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Old 09-06-2019, 03:27 PM   #12
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Originally Posted by correira99 View Post
Everybody is using propane? No problem keeping up with the cold?
I assume that "keeping up" means the ability of the propane tank to deliver propane to the heater at a rate that matches firing demand. Liquid propane in the tank must vaporize at a certain rate, and that requires absorption of heat of vaporization from the air around the tank. For propane, this is 184 BTU/lb at its normal boiling point (-44 F), but less at higher temperatures. The tank size may be selected to provide the required heat absorption rate at some design minimum air temperature. The propane inside boils at some lower temperature, at a pressure sufficient to move the propane across the valve and through piping to the burner. The difference between air temperature and boiling propane temperature, along with the surface area of the tank, leads to a certain vaporization rate that is possible. As air temperature drops, the propane boiling temperature and thus pressure inside the tank must also drop. At some point, tank pressure is insufficient to deliver gas at the required rate, and firing rate must decrease.

A propane company usually uses a chart showing tank minimum size vs firing demand. Here is one:
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