Bruce W. Maki,
Intimidated By Natural Gas:
About 10 years ago, when I was working as a design engineer, I
bought my first house. I mentioned to a co-worker, a senior
mechanical engineer, that I needed to get a plumber to install the
flexible gas connector for the stove, because it was something that
a homeowner could not, or should not, do himself. The engineer
enlightened me about natural gas.
He explained that the pressure was very low, less than 1/2 of a
pound per square inch. But more importantly, he explained the safety
of natural gas. All gaseous fuels (and vaporized liquids) have a
certain range of air-to-fuel ratios that will allow for combustion.
Natural gas, he explained, requires a very precise air-to-fuel
ratio. This fact makes it very unlikely that a minor gas leak
could result in an explosion. (But it is possible.) The smell of
gas, he told me, would be unbearably strong before the atmosphere
His confidence and knowledge convinced me to try connecting the
stove myself. As he suggested, I bought some pipe thread compound
for the fittings and, when finished, I tested the connections for leaks by
dripping some soapy water on them. I couldn't believe how
simple it was. Later, I began to notice the wide availability
of gas pipe, fittings, and flexible connectors. I saw these parts in
every hardware store and home center I shopped at. A relative who
worked in industrial maintenance confirmed how common it was for
average people to do their own gas piping. From that point onward
gas plumbing took on a new perspective.
Nevertheless, natural gas can be dangerous, and propane can
be very dangerous. They demand respect. Using pipe,
fittings, or thread compound that are not rated for natural
gas would be foolish and possibly life-threatening. And
all connections must tightened properly and be tested for
Propane is more dangerous than natural gas for at
least two reasons. First, I'm told that propane has a wider
range of air-to-fuel ratios that are combustible, so ignition
could occur with a smaller leak than would be possible with
More importantly, propane is heavier than air, while
natural gas (which is mostly methane) is lighter than air.
Leaking natural gas will rise by itself, and infiltrate the
house where it can be detected by the odor. But if propane
leaks it can "puddle" in low spots, and if the
puddle reaches a pilot light or a spark from a motor...
Kablooey! It has happened. There are combustible gas
detectors available, (like a smoke detector for gas or
propane) but I have yet to locate a place to buy them.
||This gas pipe is for a Jenn-Air indoor grill.
However, the kitchen plans have changed and the pipe is in the
wrong position. It needs to be about 10 inches to the right.
|First I laid out the new pieces of pipe.
My plan was to remove the pipe that protruded through the floor
and replace it with a shorter piece, and then install an elbow to
bring the pipe under the proper cabinet.
||I turned off the gas at the gas meter. This
required a large adjustable wrench.
|This valve is a ball valve. It only
requires 1/4 of a turn to close. It is different from most
common valves because it can be rotated forever, it has no
internal stop device. It is closed when the bar is
perpendicular to the pipe. (Also, two holes line up so the gas
company can lock the valve closed.)
With the gas turned off I could open up the system safely.
||I removed the cap with a pipe wrench.
|And then I opened the valve slowly, to release
the gas pressure. A rushing or whistling sound was heard for a
split-second, and then nothing. That told me that the shutoff
valve outside was holding properly.
||I loosened the vertical pipe that passed through
the floor. This piece was 18" long and will be replaced
with a 14" section.
|In The Basement: The other end of
||I removed the pipe.
|I replaced it with a shorter section. This pipe
is a combination of a 12" piece and a 2" piece. A
short piece of steel pipe with threads on both ends is called
a nipple. Don't ask me why.
A real plumber would have cut a long piece of pipe to the
exact length needed and then make threads on the cut end with a pipe
threading tool. But I didn't have that. The fewer joints there
are in the pipe system, the fewer places there will be for leaks to
||I tightened the new pipe. Note that after this
picture was taken, I used a second pipe wrench to hold the elbow.
This prevents the pipe assembly from being harmed by the
strong twisting forces required for tightening the
|Then I wiped the excess thread compound
from the new connection. (See below for more info.)
||Now the pipe only sticks up a few inches. It is
low enough to fit in the toe-kick space below the cabinets.
||I applied pipe thread compound to the male
|The thread compound I used, about $5 at Home
||The thread compound (also called "pipe
dope") is applied evenly and liberally. Bare spots are
|The fitting is threaded on by hand.
||Then a pipe wrench is used to tighten the
fitting. A second wrench was later used on the pipe below the
fitting, to fully tighten the connection.
How Tight Is Tight Enough?
The degree of tightness is something that takes experience to
determine, but I have learned a few general guidelines over the
- If a pipe gets crushed while tightening, the joint is too
- The best way to properly tighten a joint, in my opinion, is to
use two pipe wrenches placed in a tight "V"
arrangement, so the handles are close together and a minimum of
sideways bending force is applied to the piping.
- There is a rule of thumb for tightening iron pipe: First,
hand-tighten the fitting, and then use wrenches to further
tighten the connection at least one turn, and at most two
- Iron pipe uses a thread system called NPT, which means
National Pipe Taper. The thread is cut on a slight taper, so the
diameter at the tip of the pipe is smaller than the diameter
farther in. Look closely at a pipe thread and this should be
obvious. The more a pipe is tightened, the greater the
interference fit, and if taken too far the pipe can deform and
The Trick With Threaded Piping:
Getting the elbow fitting to point in the right direction can be
tricky. I would never back off a threaded connection to adjust the
fitting's direction, because this may cause the thread compound to
not cover the threads properly. This means that I have to keep
tightening the fitting until it points in the right direction AND
it has been tightened adequately. In my early days there were many
times when I wondered if the pipe would break off before it finally
reached the right position. Then I smartened up.
The solution to this problem is to let the next joint upstream
"absorb" some of the tightening. In the above case, I
could have had a helper go downstairs and hold a pipe wrench on the
next elbow and then two (or more) joints could rotate as I tightened
the upstairs elbow. If the upstream joints have only been tightened
one turn, then each joint can be rotated another full turn. This
allows enough extra rotation of the elbow to let it point in the
So... don't over-tighten any piece of pipe. One turn past
hand-tight, maybe a little more. Only fittings turn corners
(like elbows and tees) so these are the components that may need to
be turned more than one full turn past hand tight.
||I installed the next piece of pipe.
|And tightened it with two wrenches.
||I installed another elbow and a vertical piece.
|Note how the thread compound oozes out. This
gets wiped off.
||I removed the old valve from the 18" pipe,
using a 10" adjustable wrench and a pipe wrench.
|I installed the valve on the vertical pipe. Note
how the pipe wrench is on the elbow below the pipe. This lets two
joints absorb the tightening requirement, and gives me more
flexibility in locating the position of the blue handle. Also
note the "V" arrangement of the wrenches.
At this point, I was done with the piping changes. I went outside
and turned on the gas.
||But there is air in the line I just
worked on, so I briefly opened the gas valve to purge the air
and gas from the line. The smell of gas is rather strong.
|Then I replaced the cap on the top. Later, an adapter
will be installed here when the final flexible gas connection
is made to the cooking unit.
The stop valve: There are brass valves widely available
that have the letters "WOG" molded into the body.
This stands for Water Oil Gas, and can be used on gas lines.
Why Purge The Line?
Natural gas by itself is not explosive or even combustible. It
must have oxygen to burn. Any air in the pipe line could allow an
explosion if... and it's a big if... a malfunction in another
appliance allowed the flame to flash back upstream. This scenario is
far fetched, but it only took a few seconds to purge this line. Air
does not belong in gas lines.
Obviously, no smoking or open flames should be allowed until the
smell of gas has dissipated. Turn off all motorized devices, as many
motors create sparks that could ignite gas.
Open a couple of windows or doors while purging a gas line.
||I put a few drops of dishwashing detergent in a
cup of water, and dribbled some soapy water on each new
This is a very reliable test. I have seen gas company
employees use it. Even a tiny leak will show up as a glob of
foam that slowly grows. It takes perhaps a minute or two for a
leak to show up.
I wiped off the soapy water when done, to avoid corrosion.
Notes And Warnings:
- Read our disclaimer.
- Only use pipe, connectors and thread compound approved for gas
- Regular Teflon (or TFE) tape is forbidden on gas pipe
connections, because small pieces of tape can get shredded
during assembly, break off, and flow downstream to block a gas
valve. There is a special Teflon tape available for gas piping,
but I prefer the liquid compound.
- Any homeowner who seeks the lowest risk method of
connecting a gas appliance or re-routing a pipe should seek the
help of a licensed professional plumber or heating contractor.
- Pipe Wrenches (2)
- Adjustable Wrench,
- Black Pipe, ½"
- Black Pipe Fittings
- Shut-Off Valve
- Pipe Thread Compound
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