Accurate sizing of replacement boilers is crucial to ensure higher levels of efficiency and lower energy bills for homeowners. Helen Andrews, head of key accounts at Baxi, offers sizing tips for merchants to pass on to their installer customers.

Modern, efficient boilers can help homeowners radically reduce energy consumption within their homes. What’s more, by swapping an old boiler for a newer model, homeowners can save hundreds of pounds a year. However, in order to achieve maximum energy and cost savings, the boiler needs to be sized correctly for the property.

Every year, many boilers are installed that are either too big or too small and therefore fail to meet the demands of the property and its residents. As well as being inefficient, this also means that the boiler does not perform to the homeowner’s expectations and could potentially cause maintenance issues further down the line.

There are some misconceptions around boiler sizing and, as the first point of call for an installer looking to purchase a boiler, merchants are best placed to advise on the appropriate procedure. Here are some key points all merchant staff should be aware of so they can help installers choose the right size boiler every time.

Bigger isn’t always better

A common mistake when choosing a boiler is assuming bigger is better. Homeowners prefer to have surplus hot water available and will assume that a bigger combi boiler will do this more effectively. Installers too can be guilty of going larger, even when they have calculated the correct boiler size.

However, an oversized boiler will work harder than necessary, as it will cycle on and off to meet heating and hot water demands and consume more energy. Higher kW boilers are also more expensive to purchase, which means homeowners are already overspending on a boiler which is supposed to save them money.

Don’t just replace like-for-like

Boilers may also end up oversized when installers fit a like-for-like replacement. Merchants should advise installers to consider possible alterations to the home. For instance, the homeowner may have added double glazed windows, better loft insulation, or an extension, all of which can influence the home’s heating requirements. We’d always recommend the installer conduct a survey and calculate the correct output for every installation, and always make decisions on a case-by-case basis.

This same concept can be attributed to all aspects of a customer’s central heating system. For instance, when it comes to thermostatic or room controls, simply siting a new one in place of the old could be equally counterproductive. Changes in the home may mean a different location for the heating control is required, further compromising on the performance of the heating system.

Check the modulation ratio

Rather than choosing a boiler based on its maximum capacity – which it will rarely run at – it’s more important to look at its modulation ratio. This will show you the range the boiler can work to, as heating and hot water demands fluctuate throughout the day.

Some boilers can modulate their outputs to as much as 90%, ensuring the boiler matches demands more closely. If the boiler is modulating rather than cycling on and off it will also reduce unnecessary wear and tear on components, reducing the risk of costly call-backs and repairs.

As responsible retailers, merchants should work with installers and their customers to challenge perceptions of sizing and educate them about the impact incorrectly sized equipment has on a central heating system.

Helen Andrews is head of key accounts at Baxi.