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ARTICLES - Chimney - How to Install an Insulated HT Chimney straight up in a two story house

Installing an insulated HT chimney up through another floor is often the best way to run a chimney in a multi-story situation. This scenario might include the basement of a ranch house for a furnace or finished basement stove, or a first story of a typical colonial house. This straight up technique will result in better draft than a chimney which goes out and up (Tee installation) and also may cost less in materials for the DIYer.

As with any chimney installation, planning is the key. Study the layout of your house and the proposed location of the stove. It may be that there is a large closet or the unused corner of an upstairs room that the chimney can extend through.

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The sketch in figure 2 shows a typical manufacturers drawing on how to accomplish such an installation. However, your real world layout may differ in some ways. There is a good chance that some of your floor joints, ceiling joists and rafters may not line up verticually, which might call for the use of 15 degree elbo offsets in the second floor or attic. Once again, careful planning BEFORE you cut too many holes is the key!

Tools needed - ideally a cut-saw (reciprocating saw), circular saw and drill - as well as common carpentry tools such as hammer, caulk gun, plumb bob, level and measuring tape.

The series of pictures below are courtesy of Hearth.com forum member Pagey, who was good enough to share them with all of us. The basic steps can be described as:

1. Make your Plan - measure, use a plumb bob to determine exactly where your holes will go and whether you will need 15 or 30 degree offsets in your insulated chimney. Also plan the setting of your stove and the chimney connector (the pipe from the stove to the ceiling) type and layoout. Chimney connector can also be offet using adjustable or fixed els.

2. Purchase all needed chimney and material. In the case of a straight up chimney, this would usually include (starting at bottom):
a. Finished ceiling support box - for the 1st ceiling above the stove. This frames into the ceiling and holds the entire weight of the chimney system.
b. Pipe sections and els of enought height to get the chimney above the roofline to code.
c. Firestop or other manufacturer supplied part to make certain debris cannot fall into the ceiling support box.
d. Firestop Radiation Shield - this allows the pipe to pass through the 2nd ceiling and maintain proper distance to combustibles.
e. Attic insulation shield - this makes certain that insulation cannot rest against the pipe. HT pipe needs to have air around it to provide proper cooling.
f. Flashing, storm collar and topper to complete the installation.

3. Frame in the Ceiling support box as per the manufacturers instructions. Cut out the flooring on the second floor to provide the required clearence to the HT Chimney (usually 2”).

4. Drop a section of the HT chimney into the support box from above - then use a firestop or other specified fitting to close off the remainder of the hole in the floor above. Check the vertical leveling using your plumb line and mark and cut the hole in the 2nd floor ceiling. Install the Firestop Radiation Shield.

Note: some pros will mark and cut ALL the holes - 1st floor, 2nd floor and roof - before proceeding with the HT chimney sections.

5. Mark and cut the roof opening and install the flashing, making certain to properly place the top edge under the shingles. Depending on the age of the roof, you may be able to remove some shingles and have the sides of the flashing be properly seated under them.

6. Box (frame) in the part of the chimney which extends through the second floor, being careful to maintain the required clearance around the HT chimney. Note: You cannot leave this pipe exposed due to the danger of objects resting against it or coming in contact with it.

Congratulations on a job well done! Your HT straight up chimney is likely to have plenty of draft to make your wood burning appliance work at it’s best. In addition, you will find that cleaning this chimney from the roof is quite simple. The chimney can be swept right down into the stove in some cases where the stove design allows for it. In other cases, the chimney connector can be removed and a heavy plastic trash bag taped over the bottom of it - the soot can then be brushed right into the bag.
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