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lobos 11-07-2010 06:11 AM

Rigid vs. Flexible Chimney Liner

I'm planning to buy a wood burning fireplace insert and I've visited several vendors in my area. The topic of chimney liner type was raised by one of the salesman I talked to. He was adamant that his company only installed flexible liners as a last resort (i.e. if the chimney design forced him to use one). He claimed the advantages of a rigid liner were as follows:

  • More robust, and as a result would stand up better to a chimney sweeper that was rough or careless causing the liner to become detached.
  • Creosote was less likely to build up
He conceded that the rigid liner option was about 30% more expensive for my set up, but was adamant about the advantages outweighing the extra expense.

Of the other vendors I spoke with, none agreed with his points. All seemed to be of the opinion that there was no risks associated with a flexible liner. One salesman directly opposed his creosote claim by countering that because a flexible liner moves during burn times, the creosote has a tendency to become detached and fall back down into the insert.

Can anyone out there offer any insight into the claims of these particular salesmen?


double-d 02-08-2011 03:25 PM

Rigid vs. Flexible Chimney Liner
Most rigid chimney liner sections are made from 304 alloys or 316 stainless steel. The 316 is more resistant to saltwater and runs a little higher in price. Rigid pipe comes in sections ranging from 6 inch to 4 foot sections and is usually round in shape. The most common wall thickness is 24-gage (0.024 in.) or 22-gage (0.029 in.) stainless steel.
The seam running down the length of each liner sections has factory Smooth-Weld seams. Individual liner sections are joined together with the male end facing down. Stainless steel pop rivets and stainless steel screws secure the joints.
Pop rivets are recommended since screws may work themselves loose from the expansion and contraction of the liner. A storm collar over the support clamp at the top plate, above the chimney, prevents moisture from entering the chimney along the outside of the liner.
A smooth wall rigid liner offers the most efficient venting due to decreased turbulence, and is simple to clean. You can shape it to take full advantage of every cubic inch and offer maximum draft. It can be shaped into rectangular, square or oval. The rigid liner can become heavy when trying to install, and while attaching additional sections. Rigid liner can only be used when there are no bends or offsets in the system.
Flexible liners, unlike the rigid pipe, are one-piece liners. Flexible liners should be used if your chimney is less than perfectly straight with jogs or offsets, and are flexible enough to form to the shape of the flue. The flexible 316TI is a stainless steel alloy with a small amount of titanium added. Its make-up, allows it to resist acids and the stresses of hot and cold cycles. It can be used with solid fuels (wood, coal and pellet), gas and oil. It can withstand temperatures up to 2100 degrees.
Flexible liners are available in three thicknesses ranging from .005 for better flexibility, .006 (the long time standard) and the new .013 Double Wall Smooth Wall liner. The smooth wall interior cuts down on creosote buildup which can cause devastating chimney fires. It also increases chimney draft by 20% and makes cleaning a breeze.
Even though standard flexible liners, have a corrugated surface, they tend to collect less creosote when used to vent wood fireplaces and stoves or inserts, because they flex as they expand and contract with temperature fluctuations, causing buildups to loosen and fall away. The ease of installing a flexible liner (and affordability) far outweigh any difference between the rigid and flexible liners.
Both rigid and flexible liners use stainless steel tee sections at the thimble and clean out areas along with a variety of connectors, top plates and rain caps to make up the kits.

stuart45 02-08-2011 03:32 PM

Have you considered a perlite concrete cast insitu liner?

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