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Most Energy Efficient Boilers from Navien UK 2024

January 29th 2024


With energy bills rising and a greater focus on cost and energy efficiency, we’re highlighting the most efficient models in our ranges. From the gas-powered NCB range to the HVO-compatible LCB700, you can now heat your home without breaking the bank.

What is an energy efficient boiler?

An energy efficient boiler is designed to minimise energy consumption while maximising the level of heat output. Modern boilers are very energy efficient, using advanced technology to optimise fuel consumption whilst reducing heat loss, resulting in lower energy bills, and even reducing their impact on the environment.

Standard efficiency boilers will be less efficient than their modern counterparts, and this inefficiency could cost you hundreds of pounds each year. Replacing your old standard efficiency boiler and switching to a new one could help you bring down your bills.

What is the most energy efficient type of boiler?

The most energy efficient type of boiler is typically a gas-condensing boiler, with most modern boilers (post-2007) having condensing technology inside. Condensing boilers recover heat from the gases emitted by the fuel and reuse it as heating for your home.

Combi boilers are also highly efficient as they do not preheat or store hot water and the water is heated as needed, meaning that there is no energy wastage in maintaining water temperature. All combi boilers are also gas condensing boilers which are the most cost-efficient type of boilers on the market.

To understand which boiler is the most energy efficient you can look at the boiler’s energy efficiency rating.

What is a boiler efficiency rating?

A boiler’s efficiency rating measures how effectively it converts fuel into usable heat. Navien boilers use the ErP energy efficiency rating scale, as is the standard in Europe for many different types of heating products, including heating pumps.

ErP energy-efficiency rating

NCB700 ErP efficiency label

All European boilers are rated under the ErP (Energy-related products) label. Introduced in 2015, the scale rates heating products, like boilers, from the lowest score of F up to the highest score of A+++. As well as scoring the boiler’s heating efficiency, the label also notes the sound output in decibels (dB) and the heating output in kilowatts (kW).

There are two ratings for Combi Boilers: space heating and water heating. Space heating (scale on the left of the chart) shows how efficient your boiler is at heating your radiators, whilst the water heating rating (scale on the right) shows how efficient your boiler is at heating the water for your showers and taps.

Most gas condensing boilers available in the UK today are at an A rating on the ErP rating scale for both space and water heaters. This is after the UK government introduced the ‘Boiler Plus’ legislation in 2018 which requires all boilers in England to have a minimum ErP efficiency rating of A (or 92%).

Regular boilers, also known as ‘Heat-only’ boilers only adhere to the space-heating section of the ErP scale.

Most efficient Navien boilers

The most energy-efficient Navien boilers are the LCB700 and the NCB range, featuring the NCB700 ON, the NCB500 ON and the NCB300, thanks to the next-gen heating technology inside and their efficient sizing. A key benefit of the NCB ON range is their ability to deliver hot water without temperature fluctuations, made possible by a built-in flow adjustment valve and auto mixing valve.

All these boilers have an ErP rating of A as standard, but they all can achieve A+ when installed with three zones and  Smart Plus room thermostats.


Navien LCB700 Combi Boiler

Our LCB700 Blue Flame oil combi boiler is the first in the UK market to offer an A+ energy system rating with three zones and three smart plus controllers, due to the nature of its design and how it works in conjunction with the latest control systems.

Key features:

  • Modern and lightweight design to fit into any home.
  • Clear text display helps you understand your energy usage.
  • 10-year warranty.


NCB700 ON Gas Condensing boiler

The revolutionary NCB700 ON Combi Crossover from Navien is the first boiler capable of delivering hot water to three showers simultaneously. This A+ energy-rating boiler cleverly recirculates hot water to significantly reduce water wastage and your energy bills. With smart weather forecasting and geofencing available with your Smart Plus control pack, take complete control of your energy usage today.

Key features:

  • Powerful 54kW hot water output delivering up to 22lpm.
  • NaviCirc is a simple and fast set-up to bring your hot water return system.
  • 12-year warranty.


Navien NCB500 ON Combi Boiler

The wonderfully compact NCB500 ON gas condensing combi boiler is our all-rounder for family homes, which also offers an ErP A+ energy efficiency rating with multi zone Smart plus control for ultra-low running costs.

Key features:

  • Compact design to fit into any home.
  • Smartphone compatible allowing you to make remote adjustments of energy output.
  • 10-year warranty.

NCB300 Gas Condensing Boiler

NCB-300 Gas Condensing

The NCB300 gas condensing combi boiler is our impressive entry-level model, but still offers the smart-weather forecasting and geofencing abilities as the rest of the NCB ON range. It also has a ErP A+ energy efficiency rating, when installed with 3 Smart Plus room thermostats.

Key features:

  • Compact design that is perfect for even small homes.
  • Complete protection from water leaks.
  • 5-year parts and labour warranty.

Tips for increasing energy efficiency

Whilst modern boilers are extremely adept at heating our homes efficiently, there are several ways that you can increase its heating efficiency and bring down your energy bills even further.

Get your boiler serviced regularly

Booking an annual service will ensure that your boiler is in top condition and no internal issues are present that may be hindering its performance. During a service, a qualified engineer will inspect and clean all the parts and components in your boiler, this is typically finished within an hour or two.

Bleed your radiators

If you find that your home isn’t heating up as it should even though your boiler is running, check your radiators for any colder at the top, as this can be a sign of trapped air and they may need bleeding. Radiators with trapped air will stop your heating system from running efficiently and can lead to a rise in energy bills.

See our guide on how to bleed a radiator for step-by-step instructions.

Heat the whole room

It may sound simple, but a lot of heat can be lost from radiators when they are blocked by furniture, or the heat is mainly directed towards the walls. If possible, you should avoid blocking them as the convection of cold air at the bottom and warm air from the top need free-flowing air movement to provide convection of heat from the radiator into the room.

For more tips on how to increase your boilers’ heating efficiency, especially in winter, see our winter heating tips guide.

To learn more about our boilers and finding the most energy efficient one for your home, get in touch today.

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