Heating oil tank sizes

If you're installing a new oil storage tank, whether it's a replacement for an old one or for a new build, chances are the conversation will turn to what size oil tank you need.

Oil storage tanks come in all shapes and sizes and can be plastic or metal, single-skinned or double-skinned, and designed for domestic and commercial buildings. So, deciding which type and size of oil tank you need can be a bit of a conundrum. Let's bring some clarity to the situation.

About your oil tank (UK regulations & standards)

There are different oil storage tanks to suit different requirements, but the first thing to mention is that you need to make sure it has been manufactured in accordance with OFTEC standards:

• OFS T100 for plastic tanks.
• OFS T200 for steel tanks.

You may also find it is mandatory to have a bunded oil tank (link) (double-skinned) if it is going to be sited near any controlled water system, such as a river or a well.

Generally, oil tanks last for around 20 years, as long as they serviced annually by an OFTEC registered engineer. They will be able to advise you if you need to replace your oil tank. Your oil supplier may also notify you of any issues, such as a leaking value, and may refuse delivery if there are any safety concerns.

How to choose the right oil tank size

Before deciding on the size of oil tank you need, consider the following:

1. The size of the property

It's not just square footage - it's how many rooms need heating.

A good rule of thumb is

• Allow around 500 litres per bedroom.
• Add 500 litres for the living room and other regularly used spaces.

Examples:

• 1 - bedroom house = minimum 500 litre oil tank.
• 4 - bedroom house = minimum 2,000 litre oil tank.

This aligns with most suppliers' minimum delivery volume of 500 litres.

2. Number of people living the property

This is often linked to bedrooms, but not always.

• A couple sharing one bedroom may still need more than 500 litres.
• Children sharing rooms may increase overall usage.

If in doubt, opt for a slightly larger tank (if space allows).

3. How much oil you use

This can be difficult to estimate until you've lived in the property for a full year, as oil usage varies significantly between summer and winter.

If possible:

• Ask previous owners about usage.
• Review past delivery records.

4. Available space for your oil tank

At many properties, the available space will dictate the size of tank you can install.

Most domestic oil tanks in the UK are located outside, but they can also be installed:

• Underground.
• In a building or basement.

Oil tank installation and placement guidelines

When installing or replacing an oil tank, make sure:

• It is not near any fire or heat source.
• It is at least 1.8m from buildings or eaves.
• It is at least 1.8m from openings (windows/doors in fire-related buildings).
• It is at least 600mm from trees or hedges.
• It is at least 760mm from boundaries (e.g. fences).
• There is sufficient access for oil deliveries.
• Engineers have access for servicing and maintenance.
• It is protected from extreme weather.
• It sits on a strong, level base (e.g. concrete)

What size oil tank is most common?

Most domestic properties in the UK have oil tanks between 1,000 litres and 2,500 litres.

One important point - don't choose a bigger tank just because you can.

If you are only using 500 - 1,000 litres per month, installing a much larger tank may:

• Increase servicing costs.
• Cause oil to sit for too long.
• Lead to sludge or contamination entering your heating system.

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