Wednesday, 23 September 2015

09:08 – Welcome to autumn. It looks and feels like autumn around here. Highs in the 70’s, lows in the 50’s, and rain. Barbara is now down to five work days left, and counting.

While she was out running errands the other day, Barbara stopped at the RV place to fill the new 20-pound propane cannister we’d bought at Costco. When she returned, I looked at the receipt and was puzzled. It showed “10 @ $0.99 = $9.90”. Ten what? Surely they didn’t put only 10 pounds into the 20 pound tank, but a 20-pound tank won’t hold 10 gallons, and even if it could I couldn’t imagine that propane was selling for $0.99 per gallon.

So I called them to find out. As it turns out, they indeed sell propane for $0.99/gallon, but they have a 10-gallon minimum, or about 42 pounds. As the guy said, it would have cost the same to fill a 30-pound cannister or a 40-pound cannister. If you’re actually using the propane routinely, it’d make sense to buy a 40-pound cannister. Those cost about $80 empty, versus $25 empty for the 20-pound cannisters. With one $10 fill, you’d be paying $70 for 40 pounds in two 20-gallon cannisters versus about $90 for one 40-pound cannister, but you’d break even after three fills and then you’d be paying $1/gallon to fill the larger tank versus $2/gallon to fill the smaller ones. We don’t use that much propane, just running our gas barbecue grill occasionally, so for stockpiling it makes sense for us to use the 20-pound cannisters. You can run a Coleman propane camp stove for a long, long time on one 20-pound cannister. We keep two full 20-pound cannisters plus a third one that’s in use, so we average about 50 pounds of propane available at any given time.

With a heat content of 20,000+ BTU/pound, that means we have about a million BTUs in those cannisters, enough to run a 10,000 BTU/hr camp stove burner for about 100 hours, or three hours a day for a month. Another way to look at it is how much water we could boil. Heating water from 62F to 212F requires 150 BTU/lb. Water weighs about 8.34 pounds/gallon, so it takes about 1,250 BTUs to increase the temperature of a gallon of water by 150F, so ignoring losses we normally have enough propane on hand to boil about 800 gallons of water or the equivalent.