Be cautious about reducing the cross sectional areas of the flue when relining.
Be cautious about reducing the cross sectional areas of the flue when relining.
The smoke chamber should be parged with insulating mortar to protect any adjacent combustible materials and provide a smoother smoke path.
The smoke chamber should be parged with insulating mortar to protect any adjacent combustible materials and provide a smoother smoke path.

If you ask 100 chimney sweeps how they reline a masonry chimney you'll get 100 different answers. This is due to many factors: lack of building codes requiring licensing and training, lack of specific and complete training by the chimney industry, and an attitude by many sweeps who have figured out the basics, but have gone no further in their quest for knowledge.

A sweep may have been doing a relining method a certain way for 15 years, but it doesn't mean there may be something he has not overlooked that should be addressed. Some of the “old guys” are just as guilty of omitting important steps in relining as the “new guys.”

We often offer our customers two or three relining methods and let them choose which they prefer. They usually choose steel. If relining with tile, make sure to use a non-water soluble mortar and seal the flue to the smoke chamber.

Tile relining

The common mistakes we see with the tile relinings are:

  • Using the wrong type of mortar, or even using caulk placed between flue tiles;
  • Not cleaning off the extruded mortar from the joints;
  • Not sealing gaps between the flue tile and the smoke chamber. (If smoke goes up between these gaps what is the point of relining?); And
  • Ignoring unparged smoke chambers.
  • Tile liners are tricky. We still use a tool we invented 20 years ago that allows us to line up tiles right on top of each other, even at lengths up to 20 feet if the flue is straight. There are other products available to assist you in this process.
  • Some chimney sweeps ask why we would reline in tile since no manufacturer warrants tile liners. But in some cases it is what the customer wants. Or since materials are more readily available, we can do the job more quickly.

    Steel relining

    The most common mistakes here are:

  • Failure to properly size the liner (often down-sizing the flue);
  • Failure to seal the bottom of the flue liner to the smoke chamber;
  • Failure to install insulation (ceramic wool or TherMix); and
  • Ignoring unparged smoke chambers.
  • The manufacturer of the flue liner will have requirements for properly installing its products and will include instructions for what must be done to qualify as a laboratory listed installation. Yet some sweeps claim to be installing U.L.-listed flue liners, when in fact, if all of the requirements are not met, the liner is not U.L.-listed and the warranty is void.

    Contractors who install steel flue liners inside of tile liners without sizing the new liner to the firebox are asking for trouble. If a 40-inch-wide, 26-inch-high firebox measures 1040 square inches, and an 8-inch liner with 50.24 square inches is installed inside of 13x13-inch flue liner, the numbers don't work.

    The cross sectional area of the flue should be about 1/10 the cross sectional area of the firebox opening for best performance. For an average chimney, the flue must measure at least 104 square inches, which the 8-inch diameter flue liner does not. Poor draft and a smoking fireplace will result. Of course, other factors come into play, such as the height of the chimney, offsets in the flue, and location in the house.

    If the fireplace doesn't work, and it did before, the installer is liable. The solution to this issue is to extract the old tile flue liner and install a properly sized stainless steel liner.