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Why You Always Test for Chimney Gas Leaks

Signs of long-term condensation on building exterior

Signs of long-term condensation on building exterior

Who would have thought that this unsightly chimney provided clues to the source of a hidden gas leak?

On a recent call to replace an aging gas boiler, the owners reported a persistent gas smell. The gas company had previously inspected the building and didn’t find a gas leak using their detectors.

Yet the smell continued.  The point is – if you smell gas, however subtle the smell– there is a gas leak.   Somewhere.  The challenge can indeed be where to find it.

Built in 1923, this building was serviced by an older gravity boiler that had evidence of back drafting.  It also had an exposed chimney, a tile roof, rotting windows, scant insulation and little or no air sealing.

So the pipe started to rust …

So the pipe started to rust …

Why was the chimney in such bad shape? Each time the boiler cycled on and stayed on for a long period, the chimney dries out.  But during each short cycle of the boiler, the chimney stayed wet and dripped water.  For decades.  And those drips fell onto the basement rim joists and essentially provided a steady pool of stagnant water around 1-inch  steel gas pipe. So the pipe started to rust …. and leaks gas.

The company’s gas bills spiked last summer.  Workers thought sealing the rim joists would help cut down the bills.  Someone stuffed fiberglass insulation in the rim joists along the tight quarters of the old stone basement wall. This batt insulation also hid the horizontal gas pipe that connected the old boiler to  the outside meter.

Insulation without air sealing doesn't work.

Insulation without air sealing doesn’t work.

However, stuffing fiberglass insulation doesn’t solve condensation problems. Water drips continued. They didn’t caulk properly in the rim joist cavity, nor shine a light on the gas pipe in the dark, dank space.  If they had, they would have noticed the rusty pipe and noticed the ongoing dampness.

After taking apart a portion of the sealed rim joists, I uncovered the rusty pipe.  My detector indicated over 20 pinpoints of gas leaks over a 24 inches of pipe.

If the workers could have had simply observed the condition of the pipe, and tested it with a simple gas detection tool prior to covering the rim joists, the problem would have been found immediately.  Rust isn’t good for anything, particularly pipes that carry combustion fuels.

I replaced the pipe; resealed the rim joists properly; and re-inspected every inch of the gas line and pipe.

Problem solved.

 

Insulation without air sealing doesn’t work.  Fiberglass insulation was jammed into the rim joist, but this practice doesn’t  solve condensation issues.  Fiberglass become a filter.

When rigid insulation is not installed on the exterior of a rim joist, it must be installed on the interior to control condensation on the rim joist.

 

Insulation without air sealing doesn’t work.  Fiberglass insulation was jammed into the rim joist, but this practice doesn’t  solve condensation issues.  Fiberglass becomes a filter.  When rigid insulation is not installed on the exterior of a rim joist, it must be installed on the interior to control condensation on the rim joist.   Eric Kjelshus

Below: best practices for proper sealing of rim joists:

 

 

 

 

 

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