Propane Run Time and Refill Interval

The energy is the gallons times the fuel's heat content, and dividing by the connected load gives the continuous-firing hours -- which is a floor, not an estimate, and is the number people compute. THE DUTY CYCLE IS WHAT MAKES IT REAL. Heating equipment cycles: a furnace sized for design conditions runs a fraction of the time in average weather, so a continuous-firing figure can understate tank life by a factor of three in October and be roughly right in a January cold snap. DEGREE DAYS ARE THE HONEST METHOD and they are entered here from the customer's own record. Consumption is very nearly proportional to heating degree days, so last year's gallons-per-degree-day from the delivery history predicts this year better than any appliance rating can -- and it automatically includes the water heater, the range and everything else on the tank that nobody thought to add up. Both estimates are reported side by side, because the ratio between them is itself the finding: a history that runs well ahead of the duty-cycle estimate means something is on the tank that was not in the load. THE SCHEDULE RUNS TO THE TRIGGER, NOT TO EMPTY. Deliveries are commonly triggered around a quarter to a third full, and the run time to the trigger is the number a schedule is built on. Running a tank to empty means purging and leak-testing before it can be refilled, and the last of the liquid was struggling to vaporize anyway -- vaporization is limited by wetted surface rather than by volume, which is a second reason the trigger sits high. This computes run time from an entered load, duty cycle and history. It does not predict the duty cycle or the weather, model the building's heat loss (the degree-day energy calculation does that from a building UA), account for domestic hot water, cooking or other non-weather-sensitive load except through an entered history, schedule deliveries or account for route and minimum-delivery practice, or evaluate whether the tank can vaporize at the rate the load asks for. NFPA 58, the adopted fuel gas code, the supplier's delivery practice, and the appliance manufacturers govern.

energy = gallons x heat content; continuous run time = energy / connected load; the realistic figure divides by the duty cycle; the schedule runs to the delivery trigger; and the degree-day estimate is gallons-per-degree-day times degree days per day.

Run time from an entered load, duty cycle and delivery history. Consumption is very nearly proportional to heating degree days, and the customer's own record is the honest input.

Divisions on an entered energy content.

Estimate. AHJ and licensed professional govern.

Field names used by the API: water_capacity_gal, fill_limit_pct, current_gauge_pct, trigger_pct, connected_load_btuh, duty_cycle, btu_per_gal, gallons_per_hdd, hdd_per_day, usable_gal, usable_mmbtu, continuous_hours, continuous_days, realistic_days, gallons_per_day, gallons_to_trigger, days_to_trigger, hdd_days_to_trigger

• The duty cycle is entered it is not predicted from the weather or the equipmentthe service history
• Degree-day history is the honest input it beats any appliance rating and includes the whole tank loadthe delivery record
• The trigger, not empty the last of the tank may not vaporize at the rate the load asksthe supplier's delivery practice