Condensation in Stainless Steel Chimney Liner

Dirty Chimney Water Dripping on Basement Floor Due to Condensation Dripping Down Stainless Steel Chimney Liner

By Mark J. Donovan

We recently purchased a new home and I’ve discovered an issue with the home’s stainless steel chimney liner. Frequently on cold days when the furnace is kicking off and on, we notice dirty water dripping out of the chimney liner’s elbow near the furnace. At first I thought the problem was associated with a chimney cap that had failed, as the cap actually blew off the roof after a strong rain and wind storm. We promptly had a new chimney cap installed and the problem still persisted.

Finally, I brought an HVAC contractor in to take a look at the problem. After spending only a minute looking at our situation he explained that one of the problems with stainless steel chimney liners is that they are prone to condensation issues.

As hot home heating oil gas emissions go up the chimney they cool and particularly so on colder days. As the gas emissions cool they condense and form water droplets on the inner side walls of the stainless steel chimney liner. The water droplets then drip downwards in the stainless steel chimney liner.

When they reach the elbow near the furnace, they end up dripping out through cracks in the elbow liner and then onto the floor. By the time the water droplets have made their way down to the basement floor they’ve picked up soot and other burned oil emission contaminants to produce a black dirty watery mess on my basement floor.

The HVAC contractor said there is little I can do to resolve the problem, other than to put a wide mouth metal bucket underneath the elbow to catch the dirty water. I should add that it is not a lot of dirty water. However, without the bucket I could see a black dirty water stain form on the floor approximately 3 feet in diameter.

With clay or masonry chimney liners condensation issues in the chimney liner is not an issue. There is less condensation formed as the hot furnace gasses are expelled up the chimney, because the clay and masonry chimney liners have better insulating properties. Second, any condensation that does form is quickly absorbed by the clay or masonry chimney walls as it starts to drip down the chimney. As a result, the moisture never makes it down to the steel flue pipe that connects the furnace to the masonry chimney.

One final negative aspect of the stainless steel chimney liner is that the dirty gas emissions that do exit the chimney often end up staining the roof of the home near the chimney. The stain is a brown rusty color. Then when it rains, the dirty brown rust chimney exhaust that is on the roof, ends up dripping down the roof and over the roof edge. In my case, I have a deck just below the roofline where the dirty water drips down. The roof run off then stains the deck a brown rust color.

In addition, the water bounces up off the deck and onto the side of the home leaving a rust looking stain on the house siding. Consequently once a year I need to scrub or repaint the deck and the side of the home to eliminate the discoloring.

Stone chimney

So if you are planning to build a home think long and hard before choosing to go with a stainless steel chimney liner. Yes they are cheaper to install than a masonry chimney, but at least with a masonry chimney you won’t have to live with the annoying effects I just described of a stainless steel chimney liner.

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