Tips for Choosing the Right Boiler Size for Your Home Re June 7, 2024

Tips for Choosing the Right Boiler Size for Your Home

tips for Choosing the Right Boiler Size for Your Home
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    Choosing the right boiler size is crucial for ensuring your home’s heating system operates efficiently and meets your hot water demands.

    Key Takeaways

    • Boiler Size Matters: The size of your boiler, measured in kilwatts (kW), directly impacts its ability to efficiently heat your home and provide hot water. Choosing the right size is crucial for energy efficiency and comfort.
    • No More Oversizing: While oversizing boilers was once common, modern energy-efficient boilers and better insulation it’s now unnecessary and wasteful.
    • Factors Influencing Boiler Size: Several factors determine the ideal boiler size for your home, including the number of radiators, insulation levels, fuel type, water pressure, and potential use of alternative energy sources.

    An undersized boiler will struggle to heat your home adequately, while an oversized one will waste energy and money.

    The key factors that determine the ideal boiler size include the number of radiators, bedrooms, bathrooms, and the type of boiler you opt for – combi, system, or conventional.

    Combi boilers typically require a larger kilowatt (kW) output to heat water on demand, making them suitable for smaller to medium-sized homes. In contrast, system and conventional boilers with storage tanks have lower power outputs as they heat water gradually. Assessing your home’s size, heating requirements, and hot water usage will help you select the perfect boiler size, be it a compact combi boiler or a higher-capacity system or conventional unit.

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    Power input, output and efficiency

    Boiler efficiency is calculated by evaluating the fuel it converts into usable energy and how much fuel is wasted throughout the process. Depending on the percentage, the product will receive a rating, in the form of a letter, which will help you identify which products are more energy efficient.

    Heating up your home is a large percentage of your energy bills, so having an efficient boiler is a must. The better your ERP boiler rating, the cheaper your energy bills will be. The Energy Savings Trust estimates that installing a new boiler could save the average household up to £200 every year on their gas bill.

    Modern condensing boilers are potentially 89-94 % efficient whereas a boiler that is more than 20 years old can be as little as 60% efficient. A boiler’s efficiency is the percentage of the total energy used by the boiler to provide useful heating. For example, a boiler which is 94% efficient will have 94% of the energy used going towards heating the home and only 6% is ‘lost’.

    You’ve probably seen efficiency ratings of A-G on other domestic kitchen appliances and boilers are the same. Modern boilers must be A rated and this will be shown in their literature.

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    When we talk about boiler size, it’s not hard to get a little mixed up. It’s not height, width or depth that we’re discussing, but rather its output in kilowatts (kW). The more power the boiler can generate in kWs, the bigger it is in terms of ‘size’.

    A kilowatt (kW) is equal to 1,000 Watts and in any situation, is a unit that measures the energy generated per second by your boiler, otherwise known as the boiler’s power. From 12kW and 18kW, to 32kW and 40kW, these figures show the maximum energy the boiler is capable of producing each second.

    Calculating Your Boiler Size Requirements

    As a general rule, the bigger your home and the more radiators, hot taps, and showers you have, the more powerful the boiler you need.

    A single-occupant bungalow will require a much less powerful boiler than a family of six living in a five-bedroom house with three showers.

    However, choosing the biggest boiler is not always the best solution. If you get a boiler with a much higher capacity than required, you’ll waste money on the initial purchase and running costs. Conversely, a lower-powered boiler for a large family may frequently run out of hot water and provide tepid radiators.

    Factors to Consider

    To determine the appropriate boiler size, you need to calculate your household’s requirements, considering current and future needs (e.g., more occupants or additional bathrooms).

    The easiest way is to use our boiler survey, inputting details about your home, such as the type, number of bedrooms, bathrooms, and showers, to get a recommendation. Another method is to count the radiators in your home. As a rough estimate for combi boilers, you’ll need the following power outputs based on the number of radiators:

    • 10-15 radiators: 24-27kW
    • 15-20 radiators: 28-34kW
    • 20+ radiators: 35kW or more

    Combi boilers require more power because they heat water instantly, while system and heat-only boilers do it gradually by circulating hot water.

    A Gas Safe registered engineer can provide a more precise recommendation considering factors like home size, insulation, water pressure, and your lifestyle. They can also advise on thermostats, thermostatic radiator valves, and other accessories to optimize efficiency and effectiveness.

    Types of Boilers and Their Typical Outputs

    Combi Boilers

    Combination boilers, or combi boilers, are one of the most common types in UK homes. They heat hot water on demand, so no hot water is stored. Combi boilers combine a water heater and central heating boiler into one unit.

    They stay on standby and heat water instantly when required, but can only support one outlet at a time – either heating or hot water; not both simultaneously.If you have a large household using multiple water outlets, a combi boiler may not be ideal.

    Combi boilers are larger in size compared to system or regular boilers as they need to produce hot water on demand and heating for the home. They have two separate output ratings – central heating (CH) output and domestic hot water (DHW) output.

    The number of radiators can help determine the suitable combi boiler model, with outputs typically ranging from 24-40kW.

    Combi Boiler kW Size Guide

    No of bedrooms and bathroomsPoorly insulated propertyModerately insulated propertyWell insulated property
    1 bed + 1 bath20kW20kW18kW
    2 bed + 1 bath20kW20kW18kW
    2 bed + 2 bath24kW20kW20kW
    3 bed + 1 bath28kW26kW24kW
    3 bed + 2 bath28kW28kW24kW
    4 bed + 1 bath30kW30kW28kW
    4 bed + 2 bath32kW32kW30kW
    5 bed + 2 bath40kW35kW30kW

    System Boilers

    System boilers are ideal for larger properties or homes with higher hot water demand. They take water directly from the mains and heat it in a storage cylinder, eliminating the need for a cold water tank. This allows instant access to hot water at two or more outlets without pressure drop.

    System boilers do not need to be as powerful as combi boilers since they have a separate hot water cylinder. Their central heating output is lower, with typical outputs ranging from 15-32kW based on the number of radiators.

    System Boiler kW Size Guide

    No of bedrooms and bathroomsPoorly insulated propertyModerately insulated propertyWell insulated property
    1 bed8kW7kW5kW
    2 bed8kW7kW6kW
    3 bed10kW9kW6kW
    4 bed12kW10kW7kW
    5 bed15kW12kW9kW
    6+ bed18kW15kW12kW
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    Conventional (Regular) Boilers

    Also known as standard, traditional or regular boilers, conventional boilers use hot and cold water storage tanks to heat water. They use fuel like gas or oil to warm the water, which is then pumped to the hot water tank. When heating or water is turned on, this hot water travels to taps and showers.

    Conventional boilers are commonly found in older, traditional houses and are best for directly replacing an existing heating system. Like system boilers, they have lower central heating outputs compared to combi boilers, typically ranging from 12-36kW based on the number of radiators.

    Conventional (Regular) Boiler kW Size Guide

    No of bedrooms and bathroomsPoorly insulated propertyModerately insulated propertyWell insulated property
    1 bed7kW6kW4kW
    2 bed8kW7kW5kW
    3 bed9kW8kW6kW
    4 bed10kW9kW7kW
    5 bed14kW10kW9kW
    6+ bed16kW14kW10kW

    Getting the Right Boiler Size

    Selecting the right boiler size is crucial for ensuring optimal heating and hot water supply in your home.

    The key factors to consider include the number of radiators, bathrooms, occupants, and your household’s hot water requirements. Overlooking this can lead to either an undersized boiler struggling to meet demands or an oversized one wasting energy and money.

    While the options may seem overwhelming, understanding the differences between combi, system, and conventional boilers can help narrow down the suitable size range.

    Remember to account for potential future needs as well. Get a Quote from trusted professionals to ensure you make an informed decision tailored to your specific home and lifestyle. With the right boiler size, you can enjoy efficient and reliable heating while minimising energy costs and environmental impact.

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    1 Comment
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