Question on Existing Liner and New Liner

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Feeling the Heat
Dec 16, 2022
Hoping those smarter than me can chime in here. I got to the top of my chimney finally to measure for a new liner and cap. What I found up there surprised me a bit thus the questions.

Currently installed is a 4” liner for a propane insert that is removed (insert) and there were two liners attached to it. Up at the top of the chimney, the cap has one liner attached (pic below). There is a small hole for the other liner but it’s not attached. Is it possible it came loose? Or is the second flue a fresh air intake and all they did was run it partially up the flue?? There are no other exits to the chimney however there is a small opening with a grate outside but it’s below where the two liners pass through the damper. Can’t see the second liner from down the flue (pics attached).

Second question and more a confirmation. The oil furnace vents in it’s own separate flue that is round, approx 5” (pic attached). Why is it not capped as well? Never had an oil furnace like this previously so want to be sure it’s okay like that or not.

Final question is the current cap is attached to a 13”x13” approx clay liner. This cap appears non useable due to it appears to be designed for the 4” flue only. This cap is attached with only “compression” type bolts and my understanding is the new cap should be properly caulked to the clay liner, correct?

My current plan it to order the following, concerns?

Step 1: Select a Pre-Insulated Chimney Liner: 1 x Pre-Insulated Chimney Liner - 6 in. x 35 ft. (SKU: NDBP635-K)
Step 2: Select one stainless steel bottom connector per flue liner selected in step 1.: 1 x 6 inch Standard Tee, 10 in. Snout, and Tee Cap (SKU: NNC6FLEXTL-NC6ECL-K)
Step 3: Choose one stainless steel top plate: 1 x 6x13x13 in. Deluxe Flat Hinged Chimney Cap (SKU: RCDTCM6-88-K)

Left has liner attached with clamp. Right is just a 4” hole and no liner attached to cap.

Oil furnace flue

IMG_4339.jpeg IMG_4346.jpeg
The insert has 2 liners. One for exhaust and one for combustion air. They just didn’t run the liner to the top. It’s an option, but I don’t understand why not just hook it up? They were probably just short on the liners to do the job. It’s not wrong, a shortcut in my opinion though.
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Tks @webby3650! Late yesterday I Googled Mendota propane insert and it showed the second for combustion air. Thanks again for the confirmation.

Stove will be the Jotul F55 as I got a great deal on a new one at $2k. Plus I wanted and easy to use stove for my wife when I travel on business. She would not have liked many of the stoves with catalytic converters.
for wood stoves outside combustion air must be supplied from a location below the stove, not above like this situation. you run the risk of the combustion air pipe turning into a "chimney" if the right conditions exist. And well, the piping isn't rated or intended for this so it's a fire risk.

is 13x13" the inner dimensions of the flue you plan on using for the stove? you'll want an insulated liner for clearances purposes and to maintain flue gas temperature up to the cap. the OD of that will be close to 7.5" for a 6 " ID liner. you'll want to make sure you have enough space to fit the liner down the flue.
No need for combustion air as I always cracked a window with all the stoves I have ran and they have been fine. Also this house is not airtight as I wish it would be, then I would pups entertain running a dedicate fresh air intake and can easily do it under the stove.

The liner will be fully insulated and will fit on that flue without too many issues. There was no mortar evident hanging out from the clay flyers so it should be good down to the damper. Just need to cut that to make the liner fit.