How to Safely cut into existing LP line


Old 08-12-09, 08:32 PM
Thread Starter
Join Date: Aug 2009
Location: Texas
Posts: 2
How to Safely cut into existing LP line

I am working on an addition in my house (apartment above garage) and would like to run LP over for Stove and Water Heater. The house has an existing 1" black iron pipe distribution line and I can access the line in the attic prior to any existing appliances. My plan is to cut into the line in a short section and replace a 90' elbow with a Tee for my addition and then reconnect the existing line with a Union.

I'm reasonably comfortable with adding the black iron piping and pressure testing as I've done this before but not so comfortable with cutting the existing line and use of the union. If I cut off the LP supply at the tank and then run appliances until they deplete all of the LP in the line is it then safe to cut with a hacksaw? Sawzall? I don't have a lot of room so a Sawzall would be easier, but it seems to me that the hacksaw would be the safer option.

I'm also concerned with the flexibility of the existing piping and ability to get the union threaded into both sides.

Once I've got the new Tee in place, I'd like to install a shutoff valve so I can get the rest of the house back up and running while I complete the new work and have the added benefit of being able to shut off LP to the addition if ever needed.

I'd appreciate any thoughts on the plan and specifically on precautions/tips for the initial cut into the line.
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Old 08-12-09, 09:23 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
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Gas piping systems are usually engineered for the appliances that will be connected. Adding more appliances after the fact may end up "starving" all the appliances from the "tap" to the end of the line, including the new appliances. You really need to do the calculations for the added load to see if you have sufficient pipeline capacity to simply cut in to the existing piping.

LP gas is heavier than air and WILL accumulate in lower enclosed spaces including the spaces between joists in an attic space. There is absolutely no room for any error in LP gas piping.

Even a hand hacksaw could generate enough of a spark to ignite LP gas as it has a much wider range of flammability than does natural gas. If you need to cut a pipeline the safest way is to first burn off the gas after closing the tank valve and then using an inert gas like nitrogen or carbon dioxide flush the piping before using any tools that might spark to cut the piping. Do NOT flush the lines with compressed air as that may increase the hazard.
Old 08-13-09, 07:20 AM
Thread Starter
Join Date: Aug 2009
Location: Texas
Posts: 2
Thanks Furd for the response. Is there a commonly accessible option for N2 or CO2? I should be able to disconnect and adapt the line from my hot water heater which is nearby where I would cut the line. There is also what appears to be a pressure release or purge fitting on the regulator - is this the recommended connection point for purging the lines?

As for the capacity of the system, I've done the simple math with all of the appliances and believe it should be OK, but I'll take some better measurements and double check. I noticed that in all gas charts for BTU's they list the BTU's available "for straight line only", is there a rule of thumb for how much a 90' elbow adds in feet or reduces in BTU's?

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