Boiler Size Calculator

Choosing the right boiler size is essential to save energy, ensure your heating system runs efficiently and keep your bills within your budget.

Boiler size means the output in kilowatts (kW), which is the amount of energy needed to provide your home with heating and hot water. If you install a boiler that’s too small, it may not provide enough heat and hot water for your family. Buy one that’s too large and you’re wasting energy and money.

So, how do you find out what size boiler you need in your home? Use our free Boiler Size Calculator below to get a quick estimate. It’s based on your heating needs and the number of bedrooms, bathrooms and radiators you have.

Find the right boiler size by answering the questions about your home, then select the boiler type you want and click calculate to get your answer.

Why not try it now?

Boiler Size Calculator

What Size Boiler Do I Need?

As a general guide:

• Terraced houses or flats: 12-24kW
• Semi-detached or Bungalow: 24-30kW
• Detached home: 30-40kW

However, to find the ideal boiler type for your home, you do have to take a number of factors into consideration:

• The type of boiler
• The number of bathrooms and the hot water demand
• Number of radiators
• Property age and home insulation

If you have underfloor heating or a large family, then you are likely to need a higher hot water demand than the average household, which means you may need a slightly bigger boiler. If you are unsure, then ask a local heating engineer for any advice.

Combi Boiler

Below we take a look at what size combi boiler would be recommended if you were look at installing a new boiler in the following situations. This is also with the assumption a 3-bed semi-detached (or larger) is likely to have a second toilet or multiple bathrooms that require heating.

Combi boiler size is usually dependent on needing more power than system or regular boilers, largely due to the fact they supply hot water on demand.

System or Regular Boiler

Below we provide recommendations on what size system or regular boiler would be recommended based on property type and number of radiators. Again, this is with the assumption a 3-bed semi-detached (or larger property) has an additional bathroom or toilet that may also require new central heating.

Boiler Output vs Boiler Size

Just to clarify, by "boiler size" our calculator is referring to the boiler's output energy (measured in kW) and not the physical dimensions of the boiler or the space it requires. As such, out guide relates to how much heating and hot water the boiler is able to produce, rather than its physical measurements.

Having said that, if your system boiler size requires a high energy output, you don't necessarily need one that's going to take up a lot of room. Many modern boilers currently on the market are available as a compact design, often well-suited to properties that don't have much storage room.

Types of Boilers and Typical Sizes

There are three main types of boiler you can choose from; it’s important to assess the needs of your household so that your boiler matches those needs.

For example, if you have a large family and people are likely to use the showers at the same time, then you need a boiler that can provide strong water pressure even when more than one shower is being used.

Combi Boilers

Below are some of the key points to consider when choosing a combi boiler:

• On-demand hot water, as the heating and water come directly from the boiler unit
• Therefore a combi boiler doesn't require a separate hot water tank
• Energy efficient and space-saving
• Ideal for smaller homes
• Typical output – 12-35kW

System Boilers

• Uses a separate hot water cylinder
• Meaning you have to wait for the water to heat up
• Ideal for homes with more than one bathroom
• Delivers strong water pressure even with simultaneous use
• Typical output – 18-30kW

Regular (Conventional) Boilers

• Has a hot water cylinder and a cold-water tank
• Once the water is heated, it is automatically stored in the cylinder
• Mostly used in older, larger homes with a standard central heating system
• Your home needs space for a hot water cylinder and a cold-water tank
• Best for homes with more than one bathroom in a larger household
• Typical output - 25-40kW

How Much Does a New Boiler Cost?

Boiler prices vary according to size, brand and the type of system you choose, but as a guide you’ll find:

• Combi boilers – between £600 and £2,300
• System boiler – between £1,150 and £2,800
• Regular (conventional) boiler - between £500 and £1,700

Investing in the right size boiler for your home will save you money on energy costs and ensure that you have an efficient heating and hot water system.

Boiler Installation Costs

The average labour cost to install a boiler is between £600 and £1,700. These costs will depend on factors such as ease of access, boiler location and whether you need extras like pipework or flue changes.

If you want your boiler in a different location, then an Extension Flue Pipe will cost between £75 and £125 per metre, and extra pipework and fittings can range from £400 to £600.

You might also decide to install a smart thermostat with your new boiler so that you can control your heating from your phone. The average cost of installing a smart thermostat is around £265.

FAQs

Get Quotes From Local Heating Engineers

Only a qualified Gas Safe registered engineer can install a gas boiler. We can help you find heating engineers in your area to give you free, no-obligation quotes. Enter your postcode to get started. It’s free, quick and easy, and you’ll be able to compare at least 3 quotes to find the one that suits you best.

Request a quote from local Gas Safe Engineers today.