I've been in the trade now for a while, and it just seems to be that propane will destroy any brands heat exchanger in 7-10 years. Is there any explanation for this? Some say its the "smell" they add to the gas, some say it's not set up right......well, after replacing a few, and seeing that gas pressure, temp split is correct what does that leave? Are the new style exchangers just built that cheap? Then you got manufacturers that have known problems with their furnaces secondary exchangers plugging up, so you get a new furnace that will plug up in the next 10 years! Gotta love them ENGINEERS!