What are the benefits of installing a boiler with a wide modulation ratio?

Neil Mattock, Marketing Director at Vokèra looks at the benefits of a good modulation ratio:
Winter is on its way, Halloween is just around the corner and before we know Christmas will be here. At this time of year, homeowners naturally start to think about turning their heating on and are looking to installers to help them with lowering their energy bills.

modulation low ratio web
A low modulation ratio

When it comes to boiler replacement, installers can help their customers with better performance and energy savings by selecting a boiler with a wide modulation ratio.
In simple terms, a boiler’s modulation ratio refers to its ability to reduce from its maximum output to its minimum output. A good modulation ratio is favourable for two important reasons. Firstly, it reduces constant on/off cycling, improving efficiency and boiler longevity. To explain, if a boiler has a high maximum output of say 38kW yet only has a modulation ratio of 4:1 it will only be able to modulate down to 9.5kW. The problem with this is that when most rooms have reached the desired temperature and radiator Thermostatic Radiator Valves (TRVs) have closed, the demand on the boiler will be considerably less than 9.5kW. So the minimum output is actually higher than it needs to be and the boiler will constantly switch on and off – leading to fuel inefficiency and unnecessary wear and tear on its components and parts.
High modulation ratio
High modulation ratio

In contrast, a boiler with a high maximum output and a good modulation ratio will be able to modulate down to an extremely low output, lowering the general wear and tear on primary components and optimising fuel efficiency.
The second reason is uniquely associated with combi boilers, as it concerns the stability of domestic hot water (DHW).
The first UK combi boilers typically had outputs of 24kW and DHW flow rates of around 9.5l/m at a 35oC differential. Since then higher output models have been developed to improve hot water flow rates. Today, 38kW combis are commonplace, but installing a combi boiler with a high maximum output but a poor modulation ratio in a typical UK property is unlikely to deliver optimal efficiency, or comfort.
An appliance with a poor modulation ratio won’t be able to maintain a stable DHW flow temperature at a low flow rate, and might even cause the burner to switch off during operation. High power combis with a wide modulation ratio will allow good DHW performance without being ‘oversized’ on the space heating.
Modulation ratios matter and by educating their customers, installers can save homeowners a significant amount when it comes to their energy usage and bills.

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