Originally Posted by gasman6674
Cylinders are never 100% full by code is max is 80% so a 20# cylinder will hold 20# of gas 4.24 # per gallon or 4.71 gallons but the wc (water cap) is 47.6# or 5.95 gallons any way if you can upsize (if you have room) your cylinders to a 30# or a 40# you might eliminate the issue. I just attached a chart that I think will help you out.
Thanks for the charts. Those are some of them that I've found on the internet and used to do my calculations. The vaporization rate chart is based on 25% full tanks. I have yet to find one for smaller tanks that shows the full range from empty to full, like they have for 100 lb tanks.
I based my calculations on 100 pounds and 20 pounds and 30 pounds, which already takes into account the 20% reduction. However, that's another variable to be mindful of. Some stations don't give you a full 20 pounds. Usually that is more important for calculating and comparing price/gallon between different stations, but in this case, where frosting is an issue, I'll want to make sure my tanks are as close to the full rating as possible, to increase my runtime before I run into problems.
The RV came with 20 lb tanks. I immediately switched them over to 30 lb tanks, just to give me a longer time in between fills. Just so happens that it will also assist a bit with the possible frosting issue.
I don't have room for 40 lb tanks in the cubby hole where the tanks sit, or I would go with 40 lb tanks. I suppose another option would be to install a couple 40 lb tanks on the tongue of the RV (if they'll fit), rigged with a regulator that uses both tanks at the same time (twice the surface area), and connect the generator to those. That way I wouldn't have to lug tanks around loosely each time I go to the fish house.
The downside to this approach is that I lose the convenience of taking a fully empty tank out and filling it while still having another tank in use. I'd also still have frosting issues when the tanks are closer to empty than full and I'd need to make sure the station is charging for what they put in rather than a flat fill rate, regardless of how much is in the tank when they start, so that I don't effectively pay twice for the left over propane in the tanks.
I just got the generator and haven't used it yet with the house being used for ice fishing. I have a suspicion that I'll be well below the max rating on the generator much of the time. So even though max is estimated to be 30,000 BTU worth of propane, I could be considerably below that. If so, then I may be just fine. There may be some frosting when the furnace kicks on at the same time the generator is running, but there may also be some amount of buffer in the tanks (gas phase propane) that will handle the demand of the furnace until it shuts off, before I run into a reduced BTU output at the tank due to cold/tank level.
I'll just have to try it when I convert the generator. Right now I'm still trying to find the parts for Teeing/Y-ing off the output of the changeover regulator. If anyone has any internet sources for parts to do this, please let me know.
Thanks again for the info.