When your oil tank needs replacing, what size tank do you need to buy?
The first thing to consider is whether the present bunded oil tank size is still relevant. Some old steel tanks that are being replaced are much larger than is generally required. Back in the day, oil was much cheaper, so filling a large tank was not much of an issue; houses were less insulated and boilers less efficient, so more fuel was used just keeping warm. A better way of looking at the situation is to ask yourself how much oil you actually use during the course of a year. If you have an old 600-gallon metal tank (2700 litres) and use 1500 litres a year, this is probably too big! Rather than blindly buying a tank of a similar size – and remember bunded tanks are physically much larger than single skinned tanks, it might be better to consider a tank more 1800 litres – 2000 litres but don’t go much smaller. This would mean that you could comfortably accommodate your 1500 litres per year fill and also ensure that you do not have to run the tank right down to do so. In recent bad winters there has been a problem with tankers actually being able to go on the roads to make deliveries but also restricted availability of oil itself to the fuel companies based upon increased demand. The worst thing would be for you to run out and not be able to get any oil delivered for an extended period as your tank is too small.
Often these days people who have Aga ranges are converting them to electric and changing the oil tank is the catalyst to do this. If you are going from feeding a thirsty Aga and a boiler to a boiler only, this may mean that a smaller tank is more sensible. There are also strict regulations in place with regard to siting oil tanks and so a less intrusive oil tank may well be much easier to live with than one that is so large that it becomes a feature in its own right.
You should also have a think about the size of your home. If you live in a small cottage, a tank of around 1200 litres may be quite adequate but if two of you are rattling around a four-bedroom house, you ought to bear in mind the fact that although you may not use the heating much yourselves, you may decide to sell the house and a big family may move in who do not want to be arranging a fuel delivery every six weeks to fill their small tank.
A quick rule of thumb is a 1000 – 1250 litre tank for a 2-bedroom house; 1250 – 1800 litres for a 3-bedroom property and between 2000 and 2500 litres if your home has 4 or 5 bedrooms. If you have a big house with multiple appliances feeding from the tank, you may consider a 3500-litre tank but be mindful that beyond 3500 litres, the commercial regulations will come into force and these are much more onerous than the domestic rules with regard to positioning of the tank. We would never recommend a tank of below 1000 litres as the minimum fuel delivery will be 500 litres and anything less than 1000 litres will be risking a fuel run-out.
If you have any doubts at all about how big your tank should be, ask your boiler engineer. He will be best placed to consider the efficiency of your boiler and to point you in the right direction.