Keep-full (automatic) customers trust you to fill their tank before it runs low — without them calling. Get it right and you deliver full loads efficiently; get it wrong and you either make small, expensive deliveries or, worse, a customer runs out in a cold snap.
Degree-day forecasting is the standard way to get it right. Here is how it works in practice.
1. Heating degree days in one paragraph
A heating degree day (HDD) measures how cold a day was. In the US it is usually calculated against 65°F: a day with an average temperature of 35°F counts as 30 HDD; a day averaging 65°F or warmer counts as 0. Colder weather means more degree days — and more propane burned.
2. The K-factor: how fast each tank burns
A tank’s K-factor is the number of degree days it takes to burn one gallon. You work it out from the tank’s own history:
K-factor = degree days between two fills ÷ gallons delivered at the second fill.
For example, if 1,200 degree days passed between fills and you delivered 300 gallons, the K-factor is 4 — the tank burns a gallon every 4 degree days. Recalculate after every fill; the number settles down after a few deliveries.
Many homes also use propane for water heating or cooking all year. That base load doesn’t depend on the weather, so it is usually estimated as gallons per day and added on top.
3. Forecast each tank’s level
- Start from the gallons in the tank after the last fill.
- Each day, subtract degree days ÷ K-factor (plus any daily base load).
- Use the weather forecast to project forward and find the day the tank reaches your reorder point.
4. Choose your fill window
Tanks are normally filled to about 80% of capacity to leave room for expansion. Many distributors schedule a keep-full delivery when a tank is forecast to fall to around 25–30%. That leaves a safety margin for a forecast that turns out colder than expected, while still delivering a worthwhile number of gallons.
5. Build routes from the forecast
- Group tanks that are due in the same window by area, so each truck delivers full loads.
- Pull deliveries forward for tanks that are close to the reorder point when a cold snap is coming.
- Slot will-call orders in alongside the keep-full deliveries on the same routes.
6. Record metered gallons and safety at every stop
The gallons delivered at the meter drive the invoice and update the K-factor — so record them at the tank, not from an estimate. Record the safety work with the delivery too: leak checks, out-of-gas procedures and anything unusual about the installation. That record matters as much as the invoice.
7. Watch the outliers
A tank that suddenly needs much more or much less propane than its K-factor predicts is telling you something — a new appliance, an empty house, or a leak. Flag those for a call or a check.
Quick checklist
- Daily heating degree days for each delivery area
- K-factor per tank, updated after every fill
- Base load added for year-round use
- Reorder point set around 25–30%; tanks filled to about 80%
- Routes built from tanks due in the same window, plus will-calls
- Metered gallons and safety checks recorded at every stop
Run it in one system
Delivery Genius is propane delivery software that does this for you — routes on real roads, a driver app on any phone, invoicing at the door and AI that proposes before anything changes.