What size oil tank do I need?

Common sizes

Tanks are sold by nominal capacity, which Approved Document J says is usually 95% of the volume needed to fill the tank to the brim. One manufacturer's bunded range shows the usual spread for homes. The last column is simple arithmetic: the space up to the nominal capacity if you reorder when the tank is about a quarter full.

Start from what you use in a year

Add up the litres on your last 12 months of delivery notes. Then think in deliveries. A home using 2,000 litres a year with a 1,225 litre tank can take about 900 litres at a time, so it needs two or three deliveries a year. The same home with a 2,500 litre tank could manage with one or two. Our guide to how long 1,000 litres lasts helps if you have no records.

A bigger tank lets you buy in larger amounts. On Fueltool's figures today, 1,000 litres works out 1.4p a litre less than 500 litres. It also gives you a buffer if winter deliveries slow down.

Leave room for a delivery

Orders on Fueltool start at 500 litres. A 1,000 litre tank can take a 500 litre order once it is down to about a quarter, but it cannot take 1,000 litres in one go. If you often find yourself ordering small amounts in a hurry, the tank may be too small for the house. See minimum orders for more.

Bunded or single skin

A bunded tank is a tank inside a second outer tank, the bund, which must hold at least 110% of the inner tank so a leak is caught. A single-skin tank has no outer layer and costs less, but it is only acceptable in some places:

• Wales: every new or replacement home tank installed after 15 March 2016 must have secondary containment, so a single-skin tank on its own is out.
• England: guidance calls for a bund above 2,500 litres, or where a leak could reach water, a drain or a borehole, or the vent cannot be seen from the fill point.
• Scotland: tanks over 2,500 litres must have 110% secondary containment, and smaller ones need a bund if the building standards risk assessment finds a hazard.
• Northern Ireland: the regulations require a bund above 2,500 litres or where similar pollution risks apply.

Space, siting and the tanker

A bigger tank needs a bigger base, and in England the guidance puts it at least 1.8 m from buildings and 760 mm from a boundary unless fire protection is added, with a hard base extending 300 mm beyond the tank. Above 3,500 litres, a home in England falls under the oil storage regulations that cover businesses. The fill point also has to be reachable by the tanker's hose, which our guide to tanker access explains. An OFTEC-registered installer can weigh all of this up on site. When the new tank is in, compare prices for your postcode.