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

On 2005-09-13, Stephen E. Halpin shalpin wrote:

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.

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.

Steve,

Remember to put a dirt pocket, also called a sediment trap or drip leg
at each gas appliance. This keeps any dirt, dust or rust that travels
along the pipe from getting into the gas valve and causes it to fail.
You use a tee with a cap at the bottom of the "run" to catch debris
from the gas line. You come out the side of the tee and into the
appliance. Cheaper than replacing the gas valve, lots cheaper than
blowing up your house and required by code.

Stretch