Bottom or top outlet tank – which to choose?

Posted 4th January 2019

The safest oil storage

Double skin, bunded oil tanks are the safest way to store heating oil.  This is because the secondary containment prevents spills and leaks 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 to flow through the supply pipe to the appliance.  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.  On an oil storage tank with a top outlet, oil is drawn out of the top of the tank and along the pipe to the appliance, so there is no need to have a hole in the bottom of the tank.

By 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 that have pumps.  AGAs and vaporising burners used in some range cookers would need an oil lift pump installed to work correctly, for instance.  95% of pressure jet boilers will work with a top outlet tank but we can advise you on that.

To operate efficiently, an oil de-aerator, such as a ‘Tiger Loop‘ or ‘GOK’ will be required.  As the oil supply will be under slight negative pressure, small 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.
• 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 bund 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

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