December 19, 2020

Which Boiler is Best for a 3 Bedroom Home?

Picking the correct size combi boiler for your home

Which Boiler is Best for a 3 Bedroom Home?

When the time comes to replace your old boiler, it can be difficult to work out which boiler is best for your home, especially now there is such a wide range of boilers available on the market.

What’s in this article?

Purchasing the wrong boiler for your home could result in issues such as inadequate heating, not enough hot water to meet demand and high energy bills.

To ensure you get the right boiler for your home, there are a number of things you should consider before buying, including the type of boiler, output size, physical size, efficiency and warranty available.

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Type of Boiler and Boiler Size

When talking about boiler size, we are often referring to the output in kilowatts (kW) as opposed to the physical dimensions of the boiler itself.

Kilowatts are the measurement of energy that is output by the boiler in heat form. The right size of boiler for your home depends on a few things such as your demand for hot water and the number of bedrooms, bathrooms and radiators you have.

The general rule of thumb is the higher your demand for heat and hot water, the higher the output you’ll require.

The kW outputs are measured differently for different types of boilers, so you should choose the appropriate kW for the right type of boiler you will be buying.

Combi Boilers

A combination or ‘combi’ boiler is a gas boiler that combines a water heating system and a central heating unit into a single body to produce hot water instantly, meaning there is no need for a separate hot water tank.

As you’re combining two different boilers into one body, they take up much less room in your home than system or regular boilers, making them ideal for homes where space and storage is an issue.

Output in kW Bedrooms Bathrooms Radiators
24-28 1-2 1 Up to 10
28-35 3-4 1-2 Up to 15
35-43 4+ 2+ Up to 20

As your home has three bedrooms, you would require a combi boiler with an output between 29-35kW.

If you live in an apartment/small bungalow, you would most likely need a 29kW boiler, whereas if you live in a detached/semi-detached house, you’ll need a 35kW boiler.

System Boilers

System boilers heat your central heating system and produce hot water for a water storage cylinder, directly taking their water from the mains as opposed to using a feed and expansion tank like a regular boiler.

Output in kW Bedrooms Bathrooms Radiators
12-15 1-2 1 10
18-24 3-4 1-2 15
30+ 4+ 2+ 20

As your home has 3 bedrooms, you’ll need a boiler with an output between 18kW and 24kW. If you have 1 bathroom, you’ll likely just need an 18kW system boiler, whereas a home with 2 bathrooms will likely need a 24kW boiler.

Regular Boilers

Regular boilers are also known as conventional or heat only boilers because they don’t provide domestic hot water on demand the same way combi boilers do.

They instead store hot water in a cylinder until it is required to be delivered to a tap or shower. An advantage of this is that they can meet a high demand for hot water at once, making them ideal for properties with multiple bathrooms, though when the water does run out, you'll have to wait for it to fill up again.

Output in kW Bedrooms Bathrooms Radiators
10-18 1-2 1 10
18-26 2-3 2-3 15
27-40 4+ 3+ 20
Cylinder Capacity (Litres) Bedrooms Bathrooms
120-150 1 1
180 2 1
210 3 2
250-300 4 2
300+ 4+ 2+

As your home has 3 bedrooms, you’ll need a boiler with an output between 18kW and 26kW and a cylinder with a 210 litre capacity. If you have 2 bathrooms, you’ll likely just need an 18kW system boiler, whereas a home with 3 bathrooms will likely need a 26kW boiler.

There may be some exceptions, such as if you have a very large family which has a high demand for hot water or lots of radiators (15+) and lots of bathrooms, in which case you’ll need a bigger boiler size to accommodate your extra heat and hot water needs.

A lack of cavity wall insulation, loft insulation, double/triple glazed windows and decent sealing around doors and windows mean you could be losing a lot of heat from your home and will therefore also require a higher output if you are not intending to make those changes.

For more information on choosing the right size boiler for your home, read our helpful boiler size guide.

Physical Size

If space and storage is an issue in your home, finding the space for a physically large sized boiler can be difficult and inconvenient.

Thankfully, many manufacturers offer compact sized boilers for smaller spaces, such as in a kitchen cupboard or in a small airing cupboard. The Viessmann Vitodens 050-W 35kW is an example of a high output boiler that is small in physical size.


The efficiency of your boiler plays an important role in how well your boiler operates as well as the cost of your fuel bills.

The higher the efficiency of your boiler, the lower your fuel costs. The Energy Saving Trust estimates that you could save up to £380 a year by replacing your old inefficient boiler with a new A-rated one.

If cutting fuel costs and boiler efficiency is an important factor to you, you should make sure you purchase an A-rated efficient boiler, meaning it is 90%+ efficient.

iHeat only installs A-rated boilers because we believe efficiency is incredibly important. For more information, why not read our helpful guide to the most energy efficient boilers.


Boiler insurance can be expensive and sometimes unnecessary, providing the boiler you purchase has a good warranty period.

At iHeat, all of our boilers have warranties between 7 and 10 years, during which time the warranty covers your boiler against manufacturing/material defects for both parts and labour.

To claim under the warranty, you must ensure that the boiler has been maintained and inspected by a Gas Safe registered engineer on an annual basis. See our terms & conditions for more information.

Our Top Boiler Picks for Homes with 3 Bedrooms

Viessmann Vitodens 100-W 30kW

From £2,060 (Including Installation)

Efficient, compact, quiet and affordable, the Vitodens 100-W gas condensing boiler is the most popular solution available at iHeat.

Featuring innovative technology and services combined with reliability and longevity and comes ready for smart technology, helping you to optimise your heating and save on energy costs. Vitodens 100-W 30 kW Combi reviewed as a Which? Best Buy 2019.

Viessmann Vitodens 050-W 29kW

From £1,685 (Including Installation)

With compact dimensions, low weight and quiet operation, the attractively priced Vitodens 050-W is a low-cost gas condensing boiler that will integrate effortlessly into any living space and does not compromise on quality; making it ideal for both new build homes and modernisation's.

Worcester Bosch 8000 Style 30kW

From £2,395 (Including Installation)

The latest Worcester Bosch boiler features a modern new design whilst being packed with innovative new features that help keep your home warm and your boiler working at its best.

Alpha E-Tec 28kW

From £1,545 (Including Installation)

The E-Tec range features a brand new stainless steel heat exchanger and is our smallest yet. Being compact allows an easy fit in a standard kitchen cupboard and servicing is made easy with front access.

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