Nice- Damn that's a big one, like a nitrous tank! I got a 15lb job, it's about 2ft or so. It's also about 20 to fill. Around here it seems all sizes cost the same, 5lb, 10lb or 20 - all the same price to fill pretty much. A 5ft could certainly last a long long time, depending on room size obviously. Just make sure you got the washer in the coupler. I have forgotten to put it in there before and the tank leaked out pretty quickly.