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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: March 23, 2018. Updated: May 20, 2024

Most Energy Efficient Boiler

Saving money and reducing your environmental impact are more important than ever. Upgrading to an energy-efficient boiler is a great way to achieve both.

Modern condensing boilers are highly efficient, converting fuel into heat with minimal waste. They are required to be at least 92% efficient, meaning 92% of the fuel they use becomes usable heat. This saves you money on energy bills and reduces carbon emissions.

Choosing the right new boiler depends on your specific needs. In this guide, we look at the most efficient boilers available in the UK.

Just a couple of bits to start with…

What is boiler efficiency?

Boiler efficiency refers to the percentage of the total energy the boiler uses to provide heating.

For example, a 92% efficient boiler will use 92% of the supplied energy to heat your home. The remaining 8% will be lost.

To put this into context, for every £1 you spend on heating your home, only 8p is wasted. It should be noted though that a 92% efficient boiler is excellent. This is much more efficient than the older non-condensing boilers that are still used every day in households across the UK.

A typical non-condensing boiler could be running at 70% efficiency, meaning 30% of the energy you pay for is being lost and not being used to heat your home. Some old back boilers are estimated to be 50% efficient.

How do we rate efficiency?

Along with fridges, freezers and washing machines, boilers are rated using an energy efficiency rating scheme from A-G. The energy efficiency rating scheme can be seen below:

Efficiency Rating Efficiency (%)
A 90% and above
B 86-90%
C 82-86%
D 78-82%
E 74-78%
F 70-74%
G below 70%

Boiler Plus Regulations Overview

The Boiler Plus regulations have been in place since 2018. These regulations mandate that all newly installed boilers in the UK include a thermostat and a programmable timer, which enhances energy efficiency.

In addition, new combi boilers are required to have at least one of the following energy-saving features:

  • Flue Gas Heat Recovery System: Recovery of heat from exhaust gases.
  • Load Compensating Thermostat: Adjusts radiator temperatures based on the room’s temperature. Raising when cold and lowering it as the room warms up.
  • Weather Compensation: An outdoor sensor to monitor external temperatures. Regulates boiler operation, preventing unnecessary heating.
  • Smart Thermostat: Allows remote heating system control via an app. May include features like open window detection, geofencing, and voice control.

Why are condensing boilers more efficient than non-condensing boilers?

Choosing a condensing boiler to replace your non-condensing boiler will immediately save you money. This is down to the difference in the way they operate.

Condensing boilers recover heat that a non-condensing boiler would have lost via the flue. This is called a flue gas heat recovery system. It recovers heat by recycling exhaust gases that older non-condensing boilers waste. This condensate is mostly steam with some acidic content. These hot flue gases go through a heat exchanger before they exit through the flue.

We explain further how condensing boilers work in our condensing boiler guide.

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Boiler Efficiency by Type

Combi Boiler Efficiency

Combi boilers are a popular choice for their space-saving design and efficiency. They provide hot water on demand without the need for a separate cylinder.

All modern boilers feature condensing technology. These boilers are the most efficient on the market, with models like the Viessmann Vitodens 200-W boasting up to 98% efficiency. They are suited for small to medium-sized homes.

System Boiler Efficiency

System boilers work alongside a hot water storage cylinder for homes with higher hot water demands. This offers a larger volume over a shorter period of tim.

These boilers are known for their innovative features and high efficiency. Again, the 200-W System boiler achieves up to 98% energy efficiency.

Conventional Boiler Efficiency

Also known as regular or heat only boilers, conventional boilers are typically found in older homes. They require a hot water cylinder and a cold water storage tank. Modern conventional boilers have seen improvements in energy efficiency and design. Viessmann’s 100-W heat range is 92% efficient.

Most Efficient Combi Boiler UK

#1 Viessmann Vitodens 200-W Combi

Viessmann Vitodens 200-W 35kW Combi Boiler - Most efficient combi boiler uk | BoilerhutThe Vitodens 200-W model from Viessmann is compact and up to 98% efficient. Ideal for small to medium-sized homes. It features a touchscreen display, smart controls, and low operating noise. Available in 30kW and 35kW power outputs both with stainless steel heat exchangers for steadfast lifelong efficiency.

  • 10-year warranty with Boilerhut (7-year standard)
  • Modulation of 1:17
  • Integrated WiFi
  • LPG compatible without a conversion kit
  • 20% hydrogen-mix ready

30kW boiler only price: £1,975 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

#2 Worcester Bosch Greenstar 8000 Life and Style

Worcester Bosch Greenstar 8000 - Most efficient system boiler | BoilerhutThe Greenstar 8000 Life & Style models offer smart features, wireless connectivity, and 94% efficiency. They have an extended 12-year warranty. Available in 30kW, 35kW, 40kW, 45kW and 50kW versions.

  • Up to 12-year warranty
  • LPG compatible
  • Modulation of 1:10
  • 20% hydrogen-mix ready
  • Good reputation

30kW Life boiler only price: £1,722 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

Special Mention – Viessmann Vitodens 222-F Storage Combi

Viessmann Vitodens 222-F 19kW Storage Combi Boiler - Most efficient boiler | BoilerhutThe Vitodens 222-F Storage Combi boiler is a floor-standing boiler with a very high hot water flow rate. It didn’t make our most efficient top-2 because of the price. But, if you live in a large home with high hot water requirements, this storage combi boiler is for you.

This boiler has a 100-litre integrated hot water tank, equivalent to a 300-litre hot water tank in a system or regular boiler setup. It features a touchscreen display, smart controls, and low operating noise. Available in 19kW, 25kW and 32kW power outputs both with stainless steel heat exchangers for steadfast lifelong efficiency.

  • 10-year warranty with Boilerhut (7-year standard)
  • Modulation of 1:17
  • Integrated WiFi
  • LPG compatible without a conversion kit
  • 20% hydrogen-mix ready

19kW boiler only price: £3,399 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

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Most Efficient System Boiler UK

#1 Viessmann Vitodens 200-W System

Viessmann Vitodens 200-W 35kW Combi Boiler - Most efficient combi boiler uk | BoilerhutThat’s right, the 200-W is available as both combi and system boilers. The Viessmann Vitodens 200-W wall-mounted boiler packs a punch in a compact design. Its impressive 98% efficiency translates to lower energy bills and a reduced carbon footprint. Ideal for medium to large homes, it delivers dependable heating with minimal noise.

  • 10-year warranty with Boilerhut (7-year standard)
  • Modulation of 1:17
  • Integrated WiFi
  • LPG compatible without a conversion kit
  • 20% hydrogen-mix ready

19kW boiler only price: £1,815 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

#2 Alpha E-Tec NXS

Alpha E-Tec NXS - Most efficient system boiler | BoilerhutThe Alpha E-Tec NXS System boiler is the latest iteration of the E-Tec model. With a new stainless steel heat exchanger moulded with thermoplastic to increase efficiency. This 94% efficient system boiler is a fantastic mid-tier boiler.

  • Up to 7-year warranty
  • Modulation of 1:16
  • 20% hydrogen-mix ready

26kW boiler only price: £1,031 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

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Most Efficient Regular Boiler

#1 Worcester Bosch Greenstar 8000 Life Regular

Greenstar 8000 Life - Most efficient regular boiler | BoilerhutThe Greenstar 8000 Life Regular is 94% efficient. They have an extended 12-year warranty. Available in 35kW, 40kW, 45kW and 50kW versions.

  • Up to 12-year warranty
  • Modulation of 1:10
  • 20% hydrogen-mix ready

35kW Life regular boiler only price: £2,238 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

#2 Viessmann Vitodens 100-W Heat

Viessmann Vitodens 200-W 35kW Combi Boiler - Most efficient combi boiler uk | BoilerhutThe 100-W Heat is 92% efficient, compact and super quiet.

  • 10-year warranty with Boilerhut (7-year standard)
  • Modulation of 1:10
  • Integrated WiFi
  • LPG compatible without a conversion kit
  • 20% hydrogen-mix ready

11kW boiler only price: £1,183 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

Most Efficient Oil Boiler

#1 Navien LCB700 Blue Flame Oil Combi, System and Regular Boiler

LCB700 Oil Boiler - Most efficient oil boiler | BoilerhutThe Navien LCB700 Blue Flame Oil boiler range offers 93% efficiency. This boiler is available as a combi, system and heat only/regular boiler. There are also internal and external versions, meaning you could save space in your home. Stainless steel heat exchangers come as standard with this boiler.

  • Blue flame technology
  • 10-year warranty
  • OpenTherm compatible

21kW system boiler only price: £1,869 (excluding installation. Average price from multiple plumbers merchants – correct as of February 2024).

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Factors to Consider Before Upgrading Your Boiler

  • Fuel Type and Emissions: Gas boilers, including LPG, are commonly used due to their lower operating costs and emissions than oil boilers. Low-carbon heating systems like heat pumps are an alternative for those looking to reduce their carbon footprint further. Read about heat pumps vs gas boilers.
  • Boiler Type and Compatibility: Your choice of boiler will depend on your home’s hot water usage, space availability, and whether you plan to use renewable energy sources like solar panels.
  • Price and Installation Costs: Costs vary depending on the boiler brand, type, and the complexity of installation. It’s essential to compare multiple quotes to ensure you get the best deal. Read about how much new boilers should cost.
  • Warranty and Customer Service: Opting for a boiler from a brand known for reliable customer service and a comprehensive warranty can provide peace of mind.

Are you looking for a new, highly efficient boiler?

If you are looking for a new or replacement efficient boiler, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

  • Save up to £590 every year on your heating bill.
  • Next day boiler installation.
  • Instant, no-obligation quote in less than 1 minute.
  • Boiler finance options available for new boilers and central heating installation.
  • 10 to 12-year warranty on boilers.
  • ‘Excellent’ 5* customer satisfaction on Trustpilot.
  • Fixed prices. No hidden extras.
  • Get up to three quotes for different-tier boilers.

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