Propane Question

rhagfo wrote:

Every time I had my empty 20# tank filled, it took 5 gallons to fill, our 30# tanks will take 7 to 7.2 gallons to fill when empty.

It shouldn't take 5 gallons to fill a 20#. Propane should weigh 4.22 pounds per gallon which equates to 4.73 gallons for 20#, so I was low when I said 4.5 gallons. That's assuming it's filled to capacity which can vary by who is doing the filling. Assumption is OPD should kick in at 20# but I don't know how precise those are. 7.1-7.2 gallons should be spot on for a completely empty 30# tank.

Also, to be fair, I did round the usage saying approximately 1/4 gallon per hour. So, assuming 91500 BTU/HR capacity 20000/91500=.2185745 gallons per hour or 21.64 hours for 4.73 gallons. All these calculations are very precise, but reality isn't so precise. I seriously doubt the 20K BTU is 100% efficient and exactly 20K BTU. I also seriously doubt that if you take 10 random 20# propane tanks any of them will hold exactly 4.73 gallons of usable propane. So, I would say approximately 20 hours of continuous run time from a full 20# tank. Again noting if you use exchange tanks they will almost certainly never be full when exchanged.