How can I determine how many btu's my stove(s) are putting out? I am asking because I am looking to install a propane furnace (55,000 input, 81% efficient) . I am trying to figure out an approx. number of gallons it would use if I ran it 24 hours like I do my pellet stoves. I know if I ran my stoves together on max, they would put out what 50,000 btu's?? I have the PDVC set around heat #5 or 6 most times on a TSTAT, The EF2 I usually run 1/2 or 3/4..