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Boiler size calculator

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If you’re reading this, chances are you may be scratching your head over which boiler is the right size for your home. While many make it seem as if it’s dependent on a multitude of factors or won’t even tell you how they determine which boiler is the right one for your home, it’s actually possible to work out which boiler size you need from the following three pieces of information:

  • The number of radiators
  • The number of bathrooms (with non-electric showers)
  • The number of people in the home (basically, the demand for hot water)

Please note that taking the above as a starting point should give you a pretty good idea of what boiler size you need. However, any Gas Safe registered engineer that is worth their salt will take into account other factors such as how well your house is insulated or whether you’re planning to extend your house. By the way, people often refer colloquially to the “size of a boiler”. What they really mean by that is its output, which is measured in kW. Below we have put together a boiler sizing guide that shows you different boiler models based on the number of radiators.

What size boiler do I need?

Find out below:

Gas boilers for properties with up to 10 radiators:
Combi boilers
Regular boilers
System boilers

Gas boilers for properties with 10-15 radiators:
Combi boilers
Regular boilers
System boilers

Gas boilers for properties with 15-20 radiators:
Combi boilers
Regular boilers
System boilers

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System boilers What is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi EcoBlue System 12 Gas Boiler 12 89.10% Up to 10
Baxi Megaflo System 15 Gas Boiler 15 88.60% Up to 10
Glow-worm Energy System 12kW Gas Boiler 12 89.30% Up to 10
Glow-worm Energy System 15kW Gas Boiler 15 89.30% Up to 10
Ideal Logic Max 15kW System Gas Boiler 15 93% Up to 10
Ideal Logic System 15kW Gas Boiler 15 89% Up to 10
Ideal Vogue GEN2 S15 System Gas Boiler 15 89% Up to 10
Ideal Logic Plus System 15kW Gas Boiler 15 89% Up to 10
Potterton Ultra System 12kW Gas Boiler 12 89% Up to 10
Potterton Assure 15kW System Gas Boiler 15 93% Up to 10
Potterton Promax System 15kW Gas Boiler 15 89% Up to 10
Potterton Promax System 12kW Gas Boiler 12 89% Up to 10
Potterton Ultra System 15kW Gas Boiler 15 89% Up to 10
Vaillant ecoFIT pure 612 System Gas boiler 12 89% Up to 10
Vaillant Home 15kW System Gas Boiler 15 89% Up to 10
Vaillant ecoFIT pure 615 System Gas boiler 15 89% Up to 10
Vaillant Home 12kW System Gas Boiler 12 89% Up to 10
Worcester Bosch Greenstar 9i System Gas Boiler 9 93% Up to 10
Worcester Bosch Greenstar 12i System Gas Boiler 12 94% Up to 10
Worcester Bosch Greenstar 15i System Gas Boiler 15 94% Up to 10

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Regular boilers What is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi 412 Heat 12kW Regular Gas Boiler 12 89.20% Up to 10
Baxi 415 Heat 15kW Regular Gas Boiler 15 89.20% Up to 10
Baxi EcoBlue Advance Heat 13 Regular Gas Boiler 13 89.20% Up to 10
Baxi EcoBlue Heat 12 Regular Gas Boiler 12 89.20% Up to 10
Baxi 212 Heat 12kW Regular Gas Boiler 12 89.20% Up to 10
Baxi 215 Heat 15kW Regular Gas Boiler 15 89.20% Up to 10
Baxi EcoBlue Heat 15 Regular Gas Boiler 15 89.20% Up to 10
Glow-worm Energy Regular 12kW Gas Boiler 12 89.30% Up to 10
Glow-worm Energy Regular 15kW Gas Boiler 15 89.30% Up to 10
Ideal Mexico HE 15kW Regular Gas Boiler 15 90% Up to 10
Ideal Logic Max Heat 12kW Regular Gas Boiler 12 93% Up to 10
Ideal Logic Max Heat 15kW Regular Gas Boiler 15 93% Up to 10
Ideal Logic Plus Heat 12kW Regular Gas Boiler 12 89% Up to 10
Ideal Logic Heat 12kW Regular Gas Boiler 12 89% Up to 10
Ideal Logic Heat 15kW Regular Gas Boiler 15 90% Up to 10
Ideal Logic Plus Heat 15kW Regular Gas Boiler 15 89% Up to 10
Potterton Promax SL Heat 12kW Regular Gas Boiler 12 91% Up to 10
Potterton Promax SL Heat 15kW Regular Gas Boiler 15 89% Up to 10
Potterton Ultra Regular 15kW Gas Boiler 15 89% Up to 10
Potterton Assure Heat 13kW Regular Gas Boiler 13 93% Up to 10
Potterton Titanium 12kW Regular Gas Boiler 12 88% Up to 10
Potterton Titanium 15kW Regular Gas Boiler 15 88% Up to 10
Vaillant EcoFIT Pure 15kW Regular Gas Boiler 15 89% Up to 10
Vaillant ecoTEC plus 412 Regular Gas Boiler 12 89% Up to 10
Vaillant Home 12kW Regular Gas Boiler 12 89% Up to 10
Vaillant Home 15kW Regular Gas Boiler 15 89% Up to 10
Vaillant ecoTEC plus 415 15kW Regular Gas Boiler 15 89% Up to 10
Vaillant ecoFIT pure 12kW Regular Gas Boiler 12 89% Up to 10
Worcester Bosch Greenstar 12Ri Regular Gas Boiler 12 91% Up to 10
Worcester Bosch Greenstar 15Ri Regular Gas Boiler 15 91% Up to 10

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Best gas boilers for properties with 10-15 radiators

 

Combination boilers What is it?

Manufacturer/Model Size (kW Output) Flow rate (l/m) Energy Efficiency Radiators
Baxi EcoBlue+ Combi 28 Gas Boiler 28 11.5 89.10% 10-15
Baxi Duo-tec Combi 28 LPG Gas Boiler Gas Boiler 28 11.5 88.60% 10-15
Baxi 128 Combi Gas Boiler 28 11.5 89.10% 10-15
Baxi 228 Combi Gas Boiler 28 11.5 89% 10-15
Baxi 630 Combi Gas Boiler 30 12.2 89% 10-15
Baxi EcoBlue Advance Combi 28 Gas Boiler 28 11.5 89.10% 10-15
Baxi Platinum Combi 28 Gas Boiler 28 11.5 89% 10-15
Baxi Duo-tec Combi 28 Gas Boiler 28 11.5 88.60% 10-15
Glow-worm Essential 28kW Combi Gas Boiler 28 11.7 89.30% 10-15
Glow-worm Easicom3 28kW Combi Gas Boiler 28 11.7 89.60% 10-15
Glow-worm Energy Combi 30kW Gas Boiler 30 12.5 89.20% 10-15
Glow-worm betacom4 30kW combi gas boiler 30 12.4 89.20% 10-15
Glow-worm Ultimate3 30kw Combi Gas Boiler 30 12.4 89.60% 10-15
Potterton Promax 28kW Combi Gas Boiler 28 11.5 89% 10-15
Potterton Promax Ultra 28kW Combi Gas Boiler 28 11.5 89% 10-15
Potterton Titanium 28kW Combi Gas Boiler 28 11.5 91% 10-15
Potterton Gold Combi 28kW Gas Boiler 28 11.5 89% 10-15
Potterton Assure 30kW Combi Gas Boiler 30 12.2 93% 10-15
Vaillant ecoTEC Pro 28 kW Combi Gas Boiler 28 11.1 89% 10-15 Boiler review
Vaillant EcoFIT pure 830 Combi Gas Boiler 30 12.4 89% 10-15 Boiler review
Vaillant EcoFIT sustain 830 Combi Gas Boiler 30 12.4 89% 10-15
Vaillant ecoTEC Pro 30kW combi Gas boiler 30 12.3 89% 10-15 Boiler review
Vaillant Home 30kW Combi Gas Boiler 30 12.4 89% 10-15
Worcester Bosch Greenstar 30Si Compact Combi Gas Boiler 30 12.3 94% 10-15 Boiler review
Worcester Bosch Greenstar 30i Combi Gas Boiler 30 12.3 94% 10-15 Boiler review
Worcester Bosch Greenstar 28CDi Compact Combi Gas Boiler 28 11.4 92% 10-15 Boiler review
Worcester Bosch Greenstar 29CDi Classic Combi Gas Boiler 29 11 90.1% 10-15

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System boilers What is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi EcoBlue System 18 Gas Boiler 18 89.10% 10-15
Baxi Megaflo System 24 Gas Boiler 24 88.60% 10-15
Baxi Megaflo System 18 Gas Boiler 18 88.60% 10-15
Baxi EcoBlue System 24 Gas Boiler 24 89.10% 10-15
Glow-worm Easicom3 25 System Gas Boiler 25 89.60% 10-15
Glow-worm Ultimate3 25kW System Gas Boiler 25 89.70% 10-15
Glow-worm Energy System 18kW Gas Boiler 18 89.30% 10-15
Glow-worm Energy System 25kW Gas Boiler 25 89.30% 10-15
Ideal Logic Max 18kW System Gas Boiler 18 93% 10-15
Ideal Logic Max 24kW System Gas Boiler 24 93% 10-15
Ideal Vogue Max 18kW System Gas Boiler 18 93% 10-15
Ideal Vogue Max 26kW System Gas Boiler 26 93% 10-15
Ideal Logic Plus System 18kW Gas Boiler 18 89% 10-15
Ideal Logic Plus System 24kW Gas Boiler 24 90% 10-15
Ideal Logic System 24kW Gas Boiler 24 91% 10-15
Ideal Vogue GEN2 S26 System Gas Boiler 26 89% 10-15
Potterton Ultra System 18kW Gas Boiler 18 89% 10-15
Potterton Ultra System 21kW Gas Boiler 21 89% 10-15
Potterton Promax System 18kW Gas Boiler 18 89% 10-15
Potterton Assure 18kW System Gas Boiler 18 93% 10-15
Potterton Promax System 24kW Gas Boiler 24 89% 10-15
Potterton Ultra System 24kW Gas Boiler 24 89% 10-15
Potterton Gold 18kW System Gas Boiler 18 89% 10-15
Vaillant Home 25kW System Gas Boiler 25 89% 10-15
Vaillant ecoFIT pure 625 system Gas boiler 25 89% 10-15
Vaillant ecoFIT pure 618 system Gas boiler 18 89% 10-15
Vaillant ecoTec plus 624 System Gas Boiler 24 89% 10-15
Vaillant Home 18kW System Gas Boiler 18 89% 10-15
Worcester Bosch Greenstar 18i System Gas Boiler 18 94% 10-15
Worcester Bosch Greenstar 21i System Gas Boiler 21 94% 10-15

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Regular boilers What is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi EcoBlue Advance Heat 19 Regular Gas Boiler 19 89.20% 10-15
Baxi 418 Heat 18kW Regular Gas Boiler 18 89.20% 10-15
Baxi EcoBlue Advance Heat 16 Regular Gas Boiler 16 89.20% 10-15
Baxi EcoBlue Advance Heat 25 Regular Gas Boiler 25 89.10% 10-15
Baxi 218 Heat 18kW Regular Gas Boiler 18 89.20% 10-15
Baxi 224 Heat 24kW Regular Gas Boiler 24 89.20% 10-15
Baxi 424 Heat 24kW Regular Gas Boiler 24 89.10% 10-15
Baxi EcoBlue Heat 18 Regular Gas Boiler 18 89.20% 10-15
Baxi EcoBlue Heat 21 Regular Gas Boiler 21 89.20% 10-15
Baxi EcoBlue Heat 24 Regular Gas Boiler 24 89.10% 10-15
Glow-worm Energy Regular 18kW Gas Boiler 18 89.30% 10-15
Glow-worm Energy Regular 25kW Gas Boiler 25 89.20% 10-15
Glow-worm Easicom3 25kW Regular Gas Boiler 25 89.60% 10-15
Glow-worm Ultimate3 25kW Regular Gas Boiler 25 89.70% 10-15
Ideal Logic Max Heat 18kW Regular Gas Boiler 18 93% 10-15
Ideal Logic Max Heat 24kW Regular Gas Boiler 24 94% 10-15
Ideal Logic Plus Heat 18kW Regular Gas Boiler 18 89.40% 10-15
Ideal Logic Heat 18kW Regular Gas Boiler 18 90% 10-15
Ideal Logic Heat 24kW Regular Gas Boiler 24 90% 10-15
Ideal Mexico HE 18kW Regular Gas Boiler 18 89% 10-15
Ideal Mexico HE 24kW Regular Gas Boiler 24 89% 10-15
Potterton Promax SL Heat 24kW Regular Gas Boiler 24 89% 10-15
Potterton Promax SL Heat 18kW Regular Gas Boiler 18 89% 10-15
Potterton Ultra Regular 24kW Gas Boiler 24 89% 10-15
Potterton Assure Heat 16kW Regular Gas Boiler 16 93% 10-15
Potterton Assure Heat 19kW Regular Gas Boiler 19 93% 10-15
Potterton Assure Heat 25kW Regular Gas Boiler 25 93% 10-15
Potterton Ultra Regular 18kW Gas Boiler 18 89% 10-15
Potterton Ultra Regular 21kW Gas Boiler 21 89% 10-15
Potterton Titanium 18kW Regular Gas Boiler 18 88% 10-15
Potterton Titanium 24kW Regular Gas Boiler 24 88% 10-15
Vaillant Home 25kW Regular Gas Boiler 25 89% 10-15
Vaillant EcoFIT Pure 25kW Regular Gas Boiler 25 89% 10-15
Vaillant EcoFIT Pure 18kW Regular Gas Boiler 18 89% 10-15
Vaillant ecoTEC plus 424 24kW Regular Gas Boiler 24 89% 10-15
Vaillant Home 18kW Regular Gas Boiler 18 89% 10-15
Vaillant ecoTEC plus 418 Regular Gas Boiler 18 89% 10-15
Worcester Bosch Greenstar 24Ri Regular Gas Boiler 24 91% 10-15 Boiler review
Worcester Bosch Greenstar 18Ri Regular Gas Boiler 18 91% 10-15

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Best gas boilers for properties with 15-20 radiators

 

Combination boilers What is it?

Manufacturer/Model Size (kW Output) Flow rate (l/m) Energy Efficiency Radiators
Baxi EcoBlue+ Combi 33 Gas Boiler 33 13.5 89.10% 15-20
Baxi 636 Combi Gas Boiler 36 15 89% 15-20
Baxi EcoBlue Advance Combi 33 Gas Boiler 33 13.5 89.10% 15-20
Baxi EcoBlue Advance Combi 40 Gas Boiler 40 16.4 89.10% 15-20
Baxi Platinum Combi 33 Gas Boiler 33 13.5 88.90% 15-20
Baxi Platinum Combi 40 Gas Boiler 40 16.4 88.90% 15-20
Baxi Duo-tec Combi 40 Gas Boiler 40 16.4 88.50% 15-20
Baxi Duo-tec Combi 33 Gas Boiler 33 13.5 88.50% 15-20
Glow-worm Energy 35 Store 35kW Combi Gas Boiler 35 14.4 89.40% 15-20
Glow-worm Energy Combi 35kW Gas Boiler 35 14.4 89.20% 15-20
Glow-worm Ultimate3 35kw Combi Gas Boiler 35 14.4 89.70% 15-20
Ideal Vogue Max 32kW Combi Gas Boiler 32 13.1 92% 15-20
Ideal Logic Max 35kW Combi Gas Boiler 35 14.5 94% 15-20
Ideal Vogue GEN2 C32 Combi Gas Boiler 32 13.1 89% 15-20
Ideal Vogue Max 40kW Combi Gas Boiler 40 16.4 93% 15-20
Ideal Vogue GEN2 C40 Combi Gas Boiler 40 16.4 89% 15-20
Ideal Logic Combi 35kW Gas Boiler 35 14.5 94% 15-20
Ideal Logic Plus Combi 35kW Gas Boiler 35 14.5 94% 15-20
Potterton Promax Ultra 33kW Combi Gas Boiler 33 13.5 89% 15-20
Potterton Gold Combi 33kW Gas Boiler 33 13.5 89% 15-20
Potterton Promax 33kW Combi Gas Boiler 33 13.5 89% 15-20
Potterton Titanium 33kW Combi Gas Boiler 33 13.5 88.50% 15-20
Potterton Titanium 40kW Combi Gas Boiler 40 16.4 88.50% 15-20
Potterton Assure 36kW Combi Gas Boiler 36 15 93% 15-20
Vaillant EcoFIT pure 835 Combi Gas Boiler 35 14.4 89% 15-20 Boiler review
Vaillant EcoFIT sustain 835 Combi Gas Boiler 35 14.4 89% 15-20
Vaillant EcoTEC plus 938 Combi Gas Boiler 38 20 89% 15-20 Boiler review
Vaillant EcoTEC Exclusive Green IQ 835 Combi Gas Boiler 35 14.5 94% 15-20
Vaillant ecoTEC plus 835 Combi Gas Boiler 35 14.3 89% 15-20 Boiler review
Vaillant EcoTEC Exclusive Green IQ 843 Combi Gas Boiler 43 17.8 94% 15-20
Vaillant ecoTEC plus 832 Combi Gas Boiler 32 13 89% 15-20 Boiler review
Vaillant ecoTEC plus 838 Combi Gas Boiler 38 15.9 89% 15-20
Vaillant Home 35kW Combi Gas Boiler 35 14.4 89% 15-20
Worcester Bosch Greenstar 32CDi Compact Combi Gas Boiler 32 13.1 92% 15-20
Worcester Bosch Greenstar 36CDi Compact Combi Gas Boiler 36 14.7 94% 15-20
Worcester Bosch Greenstar Highflow 440CDi Combi Gas Boiler 29.2 20 92% 15-20
Worcester Bosch Greenstar Highflow 550CDi Combi Gas Boiler 30.6 25 92% 15-20
Worcester Bosch Greenstar 42CDi Classic Combi Gas Boiler 42 17 92% 15-20
Worcester Bosch Greenstar 34CDi Classic Combi Gas Boiler 34 14.3 92% 15-20
Worcester Bosch Greenstar 38CDi Classic Combi Gas Boiler 38 16.4 92% 15-20

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System boilers What is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi Megaflo System 28 Gas Boiler 28 88.50% 15-20
Baxi Megaflo System 32 Gas Boiler 32 88.50% 15-20
Baxi EcoBlue System 28 Gas Boiler 28 89.10% 15-20
Baxi EcoBlue System 32 Gas Boiler 32 89.10% 15-20
Glow-worm Energy System 30kW Gas Boiler 30 89.30% 15-20
Ideal Logic Max 30kW System Gas Boiler 30 93% 15-20
Ideal Vogue Max 32kW System Gas Boiler 32 93% 15-20
Ideal Logic Plus System 30kW Gas Boiler 30 90% 15-20
Ideal Vogue GEN2 S32 System Gas Boiler 32 89% 15-20
Potterton Promax System 32kW Gas Boiler 32 89% 15-20
Potterton Gold 28kW System Gas Boiler 28 89% 15-20
Vaillant ecoTEC exclusive Green iQ 627 System Gas Boiler 27 94% 15-20
Vaillant ecoFIT pure 630 system Gas boiler 30 89% 15-20
Vaillant ecoTec plus 630 System Gas Boiler 30 89% 15-20
Vaillant ecoTec plus 637 System Gas Boiler 37 89% 15-20
Vaillant EcoTEC 46kW System Gas Boiler 46 96% 15-20
Vaillant EcoTEC 65kW System Gas Boiler 65 96% 15-20
Worcester Bosch Greenstar 30CDi Classic System Gas Boiler 30 92% 15-20
Worcester Bosch Greenstar 35CDi Classic System Gas Boiler 35 92% 15-20
Worcester Bosch Greenstar 27i System Gas Boiler 27 92% 15-20
Worcester Bosch Greenstar 30i System Gas Boiler 30 92% 15-20

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Regular boilersWhat is it?

Manufacturer/Model Size (kW Output) Energy Efficiency Radiators
Baxi 430 Heat 30kW Regular Gas Boiler 30 89.10% 15-20
Baxi EcoBlue Advance Heat 30 Regular Gas Boiler 30 89.10% 15-20
Baxi 230 Heat 30kW Regular Gas Boiler 30 89.10% 15-20
Ideal Mexico HE 30kW Regular Gas Boiler 30 89% 15-20
Ideal EvoMax 60kW Regular Gas Boiler 60 89.40% 15-20
Ideal Logic Max Heat 30kW Regular Gas Boiler 30 93% 15-20
Ideal Mexico HE 36kW Regular Gas Boiler 36 89% 15-20
Ideal Vogue Max 32kW System Gas Boiler 32 93% 15-20
Ideal Vogue Max 40kW Combi Gas Boiler 40 93% 15-20
Ideal Logic Heat 30kW Regular Gas Boiler 30 89% 15-20
Ideal Logic Plus Heat 30kW Regular Gas Boiler 30 90% 15-20
Potterton Assure Heat 30kW Regular Gas Boiler 30 93% 15-20
Potterton Titanium 30kW Regular Gas Boiler 30 88% 15-20
Vaillant EcoFIT Pure 30kW Regular Gas Boiler 30 89% 15-20
Vaillant EcoFIT Pure 35kW Regular Gas Boiler 35 90% 15-20
Vaillant ecoTEC plus 435 35kW Regular Gas Boiler 35 89% 15-20
Vaillant ecoTEC plus 430 Regular Gas Boiler 30 89% 15-20
Worcester Bosch Greenstar FS 30CDi Regular gas boiler 30 92% 15-20
Worcester Bosch Greenstar 27Ri Regular Gas Boiler 27 92% 15-20
Worcester Bosch Greenstar 40CDi Classic Regular Gas Boiler 40 92% 15-20
Worcester Bosch Greenstar 30CDi Classic Regular Gas Boiler 30 92% 15-20
Worcester Bosch Greenstar 30Ri Regular Gas Boiler 30 92% 15-20
Worcester Bosch Greenstar Fs 42CDi Regular Gas Boiler 42 92% 15-20

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What else do I need to consider when replacing a boiler?

Property type

The layout of your property informs the size and type of boiler required to heat your home. Combination boilers are recommended for small to mid-sized homes with one bathroom as they rely solely on mains water pressure and can’t provide enough hot water for homes with a high demand of hot water. In these cases, a system or regular boiler is more suitable as they have a large water storage tank and hot water cylinder.

Insulation

The level of insulation in your home will also determine the size of boiler required to keep the home warm for longer. A heat loss survey will take into account the materials used in the construction of the house, as well as whether windows have been double glazed, and if there are non-insulated spaces in the home.

Number of radiators

The number of radiators installed in your home will determine which boiler is best to provide enough hot water to heat your entire home.

Please note: For combination boilers, the number of radiators and bathrooms will needed to be factored in. For system and conventional boilers, however, the number of radiators, bathrooms and the size of the cylinder will affect the size of the boiler.

Number of bedrooms

The number of bedrooms indicates the size of the home that needs to be heated. As a general boiler sizing rule of thumb, the more bedrooms you have, the higher the output needed. However, since houses are not identical, we find that taking the number of radiators as a starting point for your boiler calculations is a far more accurate way of sizing boilers.

Number of bathrooms

More than one bathroom in your home? If you have multiple bathrooms, you may need a boiler with a hot water storage cylinder to cope with the higher hot water demand, especially if people tend to take showers at the same time.

Mains water pressure

The water pressure will determine whether your boiler can produce enough water pressure on its own. A conventional boiler is better suited to areas with low mains pressure because it can guarantee high water pressure from a loft-installed tank. A combi boiler is not suited to low water pressure areas.

Current boiler

Your current boiler determines the layout of your central heating system. For this reason, like-for-like boiler replacements tend to be easier to install, which is typically reflected in a lower price, whereas switching boiler types is slightly more complicated, tends to incur higher costs, and is, in fact, not always advisable. For example, switching from a regular boiler to a combi boiler is feasible but wouldn’t work unless the mains water pressure is sufficient.

Boiler brand

In the boiler market, there are several different brands with varying levels of energy efficiency and build-quality. The energy efficiency rating of a boiler is measured on a scale from A to G. A-rated boilers are highly efficient and converts almost 90% of its fuel into heat. G-rated boilers are likely to be older than 15 years and could be costing you an addition £350 a year to run in energy bills. We recommend boilers from both Vaillant and Worcester Bosch.

The type of boiler you would like

You might have a boiler you would like in mind, or you might have been recommended a particular boiler. However, we recommend that you let the boiler calculator determine the correct boiler to suit your home. The calculator considers the significant elements, like the number of rooms in your home and your hot water requirements.

Boiler flue

Flues act as the home’s “exhaust pipe” for the boiler. The type of flue will also determine which boiler is suitable. The needs of a horizontal flue are quite different to that of a vertical flue.

What are the boiler types?


Combination boilers – Combi boilers can control both hot water and central heating. They’re the most popular boiler choice amongst UK households due to their high energy efficiency. A combi boiler heats water directly from the mains supply, which is then fed directly to a hot water outlet the minute its turned on. With combis, you can expect unlimited hot water as and when you need it, without the need for a cylinder or water tank to store water.

System boilers – If your home has more than one bathroom installed with multiple outlets, a system boiler would be your best bet. They require a hot water cylinder which stores enough hot water for several bathrooms and taps. A cold water tank isn’t needed for a system boiler seeing as many of the main components are built into the boiler. As there isn’t any need for a tank, you can expect to save space, as well as peace of mind knowing that you wouldn’t need to worry about frost damage or leaks, which makes them easier to maintain.

Conventional boilers – Conventional boilers, also known as a traditional, regular, open vent or heat only boilers, consist of a cylinder, water storage tank and the boiler itself. They might not be the best central heating system for space-saving, but they’re able to supply large volumes of hot water to multiple bathrooms, making them an excellent choice for larger homes with multiple bedrooms and bathrooms. It’s important to remember that this type of boiler is easy to replace if an existing traditional heating system is in place.

Best gas boiler for 2 – 3 bathroom houses

If your home has 2 or more bathrooms, a combi boiler may not be able to cope with the high hot water demand. We recommend that you install either a system or conventional boiler with a central heating output of 35 – 42kW. A system boiler includes a hot water storage cylinder, whereas a regular boiler includes a cylinder and cold water tank. A hot water cylinder can supply enough hot water for multiple taps, showers and baths without a loss of pressure.

Check your mains flow rate

If you’re replacing an older boiler, your mains pressure would determine whether a combi boiler is suitable for your home. System and regular boilers both take their hot water supply from a cylinder, whereas a combi boiler is completely mains-fed. To ensure you have the correct flow of hot water, the correct flow rate is essential in a combination boiler.

If you’d like to check your flow rate at home, the bucket test is a quick way to get a quick idea. If you run cold water from a tap for 1 minute into a bucket with measurements, you’ll get an idea of the flow rate from your current supply in litres per minute (l/m). Each combi boiler will specify it’s maximum flow rate so you’ll be able to find a good match with this test.

Boiler efficiency tips

Insulation

To prevent the loss of heat through your room, walls, floors or windows, having proper insulation installed is essential. A poorly insulated home will mean that your boiler has to work harder to keep your home heated, although this will waste energy. To reduce the costs of energy bills, you may want to think about installing effective insulation, as well as replacement windows with double glazing.

What radiator size?

As a general rule of thumb, the larger the surface area of the radiator, the quicker it’ll heat a room. Not all radiators are the same size, which tends to be measured in BTUs or British Thermal Units).

Smart controls

Modern boilers are now compatible with most smart thermostats which enable you to control your central heating from your smartphone or tablet, whether you’re at home or away (as long as you have mobile internet or WiFi). Due to advances in home technology, you’re now able to schedule when your heating is switched on, as well as monitor your energy use and find ways to reduce wastage. Some smart thermostats also have features that use the local weather reports to change your temperature settings automatically.

Annual boiler servicing

Boiler servicing will ensure that your boiler keeps running at its best for as long as possible. Servicing will catch any problems with your boiler early-on to prevent more significant problems from developing – causing long-term damage.

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