Ullage is the expansion space left above the fuel. It exists because oil expands when it warms and because a tank needs vapour space above the liquid. Nobody explains it at the point of order, and it is the single most common reason a delivery comes up short of what someone expected.
Common domestic sizes, and what each really takes
| Nominal | Takes to 95% | Cost of that fill | Typical setting |
|---|---|---|---|
| 1,000 litres | 950 | GBP 855.10 | Small house, single occupancy |
| 1,200 litres | 1140 | GBP 1,026.11 | The standard domestic tank |
| 1,360 litres | 1292 | GBP 1,162.93 | Common bunded plastic size |
| 2,500 litres | 2375 | GBP 2,137.74 | Farmhouse or a house that fills once a year |
| 3,500 litres | 3325 | GBP 2,992.83 | Large property or shared arrangement |
Reading the gauge honestly
A sight tube is close to linear. A float and clock gauge is not, and it usually reads optimistically in the bottom third. An electronic gauge is only as good as its calibration. Whatever you have, verify it once against a known delivery: order a measured volume into a tank you have noted the reading on, and see what the gauge says afterwards.
Siting and bunding, in brief
- A bunded tank sits inside a second shell able to hold at least 110% of the inner tank. Most new domestic installations are bunded.
- Separation distances from buildings, boundaries and openings are set out in the building control guidance for combustion appliances and fuel storage.
- A tank near a watercourse, a borehole or a drain is treated more strictly. If you are near any of those, take advice before replacing rather than after.
- A registered technician should commission the installation and leave you a record. That record is what an insurer will ask for.
The ordering consequence
If your tank is nominally 2,500 litres and reads a quarter full, the orderable volume is about 1750 litres, which is GBP 1,575.18 at today's reading. Ordering the full 2,500 into that tank means the tanker stops early, and depending on the supplier you may still be charged as if you had taken a full delivery slot.
Primary sources for this page
- Approved Document J, combustion appliances and fuel storage systemsThe building regulations guidance covering domestic oil tank installation and siting in England.
- OFTECTrade body for the UK oil heating industry. Registration scheme for technicians. Cited for installation practice, not for prices.
- DESNZ Quarterly Energy Prices, table 4.1.1Monthly typical retail price of standard grade burning oil, the fuel sold to UK households as kerosene. Priced on the Monday nearest the 15th of the month, for deliveries of up to 1,000 litres, VAT at 5% included. This is the only official UK-wide domestic heating oil price series.
- VAT rates on domestic fuel and powerDomestic heating oil is charged at the reduced rate of 5% on qualifying quantities.