Don't let oil go below 1/4 tank for optimal oil burn
Don’t let the fuel level in your tank fall below ¼ tank
The natural sludge and sediment that is contained in all home heating oil will generally fall to the bottom of your tank. The likelihood of pulling this contamination into your heating system where it can wreak havoc is greatly increased as your fuel level falls below ¼. This is mostly because the contamination will be at a higher concentration as the level of fuel falls. For this reason you should never allow your tank to fall below the ¼ level.