So if I had a sealed/vented grow room of size 4ft x 3 ft and 6 ft tall. The calc say I have 72 cubit ft, and at a setting of 1 CFH for 5.184 minutes. It says a 20lb tank would last me 174.8 hours. Does that mean 174.8 x 60(min/hr) = 10488 minutes of use? So I would be able to get 2023 (5.184...