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How Many Gallons of LP Gas Will I Burn?

Q: I want to install a decorative gas fireplace, but I do not have a space outside for a large propane tank and would like to know if there is a "rule of thumb" for propane consumption. We don't need heat, and will only burn the fire maybe two hours per day. The input rating for the fireplace is 26,000 btu / hr. What confuses me is, the tanks seem to be rated by how many pounds of propane they'll hold, but the local propane supplier, who calls it "LP" for some reason, sells it by the gallon. About how long would a 40 lb tank last? How many gallons would that be? I've tried and tried to find someone who can answer these questions, and nobody seems to know.
Roy Sidgeley

Sweepy A: "LP" is heating industry shorthand for Liquid Propane, so-called because propane gas turns into a liquid when it is compressed for storage. To burn it, a pressure valve is used to decompress the liquid so it will turn back into a gas.

The input rating on your fireplace tells you its fuel consumption rate, expressed in British Thermal Units (btus) per hour. To answer your questions, the first thing we need to do is convert your fireplace's consumption rate of 26,000 btu / hr to pounds and gallons of LP.

One gallon of LP contains 91,500 btus of heat value and weighs 4.23 lbs, so your 26,000 btu/hr fireplace burns one gallon ( 4.23 pounds ) of LP every 3-1/2 hours.

Next, we need to know whether yours is a stationary tank (the refill tank comes to your house), or a portable tank (you take it to the fill tank for refills, like the tanks used for gas grills).

Stationary LP tanks are rated by how many pounds of LP they'll hold, so a 40 lb. stationary tank holds 40 lbs. of LP, or about 9-1/2 gallons. If you burn your fireplace for two hours every day, a 40 lb. stationary tank will last 16 days, with enough LP left over for a one-hour fire on the 17th day.

Portable LP tanks are rated by total full weight, tank and all. A typical gas-grill size portable LP tank weighs about 40 lbs. when full, and 18 lbs. when empty, so it holds about 5 gallons (22 lbs) of LP. If you're fueling your fireplace for two hours a day with a 40 lb. portable tank, you can expect to run out of LP sometime on the 9th day.

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Q: When I figure out the total gallons a 200# stationary propane tank will hold (thanks to you), it comes to 47.5 gallons. My question is what is the percentage that you should put in the tank to allow for expanding? My local hardware store says it should be no more than 80% per the gauge reading.That would figure out to about 38 gallons at 80% is this correct? If this is so then my propane supplier should be charging me for 38 gallons when he fills my tank. Am I correct about this??

Thanks...My name is Pat

Sweepy A: Don't shoot your LP supplier, he's not ripping you off. Your local hardware guy is absolutely correct about the maximum fill percentage of a propane tank; the OPD valve on the tank automatically stops the fill when the level reaches 80% of the tank's total volume, to allow for expansion. Because of this, stationary propane tanks are rated, not by their actual size, but by the amount of LP they'll hold at 80% capacity. In other words, a "200 lb." stationary propane tank is a tank which holds 200 lbs. of LP with 20% left empty for expansion.

Q: Thanks for the prompt reply, my question is, he is charging me for 47.5 gallons, is this correct?? Pat

  Sweepy A: Yes, if your tank was empty. A 200 lb. stationary LP tank holds 200 lbs. (47.5 gallons) of propane.

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Q: My 40 lb LP tank refiller puts the tank on a scale and refills it until the scale reads 40 lbs. So I am not getting 40 lbs of gas, or 9.456 gallons, because the tank itself probably weighs 5 lbs empty...or am I missing something??

Thanks,
Bob Kolhouse

Sweepy A: You're missing something: the nomenclature used for portable tanks is different than that used for stationary tanks. When we refer to a 40 lb. portable LP tank, we're talking about a 5-gallon tank, which weighs around 40 lbs. when filled to capacity. If your tank was empty when your refiller put it on the scale, it should have weighed about 18 lbs, so a 5-gallon fill, which weighs 22 lbs, would make it 40 lbs.

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