When we were in Alaska in '10 we used a tremendous amount of propane in comparison to the amount we have always used in previous trips. We started noticing that when the furnace ignited it would roar like a blow torch. Today when we had the furnace out for another problem we pulled the orfice out & it has a GIANT hole in it (where the propane comes out not an "extra hole)& the number 49 on it. Not sure if the number 49 tells anything or not but thought I'd throw it out there just in case. We also noticed that the plastic part of the vent covers was getting warm enough to actually warp them out of shape. Mac feels that it is burning too hot & perhaps needs a smaller orfice but that is just a guess. Can anyone shed any light on this for us? Oh, it is a 40,000 btu furnace if that matters. Thanks for helping.
Mac & Becky
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49 is the orifice size. Generally a wire gage as in No48. As for using too much fuel? That is a matter of 1) 40K BTU and 2) outside temp vs thermostat setting. A furnace is rated at 40K BTU is going to burn a little over 1/2 gallon per hour of fuel. Considering propane has approx 91,330 BTU per gallon. So yes you will use a lot of gas if it is cold outside. Nothing wrong with it. If you install a smaller orifice you will throttle down the heat output.
40K btu would use about 1/2 gallon of propane/hr of operation. IIRC propane energy content is about 90KBTU/gallon.
Also, when the temp goes down, the vapor pressure of propane drops, so in cold temps (near 0F) you won't be able to get all the propane out of a tank before the vapor pressure drops to low. The propane cools as it boils (basic thermodynamic property of liquids) and finally gets to the point where it is so cold it no longer boils off to a gas in sufficient volume. Once the tank warms back up, you'll be able to get more out of it.
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