Propane Usage Calculator: How Long Will a Propane Tank Last?

How to use the propane usage calculator

1. Pick your tank. Grill and heater cylinders are named for the pounds of propane they hold (20, 30, 40, or 100 lb). Home tanks go by their water capacity in gallons.
2. Enter the gauge reading. 80% is full, because tanks are filled to 80% of capacity. No percent gauge? Enter 80 for a full cylinder, 40 for about half full.
3. Enter the appliance's input rating in BTU/h. The International Fuel Gas Code requires it on every appliance's label, notes the International Code Council (ICC); the estimates table below is a fallback.
4. Enter the hours it runs a day, up to 24. Count the hours the burner is lit, not the hours the appliance is switched on.
5. Add a second appliance on the same tank, such as a water heater next to a furnace, or leave both of its fields at 0.

Propane tank sizes and what they hold

Cylinder gallons are Manchester Tank's ratings; home tanks hold 80% of their water capacity. Supplier Ferrellgas lists the same 4.7 gallons for a 20 lb tank and 400 gallons for a 500 gallon tank filled to 80%.

How long does a 20 lb propane tank last?

Hours of burn from a full cylinder at a steady rating; a lower setting stretches them.

A maker's figure backs up the math: Mi-T-M lists 8.5 operating hours on a 20 lb cylinder for its MH-0042-PM11 patio heater, rated 50,000 BTU on high. The calculator gives 8.6.

How long does a 500 gallon propane tank last?

Days a full tank lasts on a 100,000 BTU/h furnace, the code's estimate for a single-family warm-air furnace:

Goodman's 96% AFUE gas furnace line runs from 40,000 to 120,000 BTU/h of input and converts to propane with an LP kit. What each step burns:

Use the input rating, not the heat output a spec sheet also lists. Choosing a furnace? The furnace size calculator estimates the heat a home needs and the input to look for.

Appliance input ratings when you can't find the label

These approximate inputs come from Annex A of the National Fuel Gas Code (ANSI Z223.1), as reprinted in an ICC gas pipe sizing guide: estimates "for initial design purposes," not your appliance's rating.

Why 80% means full

The Propane Education & Research Council (PERC) says propane cylinders "should only be filled to 80 percent of the tank's capacity," because "filling to less than 100 percent capacity allows for liquid propane expansion, which might occur on hot days." Ferrellgas fills home tanks to 80% of their water capacity and notes the gauge "should not read 100 percent because 80 percent is considered full." So 40% on the gauge is half a full fill.

Portable cylinders need an overfill prevention device (OPD), required by law, PERC says; most have a triangular handwheel marked "OPD."

Propane safety

• Leave installs and repairs to a pro. PERC: "Only qualified service technicians have the proper training to install, service, maintain, and repair appliances," and one should inspect them once a year.
• Keep CO alarms on every level. PERC advises a UL-listed carbon monoxide detector on each level of the home; the U.S. Consumer Product Safety Commission (CPSC) adds alarms outside sleeping areas, meeting UL 2034. If one sounds, CPSC says to move outside to fresh air and call 911.
• Grills and patio heaters stay outdoors. PERC says outdoor propane heaters "should never be used indoors or in enclosed spaces," and that using a barbecue grill indoors for cooking or heating "is never acceptable." Store cylinders upright and outside, never in a basement, garage, shed, or tent.
• Don't let a home tank run dry. PERC says a qualified professional must then check the system for leaks when the gas is turned back on. Check the gauge periodically and plan deliveries with your supplier.
• If you smell gas, PERC's first step is to get everyone out of the building or area right away.

Tips and common mistakes

• Treating the rating as steady use. The rating is full fire. Mi-T-M's heater is rated 22,500 BTU on low and 50,000 on high, so on low a tank lasts more than twice as long.
• Forgetting the other appliances. Enter the two biggest users. For more, add up the extras' BTU per day and enter the total as the second appliance at 1 hour a day.
• Comparing with electric heat. For a space heater, the electricity cost calculator shows the kWh it uses.
• Ignoring backup heat. A wood stove that carries part of the load cuts furnace hours; the firewood calculator tells you how many cords are in your stack.
• Skipping the insulation. Less heat loss means fewer burner hours; the attic insulation calculator shows how much ENERGY STAR recommends adding for your climate zone.