What Are the Most Efficient Boilers?

If you’re buying a boiler, you might consider the cost or performance, but possibly the most important factor is efficiency.

Swapping from an inefficient, older boiler can potentially save you hundreds of pounds every year by reducing your heating bills.

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Why Is Boiler Efficiency Important?

There are many important reasons why boiler efficiency is important. The government is keen to persuade people to trade in their older boilers for more efficient newer models to meet their goals of reducing carbon emissions.

Newer boilers are much more efficient than older models - even those which are only a few years old. If the government can persuade all of us to switch to newer models, estimates suggest they could save enough energy to heat over 1.9 million homes.

To encourage people to make a change, they are running a series of incentive programs to make it easier to move to a new boiler.

As boilers age, they also become less efficient. Buildup of lime-scale, rust and other forms of corrosion may mean your boiler must work harder to heat your home and so uses more energy.

From our perspective, though, the biggest reason is cost. During the winter, more than 60% of our energy costs come from heating our homes. With fuel prices rising every year, that’s a lot of money to spend keeping yourself warm.

A more efficient boiler can dramatically reduce your heating bills. Some estimates suggest you could save several hundred pounds a year.



What Are the Most Efficient Combi Boilers?

A combi boiler is the most common type of boiler and includes both a water heater and boiler, which reduces the space you need.

The boilers in the list below are considered to be some of the leading combi boilers for efficiency.

  • Worcester Bosch Greenstar 9i System ErP: An A-rated boiler available for just below £1,000.
  • Vaillant EcoTec Pro 30: A-Rated and costing approximately £1,050.
  • Baxi EcoBlue 24 Combi ErP: A-rated boiler with a good reputation for reliability costing approximately £1,300.

See also:

Which is the best combi boiler?

How much does a new boiler cost?

Vaillant prices and reviews



What Are the Most Efficient Heat-only or Regular Boilers?

Heat-only boilers – also known as conventional boilers – work in an open vented system which have a water storage tank and a larger cold-water cistern in the loft. The most efficient include:

  • Baxi EcoBlue +24: An A-rated boiler, small enough to fit into a small cabinet making it ideal for smaller properties where space is at a premium. Typical prices are £800.
  • Ideal Boilers Logic Plus 24 HE: An A rated boiler with a reputation for reliability and a compact size. Prices are approximately £750.
  • Worcester Bosch Greenstar 24i Junior: A small wall-mounted boiler with A-rated efficiency, perfect for small flats with only a couple of bedrooms. A typical price is £760.

See also:

Worcester Bosch prices and reviews

Baxi prices and reviews



What Are the Most Efficient System Boilers?

A system boiler incorporates the important heating and water components all in one package. However, it will still need a water cylinder. They are efficient and relatively economical to run, do not require a cylinder in the loft and are very well suited to a two-bedroom house.

The leading models for efficiency include:

  • Worcester Bosch Greenstar I System: An A-rated boiler costing around £1885.
  • Baxi Eco Blue: A popular range of A-rated boilers costing approximately £1900.


How Much Will an Energy Efficient Boiler Save You?

If you have an older boiler, the energy savings could be considerable.

Heating makes up 60% of your energy use every year so you can save a great deal. The big advantage is that modern boilers are all condensing boilers which have a larger heat exchanger, so it recovers more heat. All boilers lose efficiency over time, but these maintain performance for much longer.

That said so, you should be wary about what you read. Many articles suggest you can make enormous savings with a newer boiler, but this assumes you’re swapping out the least efficient older boiler with the most efficient new boiler.

You could consider fuel type. If you’re connected to the main supply, gas heating is normally the most cost-efficient choice. However, the recent fall of the oil price means oil heating might now be less expensive, but this may not be the case for long.

It also depends on the size of your family. A large family will use much more hot water and could benefit from a conventional boiler where a smaller household can save money and space with a combi boiler.



How Is Boiler Efficiency Calculated?

Modern boilers are given an efficiency rating of ‘A’ (for those rated at 90%) down to ‘G’ for those rated at less than 70%.

However, these ratings are measured in controlled conditions and other parameters can reduce true operating efficiency. It is likely your boiler will operate slightly below its efficiency rating most of the time.

Efficiency comprises of two figures: Combustion efficiency and thermal efficiency. Combustion efficiency measures how well the boiler burns fuel and converts it into energy. For example, how much unburned fuel will be in the exhaust. Thermal efficiency shows how well the heat exchanger is doing its job from taking energy from the fire side into the water side.

We measure this in two ways:

  • Direct efficiency measures energy input versus energy output. We divide energy input by output and multiply that figure by 100.
  • Indirect efficiency measures various losses throughout the system and subtracts that sum from 100. The efficiency rating also calculates an overall figure based on different energy losses throughout the system.

Both methods have advantages disadvantages. Indirect efficiency speaks to the sources of energy loss. However, direct efficiency is closer to reality.

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