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How Much 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

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, all 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. A 40 lb. tank holds about 9-1/2 gallons, so if you burn your fireplace for two hours every day, a 40 lb. tank will last 16 days, with enough LP left over for a one-hour fire on the 17th day.

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Q: When I figure out the total gallons a 200# 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

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, 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." 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

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

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