Question: We recently had a high-efficiency furnace installed. As the furnace is vented through the side wall, we would like to know how to go about removing the chimney on the roof and the flue lining which goes down to the basement. I would like to utilize the space in the house currently occupied by the chimney. The chimney appears to be aluminum, rather than brick.
Linda Ballantyne, Winnipeg
Answer: There are a couple of considerations to be aware of in relation to removal of the old furnace chimney and vent from your home. Although actual removal may be quite straightforward, repairs to a few areas in the home afterward can be tricky.
Although you have not given information on the exact location of your chimney, I will make the assumption that it is located somewhat near the centre of the home. I base this conclusion on the fact that you want the additional space, which would be limited if you had a chimney located on an exterior wall. If you do have an exterior chimney chase location, the exterior repairs will be more complex due to the need to rebuild part of the eaves after chimney removal.
Unlike an older brick or masonry chimney, metal chimneys can be relatively easy to remove from your home. Yours is likely a double-walled metal B-vent covered with a thin, galvanized metal chimney chase above the roof. The B-vent is the actual flue for the older furnace and is normally secured only at the basement floor and the ceiling where it enters the attic. The top may be partially secured to the metal chimney chase above the roof, but all these areas should allow for easy dismantling of the sections of B-vent.
The vent can often be partially removed by accessing the roof and attic at the same time. This will require at least one person to physically manoeuvre the metal pipe above the roof while another helps disconnect it inside the attic. If you have a roof with a typical pitch and an easily accessible attic hatch, this may be quite easy to do. Alternatively, if you have a low-slope roof or a steeply pitched roof where the chimney is located, removal may require installation of temporary platforms or opening larger sections of the roof, which will increase the complexity of the job.
Once the B-vent is removed above the attic floor, the remainder can be dismantled and removed from the basement or main floors of the home. This may require removal of wall coverings around the vent, often in a closet or other area attached to a partition wall. If the vent is not covered and can be seen inside a closet or other cavity, removal should be quite simple. Either way, the cavity occupied by the vent inside the home may yield even more usable space than the basement section after it is vacated.
The next steps will likely require the aid or one or more contractors. Once the vent is removed at the exterior, the metal chimney chase above the roof can be taken down. This will require the removal of several shingles and flashing around the base of this metal box to allow disconnection from the roof sheathing.
After this area is open, the roof sheathing will have to be patched and the entire exposed area covered with new shingles. If your roofing is older than a couple of years, repairs will require an experienced roofer to ensure a waterproof seal and proper match to the existing roofing. Once the roofing is patched, the internal repairs can be safely completed.
The final critical area to repair is the floor of the attic and the ceiling below, where the old chimney exited the living space. The underside will have to be patched with drywall.
If you currently have a polyethylene air/vapour barrier in the attic, this will have to be extended and properly caulked or sealed to a new section of poly placed over the old opening. Alternatively, a piece of rigid extruded polystyrene insulation may be cut to fit and sealed in place to provide a good air/vapour barrier.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors-Manitoba (www.cahpi.mb.ca). Questions can be emailed or sent to: Ask The Inspector, P.O. Box 69021, 110-2025 Corydon Ave., Winnipeg, MB, R3P 2G9. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca