When to order heating oil
Order when the gauge touches a quarter tank. Not because a quarter is a lot of oil, but because it is just enough to cover the time between placing the order and hearing the truck in the driveway. Here is the math behind the rule, what a run-out really costs, and how COD and automatic delivery compare.
The quarter-tank rule
Winter deliveries commonly take 2 to 5 business days, and a cold snap stretches every dealer's routes at exactly the moment every tank in town drains fastest. A quarter tank is your buffer against that queue.
The math is not comforting. On the common 275, gauge 1/4 is about 58 gallons, so call the usable buffer 50. At 8 gallons a day, a realistic cold snap burn rate, 50 gallons is under a week of heat. If the delivery window is running 5 business days, a quarter tank is not early, it is on time.
What a run-out really costs
Running dry is not just a cold night. As the level falls, the pickup starts drawing from the bottom of the tank where years of sludge settle, and that sludge clogs the filter. The burner locks out, and getting it running again usually needs a technician to bleed the line, often with a service charge on top of the emergency delivery.
COD or automatic delivery
COD (will-call) lets you shop price per gallon and order from whoever quotes best that week. In exchange, you carry the run-out risk: watching the gauge, sticking the tank, and ordering on time are entirely on you.
Automatic delivery hands that job to the dealer, who plans your fills from your K-factor and the weather. The run-out risk shifts to the dealer, and so does the gauge watching. The honest trade: you give up per-delivery price shopping, and per-gallon prices on automatic are sometimes higher than the best COD quote.
The summer fill
Keeping a steel tank full through summer reduces condensation on the tank walls, because there is less bare steel above the oil line for moisture to collect on. That is the dependable argument for a summer fill. Price is the less dependable one: seasonal dips exist some years, but they are not guaranteed.
Common questions
How many gallons a day does a house burn in winter?
It depends on the house and the weather. The worked math above uses 8 gallons a day, a realistic cold snap rate for a typical oil-heated home; mild fall and spring days burn far less. Two delivery slips give you your real number: see the heating oil usage calculator.
Is heating oil cheaper in summer?
Some years yes, some years no; seasonal dips are real but not guaranteed. The dependable reason for a summer fill is the tank itself: a full steel tank has less bare wall for condensation, which is what feeds corrosion and water at the bottom of the tank.
I already ran out. What do I do right now?
Call your dealer and say it is a run-out, so they schedule both the delivery and the restart. Expect a possible service charge. Leave the burner and its reset button alone: restarting after a run-out usually means bleeding the line, and that is technician work.