Things You Need To Know When Choosing a New Boiler Re December 16, 2021

Things You Need To Know When Choosing a New Boiler

Boiler turning off

It’s not exactly shopping around for a holiday destination, or even as exciting as hitting the high street for a new outfit for that upcoming party, but picking the right boiler from more than a hundred different brands is pretty crucial, especially if you want to keep warm! We’re here to take the hassle out of the hunt and help make the process of buying a new boiler as easy as pie!

Boiler Type

The first step of the journey is to know the type of boiler you’ve got. Put simply, there are three types of boilers on the market; combi, system, and conventional boilers. Here’s a quick breakdown to help you understand these three boiler types; 

  • Combi boilers don’t have any tanks, they heat water from the mains water supply. Combi boilers tend to be the best option for most UK homes as they don’t require storage tanks and offer heating and hot water on demand.
  • System boilers have a hot water storage tank, usually in an airing cupboard. System boilers are usually found in households with more than one bathroom in use at the same time (high hot water demand).
  • Conventional boilers (known as regular boilers) have a hot water tank and a cold water storage tank (usually in the attic). Conventional boilers are useful for homes with low water pressure as they utilise a ‘gravity fed’ system, but due to the tanks involved, most homes switch to a combi boiler when replacing a regular boiler.

After you’ve figured out the type of boiler you currently have, you need to think about the type of boiler you’ll want to replace it with. Generally speaking, it’s usually easier to swap boilers if they’re the same type, for example, swapping out a combi boiler for another combi boiler. In some cases, this might not be doable, which means your boiler will take longer to be fitted. To know more about boiler swaps and how much they cost, check out our blog.

Boiler Size

The size of the boiler is measured in kilowatts (kW). A kilowatt is a unit that defines how much energy your boiler outputs in the form of heat. 

As a general rule, the size of the boiler indicates how powerful it can be. Choosing the right size kW boiler will ensure that your home is warm enough and you always have enough hot water when you need it. To find out what size kW boiler you need to heat your home, take a look at our guide. 

Here are our guidelines on the boiler size you’ll need for your home; 

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 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

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

With better home insulation and more efficient boilers, there’s no need to oversize your boiler, unless you were considering an extension, converting a room into an en-suite, adding another shower or adding additional radiators into your home. Basically, anything that would increase the hot water or heating demand from your boiler. In a nutshell, there is no need to oversize your boiler anymore, you would just be wasting energy – it’s bad for your bank account and the environment!

Flow Rate (sizing for hot water)

One of the considerations for the kW output of your boiler is the amount of hot water it will need to output. The hot water flow rate of a combi boiler is expressed as ‘litres per minute’ (LPM), this tells you how quickly a combi boiler can heat hot water. Litres per minute vary from 9LPM to 25LPM flow rate.

The higher the flow rate you require to heat water and fill baths more quickly, the higher the output combi-boiler you will need. System and conventional boilers are more efficient for larger homes but they are more expensive to install and require the storage space for a separate hot water storage tank.

Boiler Price

Although the price could be an indicator of which boiler is best for you, it’s not always the case, that’s why it’s always important to do your research before buying a boiler (or just get a quote from WarmZilla and save your time and money!)

There are many factors that contribute to the price you’ll pay to get a new boiler installed, such as boiler type, size, location and many more.

We’ve estimated below how much it will cost you to install a combi, system or conventional boiler.

Boiler type

Boiler (without installation)

Installation cost (without boiler)

Total (boiler + installation)

Combi£500 – £2,000

£500 – £1,000 

£1,000 – £3,000


£500 – £2,500 

£500 – £1,000 

£1,000 – £3,500


£500 – £2,500 

£500 – £1,000 

£1,000 – £3,750

If you’d like to read more about how much a new boiler costs in 2022, take a look at our blog which breaks down the cost for you.

All WarmZilla boiler prices include Gas-Safe installation as standard. It also includes a system filter, system cleanse, guarantee, smart thermostat, and any other bits and bobs you need to get your boiler up and running. Not all prices include boiler installation, so make sure your quote does as you’ll be looking at between £500 and £1000 to get a boiler installed.

Installation costs

Installation costs are one of the hidden costs when buying a new boiler – not with us though! 

Installation costs aren’t as simple to calculate as a boiler cost because they include various elements such as;

  • Gas Safe boiler installation costs – minimum of £450.
  • System Cleanse/Powerflush costs

A system cleanse is included in every WarmZilla installation. A system cleanse means adding strong chemicals to your heating system to clear out any sludge (rust from radiators and general build-up of gunk). The cost of the system flush using chemicals and inhibitors is usually around £30

On the other hand, a Powerflush (or Magnacleanse) is much more expensive, ranging from £300 – £600 depending on how many radiators you have in your house and taking up to half a day to complete. 

As a money-saving tip; unless you notice cold patches on your radiators (when they’re turned on), then the chances are you don’t need a Powerflush.

  • System filter cost

A system filter is fitted on the return pipe of your boiler and uses magnets to pull out any “sludge” that gets produced by your system over time, to keep it clean. A typical Worcester Bosch mini-filter retails for around £120, which you can get as part of the installation when you buy with WarmZilla.

  • Flue cost – approximately £80.
  • Plume kit cost – £100 – £150 (if needed).
  • Moving boiler cost – £150 – £500 (if needed).
  • Gas pipe upgrade cost – £300 – £500 (if needed).

Energy Efficiency Rating

Choosing a highly-rated, energy-efficient boiler is a great way to lower your heating bills and ensure you’re doing your bit for the environment. If you want to maximise your boiler’s energy, read our blog here.

The efficiency of your boiler can depend on a number of factors such as whether your boiler is a condensing or non-condensing unit, the age of your boiler, whether your boiler’s kW size is compatible with your homes needs and demands, and how many people are using the heating system at one time, etc.

Check out our most energy-efficient boilers 2022 blog before committing to a new boiler.

Brand Reputation

Brand reputation is what customers say about the brand. To find out more about your chosen brand, check out their TrustPilot reviews, Which? score or even Twitter.

Every year, consumer organisation Which? ask 8001 members of the public who bought a boiler in the last 6 years about how satisfied they are with the boiler and how likely they are to recommend it to their friends and family. They also ask 153 trusted trader heating engineers for their views on each boiler brand.

If you’re not sure which brands are best, we’ve got you covered! Here, you’ll find the best combi boiler brands 2022best system boiler brands 2022 and best conventional boiler brands 2022.


Nobody enjoys paying out for a new boiler, after all, we can all think of more fun things to do with our hard-earned cash! The cost alone is a terrifying thought, not to mention the disruption it can cause to your daily routine! It’s for exactly this reason you should shop around for boilers that are known for their long lifespan and brands that look after your boiler as much as possible.

The average combi boiler will last between 12-15 years. This depends on how much it has been used and the TLC you’ve given it throughout its lifetime.

Here, you can find a list of hot tips on how to increase your boiler’s lifespan and give it the best chance of living a long and fruitful life.

Awards and Accolades

One good thing to check out is the “Which? Best Buy Awards”- sort of the Brit Awards of boiler brands! These awards recognise businesses that have achieved positive change and deliver excellent products and services.

Some boilers are also built to be low-noise, so those who always complain that the TV, radio (or their partner’s snoring!) is way too loud – check out the Quiet Mark certification that rates products by noise output.


This indicates the manufacturer’s confidence and trust in their boilers, and at the end of the day, a long warranty gives you the peace of mind you need when you’re making a huge purchase like investing in a new boiler. But don’t confuse a warranty with a guarantee, there’s a distinct difference and it’s worth reading up on. WarmZilla offers a range of cover between 5 – 12 years depending on the boiler manufacturer and the boiler model. 

When you buy a new boiler with us, we’ll register your guarantee or warranty with the boiler manufacturer on your behalf. That’s another thing you don’t have to worry about!


You may be asking if aftercare is something worth spending even more money on and if it’s actually worth bothering with. The answer is an emphatic yes – simply because nobody wants to spend three hours on the phone trying to get their boiler fixed on a cold evening!

That’s why you need to check out our best boiler brand aftercare blog which reviews the best 4 boiler brands out there. We look at the brands’ online support, maintenance and support plans, boiler fixing rates, and repair value. We’ll also be looking at what customers feel about the brand and their aftercare to help you decide which boiler brand and support package is best suited to you.


There are some important things you’ll need to keep in mind when shopping for a new boiler such as; boiler type, size, flow rate, boiler price, installation costs, efficiency rating, reputation, longevity, awards and accolades, warranty and aftercare.

All WarmZilla boiler prices include Gas-Safe installation as standard. Each price also includes a system filter, system cleanse, guarantee, smart thermostat, and any other bits and bobs you need to get your boiler up and running. Not all prices include boiler installation, so make sure your quote does as you’ll be looking at an additional £500 – £1000 to get a boiler installed.

We advise having a look at the Which? Best Buy Awards and the Quiet Mark certification before committing to buying a new boiler.

Because it indicates the manufacturer’s confidence and trust in their boilers and a warranty gives you peace of mind when buying a huge purchase. You’ll know you’re covered if anything happens to go wrong.

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