May 12, 2021

Which Boiler is Best for an Apartment?

When your old boiler breaks down and it comes time to replace it with a new one, it may seem difficult to select the right one for your home, particularly now there is such a wide range of boilers available on the market, each one promising something different.

Which Boiler is Best for an Apartment?

Choosing the wrong boiler for your home could result in issues such as inadequate heating, failing to meet the demand for hot water and expensive energy bills. In this guide, we’ll be taking a look at which boilers are best for an apartment.

To ensure you find the right boiler for your home, there are a few things you should consider first before buying. These include the:

  • Type of boiler
  • Output size
  • Physical size
  • Efficiency
  • Warranty Available

Type of Boiler and Boiler Size

When talking about boiler size, we are typically making reference to the output in kilowatts (kW) rather than the physical dimensions of the boiler itself. Kilowatts are the measurement of energy that is output by the boiler in the form of heat. The right size of boiler for your home depends on your demand for hot water as well as the number of bedrooms, bathrooms and radiators you have in your home. Generally, the larger your demand for heat and hot water, the higher the output you’ll require.

The kW outputs are measured differently for each type of boiler, so you should choose the appropriate kW for the type 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 instant hot water, reducing the need for a separate hot water tank. One benefit of combining two different boilers into one body is that it takes up significantly less room in your home compared to system or regular boilers, making them perfect 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

If you’re planning to purchase a combi boiler, use the table above to work out what size boiler output you’ll need for your apartment. Generally, apartments have fewer bedrooms, bathrooms and radiators than houses so you’ll likely need a boiler with an output between 24kW and 28kW. To find out which combi boiler is right for your apartment, simply answer a few quick questions here.

System Boilers

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

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

If you’re planning to purchase a system boiler, use the table above to work out what size boiler output you’ll need for your apartment. Generally, apartments have fewer bedrooms, bathrooms and radiators than houses so you’ll likely need a boiler with an output between 12kW and 15kW.

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. Instead they store hot water in a cylinder until it is 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+

If you’re planning to purchase a regular boiler, use the table above to work out what size boiler output you’ll need for your apartment. Generally, apartments have fewer bedrooms, bathrooms and radiators than houses so you’ll likely need a boiler with an output between 10kW and 18kW. You’ll also likely need a cylinder capacity between 120-180L.

There may be some exceptions when it comes to choosing the correct size of boiler, such as if you have a large family with a high demand for hot water or a home with lots of radiators (20+) and multiple bathrooms, in which case you’ll need a bigger boiler output to accommodate your additional heat and hot water needs.

You may also need a higher boiler output if If your home lacks cavity wall insulation, loft insulation, double/triple glazed windows and decent sealing around doors and windows as your home could be losing a lot of heat so would therefore need a higher output to provide the extra heat if you are not intending to make those changes in the near future.

Physical Size

If limited space is a problem in your home, finding enough room for a physically large sized boiler can be tricky and inconvenient. Thankfully, many manufacturers offer compact sized boilers for smaller spaces, such as in a kitchen cupboard or in a small airing cupboard. You may also find a combi boiler more suitable for your home than other boiler types as they are the most compact and do not require additional storage space for water tanks.


The efficiency of your boiler plays a huge part in how well your boiler operates as well as the cost of your fuel bills. The higher the efficiency of your boiler, the less fuel is burned and consumed and the lower your fuel costs. According to the Energy Saving Trust, you could save up to £380 a year by replacing your old inefficient boiler with a new A-rated efficient combi.

If cutting fuel costs and boiler efficiency are important to you, you should make sure to purchase an A-rated efficient boiler, meaning it is 90%+ efficient. At iHeat we only install A-rated boilers because we believe efficiency is incredibly important for both the environment and helping to keep homeowners’ fuel bills down. For more information, why not check out our helpful guide to the most energy efficient boilers.


Boiler insurance can be expensive and sometimes unnecessary, so long as the boiler you purchase has a lengthy 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.

Need a new boiler?

Get a quick fixed price quote

Our Top Boiler Picks for Apartments

Viessmann Vitodens 100-W 30kW

- From £2,245 (Including installation)

Efficient, compact, quiet and affordable, the Viessmann 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. It’s no wonder the Viessmann Vitodens 100-W 30kW Combi was reviewed as a Which? Best Buy in 2019.

Viessmann Vitodens 050-W 29kW

- From £1,825 (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 modernisations.

Worcester Bosch 8000 Style 30kW

- From £2,595 (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 Alpha 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.

Get a Free, Fixed Quote from iHeat

If you’re still unsure of which boiler is best for your apartment, there’s no need to worry. When you get a free, online quote for a new boiler with iHeat, we ask a few simple questions about your home to work out the right kind of boiler for you. Get a free, fixed quote here.

Get a fixed quote online

Get a fixed online quote today, installation as quick as tomorrow

Check Prices