# Natural gas pipe sizing (or "how can this ever work??")

I'm looking to have few gas appliances including a natural gas dryer installed in a house which uses natural gas for heating and hot water. I've been reading information on the net trying to make sure that what the contractors are proposing will work, and right now, I can't see how.
It seems the rules are "measure the longest run in the house, and use a given column in a table to find out what each diameter pipe can carry," and "once you restrict a passage with a smaller diameter pipe, that limits how much gas will ever pass beyond it no matter how large pipes beyond the narrowest segment are."
I know for the measurements, I'm starting at the meter, but it's unclear what the "end point" is. The point where the gas dryer would attach would be just about 60' from the meter, but there will be a flex hose of a few feet between that point and the dryer itself. Do I have to use the 70' column because of this flex hose, or do I use the 60' column?
Once I go to the 60' column, I see that the 1" pipe off the meter will carry enough gas for everything I need (259 cu ft/hr.) So far, so good. The problem is, the furnace needs 90 cu ft/hr, and the internal regulator takes a 1/2" pipe. About two feet of 1/2" pipe are run from that internal regulator to the outside of the furnace, which attach to an elbow, which attach to a 3/4" to 1/2" adapter. Now the 3/4" pipe can carry 127 cu ft/hr to a point near the furnace, which is enough, it would appear the 1/2" pipe going into the furnace (because the longest run in the house is 60') can only carry 66 cu ft/hr. How can this work?
-Steve
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On 2005-09-13, Stephen E. Halpin <shalpin> wrote:

When sizing the pipe to the furnace, you don't need to consider the longest run in the house, just the length of the run to the furnace.
Basically, for any section of pipe, you look at the total demand downstream from that pipe, then you look at the longest run that includes that particular pipe, and then size that section of pipe according to the chart.
Cheers, Wayne
P.S. I'm not sure, but I think this method is an approximation which may give you a larger required pipe size that you would need if you actually calculated the pressure drop along each segment of pipe.