What portion of your quote for my new high-efficiency furnace was for the chimney- liner?”
“That’s too much — no one else even mentioned we’d need an expensive liner — you trying to rip us off here?”
Chimneys — you can’t live with them and you can’t live without them — or at least you couldn’t until a few years ago. Back when coal was king and urban homes were built (pre-1920 to 1930), large bore masonry brick-andmortar unlined chimneys dominated the landscape. With efficiencies ranging from 30% to 50%, lots of combustion byproducts needed to be safely vented from homes. Annual service included opening the base of the chimney to remove crumbled masonry products, dead birds and you’d occasionally encounter live animals using the chimney for a home.
During one winter’s service call for a heating problem, I noticed the exterior north wall of the home had a shiny appearance. Closer inspection revealed it was a combination of frost and ice. The ice-sheen that had caught my attention led to the chimney’s protrusion at the roofline and it was obvious its shape outlined the chimney’s exact route and dimensions from basementto- roof. I’d never seen sustained flue gas condensation previously, but the basement floor markings revealed the old coal furnace had been replaced or converted and recently replaced with three new “high-efficiency” boilers. In 1978, that meant anything above 80%!
Three water heaters had been installed, too, and each apartment had its own gas meter. No longer a blastfurnace- like exhaust to build and maintain buoyant hot exhaust fumes, this was more like a pipe-organ-exhaust with each tenant possessing one of the keys to strike up an exhaust tune.
White effervescent trails ran from the chimney’s base down the wall and the same white powdery substance was evident at each joint in the combined flue piping. The flue piping looked like Swiss cheese! It was a classic case of sustained flue gas condensation, which contains both nitric and sulfuric acids. For every 100,000 Btu of combustion, a gallon of condensate can be generated!
The chimney had to be rebuilt with a terracotta liner installed. Today, we’d be either installing a chimney liner or direct-vented high-efficiency appliances.
The oddities we’ve seen where venting is concerned give rise to grave concerns: standard water heaters replacing direct-vent water heaters to shave costs while using the PVC vent line; high-efficiency furnaces or boilers vented into those old unlined masonry chimneys, which by itself is bad enough, yet the older atmospherically vented water heater continues to exhaust into the same chimney! You’ve seen similar applications, too.
Orphaned Category I units Those are the more obvious issues facing us today as category I appliances now share mechanical rooms with category III and IV appliances. As tricky as venting has become with today’s high-efficiency appliances, there’s one thing too many of us are ignoring — orphaned category I appliances and how they relate to these older chimneys.
The kind of damage I saw in 1978 caused what’s called “spalling” — a freeze/thaw cycle when moisture penetrates masonry products and expansion causes portions to flake off or crack and crumble.
NFPA 54 and 211 deal with chimney standards and sizing for the flue. Size, height, exposure (inside the structure, partially exposed or outside) and localized weather conditions all come into play, so there are no one-size-fits-all categories. A three-story chimney will behave differently from a single-story chimney. Lined chimneys vs. unlined chimneys, and so on.
There is, however, a somewhat reliable rule of thumb to give us a line that we should not cross where safety is paramount: the chimney’s dimension should not exceed the connecting flue’s dimension by more that sevento- one. In other words, the square inch area of the chimney must not be more than seven times greater than the flue piping. A 3-in. water heater flue is just a bit more than 7-sq.in., so the chimney must not be greater than 49-sq.in.; a 4-in. diameter flue is 12.588-sq.in. and its corresponding chimney flue limit is just over 88-sq.in. Those old 8 x 12 or 10 x 10 chimneys will lead to sustained flue gas condensation, damage the chimney and— eventually — result in property damage.
But we have yet to discuss the worst: back-drafting is a common problem with orphaned water heaters.
ANSI Z21.10.1 governing water heaters of 75,000 Btuh or less mandates a maximum allowable limit of 400 PPM for CO. The U.S. Department of Energy allows for one-minute of back-drafting for orphaned water heaters — maximum.
Lawyers don’t ignore this If you’re ignoring orphaned water heaters, lawyers and liability experts are not and you’d be wise to broaden the scope of your work to include chimney liners. The rules also state that orphaned water heaters vented into an unlined masonry chimney require the installation of a properly sized liner. Tell the homeowner, “Sir, you need a chimney liner because your chimney is unlined brick; its flue is too large to support proper drafting of combustion products, which include carbon monoxide. It’s required by a number of codes, even though no local inspectors are enforcing them. The other alternative would be to include the cost for a new direct-vent water heater and abandon the chimney completely.”
“Forget it; I’m going with the other guy.”
So let him and don’t be “the other guy.”