So, what you are probably re â¦ ferring to is 'energy'. The SI unit of energy is the joule (J). An alternative unit, used by electricity utility companies for the purpose of billing its consumers, is the kilowatt hour (kW.h).
a typical steel 30 pound liquid propane tank weighs about 25-28 pounds empty. propane tank markings (on collar) propane weighs about 4.125 pounds per gallon and a 30 po â¦ und tank will hold about 7.5 gallons so a full tank will weigh about 55 pounds or so. /source: wiki.answers.com/.
If you refill, you then simply add 15 pounds or so to the tank and pay for what you added. If you exchange, you are giving the propane company 5 pounds of propane and paying for the complete exchange. You will likely pay more for the exchange, even if your tank is completely empty.An empty 20 lb tank will hold about 4.7 gallons of propane. That is $18.47 at $3.93 per gallon, which is the low quantity price (I just paid $3.44 per gallon when filling several tanks).The exchange is about the same price. Keep in mind this comparison is as if the exchange gives you a FULL tank.f you refill, you then simply add 15 pounds or so to the tank and pay for what you added. If you exchange, you are giving the propane company 5 pounds of propane and paying for the complete exchange. You will likely pay more for the exchange, even if your tank is completely empty.