Pros & Cons of Installing an Oil Boiler Re January 28, 2020

Pros & Cons of Installing an Oil Boiler

Oil boiler tank

We’ve talked a lot about gas combi boilers in previous articles – what boiler do I have, how long does it take to install, how much does it cost? But we haven’t looked at alternatives to combi boilers. In this article, we’re going to look at the benefits (and disadvantages) of buying an oil boiler.

How many homes use oil heating?

Around four million households in the U.K aren’t connected to the gas grid. Of these 4 million households a range of alternative heating types are used, including LPG, oil, solid fuels, electricity and solar. 

An estimated 1.1 million homes in the U.K currently run on oil heating. Oil heating is also referred to as a ‘wet’ system because it burns fluid (oil).

Where are oil boilers installed?

You can choose to have your oil boiler installed internally or externally. Most people choose to have them fitted externally because the tanks take up a considerable amount of space that most people can’t afford to give up inside their homes.

If you choose to have your oil boiler fitted externally you can choose to have it fitted underground or overground. The tanks themselves can be a bit of an eyesore if you don’t have somewhere accessible to tuck it away, so have the tank fitted underground is an ideal option if you don’t mind paying for the initial excavation.

Is it more expensive to get oil boilers installed?

As with purchasing any boiler, there are factors involved which can affect the price you can expect to pay from the brand and model of the boiler to the size of the storage tank and whether you have it underground or not.

Tanks range in size from 1,000 litres to 3,500-litre capacities and can cost between £500 – £2000. Alternatively, you may wish to rent the tank from your oil fuel supplier.

Including the cost of the boiler and installation, prices vary between £2,500 – £4,500 depending on the job. As there is more variation in the installation between a gas combi boiler and an oil combi boiler it’s more difficult to quote on.

Labour costs will vary between £400 – £800 and the cost of the boiler between £2,000 – £3000.

A gas combi boiler from WarmZilla starts at £1499 including the boiler and installation, so an oil boiler installation is significantly more expensive.

What kind of oil is used in oil boilers?

There are predominantly two types of oil currently used as fuel in domestic oil boilers – 28sec and 35sec. They get the names 28 and 35sec from the length of time it takes for a ball bearing to pass-through a specific amount of oil (we’re just not sure how much), 35sec is obviously thicker as it takes longer for the ball bearing to pass through.

28sec is the most common fuel used for heating domestic homes. 28sec is more commonly referred to as kerosene, whereas 35sec oil is more commonly referred to as gas oil or red diesel. 35sec is more commonly used for commercial and agricultural uses.

In addition to the two most common types of oil there is also kleenburn kerosene and furnace fuel. Kleenburn kerosene is a lot cleaner burning fuel than standard kerosene, it costs a bit more but it’s a lot better for the environment as it produces less carbon. Furnace fuel is usually used in municipal buildings like schools and colleges.

Is oil a cheaper fuel to use?

Domestic oil prices are tied to the price of crude oil, so they can fluctuate with demand, availability and even political situations. Oil prices are also affected by demand, so the prices will increase during winter.

In terms of how oil prices compare against other fuel types – it’s more expensive than gas (per kWh) and LPG but cheaper than other alternative fuel sources on the market such as biomass and electric.

Based on heating a standard 3 bedroom home, electricity is the most expensive alternative fuel source at £1500 per year, followed by oil at £1400 compared with gas at £700 – £1400.

An oil boiler can be combined with solar thermal heating or solid fuel to lower the cost.

Is oil better for the environment than a gas boiler?

Regulations introduced in 2007 meant that all condensing oil boilers must have an energy efficiency rating of 86%+. Most modern oil boilers attain an energy efficiency rating of 92%+.

Oil boilers are worse for the environment than gas boilers, 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. If you want something better for the environment, then you might look at heat pumps but unless your home is very well insulated you won’t get the benefit.

What are the benefits of oil boilers?

  • More space: By having an external oil boiler you can free up space in the home that would be taken up by a combi boiler or internal oil boiler.
  • Isolated location: If you live off the mains gas grid then oil can be an excellent heating solution as it’s affordable and accessible.
  • Servicing & boiler repairs: If your oil boiler is located outside then it’s less disruptive to your daily life as your boiler can be fixed, replaced and refuelled without your home being turned into a workplace.
  • Less noise: Even modern A-rated condensing boilers create a certain level of background noise, you may not even be aware of it unless you turn the boiler off. If you have an older boiler the noise will be much more noticeable. An external oil boiler won’t be a source of noise pollution.
  • Carbon monoxide: Although carbon monoxide poisoning has become much rarer due to improved safety measures, there is still a chance of a leak causing symptoms. Having your boiler located outside negates the risk.
  • Leaks: Having an oil boiler located outside means that should the boiler leak or malfunction, there is less chance of it causing damage to your property, compared to a gas combi boiler located in your airing cupboard leaking.
  • External heating: If your oil boiler is located in an outbuilding, garage or shed it will serve to partially heat the building from heat loss.

What are the negatives of oil boilers?

  • Limited space: If you have limited outdoor space for a large oil tank then perhaps an oil boiler isn’t the right option for you. The tank also needs to be easily accessible for refilling otherwise you may have to install an expensive pipe run to get to the tank.
  • Price fluctuation: The price of oil can fluctuate depending on the market, this is also true of other fuel sources but oil is more volatile as there are more factors that affect the price and there is no official regulation.
  • Supply: Because your supply needs to be physically delivered there is the chance of delays, human error in an order, traffic or forgetting to order in time. Newer oil tanks have sensors which can automatically place an order when you get down to a certain level.
  • Cost of installation: Having an oil boiler installed for the first time is a lot more expensive than the gas boiler equivalent.
  • Environment: Oil boilers are twice as bad for the environment as gas boilers in terms of carbon dioxide production.
  • Tank location: An oil storage tank can be an eyesore if it isn’t placed underground or tucked out of the way.
  • Flow rate: The flow rate of an oil boiler is usually lower than that of a gas boiler.
  • Wear and tear: Due to the boiler and tank being located externally there is the damage that comes with weather exposure, cold, frost and rain can cause components to rust or malfunction.

Top 3 best oil boiler brands 2023

1. Worcester Bosch

Worcester Bosch is the leading boiler manufacturer in the gas boiler market, and that includes the oil boiler market too. To sum it up, Worcester Bosch offers an extensive range of boilers with a range of different fuels and is suitable for properties of all sizes.

Worcester Bosch is known as being the “Rolls-Royce of the heating industry”. It is at the premium-end, but you’ll get excellent build quality combined with elegant design. It’s a brand you can rely on.

Surely it’s no surprise that Worcester Bosch came first according to Which? Best Boiler Brand survey 2021.

During the survey, 8,001 members of the public who’ve bought a boiler in the past six years were asked to rate their Worcester Bosch oil boilers based on reliability and how likely they were to recommend Worcester Bosch to friends and family.

Which? asked 153 Which? Trusted Traders how they felt about the build quality, the ease of fixing and servicing Worcester Bosch boilers and how easy it is to get hold of boiler spare parts.

Here’s the score: 

Worcester Bosch overall score


Reliability Score

5 stars

Brand customer score

4 stars

Brand engineer score

3 stars

Worcester Bosch prides itself on its excellent customer service. It has a TrustPilot score of 4.6/5.

Worcester Bosch oil boiler warranty

Worcester Bosch oil boiler warranty is between 2-7 years, depending on the boiler model. 

Worcester Bosch oil boiler range

No matter what your house size is, Worcester Bosch has got you covered. The Worcester Bosch oil boiler comes in the following models;

  • Greenstar Danesmoor
  • Greenstar Heatslave II (best selling model)
  • Greenstar Utility

Available as a combi, system and regular oil boiler.

Worcester Bosch oil boiler cost

The cost varies depending on the model and oil boiler type. It could start from £2,600 for an oil combi boiler, £1,860 for an oil system boiler and £1,700 for an oil conventional boiler**. These boiler prices don’t include installation though, so be sure to factor that in.

2. Grant

Grant has over four decades of boiler manufacturing experience. They’re known for quality and reliability, offering a range of boilers that can be easily installed and maintained.

The entire Grant oil boiler range was awarded a Which? Best Buy Awards in 2017, 2018 and 2019. Which? Recognises Grant boilers as one of the best oil boiler brands in the market and described it as a “reliable” brand.

Grant’s rating: 

Grant overall score


Reliability Score

4 stars

Brand customer score

3 stars

Brand engineer score

5 stars

Grant has an astonishing score on TrustPilot (4.5), which indicates that their customer service is brilliant, and their customers are happy with the product. 

Grant oil boiler warranty

Nothing says that the boiler is built to last more than a long warranty and that’s what you get when you invest in a Grant boiler. 

The boiler range warranty is 5 years. (10-year guarantee when installed by a G1 Installer, if you bought a Vortex Blue) – your driving license will expire before your boiler warranty does!

Grant oil boiler range

Grant designed a wide range of products which means you’re guaranteed to find the right one for your home. 

The range includes:

  • VortexBlue (best selling model) 
  • Vortex Pro 
  • Vortex Eco 

The award-winning Vortex and VortexBlue oil-fired condensing boilers are available in internal, external, combination, boiler house and wall-hung models, all of which are endorsed by the Energy Saving Trust.

Grant oil boiler cost

To give you a rough idea, the Grant combi oil boiler prices start from £2,220, while the system oil boiler range starts from £1,610, and Grant regular boilers price range starts at £1,240.**

3. WarmFlow

WarmFlow is the most efficient oil boiler. Their combi oil boiler saves up to 5ltrs of fuel per week because it is the only AA rated oil combi boiler in the market (no other brand has an AA rated combi oil boiler). Sounds too good to be true! 

WarmFlow has over five decades of boiler manufacturing experience. It uses a unique patented stainless steel heat exchanger alongside the latest Riello burner.

Although WarmFlow isn’t featured in the Which? Best Boiler survey, it doesn’t affect its reliability. It has a 4.3 TrustPilot score which means that their customers are happy with the boilers and customer service.

WarmFlow oil boiler warranty

Warmflow offers a 5-year warranty for both parts and labours if installed by a Warmflow Connect approved installer.

WarmFlow oil boiler range

The WarmFlow Agentis oil boiler comes in combi, system and regular oil boiler range. This includes internal and external boilers. It also includes boiler houses and professional boiler systems.

Additionally, they also produce a professional range which is the only oil boiler to include a factory fitted magnetic filter saving installation time and money. 

WarmFlow oil boiler cost

WarmFlow oil boiler price range starts from £1,970 for an oil combi boiler, £1,370 for an oil system boiler and from £1,170 for regular oil boilers.**

Are oil boilers going to be banned?

According to the government’s Clean Growth Strategy (2018), the installation of high carbon fossil fuel heating in new and existing homes off the gas grid is to be phased out.

This means that any new builds have to be built with low-carbon heating like heat pumps. This does not affect homes with existing oil heating and the government has yet to confirm any plans for regulations on existing homes.

In much the same way that studies are currently being conducted on gas alternatives like hydrogen blends as fuel for gas boilers, research is underway on a low-carbon replacement for oil that would work with current oil boilers.

Who should I get to install an oil boiler?

Whether you choose to a local company, energy supplier or an online company like WarmZilla to install your boiler you should always check that the installer is OFTEC registered, this is the oil certification equivalent to Gas Safe registered for gas boiler installations.

Unlike gas boilers, however, it is not a legal requirement to be OFTEC registered to fit an oil boiler, it is a ‘competent person scheme’ meaning you can buy with more confidence. OFTEC stands for Oil Firing Technical Association.

Any OFTEC registered installer has completed an approved training course and passed an assessment. They are periodically reassessed to ensure they are maintaining standards and are up-to-date with current best practices.

Upon completion of your oil boiler installation and OFTEC registered installer will provide you with an official certificate to confirm that the work done meets industry standards. You don’t need to get the work checked by your local authority.

All WarmZilla engineers are OFTEC registered.

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