Boiler Grants FAQ

Could you be entitled to a boiler grant? Learn all about them, along with the latest government funding in our in our latest FAQ

Learn more

Boiler size calculator – What size boiler do I need?

Shopping for a new boiler can initially feel like an overwhelming process due to the number of brands and boiler options available on the market, successful marketing campaigns by big brands and varying product warranties and after-sales, however, we are here to help guide you through the process.

Due to the costs involved with purchasing and installing a new boiler and that the large purchase should last a good few years, it is important to make the right choice of boiler suitable for your property and household habits to create sufficient heat and hot water as needed.

This article aims to help a homeowner decipher the property requirements of a new boiler, explains the various boiler types and will guide you through the boiler size needed.

The type of boiler required

When needing a new boiler one of the first tasks in the process is to establish which type of boiler would be most suitable. Commonly both the property requirements and household usage will determine which type of boiler should be installed.

There are three common types of boiler to choose from when looking to install a new boiler, as follows:

  • Combination boilers – Also known as combi-boilers, provide both heating and hot water directly from the mains without the need for a water tank. Not only do combi-boilers help to save physical space without the requirements of large tanks, but also, they can save energy without heating the whole tank, only heating what is required at the point of use.

However, there are limits to combi-boilers as they are typically suited to small to medium-sized properties only, depending on the number of bathrooms and household usage requirements. Another factor when considering a combi-boiler is the water pressure requirements needed to enable the system to work effectively.

  • Heat-only boilers – This type of boiler only provides heat energy, rather than heat and hot water like a combi-boiler. Heat only boilers supply the radiators directly via the use of a hot water cylinder.
  • System boilers – A system boiler is a closed system requiring a boiler and a cylinder system. System boilers are often most suitable for properties with low water pressure; however, most system boilers also require more space, than more compact boilers such as a combi-boiler.

Now, with some background knowledge of the various types of boilers, we can move onto the other factors that will impact the boiler size that will be most suitable.

Further reading:

What Size Boiler do I need for my Property?

Boiler sizes quoted on various models are not actually dimensions or capacity. The sizing measured in kilowatts is actually referring to the energy output that a boiler produces. Typically, the more heat and hot water needed for the property and household requirements, the higher the kilowatt output, or boiler size will need to be.

It may be tempting to opt for the highest boiler size that can be afforded however this would lead to energy being wasted and therefore the household would not achieve the best economic savings from reduced energy bills when installing a new boiler.

Factors that Determine the Boiler Size

There are a number of elements that will impact the most appropriate boiler size for the property. These are as follows:

The number of bedrooms – The size of a property to be heated will determine the size of a boiler needed. The more bedrooms that a property has would illustrate a larger size property which would require a higher output boiler.

The number of bathrooms – As mentioned, typically combi-boilers are usually recommended for smaller sized properties with one bathroom. The pressure of water is also a factor especially when considering a combi-boiler as the flow of water will determine how quickly baths are poured or the level of a power shower.

Should there be more than one bathroom in a property, a combi-boiler can struggle to supply the higher flow rate needed, and therefore a hot water cylinder system is often required.

Number of Radiators – The more radiators installed in a property extends the heating system and increases the power needed to supply the system. A property with lots of radiators and towel rails will require a higher boiler output size to heat the property effectively.

Related reading: 

Boiler Size Calculator

Taking all of the above information into account, our quick, free and easy to use calculator can estimate the boiler size needed for property and advise an indicative cost.

The calculator bases its suggestions on mid-range boilers and average installation costs to provide a rough estimate of the costs involved with installing a new boiler.

Final installed boiler prices will vary depending on the selected brand of boiler, the supplier and installation costs which can also vary depending on the location of the property. Online boiler suppliers can provide a cost-effective method of sourcing a new boiler and arranging an installation.

Other factors to be aware of

Unfortunately, the boiler efficiency advertised on branding or promotional materials may not be achieved once the boiler has been installed into your property due to a number of factors such as:

  • Insulation – Typically, British properties are not well insulated and therefore some energy efficiency will be lost by heat escaping through the property walls or roof. In addition, any gaps in windows, doors or letterboxes can create draughts that heat will escape through.
  • Water Pressure – As discussed, the pressure of water is a factor that determines which time of boiler would be more suitable. Should water pressure fluctuate, the boiler efficiency can be impacted.

Recommended reading: 

Boiler size calculator summary

Boiler sizing and marketing jargon can appear overwhelming when first looking into installing a new boiler, however, throughout this article, we have aimed to explain the considerations behind boiler sizing. As discussed, there are various considerations to take into account when selecting the most suitable boiler type and the most appropriate boiler size and also, there are no benefits to over-estimating the boiler size needed.

Therefore, should you prefer more tailored advice, it is recommended that an appointment is booked with a heating engineer who would be able to provide expert advice on the best boiler options for the property.

Further reading: