Flue liners are an important part of any furnace, water heater, boiler, or fireplace system. Liners have been required by code since 1927, but have been in use since the 1870’s. In a nutshell, the purpose of a flue liner is to keep toxic flue gasses such as Carbon Monoxide, other aldehydes, and tar vapors inside the flue and allow them to exit the house. It was found early on that with masonry chimneys, the mortar joints tend to deteriorate over time and develop cracks and gaps that allow gasses to leak through them. So, liners were invented. Vitreous clay tile flue liners were created to line the interior chimney so that flue gasses could not escape the flue. This is extremely important for the health and safety of the occupants of a home.
However, over time, rainwater, moisture, and acidic flue gasses eat away at mortar joints between the liner sections. Clay tile flue liners are made in two-foot sections and installed ahead of the exterior masonry chase. They have a bed of mortar between each section. When these mortar joints erode, they create gaps between the liner sections – and we are back to square one with toxic gasses leaking into the house.
|A liner has been removed and one remains|
When rehabbing a house, a contractor may find that there is no liner installed in a masonry chimney. This is more common in older homes with utility flues serving heating appliances and water heaters, but occasionally is found with fireplaces as well. It is extremely common, however, to find a flue liner with missing mortar joints. This can be remedied in most cases with a method using a ceramic joint filler, which is applied using a heavy-duty vibrating bell sponge while pouring the mix from above the flue liner. It involves special equipment and trained professionals to do the job. In cases with large gaps between liners this method cannot be used, and relining is necessary.
A second common issue with flue liners is incorrect sizing. If a liner is not correctly sized to the appliance, smoking or backup of toxic gasses can result. This often occurs when a high efficiency furnace is installed, leaving a water heater to vent on its own, which it cannot do in an oversized flue. A liner for the water heater will be necessary unless a replacement water heater that vents out the side is used instead. An incorrectly sized flue liner serving a fireplace will cause backup of smoke and toxic gasses into the home.
|Stainless steel liner with a single flue tile on top |
involves removal of the cement cap and extraction of the clay tile flue liner,
installation of a replacement stainless steel liner with insulation, and
rebuilding the cement cap. Other demolition such as removal of a damper casing,
firebrick, or a wall may be necessary. Smoke chambers are often in poor
condition and need to be parge coated with insulating mortar. It is important to use a liner with the same
I.D. dimensions as the previous liner, or in some cases, larger, and the only
way to do that is to take the old liner out first. In rare cases, the flue is
oversized so installation of a new liner may be possible without extracting the
Clay tile flue liners being installed as masonry is built up
Codes must be followed with flue liners – Chapters 10 and 18 in the International Residential Code cover most of this information, and the National Fire Protection 211 Standard for Chimneys, Fireplaces, Vents, and Solid Fuel Appliances also applies since it is the industry standard. We also follow the NFPA 54 National Fuel Gas Code.
professional chimney contractor should do this type of work since they are
familiar with the codes and standards and have the equipment and expertise to
do the job. In the greater Kansas City area and other jurisdictions across the U.S., a Class DM Master
Mechanical (HVAC) Contractor License is needed in order to reline flues, and a
permit is required for the work, with an inspection by the building codes
A stainless steel flue liner being prepped
The cost to reline a flue can very greatly and is determined by the type, size, and length of liner needed and difficulty level of the job.