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Best Gas Boilers | Guide to Boiler Types, Sizing, Brands & Prices
QUICK GUIDE SUMMARY
Which gas boiler do I need? Which is the best gas boiler?
We help you find the right gas boiler for your home. Use our guide to find which type of gas boiler you need (combi, heat only or system) and use our tables to work out your size of gas boiler. We then show you boilers by brand and price to help you find the best gas boiler for your budget. How else can we help? Research more heating topics at our Boiler Information Hub. Ready to go? Get an estimate for installation with our Boiler Quote Calculator, book a survey with a Local Installer or consider the different ways you can Pay for a New Boiler.
Overview to finding the right type, size and model gas boiler
Gas boilers are available as a combi, heat only or system model.
Which boiler type you choose will depend on your existing heating system and requirements for the new boiler.
Use our sizing table to find your rough boiler size.
Boiler size is based property size, property age, number of bathrooms and any plans to extend your home.
Which is the best gas boiler for you?
Find the table for your boiler type and property size/age. E.g Combi, 2-bed house, 1950s. Find your best boiler in the table according to budget, warranty length and performance.
HOW TO USE THIS GUIDE
Using this Guide: use this guide to find the right type and size gas boiler for your home.
Gas boilers by type
Size your gas boiler
Brands and prices
GAS BOILERS BY TYPE
Which type of gas boiler do I have? Combi, Heat Only & System?
Combi boiler:
also known as a combination boiler, combines heating and hot water production in a single, usually wall hung, unit. Hot water is produced instantly when you turn the hot tap, as appose to it being stored in a tank.
Heat Only boiler:
also known as a regular boiler, provides heating direct from the boiler and works with a hot water tank to provide hot water. Heat only boilers can work on open vented systems and sealed systems.
System boiler:
is like a Heat Only boiler as it works with a hot water tank, however, unlike a heat only boiler, many of the system components (such as the pump and diverter valve) are integral to the unit. These are mostly found in larger new build homes with multiple bathrooms.
Should I stick with the same boiler type or switch to a new type?
Like for like swap in the same location:
keeps costs down as alternations are minimal. If you have an old combi then there will be additional pipework and new flue requirements for a new combi, which can cause complications.
Move from Heat Only to a Combi:
a common upgrade. More expensive as the hot water pipes need to be rerouted, but frees up space where the hot water used to be and provides a more comprehensive warranty from the boiler manufacturer
Move to a system boiler:
system boilers come into their own where there are multiple bathrooms. If you are extending and adding bathrooms, and the water pressure is good, a system boiler is a better option as it delivers better hot water flow rates to multiple hot water outlets at the same time.
What size gas boiler do I need?
How do you know what size gas boiler you need? We have provided a guide to sizing your boiler. If you have a system or regular boiler the size will be based on the heat requirements of your property. For combi boilers, the size is ‘bigger’ because it includes hot water production. The temptation is to oversize the boiler, just in case. Oversized boilers are in fact less efficient. A boiler should be sized accurately based on your house construction, i.e. insulation levels and hot water requirements. Just to be clear, this is a rough guide. An experienced heating engineer will properly size your boiler after a site visit.
Sizing a combi boiler
The table below gives you a rough indication based on 1) the size of your property and the number of bathrooms and 2) how well insulated it is. Property ages are given across the top and they assume standard insulation measures, such as double glazing and loft insulation, have been made. If your levels of insulation are very high in an older property then you may wish to move a column to the right. If you are planning on adding bathrooms you will need to factor in hot water flow rates (see below).
It is surprising to learn that the average heat requirement is just 6-8kW at peak times, the rest of the year it is even less. For heat-only and system boilers the smallest boilers available are 12-13kW and will match most properties. For combi boilers the heating output is much higher - 18kW and upwards - because the boiler has a higher output for hot water production. The better the hot water flow rate (expressed as LPM) the higher the heating output. This is a huge disadvantage on the heating side because there are always more than double the heat requirement of the average UK home. Oversized boilers do not operate efficiently if left on their factory settings!
The important action for combi boilers is that the heating output is down rated by the installer to closer match the heat requirement of the property. For more achieving efficient systems read our guide: Why oversized boilers are bad for your bank balance and the planet.
Sizing for Hot Water - Our Top Tips
The hot water flow rate of a combi boiler, expressed as ‘litres per minute’, indicates how quickly a combi boiler can heat hot water. This is important for houses with multiple bathrooms because the hot water flow rate will be halved if two showers are running simultaneously. We have grouped combi boilers together according to the heating output of the boiler which starts at 18kW. Most houses only require 6-8kW of heat at peak times therefore even the smallest combi will aways be oversized. In nearly all cases the gas engineer will need to reduce the output of the boiler on the heating side down to the heat requirement of your property.
Your choice of combi boiler really then comes down to other factors, for example the hot water flow rate and perhaps cost and warranty. It is is also worth noting that 15mm pipework, which is common on most combi boiler installations, will only carry 12.5 litres per minute. If you think getting a boiler with better hot water production will improve your hot water performance then think again, better hot water production will only be available if your installer runs larger supply pipes. For two or more bathrooms you may wish to consider a system boiler and high-performance hot water tank.
Combi Boilers
| Age of property | pre 1900 | 1920s-1930s | 1950-1980s | 1990s | 2000 onwards |
|---|---|---|---|---|---|
| Insulation levels | Poorly insulated | Some insulation | Moderately insulated | Reasonably insulated | Well insulated |
| No of bedrooms and bathrooms | |||||
| 1 bed + 1 bath | 7kW/9-12LPM | 7kW/9-12LPM | 6kW/9-12LPM | 6kW/9-12LPM | 4kW/9-12LPM |
| 2 bed + 1 bath | 8kW/9-12LPM | 8kW/9-12LPM | 7kW/9-12LPM | 6kW/9-12LPM | 5kW/9-12LPM |
| 2 bed + 2 bath | 8kW/12-16LPM | 8kW/12-16LPM | 7kW/12-16LPM | 6kW/12-16LPM | 5kW/12-16LPM |
| 3 bed + 1 bath | 8kW/9-12LPM | 8kW/9-12LPM | 7kW/9-12LPM | 7kW/9-12LPM | 6kW/9-12LPM |
| 3 bed + 2 bath | 8kW/12-16LPM | 8kW/12-16LPM | 8kW/12-16LPM | 8kW/12-16LPM | 6kW/12-16LPM |
| 4 bed + 1 bath | 10kW/9-12LPM | 10kW/9-12LPM | 8kW/9-12LPM | 8kW/9-12LPM | 7kW/9-12LPM |
| 4 bed + 2 bath | 10kW/12-16LPM | 10kW/12-16LPM | 8kW/12-16LPM | 8kW/12-16LPM | 7kW/12-16LPM |
| 5 bed + 2 bath | 12kW/12-16LPM | 12kW/12-16LPM | 10kW/12-16LPM | 10kW/12-16LPM | 9kW/12-16LPM |
Now find your combi gas boiler according to brand and budget:
Now you know roughly what size boiler you need, use the tables below to find a suitable model. The tables are ordered in boiler size based on heating output and closely sized boilers are grouped together in a size bracket, say 18-19kW. If the size table above recommends at 18kW boiler for example, then all the boilers in the size group of 18-19kW are suitable. As set out above, all combis are too big on the heating side for most of our housing stock! As long as it can be reduced down on the heating side then just look at hot water production, price and warranty.
18-19kW boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Glow Worm/Energy | 25kW | £700 | 2 | 2 | 18kW | 10.4 | 89% |
| Ideal/Vogue | C26 | £1,056 | 10 | 10 | 18kW | 10.6 | 91% |
| Vaillant/EcoFITpure | 825 | £865 | 2 | 7-10 | 18kW | 12.1 | 89% |
| Vaillant/EcoTEC pro | 24 | £942 | 2 | 5-10 | 19kW | 9.6 | 89% |
| Vaillant ecoTEC plus | 825 | £1,107 | 5 | 7-10 | 19kW | >10.5 | 89% |
| Vaillant/EcoTEC pro | 28 | £984 | 2 | 5-10 | 19kW | 11.1 | 89% |
20-22kW boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Baxi/Duotec | 24 | £675 | 7 | 7 | 20kW | 9.8 | 89% |
| Potterton/Titanium | 24 | £738 | 7 | 7 | 20kW | 9.8 | 91% |
| Baxi/Eco Blue + Compact | 24 | £810 | 7 | 7 | 20kW | 9.8 | 89% |
| Potterton/Promax | 24 Plus | £833 | 2 | 2 | 20kW | 9.8 | 89% |
| Baxi Ecoblue Advance | 24 | £920 | 10 | 10 | 20kW | 9.8 | 89% |
| Baxi 200 | 224 | £629 | 3 | 3 | 20kW | 9.8 | 89% |
| Baxi 400 | 424 | £663 | 3 | 3 | 20kW | 9.8 | 89% |
| Glow Worm/Easicom | 24 | £570 | 2 | 4 | 20kW | 10 | 90% |
| Glow Worm/Essential | 24 | £618 | 3 | 3 | 20kW | 10 | 89% |
| Potterton/Gold | 24 | £628 | 2 | 2 | 20kW | 9.8 | 91% |
| Baxi 200 | 228 | £651 | 5 | 5 | 20kW | 11.5 | 89% |
| Baxi 400 | 428 | £699 | 5 | 5 | 20kW | 11.5 | 89% |
| Viessmann/Vitodens 050 | 29kW | £827 | 3 | 7 | >22kW | 12.4 | 89% |
24kW boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Worcester Bosch/Greenstar i | 25i | £875 | 5 | 7 | 24kW | 9.8 | 94% |
| Worcestster Bosch/Si | 25Si | £1,010 | 7 | 9 | 24kW | 9.8 | 94% |
| Ideal/ Logic+ Combi | C24 | £794 | 7 | 7 | 24kW | 9.9 | 90% |
| Viessmann/Vitodens 100 | 26kW | £1,050 | 5 | 10 | 24kW | 8.9 | 89% |
| Worcester Greenstar Compact | 28CDi | £1,045 | 7 | 10 | 24kW | 10.0 | 94% |
| Baxi Platinum | 24 | £850 | 10 | 10 | 24kW | 9.8 | 89% |
| Ideal Independent | C24 | £607 | 5 | 5 | 24kW | >9.9 | 89% |
| Ideal Independent | C30 | £651 | 5 | 5 | 24kW | 12.4 | 89% |
| Glow Worm/Easicom | 28 | £605 | 2 | 4 | 24kW | 11.7 | 90% |
| Ferroli/Modena | 27kW | £577 | 5 | 5 | 24kW | 11.1 | 89% |
| Ideal Independent | C35 | £727 | 5 | 5 | 24kW | 14.5 | 89% |
| Potterton/Gold | 28 | £696 | 2 | 2 | 24kW | 13.3 | 91% |
| Baxi/Duotec | 28 | £795 | 7 | 7 | 24kW | 11.5 | 89% |
| Potterton/Titanium | 28 | £798 | 7 | 7 | 24kW | 11.5 | 91% |
| Worcester Bosch/Greenstar i | 30i | £990 | 5 | 7 | 24kW | 11.5 | 94% |
| Worcestster Bosch/Si | 30Si | £1,135 | 7 | 9 | 24kW | 11.5 | 94% |
| Baxi/Eco Blue + Compact | 28 | £885 | 7 | 7 | 24kW | 11.5 | 89% |
| Vaillant/EcoTEC pro | 30 | £1,080 | 2 | 5-10 | 24kW | 12.3 | 89% |
| Ideal/ Logic+ Combi | C30 | £830 | 7 | 7 | 24kW | 12.4 | 90% |
| Ideal/ Logic+ Combi | C35 | £985 | 7 | 7 | 24kW | 14.5 | 90% |
| Worcester Greenstar Compact | 32CDi | £1,140 | 7 | 10 | 24kW | 11.5 | 94% |
| Worcester Greenstar Compact | 36CDi | £1,285 | 7 | 10 | 24kW | 12.9 | 94% |
| Baxi Ecoblue Advance | 28 | £1,060 | 10 | 10 | 24kW | 11.5 | 89% |
| Vaillant ecoTEC plus | 832 | £1,226 | 5 | 7-10 | 24kW | 13.0 | 89% |
| Glow Worm/Easicom | 28 | £658 | 3 | 3 | 25kW | 11.7 | 89% |
| Glow Worm/Ultimate 2 | 30 | £694 | 5 | 5 | 25kW | 12.5 | 89% |
| Glow Worm/Energy | 30kW | £787 | 2 | 2 | 25kW | 12.5 | 89% |
| Glow Worm/Energy | 35kW | £880 | 2 | 2 | 25kW | 14.4 | 89% |
| Glow Worm/Ultimate 2 | 35 | £766 | 5 | 5 | 25kW | 14.4 | 89% |
| Potterton/Promax | 28 Plus | £877 | 2 | 2 | 25kW | 11.5 | 89% |
| Vaillant/EcoFITpure | 830 | £980 | 2 | 7-10 | 25kW | 14.2 | 89% |
| Vaillant/EcoFITpure | 835 | £1,095 | 2 | 7-10 | 25kW | 16.5 | 89% |
| Vaillant ecoTEC Green iQ | 835 | £1,651 | 5 | 7-10 | 25kW | 14.5 | 94% |
| Ideal/Vogue | C32 | £1,245 | 10 | 10 | 26kW | 13.1 | 91% |
| Main Eco Elite | 25 | £606 | 5 | 5 | 26kW | 10.1 | 90% |
| Viessmann Vitodens 200 | 26kW | £1,358 | 3 | 5 | 26kW | 10.7 | 90% |
28-29kW boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Viessmann/Vitodens 100 | 30kW | £1,100 | 5 | 10 | 27kW | 11.2 | 89% |
| Ferroli/Modena | 32kW | £632 | 5 | 5 | 28kW | 13.1 | 89% |
| Potterton/Gold | 33 | £764 | 2 | 2 | 28kW | 15.7 | 91% |
| Baxi/Duotec | 33 | £915 | 7 | 7 | 28kW | 13.5 | 89% |
| Potterton/Titanium | 33 | £858 | 7 | 7 | 28kW | 13.5 | 91% |
| Baxi/Eco Blue + Compact | 33 | £955 | 7 | 7 | 28kW | 13.5 | 89% |
| Baxi Platinum | 28 | £955 | 10 | 10 | 28kW | 11.5 | 89% |
| Baxi Ecoblue Advance | 33 | £1,175 | 10 | 10 | 28kW | 13.5 | 89% |
| Potterton/Promax | 33 Plus | £1,045 | 2 | 2 | 29kW | 13.5 | 89% |
| Vaillant ecoTEC plus | 838 | £1,394 | 5 | 7-10 | 29kW | 15.9 | 89% |
30kw boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Worcester Greenstar Classic | 29CDi | £1,100 | 7 | 10 | 30kW | 11.0 | 92% |
| Worcester Greenstar Classic | 34CDi | £1,225 | 7 | 10 | 30kW | 12.0 | 92% |
| Viessmann Vitodens 200 | 30kW | £1,435 | 3 | 5 | 30kW | 12.3 | 90% |
| Main Eco Elite | 30 | £668 | 5 | 5 | 30kW | 12.3 | 88% |
| Viessmann/Vitodens 050 | 35kW | £906 | 3 | 7 | 30kW | 14.5 | 89% |
| Worcester Greenstar Classic | 38CDi | £1,395 | 7 | 10 | 30kW | 4 | 92% |
| Vaillant ecoTEC plus | 835 | £1,110 | 5 | 7-10 | 30kW | 14.3 | 89% |
| Worcester Greenstar Classic | 42CDi | £1,665 | 7 | 10 | 30kW | 15.0 | 92% |
32kW boilers
| Manufacturer/Model | Code | Price | Standard warranty | Free Extended Warranty | Heating output (Size) | Litres per minute for hot water | Efficiency |
|---|---|---|---|---|---|---|---|
| Baxi/Duotec | 40 | £985 | 7 | 7 | 32kW | 16.4 | 89% |
| Potterton/Titanium | 40 | £930 | 7 | 7 | 32kW | 16.4 | 91% |
| Viessmann/Vitodens 100 | 35kW | £1,160 | 5 | 10 | 32kW | 13.5 | 89% |
| Baxi Ecoblue Advance | 40 | £1,240 | 10 | 10 | 32kW | 16.4 | 89% |
| Ideal/Vogue | C40 | £1,390 | 10 | 10 | 32kW | 16.4 | 91% |
| Baxi Platinum | 33 | £1,110 | 10 | 10 | 33kW | 13.5 | 89% |
| Vaillant ecoTEC Green iQ | 843 | £1,979 | 5 | 7-10 | 33kW | 17.8 | 94% |
| Ferroli/Modena | 38kW | £764 | 5 | 5 | 34kW | 16 | 89% |
Sizing a heat only boiler
It is more straightforward to size a heat only boiler than a combi as you are only sizing the heat production, not the hot water. In the table below you can get a rough idea of what size boiler you need based 1) the size of your property and 2) how well insulated it is. Property ages are given across the top and they assume standard insulation measures, such as double glazing and loft insulation, have been made. If your levels of insulation are very high in an older property then you may wish to move a column to the right.
Heat Only Boilers
| Age of property | pre 1900 | 1920s-1930s | 1950-1980s | 1990s | 2000 onwards |
|---|---|---|---|---|---|
| Insulation levels | Poorly insulated | Some insulation | Moderately insulated | Reasonably insulated | Well insulated |
| Number of bedrooms | |||||
| 1 | 7kW | 7kW | 6kW | 6kW | 4kW |
| 2 | 8kW | 8kW | 7kW | 6kW | 5kW |
| 3 | 8kW | 8kW | 7kW | 7kW | 6kW |
| 4 | 10kW | 10kW | 8kW | 8kW | 7kW |
| 5 | 12kW | 12kW | 10kW | 10kW | 9kW |
| 5+ | 15kW | 15kW | 14kW | 12kW | 10kW |
Now find your heat only gas boiler according to brand and budget:
Now you know roughly what size boiler you need, use the tables below to find a suitable model. The tables are ordered in boiler size and closely sized boilers are grouped together in a size bracket. If the size table above recommends at 12kW boiler for example, then all the boilers in the size group of 12-13kW are suitable. What the tables show is that most boilers are too big for the majority of UK homes and absolutely must be 'range rated' down to better meet the heat requirement following an accurate heat loss survey.
12-13kW boilers
| 12-13kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Main heat only boiler | 12 | £480.00 | 2 | 2 | 12kW | 89% |
| Potterton Promax SL Heat | 12 | £674.00 | 2 | 2 | 12kW | 89% |
| Ideal Logic Heat | 12 | £695.00 | 2 | 2 | 12kW | 89% |
| Vaillant ecoFIT pure regular | 12 | £702.00 | 2 | 7-10 | 12kW | 89% |
| Glow Worm Energy Regular | 12 | £704.00 | 2 | 2 | 12kW | 89% |
| Vaillant ecoTEC plus regular | 12 | £730.00 | 5 | 7-10 | 12kW | 89% |
| Ideal Logic + Heat | 12 | £765.00 | 7 | 7 | 12kW | 89% |
| Worcester Bosch Greenstar Ri | 12 | £786.00 | 7 | 8 | 12kW | 91% |
| Baxi 200 Heat | 12 | £653.00 | 3 | 3 | 13kW | 89% |
| Baxi 400 Heat | 12 | £669.00 | 5 | 5 | 13kW | 89% |
| Baxi Ecoblue Advance Heat | 13 | £776.00 | 7 | 7 | 13kW | 89% |
| Baxi Ecoblue Heat | 12 | £795.00 | 2 | 2 | 13kW | 89% |
| Viessmans Vitodens 100-W Regular | 13 | £816.00 | 5 | 5 | 13kW | 90% |
15-16kW boilers
| 15-16kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Main heat only boiler | 15 | £505.00 | 2 | 2 | 15kW | 89% |
| Glow Worm Energy Regular | 15 | £722.00 | 2 | 2 | 15kW | 89% |
| Ideal Logic Heat | 15 | £730.00 | 2 | 2 | 15kW | 89% |
| Vaillant ecoFIT pure regular | 15 | £733.00 | 2 | 7-10 | 15kW | 89% |
| Potterton Promax SL Heat | 15 | £751.00 | 2 | 2 | 15kW | 89% |
| Ideal Logic + Heat | 15 | £796.00 | 7 | 7 | 15kW | 89% |
| Worcester Bosch Greenstar Ri | 15 | £801.00 | 7 | 8 | 15kW | 91% |
| Vaillant ecoTEC plus regular | 15 | £822.00 | 5 | 7-10 | 15kW | 89% |
| Baxi 200 Heat | 15 | £677.00 | 3 | 3 | 16kW | 89% |
| Baxi 400 Heat | 15 | £691.00 | 5 | 5 | 16kW | 89% |
| Viessmans Vitodens 100-W Regular | 16 | £841.00 | 5 | 5 | 16kW | 90% |
| Baxi Ecoblue Heat | 15 | £843.00 | 2 | 2 | 16kW | 89% |
| Baxi Ecoblue Advance Heat | 16 | £855.00 | 7 | 7 | 16kW | 89% |
18-21kW boilers
| 18-21kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Main heat only boiler | 18 | £539.00 | 2 | 2 | 18kW | 89% |
| Glow Worm Energy Regular | 18 | £755.00 | 2 | 2 | 18kW | 89% |
| Ideal Logic Heat | 18 | £763.00 | 2 | 2 | 18kW | 89% |
| Potterton Promax SL Heat | 18 | £780.00 | 2 | 2 | 18kW | 89% |
| Vaillant ecoFIT pure regular | 18 | £802.00 | 2 | 7-10 | 18kW | 89% |
| Worcester Bosch Greenstar Ri | 18 | £859.00 | 7 | 8 | 18kW | 91% |
| Vaillant ecoTEC plus regular | 18 | £894.00 | 5 | 7-10 | 18kW | 89% |
| Baxi 200 Heat | 18 | £708.00 | 3 | 3 | 19kW | 89% |
| Baxi 400 Heat | 18 | £720.00 | 5 | 5 | 19kW | 89% |
| Baxi Ecoblue Heat | 18 | £860.00 | 2 | 2 | 19kW | 89% |
| Baxi Ecoblue Advance Heat | 19 | £908.00 | 7 | 7 | 19kW | 89% |
| Viessmans Vitodens 100-W Regular | 19 | £858.00 | 5 | 5 | 19kW | 90% |
| Baxi 200 Heat | 24 | £749.00 | 3 | 3 | 21kW | 89% |
| Baxi Ecoblue Heat | 21 | £913.00 | 2 | 2 | 21kW | 89% |
22-24kW boilers
| 22-24kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Potterton Promax SL Heat | 24 | £822.00 | 2 | 2 | 22kW | 89% |
| Main heat only boiler | 24 | £593.00 | 2 | 2 | 24kW | 89% |
| Ideal Logic Heat | 24 | £796.00 | 2 | 2 | 24kW | 89% |
| Ideal Logic + Heat | 24 | £828.00 | 7 | 7 | 24kW | 89% |
| Worcester Bosch Greenstar Ri | 24 | £909.00 | 7 | 8 | 24kW | 92% |
| Vaillant ecoTEC plus regular | 24 | £959.00 | 5 | 7-10 | 24kW | 89% |
25-27kW boilers
| 25-27kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Baxi 200 Heat | 30 | £756.00 | 3 | 3 | 25kW | 89% |
| Baxi 400 Heat | 24 | £763.00 | 5 | 5 | 25kW | 89% |
| Glow Worm Energy Regular | 24 | £788.00 | 2 | 2 | 25kW | 89% |
| Vaillant ecoFIT pure regular | 25 | £874.00 | 2 | 7-10 | 25kW | 89% |
| Baxi Ecoblue Heat | 24 | £1,103.00 | 2 | 2 | 25kW | 89% |
| Baxi Ecoblue Advance Heat | 25 | £925.00 | 7 | 7 | 25kW | 89% |
| Viessmans Vitodens 100-W Regular | 26 | £915.00 | 5 | 5 | 26kW | 90% |
| Worcester Bosch Greenstar Ri | 27 | £1,021.00 | 7 | 8 | 27kW | 92% |
30kW boilers
| 30kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Glow Worm Energy Regular | 30 | £826.00 | 2 | 2 | 30kW | 89% |
| Baxi 400 Heat | 30 | £834.00 | 5 | 5 | 30kW | 89% |
| Ideal Logic Heat | 30 | £905.00 | 2 | 2 | 30kW | 89% |
| Vaillant ecoFIT pure regular | 30 | £932.00 | 2 | 7-10 | 30kW | 89% |
| Baxi Ecoblue Advance Heat | 30 | £981.00 | 7 | 7 | 30kW | 89% |
| Ideal Logic + Heat | 30 | £889.00 | 7 | 7 | 30kW | 89% |
| Vaillant ecoTEC plus regular | 30 | £1,000.00 | 5 | 7-10 | 30kW | 89% |
| Worcester Bosch Greenstar Ri | 30 | £1,065.00 | 7 | 8 | 30kW | 93% |
| Worcester Bosch Greenstar Classic Cdi | 30 | £1,141.00 | 7 | 10 | 30kW | 92% |
35kW - 41kW boilers
| 35kW- 41kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Viessmans Vitodens 100-W Regular | 35 | £1,325.00 | 5 | 5 | 35kW | 90% |
| Vaillant ecoFIT pure regular | 35 | £1,449.00 | 2 | 7-10 | 35kW | 89% |
| Vaillant ecoTEC plus regular | 35 | £1,535.00 | 5 | 7-10 | 35kW | 89% |
| Worcester Bosch Greenstar Classic Cdi | 40 | £1,589.00 | 7 | 10 | 41kW | 92% |
Sizing a system boiler
Like a heat only boiler, a system boiler can be sized for heating only. Use the table below to find the right size based on 1) property size and 2) property age factoring in insulation levels. If you house has seen standard levels of improvements, such as loft insulation or double glazing, then go with its age bracket. If it has been heavily improved then consider moving one column to the right. Also like heat-only boilers, all the system boilers available to buy are too big for the majority of UK homes and must be range rated down by a gas engineer to better match the heat requirement of your home.
System Boilers
| Age of property | pre 1900 | 1920s-1930s | 1950-1980s | 1990s | 2000 onwards |
|---|---|---|---|---|---|
| Insulation levels | Poorly insulated | Some insulation | Moderately insulated | Reasonably insulated | Well insulated |
| Number of bedrooms | |||||
| 1 | 7kW | 7kW | 6kW | 6kW | 4kW |
| 2 | 8kW | 8kW | 7kW | 6kW | 5kW |
| 3 | 8kW | 8kW | 9kW | 7kW | 6kW |
| 4 | 10kW | 10kW | 8kW | 8kW | 7kW |
| 5 | 12kW | 12kW | 10kW | 10kW | 9kW |
| 5+ | 15kW | 15kW | 14kW | 12kW | 10kW |
Now find your system gas boiler according to brand and budget:
Now you know roughly what size boiler you need, use the tables below to find a suitable model. The tables are ordered in boiler size and closely sized boilers are grouped together in a size bracket, say 24-26kW. If the size table above recommends at 24kW boiler for example, then all the boilers in the size group of 24-26kW are suitable.
12-13kW boilers
| 12-13kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Glow Worm Energy System | 12 | 712 | 2 | 2 | 12kW | 89% |
| Vaillant ecoTEC plus system | 12 | 772 | 5 | 7-10 | 12kW | 89% |
| Potterton Promax System | 12 | 794 | 2 | 2 | 12kW | 89% |
| Vaillant ecoFIT pure system | 12 | 812 | 2 | 7-10 | 12kW | 89% |
| Worcester Bosch Greenstar System i | 12 | 879 | 7 | 8 | 12kW | 94% |
| Baxi Ecoblue System | 12 | 901 | 7 | 7 | 13kW | 89% |
15-17kW boilers
| 15-17kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Glow Worm Energy System | 15 | £731.00 | 2 | 2 | 15kW | 89% |
| Ideal Logic System | 15 | £741.00 | 2 | 2 | 15kW | 89% |
| Potterton Promax System | 15 | £808.00 | 2 | 2 | 15kW | 89% |
| Ideal Logic + System | 15 | £809.00 | 7 | 7 | 15kW | 89% |
| Vaillant ecoTEC plus system | 15 | £858.00 | 5 | 7-10 | 15kW | 89% |
| Vaillant ecoFIT pure system | 15 | £875.00 | 2 | 7-10 | 15kW | 89% |
| Worcester Bosch Greenstar System i | 15 | £926.00 | 7 | 8 | 15kW | 94% |
| Ideal Vogue System | 15 | £944.00 | 8 | 10 | 15kW | 93% |
| Baxi Ecoblue System | 15 | £923.00 | 7 | 7 | 17kW | 89% |
| Ferroli Modena HE 18S | 18 | £575.00 | 5 | 5 | 17kW | 89% |
18-21kW boilers
| 18-21kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Potterton Gold System | 18 | £566.00 | 2 | 2 | 18kW | 88% |
| Glow Worm Energy System | 18 | £757.00 | 2 | 2 | 18kW | 89% |
| Ideal Logic System | 18 | £810.00 | 2 | 2 | 18kW | 89% |
| Potterton Promax System | 18 | £825.00 | 2 | 2 | 18kW | 89% |
| Ideal Logic + System | 18 | £841.00 | 7 | 7 | 18kW | 89% |
| Vaillant ecoFIT pure system | 18 | £931.00 | 2 | 7-10 | 18kW | 89% |
| Vaillant ecoTEC plus system | 18 | £954.00 | 5 | 7-10 | 18kW | 89% |
| Worcester Bosch Greenstar System i | 18i | £974.00 | 7 | 8 | 18kW | 94% |
| Ideal Vogue System | 18 | £1,015.00 | 8 | 10 | 18kW | 93% |
| Viessmann 100-W System | 19 | £1,032.00 | 5 | 5 | 19kW | 90% |
| Viessmann 200-W System | 19 | £1,296.00 | 5 | 5 | 19kW | 90% |
| Baxi Ecoblue System | 18 | £962.00 | 7 | 7 | 20kW | 89% |
| Worcester Bosch Greenstar System i | 21 | £1,014.00 | 7 | 8 | 21kW | 94% |
24-25kW boilers
| 24-25kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Potterton Gold System | 21 | £589.00 | 2 | 2 | 24kW | 88% |
| Ideal Logic System | 24 | £844.00 | 2 | 2 | 24kW | 89% |
| Ideal Logic + System | 24 | £872.00 | 7 | 7 | 24kW | 89% |
| Worcester Bosch Greenstar System i | 24i | £1,035.00 | 7 | 8 | 24kW | 94% |
| Vaillant ecoTEC plus system | 24 | £1,137.00 | 5 | 7-10 | 24kW | 89% |
| Ferroli Modena HE 25S | 25 | £588.00 | 5 | 5 | 25kW | 89% |
| Glow Worm Energy System | 25 | £809.00 | 2 | 2 | 25kW | 89% |
| Potterton Promax System | 24 | £863.00 | 2 | 2 | 25kW | 89% |
| Vaillant ecoFIT pure system | 25 | £1,100.00 | 2 | 7-10 | 25kW | 89% |
| Main System Eco Elite | 24 | £617.00 | 3 | 3 | 26kW | 92% |
| Viessmann 100-W System | 26 | £1,068.00 | 5 | 5 | 26kW | 90% |
| Ideal Vogue System | 26 | £1,169.00 | 8 | 10 | 26kW | 93% |
| Viessmann 200-W System | 26 | £1,410.00 | 5 | 5 | 26kW | 90% |
26-29kW boilers
| 26-29kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Worcester Bosch Greenstar System i | 27i | £1,042.00 | 7 | 8 | 27kW | 92% |
| Baxi Ecoblue System | 24 | £1,053.00 | 7 | 7 | 27kW | 89% |
| Vaillant ecoTEC exclusive | 27 | £1,438.00 | 5 | 7-10 | 27kW | 90% |
| Potterton Gold System | 24 | £609.00 | 2 | 2 | 28kW | 88% |
| Main System Eco Elite | 28 | £680.00 | 3 | 3 | 29kW | 92% |
30-32kW boilers
| 30-32kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Glow Worm Energy System | 30 | £833.00 | 2 | 2 | 30kW | 89% |
| Ideal Logic System | 30 | £877.00 | 2 | 2 | 30kW | 89% |
| Ideal Logic + System | 30 | £902.00 | 7 | 7 | 30kW | 89% |
| Viessmann 100-W System | 30 | £1,100.00 | 5 | 5 | 30kW | 90% |
| Worcester Bosch Greenstar System i | 30i | £1,112.00 | 7 | 8 | 30kW | 92% |
| Worcester Bosch Greenstar System Cdi | 30 | £1,132.00 | 7 | 10 | 30kW | 92% |
| Vaillant ecoTEC plus system | 30 | £1,173.00 | 5 | 7-10 | 30kW | 89% |
| Vaillant ecoFIT pure system | 30 | £1,207.00 | 2 | 7-10 | 30kW | 89% |
| Viessmann 200-W System | 30 | £1,519.00 | 5 | 5 | 30kW | 90% |
| Ferroli Modena HE 32S | 32 | £669.00 | 5 | 5 | 31kW | 89% |
| Baxi Ecoblue System | 28 | £1,087.00 | 7 | 7 | 31kW | 89% |
| Ideal Vogue System | 32 | £1,256.00 | 8 | 10 | 32kW | 93% |
34-37kW boilers
| 34-37kW | Code | Price | Standard warranty | Free extended warranty | Central heating output | Efficiency |
|---|---|---|---|---|---|---|
| Potterton Promax System | 32 | £948.00 | 2 | 2 | 34kW | 89% |
| Worcester Bosch Greenstar System CDI | 35 | £1,245.00 | 7 | 10 | 34kW | 92% |
| Baxi Ecoblue System | 30 | £1,137.00 | 7 | 7 | 35kW | 89% |
| Viessmann 100-W System | 35 | £1,511.00 | 5 | 5 | 35kW | 90% |
| Viessmann 200-W System | 35 | £1,571.00 | 5 | 5 | 35kW | 90% |
| Vaillant ecoTEC plus system | 37 | £1,312.00 | 5 | 7-10 | 37kW | 89% |
