Use our boiler size calculator tables

 

How can I work out what size boiler I need?

Use our simple tables to calculate what size boiler you need and then find the best boiler in your size range. The right sized boiler is smaller than you think. We routinely oversize our boilers in the UK which contributes to lower efficiencies and shorter lifespans. Why does this happen? 99% of installers have not been trained to specify and setup condensing boilers correctly. For more on our work to expose and correct the industry failings read our Heating Heroes page.

In this guide we help you work out your heat requirements based on property size and age and review boiler models. Sizing a combi boiler is a bit more complicated as the output needed for hot water is much larger, but we offer help there too.

The correct size boiler is like car cruising on a motorway

There is often a temptation to oversize the boiler, just in case. Oversizing is very inefficient and accelerates wear and tear which can cost thousands over the lifetime of the boiler in higher fuel bills and early replacement.

Think of a boiler like a car. A car is at its most efficient traveling on a motorway for long periods. The same principle applies to boilers. A boiler is at its most efficient when it can run for long periods and to do this it must be accurately set at the same kW output required to heat your home.

Oversized boilers will ‘cycle’ on and off, as the boiler heats up too quickly, runs for short blasts and then turns off. Like the clutch of a car stuck in town centre traffic, the stop-start cycles will use more fuel and put the components under greater stress than when cruising along a motorway.

Calculating your boiler size - it's smaller than you think!

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.

As a guide, the vast majority of homes in the UK have a heat requirement of under 10kW, commonly 6-8kW. For system and heat-only boilers, this is easy to accommodate as smaller boilers are available.

For combis however the heating output tends to be around 18kW for the heating side of the system and 24kW and upwards for hot water. The good news is most modern boilers can be 'range rated' down, i.e. your installer can adjust the output of the boiler to 6-10kW to accurately meet your maximum heat requirement. Make sure you ask your installer to do this.

Impact on boiler efficiency

Condensing boilers boast efficiencies of 90% or more but the upspoken truth is they almost never reach their factory stated efficiencies in practice because 99% of installers have not be trained in condensing technology. Actual efficiencies are closer to 80%. The reasons behind this are many and concern how the boiler is sized, its minimum output, the heating control that is used and whether the radiators stay balanced. We have produced a very easy step by step guide to getting the most from your condensing boiler in our blog Why condensing boilers do not condense.

1) Sizing a combi boiler

On the table below, find your property’s age across the top and its size down the left-hand column. Property ages assume standard insulation measures, such as double glazing and loft insulation have been retrofitted or - for newer properties - were installed at the time of construction. Some older properties have been very well insulated retrospectively. If your levels of insulation are very high for the property’s age, 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).

REMEMBER, the average UK home has a maximum heat requirement of 6-8kW on a very cold day, according boiler manufacturer Viessmann, very properties exceed 10kW. You can buy a bigger boiler but your installer must reduce the output down on installation.

Sizing for hot water

The hot water flow rate of a combi boiler - expressed as ‘litres per minute’ (LPM) - indicates how quickly a combi boiler can heat hot water. Hot water flow rates vary from 9.8 LPM to 25 LPM! For houses with multiple bathrooms, the hot water flow rate will be halved if two showers are running simultaneously so it’s important to look at the flow rates. If you have multiple bathrooms you may wish to consider a boiler with a higher flow rate. NB for multiple bathroom properties it is really much better to use a system boiler and hot water tank.

Combi boiler table

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	9kW/9-12LPM	9kW/9-12LPM	8kW/9-12LPM	7kW/9-12LPM	6kW/9-12LPM
3 bed + 2 bath	9kW/12-16LPM	9kW/12-16LPM	8kW/12-16LPM	7kW/12-16LPM	6kW/12-16LPM
4 bed + 1 bath	10kW/9-12LPM	10kW/9-12LPM	9kW/9-12LPM	8kW/9-12LPM	7kW/9-12LPM
4 bed + 2 bath	10kW/12-16LPM	10kW/12-16LPM	9kW/12-16LPM	8kW/12-16LPM	7kW/12-16LPM
5 bed + 2 bath	14kW/12-16LPM	12kW/12-16LPM	10kW/12-16LPM	10kW/12-16LPM	9kW/12-16LPM
5+ bed + 2 bath	16kW/12-16LPM	15kW/12-16LPM	14kW/12-16LPM	12kW/12-16LPM	10kW/12-16LPM

 

 

Combi boilers according to brand and budget:

Remember the kW outputs for combis appear bigger because they are sized for hot water. We have grouped boilers together based on the heating output and on that basis the smallest of combi boilers will heat most homes. Look down the LPM column to determine hot water production and REMEMBER to ask your installer to range rate (reduce) the kW output down to meet your actual heat requirement. Also remember that most big combis are not suitable even for a large house. We have shown them here because they give good hot water production, but a 40kW heating boiler could heat a mansion! Its output must be reduced or better still consider a system boiler with priority hot water set up.

18-19kW boilers / 9.6-12.1 litres per minute

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Glow Worm Energy	25kW	£700	18kW	12.1	2	2	5.3kW
Ideal Vogue	C26	£1,056	18kW	10.6	10	10	4.0kW
Vaillant EcoFIT Pure	825	£865	18kW	12.1	2	7	5.3kW
Vaillant EcoTEC Pro	24	£942	19kW	9.6	2	7	5.4kW
Vaillant EcoTEC Plus	825	£1,107	19kW	10.5	5	10	3.8kW
Vaillant EcoTEC Pro	28	£984	19kW	11.1	2	7	5.8kW

20-22kW boilers / 9.8-12.4 litres per minute

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Baxi/Duotec	24	£750	21kW	9.8	7	7	7.4kW
Potterton Titanium	24	£715	20kW	9.8	7	7	7.4kW
Baxi Eco Blue Advance	24	£1,020	20kW	9.8	7	7	4.9kW
Potterton Promax	24 Plus	£833	20kW	9.8	2	2	7.4kW
Baxi 200	224	£620	22kW	9.8	3	3	5.2kW
Baxi 400	424	£670	22kW	9.8	3	3	5.2kW
Glow Worm Easicom	24	£520	20kW	10	2	4	5.3kW
Baxi 200	228	£620	22kW	11.5	5	5	5.2kW
Baxi 400	428	£699	22kW	11.5	5	5	5.2kW
Viessmann/Vitodens 050	29kW	£735	>22kW	12.4	3	7	5.9kW
Ravenheat	HE80	£649	21kW	10.2	5	5	3.6kW
Worcester Greenstar 2000	25	£780	20kW	10.0	5	10	4.8kW
Intergas Xtreme	24	£1,209	20kW	11.0	7	7	3.6kW

24-26kW boilers / 9.8-16.5 litres per minute

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Worcestster Bosch Greenstar Si	25Si	£1,045	24kW	9.8	5	10	8.1kW
Ideal Logic+	C24	£825	24kW	9.9	7	7	7.1kW
Viessmann Vitodens 100	26kW	£1,070	24kW	8.9	5	10	4.7kW
Baxi Platinum	24	£1,110	24kW	9.8	10	10	7.4kW
Ideal Independent	C24	£670	24kW	9.9	5	5	4.8kW
Ideal Independent	C30	£745	24kW	12.3	5	5	6.1kW
Glow Worm Easicom	28	£550	24kW	11.7	2	4	6.3kW
Ideal Independent	C35	£805	24kW	14.5	5	5	7.1kW
Baxi Duotec	28	£885	24kW	11.5	7	7	9.5kW
Potterton Titanium	28	£790	24kW	11.5	7	7	9.5kW
Worcester Bosch Si	30Si	£1,170	24kW	11.5	5	10	7.0kW
Baxi Eco Blue Advance	28	£1,170	25kW	11.5	7	7	6.0kW
Vaillant EcoTEC Pro	30	£1,160	30kW	12.3	2	7	6.2kW
Ideal Logic+ Combi	C30	£890	24kW	12.4	7	7	6.1kW
Ideal Logic+ Combi	C35	£1,035	24kW	14.5	7	7	7.1kW
Baxi Ecoblue Advance	28	£1,170	25kW	11.5	10	10	6.0kW
Vaillant EcoTEC Plus	832	£1,290	24kW	11.5	5	10	5.2kW
Glow Worm Easicom	28	£550	25kW	11.7	3	3	6.3kW
Glow Worm Energy	30kW	£800	25kW	12.5	2	2	6.3kW
Glow Worm Energy	35kW	£900	25kW	14.4	2	2	7.2kW
Potterton Promax	28 Plus	£877	25kW	11.5	2	2	9.5kW
Vaillant EcoFIT Pure	830	£1,110	25kW	14.2	2	7	6.3kW
Vaillant EcoFIT Pure	835	£1,140	25kW	16.5	2	7	7.5kW
Vaillant EcoTEC Green iQ	835	£1,651	25kW	14.5	5	10	3.4kW
Ideal Vogue	C32	£1,115	26kW	13.1	10	10	4.6kW
Main Eco Elite	25	£525	26kW	10.1	5	5	8.4kW
Viessmann Vitodens 200	26kW	£1,020	26kW	10.7	3	10	1.9kW
Ravenheat HE	98S	£719	26kW	12.1	5	5	3.7kW
Intergas Xtreme	30	£1,268	26kW	13.3	7	7	3.6kW

28-29kW boilers / 11.2 - 15.9 litres per minutes

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Viessmann Vitodens 100	30kW	£1,115	27kW	11.2	5	10	5.4kW
Ferroli Modena	32kW	£670	28kW	13.1	5	5	7.2kW
Baxi Duotec	33	£990	28kW	13.5	7	7	10.2kW
Potterton Titanium	33	£855	28kW	13.5	7	7	10.2kW
Baxi Platinum	28	£1,010	28kW	11.5	10	10	9.5kW
Baxi Ecoblue Advance	33	£1,300	28kW	13.5	10	10	7.1kW
Potterton Promax	33 Plus	£1,045	29kW	13.5	2	2	10.2kW
Vaillant EcoTEC Plus	838	£1,440	29kW	15.9	5	10	6.5kW

30kW boilers / 11 - 15 litres per minute

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Viessmann Vitodens 200	30kW	£1,602	30kW	12.3	3	10	1.9kW
Main Eco Elite	30	£570	30kW	12.3	5	5	9.4kW
Viessmann Vitodens 50	35kW	£855	30kW	14.5	3	7	8kW
Vaillant EcoTEC Plus	835	£1,470	30kW	14.3	5	10	5.8kW
Worcester Greenstar 2000	30	£740	30kW	12.0	5	10	4.8kW
Worcester Greenstar 8000	30	£1,275	30kW	12.3	5	10	3.0kW

32-34kW boilers / 13.5 - 16.4 litres per minutes

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Baxi Duotec	40	£1,045	32kW	16.4	7	7	12.1kW
Potterton Titanium	40	£930	32kW	16.4	7	7	12.1kW
Viessmann Vitodens 100	35kW	£1,090	32kW	13.5	5	10	5.4kW
Ideal Vogue	C40	£1,225	32kW	16.4	10	10	5.7kW
Baxi Platinum	33	£1,145	33kW	13.5	10	10	10.2kW
Ferroli Modena	38kW	£815	34kW	16	5	5	7.0kW

35-40kW boilers / 14.3 - 16.4 litres per minute

Manufacturer/Model	Code	Price	Heating output (Size)	Litres per minute for hot water	Standard warranty	Free Extended Warranty	Min Heating Output
Baxi Platinum	40	£1,260	40kW	16.4	10	10	12.1kW
Worcester Greenstar 8000	35	£1,405	35kW	14.3	5	10	3.5kW
worcester Greenstar 8000	40	£1,600	35kW	16.4	5	10	3.5kW

 

2) Sizing a heat only boiler

It is possible to get a rough idea of the size you need using the age of your property, insulation levels and the size of your property. 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 uncharacteristically high for the age of the property then you may wish to move a column to the right. You will note that for the majority of domestic properties, a 6-8kW boiler will be sufficient.

Whilst we show boilers from ranges above this size, in reality they are oversized for domestic properties. There are exceptions of course and the attending engineer should carry out a heat loss survey to accurately size your heat requirement at peak times.

Sizing for your hot water cylinder

One caveat is the output you need for your hot water cylinder, which is often above 8kW. Therefore consider your hot water requirements. Small cylinders commonly need 12kW of heat whilst larger cylinders can take 25kW and upwards. If you have multiple bathrooms in use that the same time then you will need a larger boiler on a conventional setup. The best advice is to pick a boiler than can go down really low on the heating side to get the best efficiencies. See our Guide to the Best Boilers for the most efficient boilers for every situation.

Heat only boilers sizing table

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	9kW	9kW	8kW	7kW	6kW
4	10kW	10kW	9kW	8kW	7kW
5	14kW	12kW	10kW	10kW	9kW
5+	16kW	15kW	14kW	12kW	10kW

 

Heat only boilers according to brand and budget:

Use the tables below to find a suitable model. The tables are ordered according to size and closely sized boilers are grouped together in a size bracket, for example 18-21kW. If the sizing table indicates an 18kW boiler for example, then all the boilers in the size group of 18-21kW are applicable.

12-13kW boilers

12-13kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Potterton Titanium Heat	12	£768.00	13kW	2	2	4.3kW
Ideal Logic Heat	12	£695.00	12kW	2	2	5.1kW
Vaillant EcoFIT Pure Regular	412	£740.00	12kW	2	7	4.5kW
Glow Worm Energy Regular	12	£740.00	12kW	2	2	4.5kW
Vaillant EcoTEC Plus Regular	412	£805.00	12kW	5	10	4.5kW
Ideal Logic + Heat	12	£705.00	12kW	7	7	5.1kW
Worcester Bosch Greenstar Ri	12	£810.00	12kW	5	10	3.5kW
Baxi 200 Heat	12	£600.00	13kW	3	3	7.5kW
Baxi 400 Heat	12	£65.00	13kW	5	5	7.5kW
Viessmans Vitodens 100-W Regular	13	£850.00	13kW	5	10	7.2kW

15-16kW boilers

15-16kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Main Eco Compact	15	£685.00	15kW	5	5	5.4kW
Glow Worm Energy Regular	15	£755.00	15kW	7	7	4.5kW
Ideal Logic Heat	15	£720.00	15kW	2	2	5.1kW
Vaillant EcoFIT Pure Regular	415	£775.00	15kW	2	7	4.5kW
Potterton Titanium Heat	15	£810.00	15kW	7	7	5.4kW
Ideal Logic + Heat	15	£740.00	15kW	7	7	5.1kW
Worcester Bosch Greenstar Ri	15	£830.00	15kW	5	10	4.6kW
Vaillant EcoTEC Plus Regular	15	£880.00	15kW	5	10	4.5kW
Baxi 200 Heat	15	£630.00	16kW	3	3	7.5kW
Baxi 400 Heat	15	£685.00	16kW	5	5	7.5kW
Viessmans Vitodens 100-W Regular	16	£885.00	16kW	5	10	7.2kW

18-21kW boilers

18-21kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Main Eco Compact	18	£720.00	18kW	5	5	6.4kW
Glow Worm Energy Regular	18	£790.00	18kW	7	7	5kW
Ideal Logic Heat	18	£770.00	18kW	2	2	5.1kW
Potterton Titanium Heat	18	£850.00	18kW	7	7	6.4kW
Vaillant EcoFIT Pure Regular	18	£845.00	18kW	2	7	5kW
Worcester Bosch Greenstar Ri	18	£859.00	18kW	7	8	91%
Vaillant EcoTEC Plus Regular	18	£885.00	18kW	5	10	5.5kW
Baxi 200 Heat	18	£690.00	19kW	3	3	7.5kW
Baxi 400 Heat	18	£715.00	19kW	5	5	7.5kW
Viessmans Vitodens 100-W Regular	19	£900.00	19kW	5	10	7.2kW
Baxi 200 Heat	24	£755.00	21kW	3	3	7.5kW
Baxi 400 Heat	24	780.00	21kW	5	5	7.5kW
Intergas HRE	18OV	£759.00	18kW	10	10	6.1kW

22-24kW boilers

22-24kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Potterton Titanium Heat	24	£888.00	22kW	7	7	8.4kW
Main Eco Compact	24	£755.00	24kW	5	5	8.4kW
Ideal Logic Heat	24	£805.00	24kW	2	2	5.1kW
Ideal Logic + Heat	24	£880.00	24kW	7	7	5.1kW
Worcester Bosch Greenstar Ri	24	£940.00	24kW	5	10	7.3kW
Vaillant EcoTEC Plus Regular	24	£1,035.00	24kW	5	10	6.1kW
Intergas HRE	24OV	£829.00	23kW	10	10	7.7kW

25-27kW boilers

25-27kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Baxi 200 Heat	30	£810.00	25kW	3	3	7.5kW
Baxi 400 Heat	30	£920.00	25kW	5	5	7.5kW
Glow Worm Energy Regular	25	£825.00	25kW	7	7	8.4kW
Vaillant EcoFIT Pure Regular	25	£935.00	26kW	2	7	6.1kW
Viessmans Vitodens 100-W Regular	26	£960.00	26kW	5	10	7.2kW
Intergas HRE	27OV	£899.00	27kW	10	10	7.6kW

30kW boilers

30kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Glow Worm Energy Regular	30	£855.00	30kW	7	7	7.5kW
Baxi 400 Heat	30	£850.00	30kW	5	5	7.5kW
Ideal Logic Heat	30	£910.00	30kW	2	2	6.4kW
Vaillant EcoFIT Pure Regular	30	£987.00	30kW	2	7	7.5kW
Ideal Logic + Heat	30	£922.00	30kW	7	7	6.4kW
Vaillant EcoTEC Plus Regular	30	£1,000.00	30kW	5	10	7.5kW
Worcester Bosch Greenstar Ri	30	£1,065.00	30kW	5	10	7.0kW
Worcester Bosch Greenstar 8000	30	£1,275	30kW	5	10	3.0kW

35kW - 41kW boilers

35kW- 41kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Viessmans Vitodens 100-W Regular	35	£1,290.00	35kW	5	10	7.9kW
Vaillant EcoFIT Pure Regular	35	£1,458.00	35kW	2	7	7.5kW
Vaillant EcoTEC Plus Regular	35	£1,540.00	35kW	5	10	7.5kw
Worcester Bosch Greenstar 8000	35	£1,510.00	35kW	5	10	3.5kW

 

3) Sizing a system boiler

If your house has seen standard levels of insulation improvements, such as loft insulation or double glazing, then go with the applicable age bracket. If the insulation levels are particularly high relative to its age then move one column to the right. Like heat-only boilers, it is not necessary to install a boiler with a capacity greater than 18kW for the majority of properties, but you must factor in the hot water requirements of your cylinder. Whilst your property might only need 6-8kW of heating, it may still require a bigger output for hot water. There are exceptions and the attending engineer should carry out a heat loss survey to determine the exact figures.

Sizing for your hot water cylinder

A 30-40kW heat only boiler could heat a mansion house, however larger homes with multiple bathrooms in use simultaneously will require a larger output boiler. Some hot water cylinders are set up to take big outputs from the boiler - your heating engineer will be able to assist with the sizing. The best set up is a boiler that can meet your heating and hot water demands and go down really low on the heating side. See our Guide to the best boilers to find the most efficient boilers for every situation.

System boiler sizing tables

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	9kW	9kW	8kW	7kW	6kW
4	10kW	10kW	8kW	8kW	7kW
5	14kW	12kW	10kW	10kW	9kW
5+	16kW	15kW	14kW	12kW	10kW

System boilers according to brand and budget:

Now use the tables below to find the best boiler based on your required size. The tables are in size order and closely sized boilers are grouped together, for example 24-26kW. If the sizing table recommends a 24kW boiler for example, then all the boilers in the size group of 24-26kW are applicable.

12-13kW boilers

12-13kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Glow Worm Energy System	12	£690	12kW	2	2	4.5kW
Vaillant EcoTEC Plus system	12	£910	12kW	5	10	3.3kW
Vaillant EcoFIT Pure System	12	£865	12kW	2	7	4.7kW
Worcester Bosch Greenstar System i	12	£900	12kW	5	10	3.1kW

15-17kW boilers

15-17kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Glow Worm Energy System	15	£715.00	15kW	7	7	4.5kW
Ideal Logic System	15	£765.00	15kW	2	2	5.1kW
Ideal Logic + System	15	£795.00	15kW	7	7	5.1kW
Vaillant EcoTEC Plus System	615	£960.00	15kW	5	10	3.3kW
Vaillant EcoFIT Pure System	615	£925.00	15kW	2	7	4.7kW
Worcester Bosch Greenstar System i	15	£950.00	15kW	5	10	4.6kw
Ideal Vogue System	15	£905.00	15kW	10	12	3.2kW
Ferroli Modena HE 18S	18	£600.00	17kW	5	5	4.3kW

18-21kW boilers

18-21kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Potterton Gold System	18	£590.00	18kW	2	2	4.2kW
Glow Worm Energy System	18	£795.00	18kW	7	7	5.0kW
Ideal Logic System	18	£805.00	18kW	2	2	5.1kW
Ideal Logic + System	18	£895.00	18kW	7	7	5.1kW
Vaillant EcoFIT Pure System	18	£1,000.00	18kW	2	7	5.1kW
Vaillant EcoTEC Plus System	18	£1,080.00	18kW	5	10	4.1kW
Worcester Bosch Greenstar System i	18i	£1,050.00	18kW	5	10	4.6kW
Ideal Vogue System	18	£985.00	18kW	10	10	3.9kw
Viessmann 100-W System	19	£1,035.00	19kW	5	10	4.3kW
Viessmann 200-W System	19	£1,310.00	19kW	3	10	1.9kW
Baxi 618 System	18	£930.00	19kW	7	7	4.9kW
Intergas HRE	18	£789	18kW	7	7	5.6kW

24-25kW boilers

24-25kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Potterton Gold System	24	£617.00	24kW	2	2	6.8kW
Ideal Logic System	24	£850.00	24kW	2	2	5.1kW
Ideal Logic + System	24	£860.00	24kW	7	7	5.1kW
Worcester Bosch Greenstar System i	24i	£1,060.00	24kW	5	10	7.2kW
Vaillant ecoTEC plus system	624	£1,225.00	24kW	5	10	5.7kW
Ferroli Modena HE 25S	25	£605.00	25kW	5	5	6.2kW
Glow Worm Energy System	25	£845.00	25kW	7	7	6.1kw
Vaillant ecoFIT pure system	625	£1,150.00	25kW	2	7	6.4kW
Main System Eco Elite	24	£617.00	26kW	3	3	8.3kW
Viessmann 100-W System	26	£1,095.00	26kW	5	10	4.3kW
Ideal Vogue System	26	£1,110.00	26kW	10	10	5.6kW
Viessmann 200-W System	26	£1,465.00	26kW	3	10	1.9kW
Ravenheat HE System	98S	£649.00	25kW	5	5	3.7kW
Intergas HRE	24	£689.00	23kW	7	7	7.2kW

26-29kW boilers

26-29kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Worcester Bosch Greenstar System i	27i	£1,070.00	27kW	5	10	7.0kw
Baxi System	624	£1,015.00	27kW	7	7	4.9kW
Vaillant ecoTEC exclusive	27	£1,345.00	27kW	5	10	4.2kW
Potterton Gold System	24	£615.00	28kW	2	2	6.8kW
Ravenheat CS System	24	£546	26kW	2	2	4.0kW
Intergas HRE	30	£949.00	27kW	7	7	7.6kW

30-32kW boilers

30-32kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Output
Glow Worm Energy System	30	£833.00	30kW	7	7	7.5kW
Ideal Logic System	30	£883.00	30kW	2	2	6.4kW
Ideal Logic + System	30	£902.00	30kW	7	7	6.4kW
Viessmann 100-W System	30	£1,070.00	30kW	5	10	9.1kW
Worcester Bosch Greenstar System i	30i	£1,105.00	30kW	5	10	7.0kW
Vaillant EcoTEC Plus System	30	£1,308.00	30kW	5	10	6.4kW
Vaillant EcoFIT Pure System	30	£1,212.00	30kW	2	7	7.5kW
Viessmann 200-W System	30	£1,545.00	30kW	3	10	1.9kW
Ideal Vogue System	32	£1,187.00	32kW	8	10	6.8kW
Worcester Bosch Greenstar 8000	30	£1,310	30kW	5	10	3.0kW

34-37kW boilers

34-37kW	Code	Price	Max Heating Output	Standard warranty	Free extended warranty	Min Heating Outpu
Potterton Promax System	32	£948.00	34kW	2	2	94.kW
Viessmann 100-W System	35	£1,511.00	35kW	5	5	5.4kW
Viessmann 200-W System	35	£1,571.00	35kW	3	10	1.9kW
Vaillant EcoTEC plus system	37	£1,312.00	37kW	5	10	7.1kW
Worcester Bosch Greenstar 8000	35	£1,352.00	35kW	5	10	3.5kW

Achieving even better efficiencies with compatible thermostats

Sizing the boiler correctly is the first step to an efficient heating system. The next step is to pair the boiler with an advanced heating control that can adjust the output to suit the outside temperature. These are forms of ‘modulating’ control which will reduce the output of the boiler from its maximum, say 10kW, down to 2kW during spring and summer. This means that the boiler will run efficiently at the right output required by your home all year round. For more on advance controls try our Guide to Advanced Heating Controls.