Best Oil Boilers 2020: Pros, Cons & Prices

Oil boilers have been popular heating systems in off-grid homes (homes which are not connected to the gas grid) for many years.

The oil boiler you choose needs to measure up in terms of energy efficiency, warranty and performance. But, inevitably, you also need to balance this with your budget. To help your search for a brand new oil boiler, we’ve compared the Top 5 Oil Boiler Manufacturers in 2020, as well as the pros, cons and costs involved in an oil boiler replacement.

What is an oil boiler?
Types of oil boiler
Best oil boilers
Oil boiler efficiency
Oil boiler prices
How much does oil boiler installation cost?
What size oil boiler do you need?
Should you install an oil boiler at all?
Oil boiler alternatives
Finding oil boiler installers

What is an oil boiler?

Over 85% of UK homes rely on gas fired boilers, but there are approximately 2 million homes which are not connected to the gas grid and 1.5 million of these off-grid homes use oil fired boilers. There are several off-grid heating systems to choose from but historically, most off-grid homeowners have chosen to use an oil boiler as it is cheaper to buy oil than electricity and LPG.

Oil boilers and gas boilers are very similar, but the main difference between them is how the fuel is stored. Gas boilers do not need to store gas as they are connected to a constant supply through the national gas grid. Oil boilers need a tank of oil to be stored on the property, usually in the garden, which needs to be refilled when it runs out.

How does an oil boiler work?

An oil boiler works in a similar way to a gas boiler.

1. The boiler is supplied with cold water, either from the mains in a combi or system boiler, or from a cold water tank in the attic in a regular (conventional) boiler system.

2. The fuel – oil in this case – is ignited in the boiler’s combustion chamber and the heat exchanger passes this heat to the cold water.

3. The heated water can then be used in radiators, taps and showers for heating and hot water.

Types of oil boiler

When choosing an oil boiler for your home, you may have to choose between a few different types, before choosing a brand and an installer.

Internal or external oil boilers

Some homeowners choose to have an oil boiler installed outside of their home – this is called an external oil boiler. Internal and external boilers work in the same way and both require a tank of oil to be stored outside the home which is connected to the boiler.

Installing an external boiler outside the home can have some advantages. Specifically, it frees up more space in the home, means that there is less boiler noise, no carbon monoxide risk and no risk of leaking in the home.

However, there are potential issues with external oil boilers as they are exposed to the weather. This can lead to rusting and/or freezing in winter, but many external oil boilers have been designed to withstand these problems. External boilers can be more costly to install if you are placing the storage tank underground. Some homeowners may not like the look of having a boiler outside the home.

Combi, system or regular oil boilers

There are 3 types of boiler system which are available whether you have a gas, oil or LPG boiler: combi, system and regular.

  • Combi or combination boiler: A combi boiler is an all-in-one unit which takes its cold water supply directly from the mains and heats it on demand to provide hot water for both heating and domestic use.
  • System boiler: A system boiler takes its cold water supply directly from the mains, heats it and sends it to a separate hot water cylinder to be stored. It is then ready to be used in heating and hot water when needed, but when the cylinder is empty you will need to wait for it to refill.
  • Regular or conventional boiler: A regular boiler takes its cold water supply from a cold water tank which is in the attic. The water is heated before being sent to a separate hot water cylinder to be stored. It is then ready to be used in heating and hot water when needed, but when the cylinder is empty you will need to wait for it to refill.
  • The type of boiler you need will depend on the size of your home and your hot water demand. A professional heating engineer will be able to recommend the best type of oil boiler for your home. Find out more here.

    Best oil boilers

    When you know the type of boiler you need, your next step is to choose which oil boiler brand or manufacturer you would like to install. Here we have outlined the 5 top oil boiler brands on the market today.

    • Worcester Bosch Greenstar Heatslave II
    • Grant VortexBlue
    • Mistral Combi Standard
    • Firebird Envirogreen Combi
    • Warmflow Utility HE Combi

    Worcester Bosch Greenstar Heatslave II

    Best Oil Boilers: Worcester Bosch Greenstar Heatslave II
    The Worcester Bosch Greenstar Heatslave II is a condensing combi oil boiler that can be installed externally, so it won’t take up any valuable space around the home. As a combi boiler, Heatslave II boilers provide central heating and hot water on demand, with an impressive flow rate of 15 litres per minute.

    The range includes oil boilers with output ratings of 18 kW, 25 kW and 32 kW, making it easier to find a suitably powerful boiler for your property. Each of these boilers is highly efficient, which will help to keep your energy bills down and if you choose to have an internal model installed then the compact dimensions allow it to sit between kitchen units.

    The Greenstar Heatslave II 12/18 has even been endorsed by the Energy Saving Trust.

    Worcester Bosch Greenstar Heatslave II
    Model Output Ratings Dimensions (HxWxD) Efficiency ErP Rating
    Greenstar Heatslave II 12/18 18 kW 855 x 520 x 600mm 90% Heat: A
    Hot water: B
    Greenstar Heatslave II 18/25 25 kW 855 x 520 x 600mm 90% Heat: A
    Hot water: B
    Greenstar Heatslave II 25/32 32 kW 855 x 520 x 600mm 90% Heat: A
    Hot water: B

    All of the above are designed for internal installation but external models of the Worcester Bosch Greenstar Heatslave II range are also available.

    Grant VortexBlue

    Best Oil Boilers: Grant VortexBlue
    The Grant VortexBlue is an internal combi oil boiler, which means that it’s capable of providing central heating and domestic hot water on demand without the need for any external tanks or cylinders. An efficiency rating of 91.7% makes this an A-rated unit for heat, while it also has a B for hot water.

    Availble in a range of outputs, including 21 kW, 26 kW and 36 kW, gives you a great chance of finding a suitable powerful boiler for your home. As standard, the Grant Vortex Blue is available with a 2 year warranty.

    Grant VortexBlue
    Model Output Ratings Dimensions (HxWxD) Efficiency ErP Rating
    VortexBlue Internal 21 21 kW 860 x 470 x 603mm 90.81% Heat: A
    Hot water: B
    VortexBlue Internal 26 26 kW 860 x 470 x 603mm 91.71% Heat: A
    Hot water: B
    VortexBlue Internal 36 36 kW 860 x 470 x 603mm 94.56% Heat: A
    Hot water: B

    All Grant VortexBlue boilers are also available as system boilers as well as for external installation.

    Mistral Combi Standard

    The Mistral Combi Standard boiler range includes 4 highly efficient condensing combi boilers that are available for indoor or outdoor installation. With 4 models available (CC1, CC2, CC3 and CC4), each with a different output rating between 15 kW and 41 kW, there’s likely to be a unit to suit the heating and hot water demands of almost any property.

    Manufacturer, Mistral, even claim that their Combi Standard range can produce almost twice as much hot water as any other oil combi boiler on the market.

    Mistral Combi Standard
    Model Output Rating Dimensions (HxWxD) Efficiency ErP Rating
    CC1 15 – 20 865 x 600 x 600mm 92% Heat: A
    CC2 20 – 26 865 x 600 x 600mm 92% Heat: A
    CC3 26 – 35 865 x 600 x 600mm 92% Heat: A
    CC4 35 – 41 865 x 600 x 600mm 92% Heat: A

    Firebird Envirogreen

    Firebird were the first brand in the UK to produce a SEDBUK Band A rated Combi boiler and the UK’s first Blue Flame oil fired condensing boiler. Blue flame technology perfects the combustion process and lessens the carbon emissions of the boiler.

    The Firebird Envirogreen range of condensing combi oil boilers are available as both standard and slimline models for installation in a utility room or kitchen. A range of output ratings including a 20 kW, 26 kW and 35 kW models are all available with each boasting high performance low NOx and Blue Flame burner options.

    Firebird Envirogreen Combi
    Model Output Ratings (kW) Dimensions (HxWxD) Efficiency ErP Rating
    Envirogreen Combi HE20 20 kW 845 x 595 x 614mm 93% Heat: A
    Hot water: B
    Envirogreen Combi HE26 26 kW 845 x 595 x 614mm 93% Heat: A
    Hot water: B
    Envirogreen Combi HE35 35 kW 845 x 595 x 614mm 93% Heat: A
    Hot water: B

    Warmflow Utility HE Combi

    Best Oil Boilers: Warmflow Utility HE
    Founded in 1970, Warmflow is Northern Ireland’s leading manufacturer of award winning, oil fired boilers with over 45 years experience heating homes across UK & Ireland. Their award winning range includes oil fired boilers, including the UK & Ireland’s first double A rated combi boiler.

    The Warmflow Utility HE range of oil boilers are highly efficient condensing regular boilers that includes models with a range of output ratings from 21-35 kW, helping to make it easier to find a suitable unit for your home.

    As regular boilers, Utility HE units need to be installed as part of a heating system alongside a hot water cylinder, cold water storage tank as well as a feed and expansion tank. Regular boilers are best suited to larger properties with higher demands for heating and hot water.

    Warmflow Utility HE Combi
    Model Output Rating Dimensions (HxWxD) Efficiency ErP Rating
    UC70HEE 21 kW 865 x 595 x 600mm 90.7% Heat: A
    Hot water: A
    UC90HEE 26 kW 865 x 595 x 600mm 90.8% Heat: A
    Hot water: A
    UC120HEE 35 kW 865 x 595 x 600mm 90.7% Heat: A
    Hot water: A

    Which is the best oil boiler?

    Best Oil Boilers: Worcester Bosch Greenstar Heatslave II
    When it comes to performance, warranty and reliability, the front-runners in terms of both homeowner and installer recommendations are the Worcester Bosch Greenstar Heatslave II and Grant VortexBlue ranges of oil boiler.

    While they might be amongst the most costly oil boilers, your ultimate decision needs to be based on the best long term investment for your home. A new oil boiler should last between 8-12 years and the most efficient models will save you money on heating bills.

    So, if possible, it’s not a choice you should be making based on the cheapest price. Obviously, we all have a budget to consider, but it’s important to make sure you’re getting the best warranty and efficiency for your money.

    Winner: Worcester Bosch Greenstar Heatslave II

    REMEMBER: Professional installers will have their own experiences of each brand from past installations and customer feedback so always get multiple quotes. Some installers receive incentives to install a certain brand so keep in mind that you might not be getting impartial advice. However, if the installer is specially trained to install a brand it could mean that you receive an extended manufacturer warranty.


     


    Comparing oil boiler efficiency

    In terms of energy efficiency there is very little daylight between any of the best oil boilers. According to building regulations, oil boilers must be at least 86% efficient which is rate A+. In most cases, oil boilers will be at least 89-90% efficient.

    In financial terms this means that for every £1 you spend on heating your home, only 10-11p is spent on wasted energy. When you consider that some older boilers offer as little as 60-70% efficiency, and therefore waste 30-40p of every £1, this is a considerable saving over a year.

    Comparing oil boiler warranties

    When comparing manufacturer warranties it’s important to check the smallprint. Many advertise lengthy ‘guarantees’ but with strict terms and conditions applied which, if you don’t meet, could make them meaningless. Also, while each boiler includes a ‘standard’ warranty’ it may also be possible to purchase a longer or more comprehensive guarantee.

    Grant and Worcester Bosch offer longer 10 year guarantees on some of their models, but these will be dependent on the installation being carried out by an installer who they’ve accredited themselves and meeting specific requirements.

    Best Oil Boiler Range Warranty
    Worcester Bosch Heatslave II 2 years (can be upgraded to 5 years)
    Grant VortexBlue 2 years
    Mistral Combi Standard 2 years parts / 5 years heat exchanger
    Firebird Envirogreen 2 years
    Warmflow Utility HE 5 years parts and labour with 7 years on the heat exchanger

    All manufacturers will stipulate that the boiler must be installed by an engineer who is qualified and / or registered with OFTEC (Oil Firing Technical Association). This is a standard requirement and something that’s advisable regardless of warranty; after all, having a boiler installed by an unqualified person presents a significant safety risk. Assuming that this is the case and that you register your guarantee within a specified period (usually 30 days). The vast majority of manufacturer guarantees will only remain valid if your boiler is serviced every 12 months by an accredited installer.

    You can find out more about each oil boiler manufacturer’s warranty here:

    Oil boiler prices

    One of the most influential factors in your decision is going to be the price of the oil boiler.

    Warmflow sit at the lower end of the scale, with prices starting at £1,175 (on average), while Worcester Bosch Heatslave II prices can begin at over £2,000. Mistral prices begin at around £1,900, but the company doesn’t offer much more in terms of warranty than the Warmflow or Firebird. Grant and Worcester are the pricier options starting at £2,100 at a minimum, but their warranties and service plans are more comprehensive.

    Best Oil Boiler Range Potential Cost
    Worcester Bosch Heatslave II £2,190 – £2,425
    Grant VortexBlue £1,335 – £2,665
    Mistral Combi Standard £1,990 – £2,700
    Firebird Envirogreen Combi £1,800 – £2,525
    Warmflow Utility HE £1,175 – £1,795

    These are guide prices for a like-for-like oil boiler replacement. Installation costs will also need to be taken into account.

    How much does oil boiler installation cost?

    Installation costs will vary depending on the size of the boiler, the complexity of the installation, whether it’s an internal or external oil boiler and, ultimately, based on the prices charged by the installer you hire.

    On average, you can expect to pay anything from £500 – £2,000 for the labour and installation of your new boiler with the total being affected by a number of factors. For more information visit our article on New Oil Boiler Replacement. In total, new replacement oil boiler prices, including installation, could cost between £2,500 – £4,500.

    To ensure you’re getting the most competitive price, we highly recommend comparing quotes from 2-3 fully-qualified engineers, these can be both national companies and local independents. By simply completing our online enquiry form, you can get free quotes today from up to 3 reputable installers in your area.

    What size oil boiler do you need?

    Boiler size is otherwise known as the output rating and tells you the maximum power of the unit in kilowatts (kW). A higher output rating will be able to meet higher demands for central heating and hot water.

    System and regular boilers both only have central heating (CH) output ratings. Combi boilers however also have a domestic hot water (DHW) output rating as they directly deliver hot water to the taps as well as the central heating radiators.

    Property size is the biggest factor in determining an appropriate output rating for your home. Using the number of bathrooms and radiators you have, a suitable output rating can be found. If your boiler is too powerful, you will be paying for excess fuel which you don’t need to use. If it is not powerful enough, the boiler will not be able to provide enough hot water for your home.

    The table below shows a rough guide to oil boiler sizing, but a professional heating engineer will be able to recommend the right size of oil boiler for your home.

    Number of Radiators Combi Boiler Central Heating Output Rating System Boiler Central Heating Output Rating Regular Boiler Central Heating Output Rating
    Up to 10 24-27 kW 9-18 kW 9-18 kW
    10-15 28-34 kW 18-26 kW 18-26 kW
    15-20 35-42 kW 27-40 kW 27-40 kW

    Take a look through What Size Boiler Do I Need for a complete guide to boiler sizing.

    Should you install an oil boiler at all?

    Yes

  • For off-grid homes, oil is still the cheapest central heating fuel when compared to LPG, electricity and biomass wood pellets.
  • Modern oil tanks are easy to maintain and many homes only need to have their tank refilled once a year.
  • No

  • You will need to monitor the amount of oil in your tank to ensure you do not run out and your order more in plenty of time.
  • The oil will need to be delivered by a lorry so you should consider accessibility of your property.
  • The oil tank needs to be stored on your property and must meet a range of safety regulations, including a firewall between the tank and your property.
  • Oil is a fossil fuel, supplies of which are running out. It also produces a lot of carbon when it is burnt. Carbon is a greenhouse gas which cannot escape our atmosphere and is causing the temperature of the planet to increase.
  • Because of the high levels of carbon emitted by oil boilers, the government intends to phase out the installation of oil boilers in the next 10-15 years (although no firm legislation has been confirmed). This may make oil more difficult to find and more expensive to buy.
  • Oil boiler alternatives

    You may want to reduce your heating costs and/or carbon emissions. If you are considering replacing your oil boiler with an alternative heating system, or are installing a heating system from scratch in an off-grid new build, there are several options to consider.

    LPG boilers

    LPG or liquefied petroleum gas is a fossil fuel that differs from natural gas. An LPG boiler is suitable for an off-grid home as it can be stored on the property in a tank or bottles and emits less carbon into the atmosphere than oil.

    Biomass boilers

    A biomass boiler is fueled by biomass which is plant based organisms such as wood pellets, chips or logs. As biomass is a solid material, it needs to be stored on the property and fed into the boiler manually.

    Heat pumps

    There are two types of heat pump: air source and ground source.

    Air source heat pumps extract heat from the air outside in temperatures as low as -20°C. This air passes over an exchanger coil where a refrigerant fluid is boiled and evaporates, turning into vapour. The vapour is then compressed at high temperatures to produce heat for the central heating system.

    Ground source heat pumps work in a similar way but rather than taking heat from the air, it’s extracted from 15-100m under the ground. To extract this heat, pipes are buried in the ground either vertically or horizontally (depending on the outside space available).

    Solar thermal

    Solar thermal panels use energy from the sun to heat water for a hot water cylinder. Solar thermal panels are not generally able to provide enough hot water for a whole house, but they can significantly reduce heating costs and carbon emissions.

    Installing either an air to water heat pump or a biomass boiler could also make you eligible to receive the Renewable Heat Incentive (RHI) payments from the government.

    Finding oil boiler installers

    When choosing a heating engineer to install your oil boiler, you need to ensure that they are registered with the The Oil Firing Technician Association (OFTEC). OFTEC is a scheme that recognises installers approved to install oil boilers. While it isn’t a legal requirement for an oil boiler and storage tank to be installed by an OFTEC approved installer, it’s highly recommended.

    If the installer is not OFTEC registered, you or they have to notify your local authority’s building control department before the work can begin and then, once it is installed, an OFTEC technician will need to check the installation meets regulations. So, if you don’t hire an OFTEC registered engineer the first time round, you will need one in the end.

    Get Free Oil Boiler Quotes from OFTEC Installers

    We can match you with OFTEC approved engineers who are fully qualified to carry out an oil boiler installation. All you need to do is complete our simple online form – which should only take a few moments.

    We match you with up to 3 installers, because it’s important to compare quotes when having a new oil boiler installed. By comparing at least 3 oil boiler installation quotes, you’ll have the peace of mind that you’re getting the best price from a high quality company.

    Best of all, the quotes you receive from companies through Boiler Guide are completely free and there’s no-obligation to accept any of the quotes you receive.