How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is a sediment trap or dirt leg?
Friday, June 29, 2018
A water heater or furnace sediment trap is a T-shaped pipe configuration designed to catch any debris in a gas line before it goes into the appliance. It is required by both the Florida Building Code (FBC) and International Residential Code (IRC) for any appliance that does not have one incorporated into it. Illuminating (lighting) appliances, ranges, clothes dryers, and outdoor grilles are exempt from the requirement.
Although it is part of the building codes, the sediment trap requirement is not enforced in some jurisdictions, and our local natural gas utility does not require a sediment trap when inspecting a gas system before turning on the service.
The sediment trap must be downstream from the shut-off valve and have a right angle change in the gas flow before the trap, like in the photo above, so the debris doesn’t bypass the dirt leg intended to trap it, along with a threaded nipple cap at the bottom for removal of any debris accumulation.
The Florida Building Code provides this diagram of a sediment trap.
Here’s an example of a sediment trap installed incorrectly below. The gas flow goes right past it.
And here’s an example of a water heater installation done without a dirt leg. This particular one was a job by a handyman that had several other defects and lacked a building permit.
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