I'm looking to put in a wood stove in our house, using a current masonry chimney with a clay liner. I have a flue that measures 6.625 x 10.75 on the inside, with minor alignment offsets of about a quarter inch in some places. I definitely want to insulate my liner, and based on what research I have done, I would have to go with a rectangular liner to be able to achieve the same area as a 6" wood stove exit(28.26 in sq). Putting in a 6 in round liner won't work if I want to insulate, and an oval won't give me enough area. I don't want to go too large on account of a nightmare of not being able to cram it down the chimney. At Rockford Chimney Supply they offer numerous sizes to choose from, with the closest one being an area of 27.85 in sq. Does anyone out there have a rectangular flue? Pros, cons? What is a realistic amount to estimate for insulation and wiggle room when istalling a liner...RF told me to allow .75" on each side for insulation? I've heard of cheap liners, are Rockford's good? Thoughts?
A few thoughts and things I learned a while back. A round liner is better for venting. Smoke rises in a flue in a helical pattern. Rectangular flues have corners that disturb the smoke path. Rectanglular flues are a little more difficult to sweep in the corners. I would think an oval would be better than rectangular. Did you call or chat with Rockford? A quick check of their site has several oval liner sizes. 5" x 8.5" gives you 28.22 Sq inches. 5.5" x 7.85" gives you 30.07 Sq inches. They have a conversion chart for round to oval and rectangular liners. I purchased from them and their quality is fine. I would not hesitate buying from them again. As far as insulating, is this an interior or exterior chimney? If exterior, there is some benefit to insulating. When you insulate, there is a mesh roll that goes around the insulation to keep it in place. Adding extra wire around the mesh every few feet can help minimize hang ups down the tile. If interior, little may be gained. A block off plate at the damper is important, and the top cap plate is sealed at the top. Did you measure the opening of your damper plate? This can be a hang up point where grinding or cutting out some of the damper may be necessary to get a liner in. You may be able to purchase a small section of liner to pull through your flue on a dry run before purchase of a full liner.
It's an interior chimney. I did consider going larger or oval and not insulating, which would be great, but I was advised by the a local stove shop not to do that. My logic was just like you said, cap it at the top and bottom and the airspace insulates it, not? I suppose the fitting up top would have to be a really good seal, or a good wind would blow in and cool things down. Thoughts? I did measure the damper plate, and I do have to cut it out to gain clearance....not going to shove it through and reshape it.
If your flue tiles stick up a few inches above the top of the brick or cap on the chimney, that would be great. The top cap is sealed with an exterior weather siliconized sealant and a few pointed screws secure it to the clay liner. The liner is supported by the top cap also. If it is sealed good, there is little issue with cold air infiltration. I would call around to a few installers and get their opinion on the rectangular liner. Would the oval liner make the passing through the damper opening a bit closer to fitting through without cutting the opening? I know of a few people with uninsulated liners on interior chimneys and they have no problems running.
