Drip leg

[pnarron]

I'm putting another furnace furnace in the attic and the old one did not have a drip leg on the gas line. The furnce is a horizontal one; the gas line will come out of the top of the furnace. The main line for the gas is on the far side of the furnace and is run along the bottom of the truss, if I put a drip leg closest to the furnace it will be in front of the service panel or is it ok to have the drip leg 35 inches away on the far side of the furnace? Thanks for any help.

[Michael Larson]

Check with your local jurisdiction and manufacturer installation instructions for requirements.

[Joe Funderburk, CMI]

Originally Posted by mlarson

Check with your local jurisdiction and manufacturer installation instructions for requirements.

The code IS the requirement in the case of a sediment trap (if you are regulated by the IRC or IFGC). Your AHJ may not enforce it, but it's still required if the IRC or IFGC has been adopted.

2009 IRC G2419.4 (408.4) Sediment trap. Where a sediment trap is not
incorporated as part of the appliance, a sediment trap shall be
installed downstream of the appliance shutoff valve as close to
the inlet of the appliance as practical. The sediment trap shall
be either a tee fitting having a capped nipple of any length
installed vertically in the bottom-most opening of the tee or
other device approved as an effective sediment trap. Illuminating
appliances, ranges, clothes dryers and outdoor grills need
not be so equipped.

IRC Commentary: In addition to the code requirement, most appliance
manufacturers require the installation of a sediment
trap (dirt leg) to protect the appliance from debris in the
gas. Note that a drip leg is not the same as a sediment
trap (see Section G2419.2). Sediment traps are necessary
to protect appliance gas controls from the dirt, soil,
pipe chips, pipe joint tapes and compounds and construction
site debris that enter the piping during installation
and repairs. Hazardous appliance operation could
result from debris entering gas controls and burners.
Despite the fact that utilities supply clean gas, debris
can enter the piping prior to and during installation on
the utility side of the system and on the customer side.
Sediment traps are designed to cause the gas flow to
change direction 90 degrees (1.57 rad) at the sediment
collection point, thus causing the solid or liquid contaminants
to drop out of the gas flow [see Commentary Figure
G2419.4(1)]. The nipple and cap should not be
placed in the branch opening of a tee fitting because
this would not create a change in direction of flow and
would allow debris to simply pass/jump over the capped
nipple collection point. Commentary Figure G2419.4(2)
illustrates a relatively ineffective sediment trap, however,
such configurations are not expressly prohibited
by this section. The code does not specify a minimum
length for the capped nipple, therefore, it could be from
a close nipple on up. Three to 6 inches (76 to 152 mm)
is the customary length. The capped nipple must be in a
vertical plane to allow the sediments to fall in by gravity.
The sediment trap must be as close to the appliance inlet
as practical to be able to capture sediment from all of
the piping upstream of the appliance connection. The
sediment trap must be downstream of the appliance
shutoff valve to allow the trap to be serviced after closing
the upstream shutoff valve. Manufactured sediment
traps are available that have the configuration of a
straight section of pipe and are equipped with cleanout
openings. Although it would be wise to install sediment
traps at all appliance connections, they are not mandated
by code for gas lights, ranges, clothes dryers and
outdoor grills. These appliances are also susceptible to
harm from debris in gas, especially ranges and clothes
dryers, and the appliance manufacturer may require
sediment traps where the code does not. The code’s
logic is that these exempt appliances are manually operated
rather than automatically operated; therefore,
the user would be in attendance and aware of a
problem.

[pnarron]

Thanks for the help!

[Charley L. Bottger]

You don't state where you live, in Okla with cold temps we do not install drip legs on attic installs or exterior pkg units due to the amount of moisture in natural gas this moisture accumulates in the dirty trap and can freeze and burst the line then you have big problems. Different areas may have different amounts of moisture in the natural gas