Why Gas Combi Boilers Are Better Than Oil Combi boilers

Why Gas Combi Boilers Are Better Than Oil Combi boilers - by Greener Homes

In this article we take a detailed look into the main benefits and why gas combi boilers are better than oil combi boilers.


Greener Homes Group are a team of friendly and professional heating engineers who can help with a variety of boiler services. From boiler repairs and servicing to energy efficiency advice and gas safety inspections. Safety is a top concern and all the staff are Gas Safe registered.

If you already know which boiler to choose for your home, you can get a quote from the Greener Homes Group website and book an installation date. However, if you’re not sure about the types of boiler or which one is better for you, this article may help. Alternatively, you can always ask one of the engineers at Greener Homes Group for advice.

Table of contents:

    Different Boiler Types

    To start with, there are three main types of gas boiler:

    Combi Boiler

    A combination or gas combi boiler system contains almost all the components within the boiler itself. Therefore, you don’t need an extra tank or cylinder to make a combi boiler function. Hence, its size is compact and neat, which means it can fit nicely into a kitchen cupboard and doesn’t need too much space. Additionally, you can get hot water on demand. That’s why the combi boiler is the most common type of boiler system in the UK.

    However, a combi gas system is better for a home with a smaller number of people because you can only use hot water for one task at a time. For example, if one person is taking a shower, you won’t be able to use hot running water for the washing up at the same time.

    Conventional Boiler

    Unlike a combi boiler, a conventional boiler has extra parts in addition to the boiler itself, such as a circulation pump. Conventional boilers are also known as open vented heat only gas boilers. Hence it requires a cold water tank in the loft which means it needs much more space than a combi boiler.

    With a heat only boiler, the hot water is stored in a hot water cylinder or hot water storage tank. You can heat water in the tank when you know you are going to need it, and leave it switched off when you don’t need it. Conventional boilers are good for larger households where several people want to use hot water at the same time.

    System Boilers

    System boilers are also known as closed vent boilers. These are a good choice if you think you’ll need a heat only boiler, without lots of external parts. Most of the external components are built into the boiler, a bit like the combi boiler.

    A system boiler still has a hot water cylinder, but it doesn’t need an expansion tank in the loft. Therefore it requires less space than a conventional boiler.

    How Does A Gas Combi Boiler Work

    In simple terms, a gas boiler heats up water. It’s similar to a big fire that has a continuous supply of natural gas flowing into it from a pipe that goes out to a gas main in the street. The boiler pumps the circulated water in pipework over a series of gas flames. As the water passes the flames, it heats up, like water in a kettle. The water provides central heating and hot water.

    A combi boiler works by taking water directly from the mains. When you turn on a hot water tap, the gas burner is ignited and the heat exchanger transfers the energy to the water. This system allows hot water to be generated almost instantly. Hence one of the great benefits of a gas combi boiler is that you can get hot water on demand as and when you need it.

    How Does An Oil Combi Boiler Work

    If you are not connected to the mains gas network, it’s likely that you will heat your home using oil. Around 4 million households in the UK live off the gas grid, many of them in remote or rural locations. If you are not connected to the mains gas network, you will need to pay for your fuel in terms of quantity and get it delivered to your home. Then, you need to store it in an oil tank, which is usually outside the home. If you are running low on oil, it’s completely up to you to get it topped up again, before your house gets too cold. So, you do have to think ahead when using oil as a fuel.

    However, most modern oil boilers can reach an energy efficiency rating of 92% or more. When compared with gas, it is a more efficient fuel. But burning oil produces twice as much carbon as gas. So if you’re looking for an environmentally friendly option, then oil boilers are not the best choice. Although for some people in remote areas, there isn’t an alternative option.

    Oil combi boilers are good for households that want the functions of a combi boiler but lack the gas supply. In comparison to a gas combi boiler, oil combi boilers work in a similar way. The oil fired boiler will heat water, which supplies the central heating via radiators and hot water through taps.

    Pros and Cons of Oil

    You can choose to have your oil boiler internally or externally. By having your boiler outside, you can free up more space that would be taken up by an internal combi boiler. Furthermore, if your boiler needs maintenance or refuelling, this can happen outside with little disruption to you.
    Additionally, because it’s outside, you won’t notice any noises coming from the boiler, even modern boilers create a certain level of background noise.

    Another pro with oil is that it’s accessible if you live off the mains gas grid. Also in terms of safety, having your boiler outside means that there is no risk of leakage inside your home. Additionally, if your oil boiler is in an outbuilding, garage or shed, it can even partially heat the building, making it warmer to work in.

    However, the oil tanks that hold the fuel can be unsightly and take up space. The tank needs to be easily accessible for refilling, so you can’t just hide it away. In terms of costs, the price of oil can fluctuate depending on demand. This is true of other fuel sources, but oil is more problematic as there is no official regulation in place.

    Additionally, because your supply depends on others and needs to be physically delivered, there’s always a chance it may be delayed. You have to remember to book your oil supply for when you need it. More modern oil tanks have sensors on them which can automatically place an order when you get down to a certain level.

    Also, having an oil boiler installed for the first time is more expensive than having a gas boiler installed. Another negative is that oil boilers are twice as bad for the environment as gas boilers as they produce more carbon dioxide.

    Pros and Cons of Gas

    When it comes to modern boilers, Gas combi boilers are highly efficient. In fact, installing a new combi boiler could save you up to £300 a year on your heating bills. Furthermore, combi boilers are less complex than traditional heating systems. This is because you don’t need additional equipment such as a water tank or cylinder. Hence installing a gas combi boiler can be quite straightforward which means it’s cheaper to install.

    An obvious benefit to having a gas combi boiler is that you can get your hot water on demand. Just turn on your hot water tap and it’s there instantly. So, you don’t have to wait for your water to heat up in a tank in the loft before you can enjoy a nice warm bath or shower.

    Generally speaking, if you’re thinking of selling your home in the future, it’s probably easier to sell with a modern gas boiler heating system than if you use an older, more complex form of heating or oil for example.

    In terms of the cons of installing a gas combi boiler, you do have to rely on the mains pressure. Hence you need good mains pressure to ensure your water and central heating works to its maximum potential. You can’t have a power shower with a combi boiler, as the water pressure is set by the pressure level at the water mains. Hence, if you live in an area with low mains pressure, a gas combi boiler may not be your best option.

    Additionally, if you live in a larger household, you may want to run more than one shower at a time. In this case, a gas combi boiler can provide your central heating and hot water, but may not be enough for your needs.

    Is Oil or Gas Cheaper?

    Oil prices are tied to the price of crude oil, which means they can change with demand and availability. For example, prices can increase during winter when there is more demand. In comparison with gas, oil is more expensive, but cheaper than other alternative fuel sources such as biomass and electric.

    For example, in a 3 bedroom home, gas will cost between £700-£1400 per year. Electricity is more expensive as a fuel, this will cost approximately £1500. Then, oil will cost around £1400. So you can see that by using gas, it is a cheaper fuel as well as being the most convenient.

    Oil tanks range in size so they can cost between £500 and £2000. Alternatively, you can rent the tank from your oil supplier. Additionally, the cost of the boiler and installation varies between £2,500 to £4,500 depending on the job. Labour costs will vary between £400 – £800 and the cost of the boiler between £2,000 – £3000.

    In comparison, a gas combi boiler with installation starts at around £1400 depending on who installs it. Thus an oil boiler installation is definitely more expensive.

    To summarise, gas is the cheapest option and it’s piped straight into your home which means it doesn’t need a tank or any storage. Furthermore, it’s very easy to control.

    Gas Or Oil, Which Is Better For The Environment

    Gas is a fossil fuel, which means that you are burning a fuel which is releasing pollutants into the atmosphere. Using gas central heating will contribute to your carbon footprint. However, modern condensing gas combi boilers are increasingly efficient, up to 90% of the energy is used within your home. Which means 10% or sometimes even less is released outside it.

    Oil is also a fossil fuel but it’s a good alternative if you are not linked to the mains gas supply. It doesn’t produce carbon monoxide. However, burning oil creates far more carbon emissions than gas. Also, you will need to store oil and if there is a leak or spillage from your storage tank, the oil can seep into the environment and pollute it. If there is a leakage, you will need to pay for the area to be cleaned up.

    There is an alternative to oil for homes without gas. LPG is a more sustainable fuel which can cut carbon emissions. It’s a cleaner burning fuel which produces less ash and soot than oil boilers. This means that an LPG boiler is usually easier, and therefore cheaper, to maintain and service.

    However, when looking at the options between a gas and oil combi boiler overall, gas is better for the environment.

    How To Tell If You Need A New Boiler

    Perhaps you are not sure if you need a new boiler. Generally speaking, a boiler can last for between 12-15 years if well maintained and looked after. So if your boiler is over 10 years old, it may show signs of ageing and you might want to consider replacing it.

    For example, are you noticing that some of your rooms in the house take ages to heat up? Or are there any odd noises coming from your boiler? Maybe you’ve seen leaks from your water tank? Of course, you can continue to get your boiler serviced and repaired. However, a new boiler is more efficient and consequently more cost effective in the long run.

    How to Choose A Gas Combi Boiler

    When it comes to deciding on a new gas combi boiler for your home, there are five things to consider which may help you.

    Choose a Trusted Brand

    Are you confused by the amount of boilers on the market? How do you know which is the right one? It can become overwhelming if you’re new to this. As with any decision, you want to make sure that it’s a good one if you are paying out a lot of money.

    So, it’s a wise idea to choose from a trusted brand. You may see a cheaper boiler on the market, but it won’t offer you the same guarantees as one of the trusted brands. Remember, a boiler is a gas installation within your home, so safety needs to be paramount.

    With Greener Homes Group, you can choose from a range of trusted brands including Worcester Bosch, Valliant, Ideal and Baxi among others.

    Ask the Engineer

    Not everyone is an expert on boilers. So if you need some advice, you can always ask an engineer. Most engineers have experience installing many boilers in different types of homes. Even if you have an unusual home or a question you’re not sure about, an engineer can help you.

    Check the Warranty

    Many boilers come with warranties, but it may pay you to shop around a bit. Some boilers can come with a 12 year guarantee. While others may only be 2 years. This is another factor to consider. For example, if a cheap boiler with a 2 year warranty breaks down several times over its 15 year lifetime, you may end up paying more money on it than if you had bought the expensive boiler with the 12 year warranty.

    Find the Right Boiler

    This article is particularly about gas combi boilers, but it is also vitally important to get the right boiler for your household. For example, if you are in a larger household with several bathrooms, then a small gas combi boiler may not be suitable for your needs. Again, it’s worth asking an engineer for advice on the right boiler for your home.

    Get Quotes

    Getting a new boiler is not cheap. Therefore it’s worth getting a few quotes to compare and get the best possible deal you can. The cheapest one may not always be the right one. With this in mind, you also need to consider the cost of installation as well as the boiler itself.

    What Happens With A Gas Combi Boiler Installation

    So, if you need a new gas combi boiler, the first thing to do is to get a quote from Greener Homes. If you’re happy with the quote, then make an appointment for an engineer to visit your home. They will assess the situation and give you a free quotation. This quotation is based on the brand and type of boiler you would like installed and where it will go in your home.

    Meanwhile, you need to decide on the type and brand of boiler you’d like. Having a like for like swap makes the change over easier and can reduce costs. However, Greener homes engineers will always advise you on what is best after assessing your home. For example, perhaps your family has grown since you had your last boiler installed. Subsequently, that will affect the amount of water you need to heat up. Some boilers are not designed for homes with excessive use.

    If you’re happy to go ahead, your engineer will arrive on the selected day with specialist tools and equipment. You just need to make sure there is enough space for them to work and easy access to the boiler with no obstructions. To ensure your safety, you can check their GasSafe ID which carries a picture of your engineer and a date.

    After the work is done, the engineer will give you all the documents you need for your new boiler. You should receive a building regulations certificate as well as a completed Benchmark certificate to prove compliance.

    How Much Does A Boiler Cost?

    Your boiler is one of the most important items in your home. It keeps you warm and heats your water. Hence it may seem like an expensive outlay to begin with, but it’s a vital part of your home. Most of us know how grateful we are for the heating in the cold British winter months.

    Typically, if you’re looking at having a brand new boiler installation, you can expect to be spending around £500 to £2500 in price. In the longer term, a new boiler can save you money in energy bills. You could save between £50 – £300 a year because you have a more energy efficient boiler than your old one. When looking ahead, you can see that having a new boiler installed will almost pay for itself in 3-5 years.


    The price of your boiler installation depends on a few factors. These include the type of boiler, whether it’s brand new or a replacement, moving the boiler and any optional extras such as smart controls. Furthermore, it depends on who you choose to install your boiler. Sometimes a local company is cheaper than choosing a big national brand. Again, it’s worth shopping around here and comparing quotes. Whatever your budget, there will be an option that suits you.

    Boiler Installation Scenarios

    The amount the boiler installation costs will depend on the amount of labour required to do the job. Prices can vary on your location and even the organisation you use. For example, having a new combi boiler could cost you between £1500-£4000. This includes the full installation as well as the boiler, any included warranties and how complex the installation is to complete. Replacing a combi boiler should take around 1 day. However, if you need to move the boiler to a new location in your home, it may take 2-3 days. So you can see how the costs of labour build up depending on the scenario.

    How Much is a Boiler on its Own?

    Taking installation out of the equation, you are left with this question. How much is a boiler on its own? Generally speaking, new combi boilers can range between £500-£1000 on most budget models. Mid range models can cost between £1000- £1200. While premium models often cost in excess of £1500. Systems boilers have a similar range of pricing. Whereas conventional boilers can cost between £500 and £2000 depending on the size, brand and quality of the unit.

    To sum up, the cost of a new gas boiler can range a lot. However, with the option of budget, mid level and premium, there should be something that will suit you, no matter what your budget.

    How Long Do Gas Combi Boilers Last?

    A gas combi boiler should last between 12 and 15 years. However, you can help to increase its longevity with a few tips at home.

    Annual servicing is one of the best ways to ensure your boiler lasts longer. By having an annual service you are catching any small problems before they turn into costly breakdowns. Most heating engineers will open the casing and check the inner workings of the boiler. This helps to ensure that all the parts are working well and as they should be. Another benefit to an annual service is that it helps to ensure your boiler is working as efficiently as possible. A boiler that has to work harder will cost more to run.

    Another good maintenance method is a powerflush. This is designed to get rid of any sludge or debris in your pipework which could affect how the boiler functions. Boilers do age. Over time there is a build up of sludge simply due to the way a boiler is used. At some point, this can affect the way a boiler functions and stops it from working efficiently. Alongside regular maintenance, you probably only need book a power flush once every 5-8 years. If you are having a brand new heating system installed, it’s probably a good idea to get a powerflush done immediately, as this will get rid of any debris left over from a previous system. Hence clearing the pipes to ensure your new boiler works to the best of its ability.

    Finally, another top tip is to prepare for any weather. During the winter, your boiler is stretched to its limits, heating the home more often than in the summer. When temperatures sink low, the pipes can freeze. To stop this happening, it’s worth insulating your pipework. This doesn’t need to be expensive. You can simply get the materials from a local DIY store to insulate the pipes. Then in winter, the water will still be able to travel freely around the pipes without freezing and affecting your boiler.

    What Size Boiler Do You Need?

    Getting the right boiler for your home is important. Each boiler has to be able to cope with a different set of demands being placed on it.

    One of the most important parts about choosing a combi boiler is to get the right size. This doesn’t mean the right size for your kitchen, it’s about the actual output power. Without the correct output power, you boiler may not be able to cope with the demands of your household. Thus you have spent a lot of money on a boiler that doesn’t deliver what you need. Furthermore, it will have to work extra hard in order to be effective, so your energy bills will be higher.

    As well as being able to keep up with your hot water requirements, you also need a boiler that can handle the mains pressure as it flows through.

    It’s worth noting here that the size of your house is also a deciding factor on what size of boiler you need. For example, a small house or flat with 1-2 bedrooms and 1 bathroom will need around 24-27kW of output. A medium house with 3-4 bedrooms and 1-2 bathrooms will need around 28-34 kW of output. Whereas a large house with 4 or more bedrooms and 2 or more bathrooms needs between 35 and 42 kW.

    What Are The Best Combi Boilers in 2021

    As you have seen there is a wide choice of gas combi boilers. All the engineers at Greener Homes are accredited fitters for the Worcester Bosch brand. This means that the team is trained to give expert advice regarding Worcester Bosch. However, the engineers can also fit many other boiler brand types. You don’t have to choose a Worcester Bosch boiler to get an installation with Greener Homes. Here are four of the main brands to choose from, but there are many others.

    Worcester Bosch

    Worcester Bosch is a brand with an excellent reputation in the industry. The brand has achieved several Which? Best Buy awards over the years. Its Greenstar I boiler is a bestseller and can be found in more than a million UK homes.


    Vaillant is a premium brand, also with awards from Which? Best Buy. They offer a 5 star boiler range for properties of any size. As a premium brand, it is on the expensive side, so it’s not ideal if you’re on a tight budget. The brand’s ecoTEC exclusive boiler is ideal for larger homes which may have higher outputs.


    Viessmann is a brand made with German engineering. Their boilers are good value for money. The Vitodens 050-W 29kW is the most reliable boiler in their range. It has compact dimensions, low weight and a stainless steel heat exchanger, along with a 10 year warranty. As well as this, it won an award for its energy efficiency.


    The Ideal brand is suitable for customers with different budgets. It has both affordable and premium models of boiler. Its Logic boilers are reliable and award winning. Logic boilers are compact and easy to control with a large digital display and an easily accessible pressure gauge. An Ideal boiler comes with a 2 year warranty that can be extended to 5 years.

    So as you can see, there are many factors to consider when deciding on your gas combi boiler, including your budget and your heating needs. In the UK, the combi boiler is the most popular heating solution for its reliability and efficiency when it comes to fuel and cost.

    Don’t forget, you can always ask a heating engineer for more advice if you’re not sure what boiler to buy for your home.

    Oil v Gas v LPG

    For homes in the UK not connected to the mains gas supply, there needs to be an alternative. One of those alternatives is oil.

    Oil boilers work in s similar way to gas boilers. The only difference is that an oil boiler burns oil instead of gas. That’s why you will need an oil storage tank. You also have to decide how and when your oil is going to be delivered.

    LPG is also known as Liquid Petroleum Gas, and it’s a type of gas, but unlike natural gas it’s not fed into the boiler. Instead, you will need a storage tank to keep the LPG, similar to an oil storage tank. LPG produces less carbon than burning oil, so it’s a more environmentally friendly option. It also has multiple household uses. For example, LPG fuel can also be used for an oven or the hob.

    Additionally, there are renewable alternatives for heating homes. For example, an electric boiler, this is almost 100% efficient due to the fact it hardly wastes any electricity. Instead, the energy is used to heat the water for the central heating. However, electricity is currently more expensive than gas to run.

    Alternatively, a biomass boiler burns pellets, chips and logs of wood instead of burning fossil fuels. However, the downside of a biomass boiler is that it does emit carbon into the atmosphere.

    Meanwhile, an air source heat pump is another option. These work by extracting air from the outside even during winter. The air is then used in conjunction with an exchanger which creates compressed air for added heat.

    Or you could try a ground source heat pump. These are great due to the way they are fitted. With underground temperatures sitting at around 10 degrees plus, they are always able to take this heat in to be used for central heating. The water and antifreeze solutions contained in the heat pump are then circulated around the heat exchanger. Then, it’s transferred into the home for use within a central heating system.

    Finally, solar PV panels can generate renewable electricity for the home by using solar thermal panels to capture the sun’s rays. These rays are then turned into an energy source that heats the water in a hot water cylinder for central heating and also hot water. Most solar panels are installed in the roof.

    If you live in a home that isn’t connected to the gas network, you might want to consider some of these alternatives. The Greener Homes Group team are all specialist heating engineers who can give you advice on alternative heating methods. However, if you are connected to the gas mains, it’s still the most convenient way to get your home heating supply.


    When it comes to choosing a combi boiler for your home, as most of us are on the mains gas network, a gas combi boiler is probably the easiest and best option.

    Firstly, the gas is pumped straight into your home so you have a ready made fuel supply. You don’t need to store your fuel in a tank outside your home, as with oil. This means you don’t have to think about when the fuel will be delivered next, or if you’re running out. If you suspect a gas leak outside your house, or you smell gas, you can alert the National Grid whose responsibility it is to investigate. However, if your oil storage tank leaks, it’s up to you as the owner of the tank to pay for a clear up operation.

    Furthermore, with a combi boiler, when you turn the tap on, you can benefit instantly from hot water. You don’t have to wait for your water to heat up in a tank before you use it. So you can put the shower on or bath and expect hot water immediately.

    As you have seen from this article, there are a variety of options in terms of brand and model when it comes to buying a combi boiler. However, this also means there is something to suit every budget. From budget models to mid range and premium, there are also different outputs to suit different homes. Moreover, if you are looking for a more eco friendly and energy efficient boiler, there are options to suit you too.

    At Greener Homes Group, the aim is to ensure all customers have the most cost efficient boilers possible. Therefore the engineers will endeavour to give you the best advice on your home heating needs. You can even spread the cost of your new boiler in monthly payments with a finance option.

    If you are considering a new boiler, get in touch with Greener Homes today. You can visit the website at greenerhomesgroup.co.uk, fill in some basic details online and you’ll get an initial quote on the same day. Or call 01179 898 230 to talk through your requirements. Services include boiler installations, repairs, replacements, central heating installations and advice to improve energy efficiency. Furthermore, engineers can carry out gas safety inspections and issue landlord safety certificates.