I'm trying to figure out the right pipe to buy for a direct vent wall furnace. The instructions show 3/8 inch npt, and also say that the gas inlet is 1/2 inch. When I measure the gas inlet it appears to be about 3/4 inch. I'm attaching pictures of the instructions and the gas Inlet to show what I mean. It's an Empire Heating Systems furnace, DV210SGXLP-1.

I could use some explanation of what the numbers mean.

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Generally, the bigger the better. Assuming you already have gas, you should match what you have already installed. The size shown is the minimum for each of the 2 gases, Propane vs Natural Gas. You can use a pipe nipple/reducer to reduce the size of the valve inlet as needed. As for the other numbers, BTU is the heating factor (British Thermal Unit), higher number means it will heat a larger space, or a smaller one faster. The dimensions are used for the place you plan to install the furnace. Your gas valve is 1/2"ID(Inside Diameter), your measurement is 3/4"OD(Outside Diameter). So a 1/2" ID NPT(National Pipe Thread) is what you need at the valve, however, up to the valve you can plumb 3/4"ID. If you are doing a new install from the meter, best to go with the 3/4" in case you plan to upgrade in the future or add additional gas appliances.

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  • Excellent, thank you. It's a new install, so I don't have any existing pipe to compare with. – Don Branson Mar 24 '19 at 22:27

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