I calculated that a 30,000 BTU/hr propane furnace uses 1.4 pounds of propane in one hour. That is equivalent to one 30 pound propane cylinder in 21 hours of continuous use. Does 1.4 pounds/hr seem correct?
Probably about as close as we care to estimate. There will always be some of that cylinder that goes unused because you can never get consistent pressure below 5% fill, so you'll not get that full 30 pounds in use when the pressure switch drops out the furnace. But 20 hours of run time may be about right.
Its my understanding as well, that due to transport regulations, Blue Rhino and the like, don't really fill the tanks. I've told you are better off filling them from a propane dealer or tractor supply. Use Blue Rhino, when your tanks age out.
My tanks have aged out; I just take the "rented" tanks to get filled at my local farm supply. I could have taken my original tanks to be re-certified, but that is cost prohibitive on smaller tanks. It makes sense to re-cert larger tanks, but not small ones, because the re-cert outspends the new smaller tanks. With a rented tank they are supposed to check the tanks prior to filling so anything we'd rent would be "OK" for use. But in theory, you could rent a tank that we OK to fill at Blue Rhino at year 9.5, then it might sit in the back of your barn for three years, and once you deplete the gas, it cannot be refilled without being inspected. You can turn it back in and get the credit for exchange, but you cannot have it filled at a private service fill center.
Spasm3 is correct:
All tanks should be filled to around 85% capacity; needs to be some headroom for expansion of the gas.
If Blue Rhino is under-filling less than that as a conscious matter of practice, then I would consider that as type of improper marketing and consumer fraud. You pay for a "full" cylinder (85% full, at least). If they are only filling it to 75%, then they are ripping us off. The industry says it's a "20 lb" cylinder, and it should contain X gallons of fuel. If they are shorting us from the value of X gallons, then it's consumer fraud. That doesn't mean it doesn't happen, just shouldn't happen.
All portable tanks have an OPD (overfill protection device). When they fill it, it's a float-operated valve that opens a bleed port once it reaches around 85%. That keeps them from putting in 90%, or worse, truly "full" levels. There has to be a gaseous level above the liquid for proper operation AND safe pressure levels. That's why the tanks for the last couple of decades have had the triangular handle on top; that indicates an OPD is in place. The old knurled valve handles don't have the OPD, and are illegal to refill. A person who is doing their job correctly when filling will use that OPD bleed valve as a guide to know when the tank is truly at the right level. At least that's the way it's been explained to me and it makes sense.
Great info - did not know about the OPD, nor did I know that at 10 years of age a tank has to be tested. I assume that's a pressure burst test like SCUBA tanks? Put them in a test vessel at X pressure for Y time and if they don't rupture, then they are good.
Yes; that's right Wayne. The test costs outweigh just getting a new small tank at a farm supply store. The typical 20lb tanks we all see on RVs is about $33 to replace with a new one. However, when you're talking 100lb tanks (the tall narrow ones), it's worth the cost to re-certify them as long as they're in decent shape otherwise.
But I can drive 5 min down the road and get a refilled BR tank for $15 at Rural King, with no hassle and no worry about filling or certifications.