Photograph of Carbery, Diamond and Harlequin Oil Tanks on an orange background

Why You Really Are #BetterOffBunded

The arrival of Bunded Tanks is almost certainly the single biggest innovation within the fuel storage tank sector in recent decades. Today, a legal requirement at almost all aboveground oil storage installations, more Bunded Heating Oil Tanks are now fitted in Great Britain and Ireland than any other tank type. But what is a Bunded Tank? Why are they required? And when should they be installed?

What is a Bunded Tank?

A Bunded Tank is simply a tank within a tank. The inner tank stores fuel, whilst the outer tank can contain at least 110% of the volume of the inner tank. So, in the unlikely event of a spill arising from the inner tank, spilt fuel is contained safely in the outer tank or bund. 

Why are Bunded Tanks so important?

More efficient than gas, less polluting than solid fuel and more affordable than LPG, when stored securely, sensibly and safely, Heating Oil is a responsible choice for domestic space and water heating. However, even a small spill of oil can have a devastating impact upon the environment. When compared with old-fashioned Single Skin Heating Oil Tanks, Bunded Tanks are proven to significantly reduce the frequency and seriousness of oil-related pollution incidents. 

Where should Bunded Tanks be installed?

The simple answer is a Bunded Tank should be fitted almost anywhere there is a requirement to store fuel oil aboveground. At most fuel oil storage installations, if you’re fitting anything other than a Bunded Tank, you’re almost certainly fitting the wrong tank, in the wrong place. 

How can I tell if I require a Bunded Tank? 

There are only a small number of instances where storing oil aboveground in anything other than a Bunded Tank remains permissible. If you can answer 'Yes', 'Maybe', 'Possibly' or 'Not Sure' to any of the questions below, then a Bunded Tank must be fitted when replacing or installing a Heating Oil Tank:

  • Is the total installed storage capacity on-site greater than 2,500 litres at single family dwellings, or greater than 200 litres at commercial, industrial or institutional premises?
  • Will the Oil Tank be positioned within 10 metres of controlled water? Controlled water includes streams, lakes, loughs, lochs, ponds, canals, coastal waters, estuaries and groundwater, as well all water which is below the surface of the ground in the saturation zone, and in direct contact with the ground or subsoil;
  • In the event of a spill from the tank, could spilt fuel reach a drain or manhole cover?
  • Is the Oil Tank located within 50 metres of a well, borehole, aquifer or spring?
  • Will the Oil Tank be positioned over hard or hard surfaced ground that would allow a spill to reach controlled water?
  • Is the Oil Tank located in a position where the vent pipe is not visible from the fill point?
  • Is the Oil Tank located in a Groundwater Special Protection Zone?
  • Are there any other site-specific risks or hazards, including but not limited to ditches (whether wet or dry), septic tanks, effluent treatment systems, soakaways or gullies?
  • Is the Oil Tank being installed in Wales, The Isle of Man or Channel Islands?

Photograph of Carbery 1000SB Superslim Slimline Bunded Oil Tank, Carbery 1350VB Vertical Bunded Oil Tank and Harlequin 1400ITE Bunded Oil Tank 

So, what happens if I don’t fit a Bunded Tank?

Fitting a Single Skin Tank where a Bunded Tank is required, is a serious offence. You could face the prospect of a fine and legal expenses. In the event of a spill – however caused – you could also incur significant clean-up and remediation costs, additional legal expenses, together with a victim surcharge. And of course, fitting a Single Skin Tank where a Bunded Tank is required, will likely invalidate any warranty supplied. 

Anything else I should consider when installing a new Heating Oil Tank?


  • Before completing any installation, an Environmental and Fire Safety Risk Assessment must be completed. This should be undertaken only by a suitably competent person – again, we’d recommend an OFTEC Registered Technician. Click here to find your local technician;
  • Heating Oil Tanks are not suitable for DIY installation. They should only be installed by a suitably competent person e.g. an installer registered with The Oil Firing Technical Association (OFTEC);
  • To further reduce the risk of spills, choose a Top Outlet Bunded Heating Oil Tank. Unlike Bottom Outlet Oil Tanks, Top Outlet Tanks draw fuel from above the maximum level of oil inside the tank – significantly reducing the likelihood of an environmental pollution incident, should the oil supply line become detached. Top Outlet Tanks are already the norm in many countries worldwide;
  • Choose a Bunded Tank and in most instances you’ll benefit from a conditional, 10 year manufacturer’s warranty. By contrast, choose a Single Skin Heating Oil Tank and you’ll likely benefit from just a 2 year warranty, albeit Carbery does offer a 5 year warranty on its Single Skin models;
  • When choosing a Bunded Tank, always ensure it has been independently tested in accordance with OFS T100 and is licensed by The Oil Firing Technical Association (OFTEC). As a responsible supplier, all our Domestic Heating Oil Tanks are compliant with OFS T100 and are OFTEC approved. 

Queries? Questions?

If you’ve any queries or questions, you’re very welcome to get in touch with us. 

We’re Fuel Tank Store. We’re a leading supplier of Heating Oil Tanks to customers across the United Kingdom, Republic of Ireland, Channel Islands and Isle of Man. Our Customer Support Team is available to answer your queries and questions from 9am to 5pm weekdays. You can call us in the UK on 01789 632 151 and in the Republic of Ireland on 01 526 8642. You can also e-mail hello@fueltank.store, or why not complete our Online Contact Form?