Bottom or top outlet tank – which to choose?

The safest oil storage

Bunded oil tanks, which are double skin with a top outlet, are the safest way to store heating oil.  The bund or secondary containment prevents spills and leaks from the tank from affecting the environment.  There is, however, still a risk of leakage in the pipework.  What’s the best solution? There are options for both bottom outlet and top outlet tanks.

Bottom outlet tank

A bottom outlet kit uses gravity to allow the oil flow through the appliance's oil supply pipe.  That’s great until you have a leak or weep in the outlet valve or any of the pipework.  Unfortunately, they can go undetected for years, especially if underground.  Using a top outlet, fuel oil is drawn out from the tank and then through the pipe to the appliance.  Therefore, no need to have a hole in the bottom of the tank.

Using an oil tank with a top outlet and an anti-siphon valve, when the boiler demands oil, the anti-siphon valve will open and allow the oil to flow. In the event of a damaged or leaking pipe or joint, no oil will flow from the tank, saving oil loss to the environment.

Top outlet tank

Top outlet tank fitting kits will only work with boilers with pumps capable of being configured for a ‘2-pipe system’.  AGAs and vaporising burners used in some range cookers need an oil lift pump installed to work correctly.  95% of pressure jet boilers will work with a top outlet tank, but we can advise you on that.

An oil de-aerator, such as a ‘Tiger Loop‘ or ‘GOK’, will be required to operate efficiently.  As the oil supply will be under slight negative pressure, tiny bubbles of air can form in the pipework (similar to opening a bottle of fizzy drink).  In short, the de-aerator will allow this air to bleed away and the boiler to run efficiently. 

The advantages of the top outlet system:

  • Environmentally safest, no chance of a continuous undetected oil pipe leak emptying the tank.
  • Works well with existing pipework or new installations.
  • De-aerator oil loop improves boiler efficiency.
  • A Floating oil pick-up supplies the cleanest fuel to the boiler.
  • No bottom outlet reduces the change of the valve and filter leaking.
  • The top outlet valve will be within the bunded secondary containment for the environmentally safest installation.
  • They are compatible with plastic bunded oil tanks and plastic single skin oil tanks.
  • Available on conveniently sized tanks 1000 litre to 1400 litre tanks

Here is a link to the OFTEC website ‘Home Guide to Domestic Fuel Storage up to 3500L’

If you would like more information on top outlet tanks for domestic heating oil, please call us on 01722 714514.