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BOILER SIZE CALCULATOR

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

Best gas boilers for properties with up to 10 radiators

Combination boilers What is it?

Manufacturer/ModelSize (kW Output)Flow rate (l/m)Energy EfficiencyRadiators
Baxi 424 Combi Gas Boiler249.889%Up to 10
Baxi 224 Combi Gas Boiler249.889%Up to 10
Baxi 124 Combi Gas Boiler249.889.10%Up to 10
Baxi Platinum Combi 24 Gas Boiler249.889%Up to 10
Baxi EcoBlue Advance Combi 24 Gas Boiler249.889.10%Up to 10
Baxi EcoBlue+ Combi 24 Gas Boiler249.889.10%Up to 10
Baxi Duo-Tec Combi 24 Gas Boiler249.889.10%Up to 10
Glow-worm Essential 24kW Combi Gas Boiler241089.30%Up to 10
Glow-worm Energy Combi 25kW Gas Boiler2510.489.20%Up to 10
Glow-worm Betacom4 24kW Combi Gas Boiler241089.20%Up to 10
Glow-worm Easicom3 24kW Combi Gas Boiler241089.60%Up to 10
Ideal Logic Combi 24kW Gas Boiler249.989%Up to 10
Ideal Logic Plus Combi 24kW Gas Combi249.989%Up to 10Boiler review
Ideal Logic Max 24kW Combi Gas Boiler249.994%Up to 10
Ideal Vogue Max 26kW Combi Gas Boiler2610.693%Up to 10
Ideal Vogue GEN2 C26 Combi Gas Boiler2610.689%Up to 10
Potterton Titanium 24kW Combi Gas Boiler249.491%Up to 10
Potterton Gold Combi 24kW Gas Boiler24991%Up to 10
Potterton Promax Ultra 24kW Combi Gas Boiler249.889%Up to 10
Potterton Assure 25kW Combi Gas Boiler2510.293%Up to 10
Potterton Promax 24kW Combi Gas Boiler249.889%Up to 10
Vaillant ecoTec Pro 24 Combi Gas Boiler249.689.30%Up to 10Boiler review
Vaillant ecoFit Sustain 825 Combi Gas Boiler2510.489%Up to 10
Vaillant ecoFit Pure 825 Combi Gas Boiler2510.489%Up to 10Boiler review
Vaillant ecoTec Plus 825 Combi Gas Boiler2510.589.70%Up to 10Boiler review
Vaillant Home 25kW Combi Gas Boiler2510.489%Up to 10
Worcester Bosch Greenstar 25i Combi Gas Boiler2410.294%Up to 10Boiler review
Worcester Bosch Greenstar 25Si Compact Combi Gas Boiler2410.294%Up to 10Boiler review

Regular boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi 412 Heat 12kW Regular Gas Boiler1289.20%Up to 10
Baxi 415 Heat 15kW Regular Gas Boiler1589.20%Up to 10
Baxi EcoBlue Advance Heat 13 Regular Gas Boiler1389.20%Up to 10
Baxi EcoBlue Heat 12 Regular Gas Boiler1289.20%Up to 10
Baxi 212 Heat 12kW Regular Gas Boiler1289.20%Up to 10
Baxi 215 Heat 15kW Regular Gas Boiler1589.20%Up to 10
Baxi EcoBlue Heat 15 Regular Gas Boiler1589.20%Up to 10
Glow-worm Energy Regular 12kW Gas Boiler1289.30%Up to 10
Glow-worm Energy Regular 15kW Gas Boiler1589.30%Up to 10
Ideal Mexico HE 15kW Regular Gas Boiler1590%Up to 10
Ideal Logic Max Heat 12kW Regular Gas Boiler1293%Up to 10
Ideal Logic Max Heat 15kW Regular Gas Boiler1593%Up to 10
Ideal Logic Plus Heat 12kW Regular Gas Boiler1289%Up to 10
Ideal Logic Heat 12kW Regular Gas Boiler1289%Up to 10
Ideal Logic Heat 15kW Regular Gas Boiler1590%Up to 10
Ideal Logic Plus Heat 15kW Regular Gas Boiler1589%Up to 10
Potterton Promax SL Heat 12kW Regular Gas Boiler1291%Up to 10
Potterton Promax SL Heat 15kW Regular Gas Boiler1589%Up to 10
Potterton Ultra Regular 15kW Gas Boiler1589%Up to 10
Potterton Assure Heat 13kW Regular Gas Boiler1393%Up to 10
Potterton Titanium 12kW Regular Gas Boiler1288%Up to 10
Potterton Titanium 15kW Regular Gas Boiler1588%Up to 10
Vaillant EcoFIT Pure 15kW Regular Gas Boiler1589%Up to 10
Vaillant ecoTEC plus 412 Regular Gas Boiler1289%Up to 10
Vaillant Home 12kW Regular Gas Boiler1289%Up to 10
Vaillant Home 15kW Regular Gas Boiler1589%Up to 10
Vaillant ecoTEC plus 415 15kW Regular Gas Boiler1589%Up to 10
Vaillant ecoFIT pure 12kW Regular Gas Boiler1289%Up to 10
Worcester Bosch Greenstar 12Ri Regular Gas Boiler1291%Up to 10
Worcester Bosch Greenstar 15Ri Regular Gas Boiler1591%Up to 10

System boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi EcoBlue System 12 Gas Boiler1289.10%Up to 10
Baxi Megaflo System 15 Gas Boiler1588.60%Up to 10
Glow-worm Energy System 12kW Gas Boiler1289.30%Up to 10
Glow-worm Energy System 15kW Gas Boiler1589.30%Up to 10
Ideal Logic Max 15kW System Gas Boiler1593%Up to 10
Ideal Logic System 15kW Gas Boiler1589%Up to 10
Ideal Vogue GEN2 S15 System Gas Boiler1589%Up to 10
Ideal Logic Plus System 15kW Gas Boiler1589%Up to 10
Potterton Ultra System 12kW Gas Boiler1289%Up to 10
Potterton Assure 15kW System Gas Boiler1593%Up to 10
Potterton Promax System 15kW Gas Boiler1589%Up to 10
Potterton Promax System 12kW Gas Boiler1289%Up to 10
Potterton Ultra System 15kW Gas Boiler1589%Up to 10
Vaillant ecoFIT pure 612 System Gas boiler1289%Up to 10
Vaillant Home 15kW System Gas Boiler1589%Up to 10
Vaillant ecoFIT pure 615 System Gas boiler1589%Up to 10
Vaillant Home 12kW System Gas Boiler1289%Up to 10
Worcester Bosch Greenstar 9i System Gas Boiler993%Up to 10
Worcester Bosch Greenstar 12i System Gas Boiler1294%Up to 10
Worcester Bosch Greenstar 15i System Gas Boiler1594%Up to 10

Best gas boilers for properties with 10-15 radiators

Combination boilers What is it?

Manufacturer/ModelSize (kW Output)Flow rate (l/m)Energy EfficiencyRadiators
Baxi EcoBlue+ Combi 28 Gas Boiler2811.589.10%10-15
Baxi Duo-tec Combi 28 LPG Gas Boiler Gas Boiler2811.588.60%10-15
Baxi 128 Combi Gas Boiler2811.589.10%10-15
Baxi 228 Combi Gas Boiler2811.589%10-15
Baxi 630 Combi Gas Boiler3012.289%10-15
Baxi EcoBlue Advance Combi 28 Gas Boiler2811.589.10%10-15
Baxi Platinum Combi 28 Gas Boiler2811.589%10-15
Baxi Duo-tec Combi 28 Gas Boiler2811.588.60%10-15
Glow-worm Essential 28kW Combi Gas Boiler2811.789.30%10-15
Glow-worm Easicom3 28kW Combi Gas Boiler2811.789.60%10-15
Glow-worm Energy Combi 30kW Gas Boiler3012.589.20%10-15
Glow-worm betacom4 30kW combi gas boiler3012.489.20%10-15
Glow-worm Ultimate3 30kw Combi Gas Boiler3012.489.60%10-15
Potterton Promax 28kW Combi Gas Boiler2811.589%10-15
Potterton Promax Ultra 28kW Combi Gas Boiler2811.589%10-15
Potterton Titanium 28kW Combi Gas Boiler2811.591%10-15
Potterton Gold Combi 28kW Gas Boiler2811.589%10-15
Potterton Assure 30kW Combi Gas Boiler3012.293%10-15
Vaillant ecoTEC Pro 28 kW Combi Gas Boiler2811.189%10-15Boiler review
Vaillant EcoFIT pure 830 Combi Gas Boiler3012.489%10-15Boiler review
Vaillant EcoFIT sustain 830 Combi Gas Boiler3012.489%10-15
Vaillant ecoTEC Pro 30kW combi Gas boiler3012.389%10-15Boiler review
Vaillant Home 30kW Combi Gas Boiler3012.489%10-15
Worcester Bosch Greenstar 30Si Compact Combi Gas Boiler3012.394%10-15Boiler review
Worcester Bosch Greenstar 30i Combi Gas Boiler3012.394%10-15Boiler review
Worcester Bosch Greenstar 28CDi Compact Combi Gas Boiler2811.492%10-15Boiler review
Worcester Bosch Greenstar 29CDi Classic Combi Gas Boiler291190.1%10-15

Regular boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi EcoBlue Advance Heat 19 Regular Gas Boiler1989.20%10-15
Baxi 418 Heat 18kW Regular Gas Boiler1889.20%10-15
Baxi EcoBlue Advance Heat 16 Regular Gas Boiler1689.20%10-15
Baxi EcoBlue Advance Heat 25 Regular Gas Boiler2589.10%10-15
Baxi 218 Heat 18kW Regular Gas Boiler1889.20%10-15
Baxi 224 Heat 24kW Regular Gas Boiler2489.20%10-15
Baxi 424 Heat 24kW Regular Gas Boiler2489.10%10-15
Baxi EcoBlue Heat 18 Regular Gas Boiler1889.20%10-15
Baxi EcoBlue Heat 21 Regular Gas Boiler2189.20%10-15
Baxi EcoBlue Heat 24 Regular Gas Boiler2489.10%10-15
Glow-worm Energy Regular 18kW Gas Boiler1889.30%10-15
Glow-worm Energy Regular 25kW Gas Boiler2589.20%10-15
Glow-worm Easicom3 25kW Regular Gas Boiler2589.60%10-15
Glow-worm Ultimate3 25kW Regular Gas Boiler2589.70%10-15
Ideal Logic Max Heat 18kW Regular Gas Boiler1893%10-15
Ideal Logic Max Heat 24kW Regular Gas Boiler2494%10-15
Ideal Logic Plus Heat 18kW Regular Gas Boiler1889.40%10-15
Ideal Logic Heat 18kW Regular Gas Boiler1890%10-15
Ideal Logic Heat 24kW Regular Gas Boiler2490%10-15
Ideal Mexico HE 18kW Regular Gas Boiler1889%10-15
Ideal Mexico HE 24kW Regular Gas Boiler2489%10-15
Potterton Promax SL Heat 24kW Regular Gas Boiler2489%10-15
Potterton Promax SL Heat 18kW Regular Gas Boiler1889%10-15
Potterton Ultra Regular 24kW Gas Boiler2489%10-15
Potterton Assure Heat 16kW Regular Gas Boiler1693%10-15
Potterton Assure Heat 19kW Regular Gas Boiler1993%10-15
Potterton Assure Heat 25kW Regular Gas Boiler2593%10-15
Potterton Ultra Regular 18kW Gas Boiler1889%10-15
Potterton Ultra Regular 21kW Gas Boiler2189%10-15
Potterton Titanium 18kW Regular Gas Boiler1888%10-15
Potterton Titanium 24kW Regular Gas Boiler2488%10-15
Vaillant Home 25kW Regular Gas Boiler2589%10-15
Vaillant EcoFIT Pure 25kW Regular Gas Boiler2589%10-15
Vaillant EcoFIT Pure 18kW Regular Gas Boiler1889%10-15
Vaillant ecoTEC plus 424 24kW Regular Gas Boiler2489%10-15
Vaillant Home 18kW Regular Gas Boiler1889%10-15
Vaillant ecoTEC plus 418 Regular Gas Boiler1889%10-15
Worcester Bosch Greenstar 24Ri Regular Gas Boiler2491%10-15Boiler review
Worcester Bosch Greenstar 18Ri Regular Gas Boiler1891%10-15

System boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi EcoBlue System 18 Gas Boiler1889.10%10-15
Baxi Megaflo System 24 Gas Boiler2488.60%10-15
Baxi Megaflo System 18 Gas Boiler1888.60%10-15
Baxi EcoBlue System 24 Gas Boiler2489.10%10-15
Glow-worm Easicom3 25 System Gas Boiler2589.60%10-15
Glow-worm Ultimate3 25kW System Gas Boiler2589.70%10-15
Glow-worm Energy System 18kW Gas Boiler1889.30%10-15
Glow-worm Energy System 25kW Gas Boiler2589.30%10-15
Ideal Logic Max 18kW System Gas Boiler1893%10-15
Ideal Logic Max 24kW System Gas Boiler2493%10-15
Ideal Vogue Max 18kW System Gas Boiler1893%10-15
Ideal Vogue Max 26kW System Gas Boiler2693%10-15
Ideal Logic Plus System 18kW Gas Boiler1889%10-15
Ideal Logic Plus System 24kW Gas Boiler2490%10-15
Ideal Logic System 24kW Gas Boiler2491%10-15
Ideal Vogue GEN2 S26 System Gas Boiler2689%10-15
Potterton Ultra System 18kW Gas Boiler1889%10-15
Potterton Ultra System 21kW Gas Boiler2189%10-15
Potterton Promax System 18kW Gas Boiler1889%10-15
Potterton Assure 18kW System Gas Boiler1893%10-15
Potterton Promax System 24kW Gas Boiler2489%10-15
Potterton Ultra System 24kW Gas Boiler2489%10-15
Potterton Gold 18kW System Gas Boiler1889%10-15
Vaillant Home 25kW System Gas Boiler2589%10-15
Vaillant ecoFIT pure 625 system Gas boiler2589%10-15
Vaillant ecoFIT pure 618 system Gas boiler1889%10-15
Vaillant ecoTec plus 624 System Gas Boiler2489%10-15
Vaillant Home 18kW System Gas Boiler1889%10-15
Worcester Bosch Greenstar 18i System Gas Boiler1894%10-15
Worcester Bosch Greenstar 21i System Gas Boiler2194%10-15

Best gas boilers for properties with 15-20 radiators

Combination boilers What is it?

Manufacturer/ModelSize (kW Output)Flow rate (l/m)Energy EfficiencyRadiators
Baxi EcoBlue+ Combi 33 Gas Boiler3313.589.10%15-20
Baxi 636 Combi Gas Boiler361589%15-20
Baxi EcoBlue Advance Combi 33 Gas Boiler3313.589.10%15-20
Baxi EcoBlue Advance Combi 40 Gas Boiler4016.489.10%15-20
Baxi Platinum Combi 33 Gas Boiler3313.588.90%15-20
Baxi Platinum Combi 40 Gas Boiler4016.488.90%15-20
Baxi Duo-tec Combi 40 Gas Boiler4016.488.50%15-20
Baxi Duo-tec Combi 33 Gas Boiler3313.588.50%15-20
Glow-worm Energy 35 Store 35kW Combi Gas Boiler3514.489.40%15-20
Glow-worm Energy Combi 35kW Gas Boiler3514.489.20%15-20
Glow-worm Ultimate3 35kw Combi Gas Boiler3514.489.70%15-20
Ideal Vogue Max 32kW Combi Gas Boiler3213.192%15-20
Ideal Logic Max 35kW Combi Gas Boiler3514.594%15-20
Ideal Vogue GEN2 C32 Combi Gas Boiler3213.189%15-20
Ideal Vogue Max 40kW Combi Gas Boiler4016.493%15-20
Ideal Vogue GEN2 C40 Combi Gas Boiler4016.489%15-20
Ideal Logic Combi 35kW Gas Boiler3514.594%15-20
Ideal Logic Plus Combi 35kW Gas Boiler3514.594%15-20
Potterton Promax Ultra 33kW Combi Gas Boiler3313.589%15-20
Potterton Gold Combi 33kW Gas Boiler3313.589%15-20
Potterton Promax 33kW Combi Gas Boiler3313.589%15-20
Potterton Titanium 33kW Combi Gas Boiler3313.588.50%15-20
Potterton Titanium 40kW Combi Gas Boiler4016.488.50%15-20
Potterton Assure 36kW Combi Gas Boiler361593%15-20
Vaillant EcoFIT pure 835 Combi Gas Boiler3514.489%15-20Boiler review
Vaillant EcoFIT sustain 835 Combi Gas Boiler3514.489%15-20
Vaillant EcoTEC plus 938 Combi Gas Boiler382089%15-20Boiler review
Vaillant EcoTEC Exclusive Green IQ 835 Combi Gas Boiler3514.594%15-20
Vaillant ecoTEC plus 835 Combi Gas Boiler3514.389%15-20Boiler review
Vaillant EcoTEC Exclusive Green IQ 843 Combi Gas Boiler4317.894%15-20
Vaillant ecoTEC plus 832 Combi Gas Boiler321389%15-20Boiler review
Vaillant ecoTEC plus 838 Combi Gas Boiler3815.989%15-20
Vaillant Home 35kW Combi Gas Boiler3514.489%15-20
Worcester Bosch Greenstar 32CDi Compact Combi Gas Boiler3213.192%15-20
Worcester Bosch Greenstar 36CDi Compact Combi Gas Boiler3614.794%15-20
Worcester Bosch Greenstar Highflow 440CDi Combi Gas Boiler29.22092%15-20
Worcester Bosch Greenstar Highflow 550CDi Combi Gas Boiler30.62592%15-20
Worcester Bosch Greenstar 42CDi Classic Combi Gas Boiler421792%15-20
Worcester Bosch Greenstar 34CDi Classic Combi Gas Boiler3414.392%15-20
Worcester Bosch Greenstar 38CDi Classic Combi Gas Boiler3816.492%15-20

Regular boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi 430 Heat 30kW Regular Gas Boiler3089.10%15-20
Baxi EcoBlue Advance Heat 30 Regular Gas Boiler3089.10%15-20
Baxi 230 Heat 30kW Regular Gas Boiler3089.10%15-20
Ideal Mexico HE 30kW Regular Gas Boiler3089%15-20
Ideal EvoMax 60kW Regular Gas Boiler6089.40%15-20
Ideal Logic Max Heat 30kW Regular Gas Boiler3093%15-20
Ideal Mexico HE 36kW Regular Gas Boiler3689%15-20
Ideal Vogue Max 32kW System Gas Boiler3293%15-20
Ideal Vogue Max 40kW Combi Gas Boiler4093%15-20
Ideal Logic Heat 30kW Regular Gas Boiler3089%15-20
Ideal Logic Plus Heat 30kW Regular Gas Boiler3090%15-20
Potterton Assure Heat 30kW Regular Gas Boiler3093%15-20
Potterton Titanium 30kW Regular Gas Boiler3088%15-20
Vaillant EcoFIT Pure 30kW Regular Gas Boiler3089%15-20
Vaillant EcoFIT Pure 35kW Regular Gas Boiler3590%15-20
Vaillant ecoTEC plus 435 35kW Regular Gas Boiler3589%15-20
Vaillant ecoTEC plus 430 Regular Gas Boiler3089%15-20
Worcester Bosch Greenstar FS 30CDi Regular gas boiler3092%15-20
Worcester Bosch Greenstar 27Ri Regular Gas Boiler2792%15-20
Worcester Bosch Greenstar 40CDi Classic Regular Gas Boiler4092%15-20
Worcester Bosch Greenstar 30CDi Classic Regular Gas Boiler3092%15-20
Worcester Bosch Greenstar 30Ri Regular Gas Boiler3092%15-20
Worcester Bosch Greenstar Fs 42CDi Regular Gas Boiler4292%15-20

System boilers What is it?

Manufacturer/ModelSize (kW Output)Energy EfficiencyRadiators
Baxi Megaflo System 28 Gas Boiler2888.50%15-20
Baxi Megaflo System 32 Gas Boiler3288.50%15-20
Baxi EcoBlue System 28 Gas Boiler2889.10%15-20
Baxi EcoBlue System 32 Gas Boiler3289.10%15-20
Glow-worm Energy System 30kW Gas Boiler3089.30%15-20
Ideal Logic Max 30kW System Gas Boiler3093%15-20
Ideal Vogue Max 32kW System Gas Boiler3293%15-20
Ideal Logic Plus System 30kW Gas Boiler3090%15-20
Ideal Vogue GEN2 S32 System Gas Boiler3289%15-20
Potterton Promax System 32kW Gas Boiler3289%15-20
Potterton Gold 28kW System Gas Boiler2889%15-20
Vaillant ecoTEC exclusive Green iQ 627 System Gas Boiler2794%15-20
Vaillant ecoFIT pure 630 system Gas boiler3089%15-20
Vaillant ecoTec plus 630 System Gas Boiler3089%15-20
Vaillant ecoTec plus 637 System Gas Boiler3789%15-20
Vaillant EcoTEC 46kW System Gas Boiler4696%15-20
Vaillant EcoTEC 65kW System Gas Boiler6596%15-20
Worcester Bosch Greenstar 30CDi Classic System Gas Boiler3092%15-20
Worcester Bosch Greenstar 35CDi Classic System Gas Boiler3592%15-20
Worcester Bosch Greenstar 27i System Gas Boiler2792%15-20
Worcester Bosch Greenstar 30i System Gas Boiler3092%15-20


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.

Looking to get started now?

You can find your perfect boiler match here.

Get started
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