating boiler your space requires. Ultimately, the size of your building, the number of bathrooms and the number of people who occupy the house will determine the capacity you need. Below is a method to get a rough estimate of your needed capacity: 1. Add together the manufacturer's recommended heat output for every radiator in your home 2. Add 3kW to account for a hot water cylinder if your unit will also be used to heat water 3. Add 10 per cent to this figure to take into account very cold winter weather

Consider which type of central boiler heater best suits your needs--a combination, conventional or a system boiler. Conventional units are the most common--and can heat a home as well as its water throughout the house. The conventional boiler requires a holding tank and consumes the most energy of all boiler types. A combination unit supplies hot water on demand and does not require a holding tank or extra pipe work. Combination boilers usually cost less than conventional counterparts, but can take a while for water to heat up and are limited to only heating one tap at a time. System boilers give more consistent temperatures and flow rates as a result of the heating element being located within the storage tank. System boilers are by far the most expensive to install.

Compare energy efficiency ratings. Similar to furnaces, boiler energy efficiency is measured by assigning each unit an AFUE (annual fuel utilisation efficiency) rating. Cut your home heating costs by at least 30 per cent by installing a boiler with an AFUE rating of 90 or higher.

Choose which position is better suited to your home--wall hung or floor standing. Wall-hung boilers take up less space and are designed for installation in commonly used places in your house, such as a kitchen. Floor-standing boilers tend to be larger and noisier, have a higher output, and are installed in less frequented areas, like cellars or garages. The heat exchanger in floor-standing models can last longer than that of wall-hung models.


All boilers require regular maintenance to run properly with maximum efficiency. Consider getting a maintenance contract with a certified technician or company that is experienced in working with boiler heaters.


If you choose a boiler that is too small, it will run harder in an attempt to meet the needs of your household. You will see the extra labour reflected in your utility bills, and it will also cause your unit's energy efficiency to drop.

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