chimneys

jim lockard

I'm with Mark H the top of the chimney is wearing away. How will a flue liner protect that? J.Lockard

Karl_4

chimney's

I've got a 80,000 btu oil forced air and a Bock 40,000 oil water heater using the same flue. The problem is that it seems that the top flue tile is deteriorating. I have'nt ruled out moisture finding its way in and freezing. Does fuel oil give off any sort of chemical by-product that would eat the tile?

Bob Harper

oil flue corrosion?

Sulfuric acid is the biggy along with water vapor. Incidentally, the higher the sulfur content of the oil, the higher the dewpoint.

Call a chimney pro. Sounds like you need a liner. From those BTUs, all you'd need is a 5" but have the pro double check everything. Make sure you have a clean out feature at the base of the liner.

Mark Hunt

Bob


How would a liner correct this issue?

Mark H

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[Deleted User]

How old it the

chimney?? if the chimney was errected in 1920 some tile degradition is normal. have it lined

Bob Harper

chimney damage

Almost all chimneys suffer some damage at the top from 'freeze-thaw' cycles. Water repellents and coatings can minimize water intrusion into the chimney so the flue doesn't get damaged so much that way.

The main culprit here is condensation. Apparently, for this chimney the amt. of heat lost up the stack is not enough to eliminate condensation. Once condensation occurs, the masonry is no match for the acidic conditions. As the insidious cycle repeats, the flue spalls, flakes, cracks, and erodes dropping flakes, chunks, mortar, bricks, etc. down into the breeching where it can block the flue. In extreme cases, it can leak water vapor and CO into the home.

A stainless liner does not reverse all the conditions causing the condensation but it does effectively deal with their sequelae. First, the liner should be sized to the appliances connected to it.By matching the cross sectional flue area to the burden placed upon it, there is a better chance for proper venting and firing of the appliances. Oversized cold, damp high thermal mass flues are hard to start and can kill a borderline draft. If the appliance cycle rate, efficiency, temp. rise, etc. all add up to shorter,cooler cycles, condensation becomes even more of a concern. While not correcting the firing of the appliance, the liner tolerates the net result much better than the masonry. Once condensation occurs, the stainless tolerates it much better than the masonry without the fear of tiles collapsing causing a fatal blockage. The low thermal mass of a liner means it heats up very quickly for a stable draft. If the liner is insulated, it will help maintain a decent draft during tail out or when off duty.

With a properly sized liner, often adjustments can be made to the heater so it has a better chance of operating at its optimum potential.

Just don't forget to incorporate a clean out feature for oil flues.

Mark, did that answer your question about where I was coming from?

Mark Hunt

Yup

Have you seen this picture? Pretty amazing.

I find that most of the time chimney rot is directly tied to underfired equipment. Exhaust temps lower than where they should be. You mentioned this in your post.

Chimney liners, as you stated, do not correct combustion issues. Unfortunately, they have become the cure-all when venting issues arise.

Your analysis may very well be correct. The top of the chimney is exposed to weather and it could be that the morter is finally succumbing to years of exposure. Combine that with the SOx and NOx coming out of the oil burning appliances.

Before I would recommend a liner, I would test the combustion appliances to make sure they are not the leading cause of the chimney failure.

I am going to send you my cell phone number via e-mail. I'd like to chat with you if you ever get a chance.

Mark H

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