Gas sediment trap requirements when buying a house
The model fuel gas code calls for a sediment trap, often called a drip leg, at gas furnaces and water heaters. Missing one? Get a plumber's bid.
Updated · By 
Ben Sikes
What are the gas sediment trap requirements?
The model residential code requires a sediment trap at the gas inlet of appliances like a furnace, boiler or water heater, unless the appliance has one built in. If your report flags a missing one, get a licensed plumber's written bid and ask the seller to have it installed or to credit you that amount. Treat it as gas work for a professional, not a weekend job.
Key takeaways
- The trap goes after the appliance's shutoff valve, as close to the inlet as practical. The code's standard version is a tee with a capped leg pointing straight down.
- The code text exempts ranges, clothes dryers, gas fireplaces and outdoor grills, so check which appliance your report names.
- One Tampa-area plumber's fitting plus labor comes to $120 to $350, a small line to ask for.
Is a missing sediment trap dangerous?
The trap is there to catch debris in the gas line before it reaches the appliance. Minnesota home inspector Structure Tech says it helps keep sediment in the gas piping out of the appliance's gas valve and burner.
Appliance makers call for it too. Rheem's water heater manual requires a trap. If its instructions are "not followed exactly, a fire or explosion may result causing property damage, personal injury or death," its cover warns. Installation and service "must be performed by a qualified installer, service agency, or gas supplier," the manual adds.
A gas smell is a different, urgent problem. Leave the house right away, then "call your gas supplier from a neighbor's phone," as Rheem's manual puts it. If you can't reach them, call the fire department (911), and don't go back in until they say so. Then a licensed plumber finds and fixes the leak.
What is the code for a drip leg on a gas line?
The rule sits in the fuel gas chapter of the International Residential Code (IRC), section G2419.4, which is 408.4 in the International Fuel Gas Code. It applies "where a sediment trap is not incorporated as part of the appliance." Your state or city adopts its own edition, sometimes with amendments. The local building department or a licensed plumber answers which version applies at your address.
"Drip leg" and "dirt leg" are older trade names for the same fitting, and Structure Tech notes the current code does not use them. In the code, a drip is a separate part, required "where wet gas exists" to collect condensate. Plumbers and some inspectors often use the two terms interchangeably, Buyers Ask notes.
Where should it go, and how long should it be?
The IRC puts the trap "downstream of the appliance shutoff valve as close to the inlet of the appliance as practical." In plain terms, it sits after the valve that shuts off that appliance, right before the gas enters it. Rheem's manual uses the same placement for its heaters.
The standard trap is a tee fitting with a capped nipple "installed vertically in the bottommost opening of the tee," per the IRC, which also accepts another approved sediment trap device. Gas should enter the tee from the top, so it changes direction and sediment falls straight down into the trap, says San Antonio home inspector Ensure Inspections. The same inspector commonly finds traps installed incorrectly, so your report may flag a trap that exists but is set up wrong.
On length, the IRC text allows "a capped nipple of any length," with no minimum. Ask your plumber whether your jurisdiction changed that.
How much does it cost to add a sediment trap?
| Source | What the figure covers | Cost |
|---|---|---|
| Complete Plumbing and Drain, local plumber, Tampa Bay area, Florida | The sediment trap fitting, material only | $20 to $50 |
| Complete Plumbing and Drain, same plumber | Plumber's labor to install it | $100 to $300 |
| Kukun, home cost site | A plumber installs one | Around $100 |
| Ensure Inspections, local inspector, San Antonio, Texas | Fittings to build one | Less than $20 |
Adding that plumber's two rows ($20 + $100, and $50 + $300), fitting plus labor runs $120 to $350. The same plumber says the total can rise if the gas supply or valves need changes. Your plumber's written bid sets the real number.
Kept prices every line of an inspection report for $79, usually under 4 hours, and marks the ones that need a professional quote.
Who can check it before my deadline?
Call a licensed plumber, or the HVAC technician who services your gas furnace. Ensure Inspections names either trade for the fix. Buyers Ask says a plumber can usually install one in 15 minutes to half an hour.
Have the plumber look at every gas appliance inlet in the house, not only the one the report names, since the rule applies at each appliance it covers. Ask for a written bid that names each appliance, the fitting and the price. How to get repair estimates during the inspection period covers booking that visit fast.
What should I ask the seller for?
Name the appliance, the trade and the bid:
- Repair: "Install a sediment trap at the gas inlet of the water heater, by a licensed plumber, with a receipt before closing."
- Credit: a credit equal to your plumber's written bid, so you hire the plumber after closing.
What to ask for after a home inspection shows how this line fits next to the rest of your list. The buyer repair request letter template has the wording around it.
If the seller says no, the bid is what you'll pay after closing, so book the plumber for your first weeks in the house. Your contract sets the deadline for the request, so confirm the date with your agent.
Do gas stoves and dryers need a sediment trap?
Not under the IRC text. Its list of appliances that "need not be so equipped" includes "ranges, clothes dryers, decorative vented appliances for installation in vented fireplaces, gas fireplaces and outdoor grills," along with gas lights. Have the plumber confirm it against your local code and the appliance's manual.
How do I know what the rest of my report is worth?
Price every line before you write the request. A sediment trap is one small plumbing line.
If the trap is one line in a long report, upload your inspection report to Kept and spend your remaining days on the lines that need a contractor.
Sources
- International Residential Code, G2419.4 (408.4) Sediment Trap, on UpCodes
- International Residential Code, G2419 (408) Drips and Sloped Piping, on UpCodes
- Rheem, Residential Super High Efficiency Water Heater Use and Care Manual
- Structure Tech, "Sediment traps: what and why"
- Complete Plumbing and Drain, "The Cost to Install a Sediment Trap on a Water Heater"
- Kukun, "Gas Line Sediment Trap"
- Ensure Inspections, "What is a Water Heater Sediment Trap and Where Does it Go?"
- Buyers Ask, "Sediment Trap and Drip Leg on Water Heaters"
- Minnesota Fuel Gas Code 2020, Chapter 4, on UpCodes
Cost figures are modeled from public wage and materials data unless a line says observed. Kept is accountable for the numbers on this page, and corrections go to support@usekept.com. How we price.