Which is the Best 40kW System Boiler?
A 40kW system boiler is perfectly suited to larger properties with around 20 radiators and 3 or more bedrooms. When it comes to finding the best 40kW system boiler, there’s only one option: the ATAG IS40. So if you’re specifically looking for a 40 kW system boiler, your decision is pretty straightforward.
Fortunately, the ATAG IS40 is a highly efficient system boiler that comes with a lengthy 10 year warranty but it is possible that any system boiler with an output rating of 35 and 42 kW will also be suitable. And for that reason we’re going to compare the following system boilers, which all have an output rating of 35-42kW:
- ATAG i40S
- Intergas Compact HRE SB 40
- Vaillant ecoTEC Plus 637
- Viessmann Vitodens 200-W 35
- Worcester Bosch Greenstar 8000 Life 35
- Worcester Bosch Greenstar 8000 Style 35
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Is a 40kW system boiler suitable for my home?
40 kW system boilers are powerful heating systems that are best suited to larger properties with 3 or more bathrooms and around 20 radiators. As system boilers store hot water in a cylinder, there will be plenty to go around should more than 1 bathroom be occupied at a time.
Before investing in a 40 kW system boiler, you should get expert advice from a fully-qualified heating engineer. Using Boiler Guide, you can get free quotes from up to 3 Gas Safe registered engineers in your area by simply completing our quick online form. They’ll be in touch to arrange a quote and will take a look at your property and recommend a type of boiler and size based on the heating and hot water demands of your home.
In the case that a lower output would be sufficient for your heating and hot water demands, we have more comparison articles:
Best 40kW system boilers
As we mentioned, there’s currently only one 40kW system boiler available, the ATAG i40S, making it the best 40kW system boiler by default. So, for that reason, we’re comparing the best system boilers with outputs of 35-42 kW which could all suit similar property types and sizes.
|Best 35-42 kW System Boilers||Output Rating||Space Heating Efficiency Rating||ErP Rating||Warranty|
|ATAG i40S||40 kW||94%||A||10 years|
|Intergas Compact HRE SB||41 kW||92%||A||7 years|
|Vaillant ecoTEC Plus 637||37 kW||94%||A||5 years|
|Viessmann Vitodens 200-W||35 kW||Up to 98%||A||3 years|
|Worcester Bosch Greenstar 8000 Life||35 kW||94%||A||10 years|
|Worcester Bosch Greenstar 8000 Style||35 kW||94%||A||10 years|
ATAG are well known for making lengthy 10 year warranties available on all of their boilers which shows how much faith they have in their products. The i40S system boiler is highly efficient and the simple controls make it very easy to operate.
- Built-in ErP pump which helps to maximise efficiency
- User-friendly controls
- The iCON heat exchanger has a lifetime guarantee
- Compatible with ATAG iSteel hot water tanks
This range also includes smaller outputs of 15, 18, 24 and 32 kW should a Gas Safe registered engineer recommend something less powerful for your home.
Intergas Compact HRE SB 40
Intergas offer the most affordable option when it comes to finding a powerful system boiler but it can still compete with the more premium models and has even been endorsed by the Energy Saving Trust.
- Only 4 moving parts which greatly reduces the risk of any faults developing
- Choice between horizontal and vertical flues for a more flexible installation
- Built-in boiler frost protection to keep the unit running through cold winter months (particularly important when the boiler is installed in a garage or loft)
- A 10 year warranty on the heat exchanger
Smaller outputs of 18, 24 and 30 kW are also available in the Intergas HRE SB range of system boilers.
Vaillant ecoTEC Plus 637
The Vaillant ecoTEC range is made up of modern stylish boilers that boast a stainless steel heat exchanger which helps to boost efficiency and are well covered by an extensive warranty.
- Stainless steel heat exchanger for increased efficiency
- Compact dimensions make it possible for the boiler to be installed into a small cupboard
- Quiet Mark accreditation shows that you won’t have to worry about operating noises
- Frost protection to prevent water in the pipes from freezing during the winter
- With the Vaillant vSmart app you can control your central heating and domestic hot water from wherever you are
For properties with lower demand for central heating and domestic hot water, system boilers with outputs of 12 kW, 15 kW, 24 kW and 30 kW are also available in the ecoTEC range.
Viessmann Vitodens 200-W 35
Viessmann have labelled their Vitodens 200-W range as being a ‘new generation’ of heating system that ‘sets the standard for the future’. And they may have a point. The Vitodens 200-W system boiler delivers high efficiency, user-friendly controls and will help to reduce the carbon footprint of your home.
- Efficiency of up to 98% will help to keep your energy bills down to a minimum
- A Vitoconnect 100 WLAN adapter allows you to take control of your boiler via a smartphone or tablet
- A 5 inch colour touchscreen display gives you clearer visibility and greater control
- A MatriX cylinder burner distributes heat efficiently around the property
- Low fan speed results in quiet operation
- A width of only 450mm makes this a compact unit
Viessmann have also included a couple of smaller outputs in their 200-W system boiler range, including 26 kW and 35 kW models.
Worcester Bosch Greenstar 8000 Lifestyle 35
Worcester Bosch have been an industry leading boiler manufacturer for a number of years and with the Greenstar 8000 Lifestyle range, they’ve further cemented their place.
- Greenstar 8000 Lifestyle boilers are available in black as well as the conventional white
- Modulation ratio of 1:10 which means that the boiler won’t use more energy than it needs to for increased efficiency
- An on/off cycling prevention feature helps to keep the boiler running for longer
- Front, top and side panels are all removable which makes life much easier for a heating engineer and will save you money when it comes to servicing and any necessary maintenance
The Greenstar 8000 Lifestyle range is the most advanced available from leading manufacturer, Worcester Bosch. As well as these 35 kW units, there are also 30 kW and 40 kW system boilers, plus a selection of combi and regular boilers too.
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How do system boilers work?
A system boiler is ideally suited to larger properties as they store hot water for domestic use in a cylinder. System boilers take water from the mains, removing the need for a cold water tank in the loft (a requirement of a regular boiler).
This is different to a combi boiler which delivers hot water on demand without storing any in a cylinder.
Find out more in System Boilers Explained.
How much do 40 kW system boilers cost?
A powerful 40kW system boiler is likely to cost at least £1,000 before factoring the need for a hot water cylinder and installation. The Intergas Compact HRE SB is potentially the most affordable but all of the system boilers in this comparison have a similar price, although the price tag of the ATAG i40S hasn’t been made publically available.
|Best 40kW System Boiler||Potential Cost (before installation)|
|Intergas Compact HRE SB||£1,125 – £1,600|
|Vaillant ecoTEC Plus 637||£1,390 – £1,500|
|Viessmann Vitodens 200-W||£1,300|
|Worcester Bosch Greenstar 8000 Life||£1,300 – £1,550|
|Worcester Bosch Greenstar 8000 Style||£1,300 – £1,550|
Best system boilers for off-grid homes
The system boilers we’ve looked at in this article all run on natural gas but not every property is connected to the gas network. In those cases, you will need to store fuel onsite and that means turning to liquified petroleum gas (LPG) or oil. Fortunately, all of these natural gas system boilers run on LPG.
|Best 40kW System Boiler||LPG Compatible?|
|Intergas Compact HRE SB||Yes|
|Vaillant ecoTEC Plus 637||Yes|
|Viessmann Vitodens 200-W||Yes|
|Worcester Bosch Greenstar 8000 Life||Yes|
|Worcester Bosch Greenstar 8000 Style||Yes|
Should you prefer an oil boiler, then there are plenty of options available that are capable of meeting the heating and hot water demands as a gas-fired boiler.
|Best 35-42 kW System Oil Boilers||Output Rating||Space Heating Efficiency Rating||ErP Rating||Warranty|
|Firebird EnviroBlue SystemPac C35||35 kW||94.4%||A||2 years|
|Grant VortexBlue||36 kW||94.5%||A||2 years|
|Mistral Sealed System CS4||41 kW||93%||A||2 years|
|Navien LCB700||36 kW||93%||A||10 years|
|Viessmann Vitorondens 200-T||42 kW||97%||A||10 years|
Should you want to have an oil boiler installed, then you will need to hire an OFTEC registered heating engineer to carry out the installation. We can connect you with OFTEC or Gas Safe registered engineers in your area who will provide you with free quotes.
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