Knowledge Hub

Frequently Asked Questions

Your questions, answered

Condensing Oil Boilers

What is a condensing boiler?
In standard boilers up to 20% of the energy produced is lost to the atmosphere through the flue system. Condensing boilers are designed to capture part of this lost energy (latent heat) and can therefore maintain extremely high efficiency levels. See our article ‘What are Condensing Oil Boilers?’ for more details.
Are condensing boilers better than non-condensing boilers?
The main reason why condensing boilers are better than non-condensing models is that they are at least 25% more efficient. By reaching up to 97% efficiency, a condensing boiler can help you lower your fuel bills significantly and reduce your carbon footprint, making them a great alternative heating system.
Can condensing oil boilers be used on gas oil?
No, condensing oil boilers can only run on kerosene. All Grant condensing boilers are also HVO biofuel compatible and so can future-proof your home for its changing heating needs.
What is the difference between a combi and condensing boiler?
Unlike an immersion heater, a combi boiler heats your water on demand, instead of storing it in a tank. A condensing boiler is any boiler that uses condensing technology to make better use of the heat they generate from burning fuels such as gas or oil-so a combi boiler can also be a condensing boiler.
How long do condensing boilers last?
The average life expectancy for a boiler is between 12 and 18 years. You should ensure that your boiler is maintained properly in order to keep it functioning for as long as possible.
How much more efficient is a condensing oil boiler?
Usually, a new condensing oil-fired boiler will have an efficiency of 92% to 93%, compared with 85% for a new non-condensing boiler and 60% to 70% for older systems. An oil boiler purchased from a well-established company should be just as efficient as a gas-powered boiler system, if not more.
Does a condensing boiler need a drain?
All modern condensing boilers require a condensate pipe to run to a suitable drain it can be taken to the outside, run internally, or even pumped through a 22mm plastic pipe rising vertically to a drain.
What temperature should a Grant condensing boiler be set at?
You should set the temperature between 60 and 65*C but for maximum efficiency, it should be set around 60*C
How do I know if I have a condensing boiler?
Condensing boilers are also known as high-efficiency boilers. If you have a white plastic pipe coming out of the bottom of the boiler, it is more than likely to be a condensing boiler.
Do condensing boilers use less oil?
Condensing boilers are water heating appliances that run on gas or oil. In so doing, a condensing boiler can deliver a higher efficiency rate, which ranges from 86 to 95% depending on the model.
What is condensate and is it dangerous?
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.
Will it damage my boiler if I run out of oil?
Running out of oil will not damage your oil boiler. If you run out of oil, your boiler stops working and you’ll need to order more. There`s a safety system in place in every oil boiler that disables the burner when there`s no flame, so you don`t need to worry about any safety issues.
How often should your boiler be serviced?
You should have your oil burner serviced annually by a competent oil service technician.
Where can I find my boiler serial number?
The serial number is a 15 digit number , located on a data plate on the inside panel of your boiler.

EZ-Fit Flue

What is a flue?
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 EZ-Fit Flue options Grant has a range of unique EZ-Fit Flues. These are available as low level, high level or vertical kits, for internal and external applications, and even as unique EZ-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. Flue Terminals 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. See our article on clearance for balanced flues for clearance distances in accordance with Building Regulations.
What is "pluming"?
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 kit flue.
If I change my boiler for a new condensing boiler can I use the existing flue?
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.
Can Grant EZ-Fit flues be top or side exits?
The flues are suitable for rear, side and top exits.

Air Source Heat Pump

What are the advantages of a heat pump?
Installing a heat pump is a big decision, and the initial investment will be more than a traditional heating system. However, once you learn about the advantages of heat pumps, you’ll quickly discover that the additional expense is worth it. Long term, your energy bills will be reduced, using a heat pump is much better for the environment and you will have 24/7 heat and hot water.
How much will it cost to buy and install a heat pump?
Requirements for each home are unique and the cost for installing a heat pump at your home will vary depending on the size and type of heat pump required, as well as where you would like the outdoor compressor unit positioned. For a quote, please send your house plans to:
What kind of maintenance does a heat pump need?
We advise that you get your heat pump serviced by an experienced service engineer once per year. Grant offers on-site and online training courses for installers on the Aerona3 heat pump range – visit
Do heat pumps work in old houses?
For a heat pump to work most efficiently, your home needs to be well insulated to prevent as much heat from escaping as possible. Older poorly insulated homes may need higher temperatures than the heat pump can cope with to get the house warm.
Are heat pumps reliable?
Yes. Heat pumps are extremely reliable. They use the same process as a home fridge or freezer and have the same level of dependability and life expectancy.
Do heat pumps use a lot of electricity?
Heat pumps require some electricity to run, but it is a relatively small amount once your home is well insulated. Modern heat pump systems can transfer three or four times more thermal energy in the form of heat than they consume in electrical energy, making them a highly efficient main heat source.
How long will my heat pump last?
Good quality equipment, installed by qualified contractors, can have a life span of 14 to 17 years. Poor maintenance and environmental factors can cause the lifespan of your heat pump to decrease. Regular inspection and maintenance will allow your system to operate efficiently for as long as possible.
Can I heat my whole house with a heat pump?
Yes, a heat pump can be installed as your primary heating source for your entire home.
What temperature should I set my heat pump to in the winter?
To balance comfort and efficiency your heat pump should be set to 18 to 19 degrees during the winter months. When your home is occupied and when family members are awake, a heat pump setting of 18 to 19 degrees keeps the living areas sufficiently warm.
Can I install a heat pump if I live near the coast or sea?
Yes you can install a heat pump if you live near the coast or sea. For homes within 10km of the coast, the best option is to have a Blygold coated Grant Aerona heat pump fitted, this protection helps to triple the lifespan of the unit compared to a non-treated unit. See video for more information -
Are heat pumps noisy?
The Grant Aerona³ air to water air source heat pump does have a fan which draws the air across the internal components, and this will make a slight noise in operation. However, the Grant Aerona³ has always been one of the quietest heat pumps available with the 13kW and 17kW models recognised by Quiet Mark for their quiet operation.
How long is the warranty period on a heat pump?
Grant Engineering (IRL) guarantees the manufacture of the heat pump including all electrical and mechanical components for a period of twelve months from the date of installation, provided that the air source heat pump has been installed in full accordance with the installation and servicing instructions issued. This will be extended to a total period of five years if the air source heat pump is registered with Grant Engineering (IRL) ULC within thirty days of installation and is serviced at twelve monthly intervals.
What’s better underfloor heating or radiators?
Both Uflex underfloor heating and Grant Afinia radiators compliment high and low-temperature systems. Underfloor heating offers versatility to support the overall design and architecture of a more modern, open-plan space. Grant Afinia radiators are sleek and stylish and can quickly heat up individual rooms within the home. Both heat emitters can be used separately or installed to work in tandem.
Are heat pumps suitable for radiators?
Yes, you can use radiators with a heat-pump. Due to the low flow temperatures, your heat emitting surface area must be bigger than for boiler-operated heating. This means existing radiators may not be suitable. We provide a range of Grant Afinia radiators that are compatible for use with our Grant Aerona heat pumps.
Is underfloor heating bad for your health?
No, in fact by installing underfloor heating results in increased hygiene levels due to reduced air circulation transferring dust particles throughout the home.
What is the most economical way to run underfloor heating?
For an efficient system and quick response times, set your underfloor heating temperature to 16*C. This will result in a quicker warm up time as the heating system needs to supply less energy.
Can Grant help me select the right heating technologies for my new home?
Yes, popular amongst self-builders, architects and those in trade, our free of charge home heating design service enables those working on new build or retrofit projects the opportunity to have a bespoke heating solution for the property created and specified under one roof.
How to avail of Grant’s Home Heating Design Service
1. Send planning drawings, a contact number, and your preference of underfloor heating, radiators, or both to 2. Grant technical specialists will be in touch to discuss your requirements 3. Full property specifications with recommended Grant products will be provided

Underfloor Heating

Is UFH specifically for new builds?
Underfloor heating is generally installed into new builds since new floors are being installed. Underfloor can be retrofitted into existing building if existing floorboards are being lifted or new floor compositions being installed.
Can UFH and radiators be mixed?
Yes, but usually they would be mixed on separate floors i.e. underfloor on the ground floor and radiators on the first floor.
Can heat be put into UFH straight away?
No, the pipework would be pressure tested. Once it is confirmed that all pipework and connections are good then the concrete screed is poured. This is allowed to dry naturally for up to 30 days depending on thickness. Heat can then be introduced to the pipework at a low level and then slowly increased on a daily basis to required level.
How hot will the floor surface get?
Ideally the floor surface will be in the region of 24-27°C depending on desired room temperature. Floor surface temperature should not exceed 29°C.
Can each room have a different temperature?
Yes, this can be achieved by zoning of the house. Individual loops of pipework can be ran to each room and controlled by an individual thermostat. The quantity of heating zones can be determined at design stage.
Can underfloor heating be used with high temperature systems?
Yes underfloor can be used with high temperature systems such as oil boilers and wood pellet boilers, a mixing unit will need to be added to the underfloor manifold to mix down the temperature to 35-40°C.
Should I turn on/off my underfloor heating?
It is best practice to leave UFH stat controlled. When the room temperature drops below the set temperature a signal will be sent to the heat source. The heat source will then activate and bring room temperature up to required level. It is more efficient to maintain a rooms temperature as opposed to reheating rooms.
Where is the best manifold location?
The manifold should be located as centrally as possible so as to reduce pipe run lengths and also to eliminate waste heat lost in distribution.
Should UFH be installed under fixed units?
UFH is generally not installed underneath fixed items such as kitchen units, built in wardrobes, stairs, sanitary ware or showers/baths. These units are usually bolted to the floor and can damaged the pipework hidden below the screed surface.
What type of floor coverings can I use?
UFH will work with most floor coverings, although some coverings work better than others. Some of the better working floor types include ceramic tiles, polished concrete, stone, engineered boards and carpet (with a TOG value of less than 2).
What are the advantages of UFH?
UFH does not rely on air circulation to disperse heat throughout a room, as the entire floor is radiating heat, an even dispersal of heat is given to all areas of the house eliminating any cold spots.

Afinia Radiators

What guarantee do I get with Afinia radiators?
Grant offers a 15 year guarantee with our Afinia range.
Can you install the Afinia radiators to an existing heating system?
Yes you can install Afinia radiators with both high and low temperature systems.
What sizes do the Afinia radiators come in?
Afinia radiators are made up of 80mm panel sections and can be ordered in 6 panels right up to 20 panel rads on request.
Can they be used on an air source heat pump?
Yes Afinia radiators are a great pairing for the Grant Aerona heat pump range as the work on low temperature heating systems and they heat up much quicker than conventional steel rads.

Solar Thermal Solutions

What are the benefits of solar thermal panels?
Solar thermal panels are very efficient, as heat waves carry more energy than sunlight. Also, since there is no process of transformation into electricity, solar thermal panels can help you to save up to 600kg of carbon dioxide emissions in a year, having a positive impact on the environment.
How long do solar thermal panels last?
Generally, solar thermal systems last up to twenty years. In some cases, they have been known to last much longer.
Do solar thermal panels need direct sunlight?
No, solar thermal panels do not require direct sunlight to operate. They use the heat of the sun or sunlight to generate energy but can still do this on a dull or cloudy day.
Do solar thermal panels need servicing?
Solar thermal systems should be regularly serviced and maintained every two years. This is to change the anti-freeze, glycol heat transfer fluid in the system.
Do solar thermal panels work in rain?
While solar thermal panels are most effective in direct sunlight, they will still work when light is reflected or partially blocked by clouds. Rain can also help your panels to operate efficiently by washing away any dust or dirt.
Do solar thermal panels get damaged in hail?
Grant solar thermal panels are extremely resistant to hail damage.
What are the advantages of solar thermal panels?
Solar thermal panels are low maintenance, environmentally friendly, and can save you money on your water heating bill.

Biomass Boilers

What are wood pellets?
Wood pellets are cylindrical in shape and generally made from compressed sawdust, which is often the waste product from industries (e.g sawmills). They are fused by the natural lignin present in dry wood. It strengthens the wood as well as having water proofing properties. All pellets used must meet ENplus standard EN14961-2 and be bark and sand free and must be approved by Grant before being used in the current Spira boilers. Failure to use approved pellets will invalidate the product warranty. Moisture content below 10% Calorific value of 4.8 – 5.2kWh/kg Ash content of <1% (Low) Bulk density of 650kg/m³ or less Chlorine content of 0.03% or less No additives Using pellets which are not approved by Grant will void your boiler warranty. If you are in any doubt, please contact Grant before purchasing your pellets.
Are wood pellets from a sustainable source?
As the sawdust used to make wood pellets is a by-product e.g. from sawmill industries, or has been sourced from a managed forest where trees are planted to replace the ones cut down, they are classed a sustainable ‘carbon neutral’ source of fuel.
Are wood pellets readily available in Ireland?
Yes. Wood pellets are available from a number of manufacturers and specialist suppliers. Also, some of the larger Plumbing and Heating merchants are now stocking wood pellets.
How are wood pellets supplied?
Pellets are available in both bagged quantities – usually in 10kg bags – or in bulk. The minimum bulk pellet delivery is typically 3 tonnes but this needs to be checked with the supplier concerned, as smaller deliveries may be possible.
Do Grant recommend which type of wood pellet to use?
There are a wide range of wood pellets, of differing qualities, available on the market. Only 6mm diameter pellets should be used in Grant wood pellet boilers. These pellets must first conform to EN plus standard EN14961-2. Currently, Grant have tested and approved Balcas ‘Brites’, Laois Pellets (GWP) and Premium Pellets for use with the Grant Spira wood pellet boilers. The use of pellets not conforming to the foregoing EN standard, may cause operating problems with the boiler and would invalidate the product warranty.
Will I need to manually fill the boiler with wood pellets?
If the indoor pellet hopper (supplied with the boiler) is the only form of storage used then this will need to be filled manually with pellets supplied in bags. The hopper has a maximum capacity of 110kg or, eleven 10 kg bags of pellets. If a bulk pellet store is used to feed the pellet hopper, the hopper will be filled automatically from the bulk store. Of course, it is important to regularly check the bulk store and to order a bulk delivery before it is empty.
How will I know that the hopper requires refilling and how often will it need to be done?
If the indoor hopper only is used, then the boiler will automatically stop when the pellet level in the hopper reaches minimum. There is a facility to have a warning light to indicate when this minimum level of pellets is reached. Topping up the hopper with pellets will automatically re-start the boiler. However, to avoid this happening, the pellet level in the hopper should be regularly checked and topped up as required –usually once to twice a week. If a bulk pellet store is used, then this will automatically top up the indoor pellet hopper. However, the pellet level in the bulk pellet store must be regularly checked and a delivery of pellets ordered before it becomes empty. The time between deliveries will depend on the size of the bulk store, the size of the boiler and how it is used. Typically, for a 26kW boiler around 3 tonne of pellets should last for about a year, based on a heating demand of 14,400kW input.
How are wood pellets stored?
Wood pellets should always be stored in a damp free environment. Care must be taken to ensure that stored wood pellets never come into contact with water. Any external stores must be sealed and protected against rainwater entry. Grant market a range of internal and external pellet storage solutions, but advice on the type and location of bulk pellet storage is also available from the pellet suppliers.
How does a wood pellet boiler work?
On start up the auger feeds the wood pellets from the hopper into the burner where it is lit by an ignition element. The burner output is adjusted automatically (modulates) to achieve the set temperature by controlling the feed rate of pellets. The fan in the burner propels hot gas generated from the fuel into the Spira’s primary heat exchanger. The heat energy is then transferred to water from the central heating system, before being circulated around the house to either radiators and/or underfloor heating.
Is the Grant Spira wood pellet boiler noisy in operation?
The noise from Grant wood pellet boiler comes from the following main sources; the flue fan, burner fan, self-cleaning process and the pellets themselves dropping into the burner. Whilst the combination of these is not excessively noisy, the Spira would be unsuitable for installation within ‘habitable’ rooms of a house, e.g. kitchen, utility room etc. which are more commonly used for locating conventional oil and gas boilers.
How much space is required to install the boiler and hopper?
Suitable space must be allowed around the boiler for servicing and maintenance. Full details of the precise minimum clearances are to be found in the Installation and Servicing instructions provided with the boiler. Typically, an overall floor area of 1700mm wide x 1500mm deep will be required to locate the boiler/hopper and provide the clearances required.
Can the Grant Spira wood pellet boiler be installed outside?
No. Grant Spira wood pellet boilers must be installed in a damp free environment along with the accompanying pellet hopper. The boiler can be located in an outbuilding, etc. but must not, under any circumstances be exposed to the elements (e.g. located under a car port or lean to canopy).
Are there any special requirements for the base on which the boiler and hopper are installed?
Yes. The base must conform to the requirements of Building Regulations. Full details are given in the Installation and servicing instructions supplied with the boilers.
What type of heating system can a Grant Spira wood pellet boiler be used with?
Grant Spira wood pellet boilers can be used with 2-pipe, fully pumped hot water heating systems – either open-vented or sealed system – using radiators and/or underfloor heating. Sealed heating systems must incorporate a suitably sized expansion vessel, a pressure gauge and approved filling loop. The 2.5 bar pressure relief valve required is supplied with the boiler.
What type of heating system controls can be used with a Grant Spira wood pellet boiler?
Grant Spira wood pellet boilers can be used with most commonly installed domestic heating control systems, e.g. Y-plan and S-plan type control systems, where a programmer and room thermostat will control the operation of the boiler to the requirements of the householder.
Can a Grant Spira wood pellet boiler be fitted as a replacement boiler on an existing heating system?
Yes, provided that the existing system is chemically cleaned and flushed, and complies with current Building Regulations. The existing control system may also be used providing that it also complies with these regulations. If not the system and/or controls will need to brought in line with these requirements.
How should a Grant Spira wood pellet boiler be sized?
As with all boilers, a full heat loss calculation for the property should be made to determine the heat load that the boiler will be required to meet, under design conditions. If the heating system includes a circuit to a hot water cylinder then an allowance for water heating should normally be included in determining the final heat load to be met by the boiler.
What does condensing mean?
During combustion a proportion of the heat produced is locked up in the flue gas. A conventional boiler cannot recover any of this heat and this energy is lost to the atmosphere through the flue. The Grant SPIRA Condensing wood pellet boiler contains an extra heat exchanger which is designed to recover this heat normally lost by a conventional boiler. It does this by cooling the flue gases to below 90°C (Typically conventional boiler flue gases are 200°C plus) thus extracting more heat. This is achieved by cooling the flue gases to their dew point.
How efficient are the Grant Spira wood pellet boilers?
The Grant Spira is a condensing wood pellet boiler with a modulating burner and has exceptionally high efficiency levels. The 6-26kW model has a tested and approved full load efficiency of 97.4% and the 9-36kW model 93.1%. This is comparable with high efficiency condensing domestic oil fired boilers (and better than many high efficiency gasfired boilers), making the Grant Spira both an energy efficient and ‘Green‘ alternative to fossil fuel burning boilers.
What is unique about the Grant Spira wood pellet boiler?
Grant Spira wood pellet boilers benefit from the use of award winning condensing technology, originally developed for Grant’s market leading Vortex oil-fired boiler range. This, in conjunction with the all-new fully modulating pellet burner, has resulted in an extremely efficient range of renewable home heating appliances. Higher efficiencies, coupled with lower and more stable fuel costs, creates a very environmentally and consumer friendly heating solution.
Who can install, commission and service a Grant Spira wood pellet boiler?
Only Grant trained and accredited wood pellet boiler installers can install the Grant Spira wood pellet boiler. Courses are available via the Grant Training Academy and can be booked by calling (057) 912 0089.
How often should a Grant Spira wood pellet boiler be serviced?
In order to ensure efficient and safe operation, Grant Spira wood pellet boilers must be serviced annually when amongst other things, the primary and condensing heat exchangers, combustion chamber, flue fan box and burner, must all be cleaned of any ash deposits and the burner re-set for a further year’s operation. The boiler will indicate when this is due, by displaying a ‘SERVICE’ message on the burner control panel. This service interval is based on the actual running time of the burner and thus may vary in length depending on the degree of use of the boiler.
How often does a Grant Spira wood pellet boiler require cleaning out?
The efficient combustion of the Grant Spira burner, coupled with the consistently high quality of the wood pellets approved for use with the appliance, results in a relatively small amount of fine ash being produced within the boiler. The majority of this will be collected within the easily accessible ash pan located inside the combustion chamber. Furthermore, as the Spira incorporates automatic cleaning of both the primary and condensing heat exchangers, and the burner brazier, at pre-set intervals to remove any ash deposits, they generally only require manually cleaning out around once per year i.e. the ash pan requires emptying, or after about 3 tonnes of pellets have been burnt.
Is the Grant Spira MCS approved?
Yes, all boilers within the Grant Spira Wood Pellet Range are MCS approved.


Use our online enquiry form to send us any comments or questions

Contact Us


Brochures, manuals and data sheets available here!

Find a manual

Find a merchant

Enter your location to find your nearest Grant supplier

Find a merchant