Chimney Provisions on the F-9A
Normally, JUCA builds the F-9A units with a 10" round stub connector. This is to make it compatible with any of the brands of Class-A Chimney which are available. The 10" size is for "standard-sized" door openings, and may be different for larger or smaller doorsets (see below). In recent years, most contractors and remodelers seem to prefer using Factory-Built Class-A Chimney over building a traditional entirely masonry chimney.
Metal Class-A ChimneyWhen we describe the pre-fab chimney as a 10" size, we are referring to the inside dimension. The various brands of Class-A chimney have different thickness walls. Many solid-pack brands have one-inch thick walls, making the outside diameter 12". A few have walls which are 1.5" thick, and there are some products with about 2" thick walls. Only one manufacturer still makes the once-popular Triple-Wall chimney which has a wall thickness of about 3.5", making its outside diameter about 17". When planning installation, these chimney sections also require a clearance to anything wood or otherwise combustible. Generally, this clearance is 1" to 2".
Masonry ChimneyOn request, the JUCA F-9A series units can be made with a "pocket" on top to be compatible with various sized tile liners used in standard masonry chimney construction. If this is the plan you want to follow, just specify the size tile liner to be used, such as 13 by 13, 13 by 17, 17 by 17, or whatever.
The "pocket" on top of a JUCA F-9A made for a masonry chimney is designed to allow a tight but sliding connection where the differential expansion of the metal and the masonry are provided for. The very lower end of the chimney tile liner actually "hangs" inside the pocket and is sealed around its perimeter.
There is no extra charge for the F-9A to be built for a masonry chimney.
For example, a traditionally wide-framed 36x28 doorset (with doors wide open) will usually have a clear opening of about 30" by 25" high. That's 750 square inches of opening area. The 10" round chimney has an area of 78.54 square inches, which complies with the 1:10 or better requirement. This ensures proper drafting.
Other size fireplace openings can require different sized chimney size (the corners in rectangular flues have little function):
|Opening Area Range||Round Chimney Size||Tile Chim Size|
|640-785||10"||8" by 12"|
|950-1130||12"||12" by 12"|
|1130-1540||14"||12" by 16"|
|1540-2010||16"||16" by 16"|
|2010-2600||18"||16" by 20"|
|up to 500||8"||8" by 8"|
How about a 48" wide doorset which has an opening approximately 43" by 26"? The area is 1118 sq.in., which means that a 12" chimney is appropriate to make sure it draws properly.
If your expected usage of an F-9AX see-through fireplace is such that you expect to regularly have both door sets open at the same time, then you need to DOUBLE the opening area in the table above, which is certain to then indicate a much larger (and more expensive) chimney system.
Sometimes, unusual circumstances also affect how a chimney draws. In most of the USA, where winter winds commonly come from the west and north, a relatively short chimney on the east side of a tall house may draw as well as one 10 feet taller on the west side of the same house! Tall trees 50 yards to the west of a house can cause occasional turbulence that might occasional draft problems for a chimney, again, especially if the chimney is on the west side of the structure. Even the shape of the building and its roof can influence the performance of a chimney. Contrary to some currently popular beliefs, going a little larger is sometimes a good precaution if there's any uncertainty as to the appropriate size. (Some people in recent years have argued that it's better to REDUCE the size of a troublesome chimney to reduce the chance of winds blowing air back down the chimney. Unfortunately, that logic also reduces the opportunity for the smoke to leave in the first place!)
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