Tips & Tricks for Historic Chimney Restoration

On a weekly basis we get phone calls from homeowners across New England who are frustrated and confused. They typically have pre-1900’s New England Colonial and Federal-style homes, and want to bring their original fireplaces back into working condition. 

Usually they have already had one or several chimney sweeps look at their fireplaces, and each time it’s the same story: The chimney sweep says that the flues have no chimney liner and that they can’t reline the chimney to get the fireplace working again. The only option, they say, is to install a wood stove or some type of insert in the fireplace. If you own one of these beautiful homes, you know this “solution” doesn’t achieve the goal of keeping a house in its original condition.

Why can’t a liner be installed for a fireplace? (Hint: it can!)

This is a trick question, because the answer is: IT CAN! Older chimneys often vent multiple fireplaces, and they were designed with long narrow flues. These flues are usually under 6 inches across and much longer the other way (sometimes over 4 feet!). The only way to reline a flue of this shape and size for a fireplace is to use a long rectangular chimney liner to mimic the existing passageway in the chimney. Round, stainless steel liners cannot be used because you cannot install a single round liner with enough volume to vent a fireplace.  Let’s illustrate this with an example.

Picture Below Shows 7” round liner (38.5 in2)
Picture Below Shows 7”x23” rectangle liner (161 in2)

The first thing to understand is that the size of the fireplace chimney liner needed depends on the size of the fireplace opening. You can figure this out by measuring the height of the fireplace opening and multiplying it by the length of the fireplace opening. Let’s say your fireplace is 42” in length by 32” in height, making the cross-sectional area of your fireplace opening 1344 in2. Now, if you wanted to install a round liner in the flue, you would take the cross-sectional area and divide it by 12; this gives you the cross-sectional area of the liner needed. 1344in2/12 = 112in2, so you would need to install, at a minimum, 12” round chimney liner to vent this fireplace properly ((6in*6in)*3.14= 113in2). The equation gets more complicated from here, so we’ll just leave it at that for now.

Now let’s say the flue venting your fireplace is a rectangular shape that is 8”x24”. Clearly, a 12” round chimney liner is not going to fit into this flue; your liner needs to be less than 8” across. If you had a 7” round liner, the cross-sectional area would be 38.5 in2 ((3.5in*3.5in)*3.14). This is not large enough to vent the fireplace, which we determined needed a liner of at least 112 in2. In fact, it’s a third of what the fireplace liner should be. If you installed this small of a liner for the fireplace, the fireplace would not draft properly and smoke would fill the house when in use.

Since these kinds of chimneys have long, narrow flues, it’s better to install a rectangular liner. For instance, if we installed a 7”x23” chimney liner in the example above, this would give us a cross-sectional area of 161 in2, which is more than sufficient to properly vent the fireplace.

Picture above showing a 5 fireplace reline project in Woodstock Vermont. Notice the top left chimney liner (long rectangular shape).

What type of chimney liner would you install in this situation?

We would install a stainless-steel chimney liner known as “heavy-wall flex”. It is flexible (which is needed to navigate down the chimney) but has very little corrugation on the inside (meaning it is fairly smooth). This increases draft in the chimney and reduces turbulence of the flue gases, therefore reducing creosote buildup. We believe this is the most durable chimney liner made today, which is important because we want it to last as long as possible.

Why can’t most chimney sweeps install these liners?

A large rectangular chimney liner constructed of the proper material and wrapped with the proper insulation can be extremely heavy—sometimes over 500 pounds. Furthermore, scaffolding must be erected, or a crane used, to raise this liner up above the chimney and then lower it slowly down the chimney. A one- or two-person crew simply can’t handle the scale of this installation.

Why can’t most chimney sweeps install these liners?

Although Chimney Savers is one of the few companies in New England that still gives you the option of cast-in-place chimney liners, a cast-in-place liner isn’t the best solution for venting this type of fireplace.

For one thing, cast-in-place liners are round. As discussed above, pre/early-1900’s homes often have long, narrow flues, which makes getting a liner with enough volume to vent the fireplace a challenge.

It is also a common misconception, even among chimney professionals, that the cast-in-place system allows you to navigate large bends in flues. This is not the case; it is actually more difficult to install cast-in-place liners in chimneys that have bends.

How do you seal the liner in the smoke chamber?

We have developed and mastered several ways to seal up the chimney liner in the smoke chamber area.  When a liner is installed, there is often a gap between the stainless-steel chimney liner and the brick passageway (flue) that it is installed inside of. This area, known as the smoke chamber, is often several feet above the damper of your fireplace and is hard to reach. This gap needs to be sealed; otherwise, smoke and gases can travel up around the chimney liner. We use the cast-in-place lining material to pour this smoke chamber and seal the gap. We do this by blocking off the fireplace damper and pouring the cast-in-place lining material down the chimney. You can think of it like we’re filling the smoke chamber with concrete. We then allow this concrete-like material to harden and then remove the blocking from the fireplace damper. The cast-in-place material is still not completely dry and we are able to carve a passageway from the fireplace throat to the liner. This cast-in-place material not only seals the gap between the smoke chamber and the liner, it also insulates the smoke chamber, making it safer.  

Before Parging
After Parging

Would I see the stainless-steel liner at the top?

No. In our historic restoration projects we have several methods of finishing the chimney top to hide the stainless-steel chimney liner and keep the top of the chimney looking original. on.

What other obstacles may we run into?

Sometimes the flue passageway was designed too small for the fireplace. Or, in some cases, the flue makes very sharp bends inside the chimney, instead of going straight up. In cases like this we have lowered our technicians into the chimney and removed Wythe, or divider, walls inside the flue. Wythe walls are brick walls used to separate flues within the same chimney. Removing these walls gives us more room to install a larger chimney liner.
Removing Divider Wall
After Parging

Why does Chimney Savers get the call?

We have developed a reputation in New England for being able to solve chimney problems that no one else can, and to be clean, friendly and professional while doing so. Through word-of-mouth of contractors, homeowners, engineers and other chimney professionals, we now have had the opportunity to work on large historic projects and unusual projects across New England.