Choosing the right boiler will ensure that your home is warm enough and that you have enough hot water whenever you need it, without spending more than you have to on your energy bills.

The INVESTA Real Estate team presents you with the factors to consider before choosing which boiler your home needs.

Before we look at the factors that affect boiler size, it must be ensured that we understand how its size is measured. Boiler size refers to output in kilowatts (kW) and not physical dimensions. A kilowatt is a unit used to measure the energy produced by the boiler in the form of heat. In general, the more heat and hot water you need, the higher the efficiency will be, although other factors also play a role in choosing the right size.

Modern developments in boiler technology mean they are now more efficient than ever. In the past home owners were often advised to choose a higher burning boiler to compensate for heat loss, this is no longer recommended. It will lead to wasted energy and is likely to result in you paying more than you need to on your gas bill.

Most households use a combination boiler, which serves both heating and hot water. They are practical and quite low cost to use and where there is only one bathroom they are sufficient to cover hot water needs.

If, however, you have a large family or your home has more than one bathroom, it may struggle to provide enough hot water. This is because the water is heated as it is used, rather than being stored in a tank – as in the past.

If you find yourself using more hot water, you will definitely want to consider whether a conventional boiler is the right choice.

Depending on the type of system you choose, it will also affect the size of the boiler you will need. A combination boiler is sized to provide hot water on demand and you will see its capacity in terms of how much water it can heat per minute up to a set temperature rise, eg. 12 liters per minute at 35 ° C.

A key factor that will affect the size of boiler you need is the number of radiators. If you have little, for example in a small apartment, then choosing the smallest boiler will give you the greatest level of economy and ensure that you avoid paying more than you need for energy.

An average three or four bedroom house usually has around ten radiators and usually requires a small or medium combination boiler, for example 24-30 kW. A larger house with many more radiators or a private bathroom will generally need one that is larger, usually 30-35kW.

If you have a house with up to twenty radiators, you may need a large 35-42 kW combination boiler to provide sufficient heat with the best economy, or better to change to a system boiler that could be larger in size.

In the past, the physical size of the home was often used as a factor in considering the appropriate boiler size. While this still plays a role, a much better way to choose the most effective and efficient boiler size is to have an expert calculate your home's heat loss.

Heat loss calculations take into account a number of factors such as floor area, number of radiators, number and type of windows, insulation and other aspects that will cause heat to be lost from your home.

The specialist will then use this information to calculate how much heat your home will lose on the coldest day of the year, allowing them to advise you on the optimal boiler size.

While this is usually not a concern for newer homes with a water supply, some older homes may not have a proper high pressure water supply and this can affect the type and size of boiler you choose.

A combination boiler must be large enough to cope with the amount of water that passes through it to be heated. The higher the flow rate, the larger the boiler will be.