Oil Boilers & HVO Biofuels FAQs

An oil boiler works in a very similar way to a gas boiler. They comprise of several key components that include a pressure jet burner, a combustion chamber, a water jacket containing both a primary and secondary condensing heat exchanger and a flue system to safely remove the unwanted combustion gases that are produced by the boiler. Oil boilers also need their own fuel supply which will require an oil tank to be installed at the property. Oil boilers generally use kerosene as their primary fuel source but with an ever increasing demand for more sustainable home heating the introduction of biofuels such as HVO is well underway. The fuel used is ignited within the combustion chamber by the pressure jet burner. As the hot combustion gasses rise up through the heat exchangers, they heat the surrounding water within the boiler, and the heated water is then used to heat both the emitters, such as radiators and underfloor heating, and the domestic hot water within the property. Once the combustion gases have passed through the boiler they will enter and pass through the flue system and disperse safely outside of the property.

Oil boilers are categorised as either heat-only boilers, which provide heat into both the space heating and domestic hot water system and require a cylinder to supply the hot water to the property. Or a combination boiler (combi) which provides both heating and hot water direct from the appliance and do not require an additional cylinder. Both are usually available as both internal and external models.

Grant Vortex boilers are condensing oil-fired boilers – please click here to read more about how condensing boiler technology works.

A condensing boiler has second (condensing) heat exchanger where the flue gases are cooled to below their dew point by the water returning from the heating system. This has the effect of condensing the water vapour present in the flue gases, and liberating the heat energy that would otherwise be lost to outside through the flue system.

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Biofuels, which are a type of renewable energy, produce significantly less carbon dioxide emissions compared to traditional fossil fuels so their use could help reduce the emissions of a biofuel compatible oil boiler. 

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All Grant Vortex floor standing oil boilers are biofuel compatible (depending on type of biofuel and % blend, for example: HVO or FAME). Biofuels are a renewable energy source, created from organic matter or waste. It will likely play an important role in reducing carbon dioxide emissions in the future. As biofuels emit less carbon dioxide than conventional fuels they can be blended with existing fuels, or used as 100% sustainable fuels, as an effective way of lowering carbon emissions.

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HVO stands for Hydrotreated Vegetable Oil and it is a second generation biofuel. HVO can be a ‘drop-in fuel’ which means it is suitable to be a replacement for existing fossil fuels, providing a 100% biofuel option.

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NOx or Nitrogen Oxides are gases that form when fuel is burned at high temperatures. Emissions of this gas are bad for the ozone layer so the Energy Related Products (ErP) Directive have implemented lower targets, for oil-fired boilers, the NOx emissions target will be a maximum of 120mg/kWh

Seasonal Efficiency is the average annual efficiency achieved in typical domestic situations, and is confirmed by independent testing bodies. These figures are verified on www.ncm-pcdb.org.uk. A simplified explanation of Seasonal Efficiency is that this is the average efficiency of the boiler over a year, taking into account climate, housing conditions, occupancy patterns, and controls. Combustion Efficiency is defined as the amount of heat released during combustion over the heating value of the fuel burned. This is usually shown as the net efficiency on a digital flue gas analyser, and may be higher or lower than the Seasonal Efficiency, depending on the time of year and the heat load.

The award winning Vortex boiler was launched in 2002. In the subsequent years that followed there was a customer demand for a competitively priced ‘A’ rated boiler, so the R&D Team at Grant devised the Eco range to meet this growing demand. The Vortex Pro has a larger heat exchanger area and more case insulation which gives it a slightly higher efficiency than the equivalent Eco model output.

An energy efficient boiler is an appliance which operates as effectively as possible by reducing the amount of energy lost through insulation and out the exhaust. 

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Choosing the best boiler for your home is important so that it meets all of your requirements. Whether you need an internal or external boiler, one for your utility room or garage, your installer will help you find the best boiler type for your property and with thirty-four models available, a Grant boiler should meet your requirements.

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No, condensing oil boilers can only run on kerosene.

As flue gas temperatures are very low on condensing boilers, a plume of water vapour can often be seen at the terminal (similar to your breath on a cold day). This is the boilers normal operating mode, but if this is likely to cause a nuisance to yourself or a neighbour’s property, we recommend you install a high level, vertical or a plume

Condensate occurs when the flue gas temperature of an appliance drops to below the ‘dew point’ and the steam present in the flue gases condenses and becomes a liquid. This liquid is slightly acidic but no more so than tomato juice and can be run directly into the household waste system.

We recommend that external boilers have a frost stat fitted.  Grant outdoor modules come with a factory fitted frost stat set at 5ºC plus or minus 1ºC.  A permanent live is required with a frost stat. For added frost protection, you should fit a pipe thermostat on a return pipe, set at 30ºC and wired to number 5 & 6 on the control panel.  This will prevent the boiler heating the house unnecessarily.  A bypass must also be fitted when wired as above.

A combi is a combination boiler that produces both heating and hot water from one compact appliance.

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Combi boilers which incorporate the latest burner and heat exchanger technology will be highly efficient. When comparing combi boiler efficiency, there will be two ratings – one for the space heating efficiency and one for the hot water efficiency.

An external oil boiler is designed for installation outdoors. The components within an external boiler are the same as those used in an internal boiler but external boilers have a different casing which is suitable for being installed outside. This casing is insulated and weatherproofed, being durable in material and with a paint finish which is designed for being sited outside.

An external oil boiler is an ideal solution when space inside the property is at a premium or when it is more preferable to install the boiler outside rather than inside a kitchen, utility room or garage. Grant’s external boilers have the same performance levels as their equivalent internal boiler models so they are just as efficient. Grant’s external oil boilers also come with a factory flue which is included with the boiler. When it comes to installation, it is important that a level and sound base is in place for the boiler to be sited on top of, so a suitable foundation is needed when installing an external boiler. If an external boiler is replacing an internal boiler, your installer may also need alter the existing pipework leading to and from the boiler.

Yes. The boilers are exactly the same as those fitted indoors, but are fitted inside a highly insulated weatherproof casing instead.

An internal oil boiler is usually white cased and designed for installation in a kitchen or utility room. The boiler will incorporate a burner, control panel, heat exchanger and other core components which are enclosed within a white casing. Some internal boilers have a powder coated casing to enable them to be sited in a garage, such as the Vortex Boiler House range – these alternative internal boiler models are ideal when a white cased boiler is not suitable.

Grant’s internal and external oil boilers have the same performance levels. An internal boiler is ideal when a direct boiler replacement is needed, with the new boiler being installed in the same location as the old boiler. When the location of the boiler is not changed, this can make for a straightforward installation with minimal alterations needed to elsewhere on the system. Sometimes, the size of a new boiler can be different to the old boiler – for example, if the new boiler is larger, alterations may need to be made to adjacent cupboards to accommodate the new boiler.

The size of oil boiler that you will need will be determined by the heat loss of your property, the size of your home and your requirements for heating and hot water demand.

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When your oil level falls below a certain level in your tank, there is a risk of air and contaminants that are in the bottom of the tank getting into your oil line which will affect the operation of your oil boiler. We always recommend that there is adequate filtration on your oil line and that your oil tank is kept topped up with fuel. If you have run out of oil, you must contact a competent oil heating engineer to bleed the system.

Yes, although we recommend the return temperature remains above 40°C. However, it is more usual to connect underfloor heating via a system of mixing valves or even a separate calorifier so that radiators which are normally heated to a higher temperature can be served as well. In order for the boiler to remain under guarantee, we stipulate it must be serviced every twelve months. Any work undertaken must be carried out by a competent service engineer.

Yes, providing the system is cleansed thoroughly and updated to fully pumped operation (not gravity hot water).

It is advisable to let your condensate run into a soil stack or the larger the diameter of pipe the better as this will help to prevent freezing water.  If your condensate trap is not run off into a soil stack pipe and its running into a smaller waste pipe then remove the bung on the condensate trap.

When you install a new oil boiler, you may need to install a new flue system – this is needed to safely remove the combustion gases produced by the boiler and discharge them outdoors. You may need to replace your external oil tank but speak to your installer as it may be possible to connect a new boiler to your existing tank provided your oil tank is in a suitable condition and complies with both current Fire Protection and Environmental regulations.

It is possible, but your installer should carry out a risk assessment on your oil tank to ensure that it complies with current Fire Protection and Environmental regulations.

To meet Building Regulations an oil boiler should be installed and commissioned by a Registered oil technician (e.g. OFTEC) or be installed by a competent person under a Building Control Notice

The serial number is a 15 digit long number sequence, located on a data plate on the inside panel of your boiler (Example 205122367811171).

Condensing boilers work at their most efficient when they condense, and this requires the return water temperature to the boiler to be around 50°C or less. However, we do not recommend changing radiators for larger versions to achieve this as it is uneconomical, and for most of the year the radiators will be oversized anyway. The Grant Vortex will operate efficiently on any system and even when not condensing, the larger heat exchange area will mean you will still be saving money against a standard boiler.

You can see how energy efficient a boiler is by reviewing the technical data provided by manufacturers. For Grant boilers, you can find the boiler efficiency rating of individual models via our website – please read more about oil-fired boilers here.

No. Your existing flue system should be replaced when a new boiler is fitted.

Grant oil condensing boilers need to be connected to a flue to remove the combustion gasses. Even if you are replacing your Grant boiler with a new version, you will require a new flue system too. It is not possible to connect to the old existing flue or liner, due to build-up of debris, which could fall back into your new boiler and affect its performance. Grant has a range of unique EZ-Fit Flues which are available as low level, high level or vertical kits, for internal and external applications, and even as unique flexi liner packs, designed to enable condensing boilers to utilise an existing chimney. It is also possible to convert existing low-level flues to high level after installation. Apart from the benefits of so many options the Grant EZ-Fit flue systems ensure ‘pluming’ is kept well out of the way of any windows, air vent or doors and out of sight. The flue terminal (end part of flue situated externally) should be positioned so as to avoid combustion gasses accumulating in stagnant pockets around, or entering inside the property. Care should also be taken that the plume from a condensing flue does not cause a nuisance. Please talk to your installing engineer for more information about the Grant EZ-Fit Flue systems.

In almost all applications you will not be able to use the existing flue. With condensing boilers there is a lower flue gas temp which leads to condensation/ moisture in the chimney/flue. The condensing boiler will need a Grant approved flue which is stainless steel and properly sealed at the joints to prevent leakage. All Grant external modules come with a factory fitted flue system.

Grant oil boilers operating on kerosene, the most common heating oil in the UK, should be serviced annually. However, those operating on biofuel should be serviced twice a year.

A boiler service is recommended to help the appliance operate correctly. Grant recommend that your oil boiler is serviced every twelve months (even when the guarantee has expired) to prolong the lifespan and ensure it is operating safely and efficiently. 

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HVO feedstocks are generally used oils that contain rapeseed oil, sunflower oil, soybean oil and non-food oils such as jatropha oil and algae oil as well as waste animal fats. Waste and residue oils are now a substantial contributor to the feedstock which makes this biofuel even more sustainable.

HVO is produced in the process of hydrogenation, which is treatment with hydrogen. The HVO process uses hydrogen and not methanol as the catalyst. As a result, it is not glycerine but propane that is the by-product of hydrogenation. Another important point to note is the fact that hydrogenation removes all oxygen from the vegetable oils while esterification does not. It gives an advantage to the HVO production as it helps to avoid oxidation.

The widespread supply and availability of HVO is subject to the completion of the ongoing field trials as well as Government approving the use of HVO as a heating fuel.