Question: When the second storey to my house was added on, about 30 years ago, the HVAC people ran the vents for the second floor through a bedroom on the second floor. These were for the heating system that was in the basement, right next to the chimney. Therefore, this bedroom has a four-foot by four-foot finished box in the centre of the room, six feet away from the outside wall, which contains the chimney and the ductwork. This goes into the attic and from there the heat is piped into the rooms on the second floor. This occurs through small ducts in the ceiling, via flexible tubes that are on the attic floor. We have lived with this for 30 years and now would like to fix this situation, once and for all. Can a gas furnace in the basement be vented out a side wall that is six feet away? If so, we can get rid of the chimney that goes from the basement right up through the roof. Can heating/AC ducts be located on the outside of the building if they are super insulated? What can be done about this situation? I surmise we will have to hire a structural engineer to come up with a plan, but I am hoping that you can give a brief answer so I know in which direction to turn. Someone suggested just leaving the chimney, furnace, and duct work and putting an eight-foot bump-out onto that second floor bedroom. But, I suppose this would be more work and would have to sit on pilings and footings.
I thank you for your time, Martha
Answer: Relocating heating ducts for a forced air heating system can be a tricky job for a home that is already complete. While this may be a worthwhile endeavour, moving them out of the attic should be part of any planned renovation, to prevent issues with condensation and moisture.
A new high-efficiency gas-fired furnace should be able to vent out the foundation or side wall of your home, as long as it is not too close to any existing windows or other restricted items. A licensed HVAC technician or contractor should be able to immediately tell you that by looking at the location. If there is an issue, relocating the new vent and air intake may be possible on an alternate side of the home.
Moving your heating ducts and registers to a new location on the upper floor of your home will make sense once you have upgraded your furnace. This will allow removal of your old chimney, which will give you more unencumbered space in the bedroom in question. As long as the chimney is not supporting any portion of the upper floor system, this should be possible. Evaluation by a professional structural engineer will indeed be required.
As far as installing the new ducting in an exterior wall, that should not be considered an option. In fact, moving the small, flexible ducting from the floor of the attic to interior walls should be seriously looked at. The reason that heating ducts are not installed in exterior walls is that there is no way to properly insulate and air seal them, especially in an older home with minimal space in the wall cavity. Without this protection, condensation on the cold metal ducts in the winter is a given. This could also occur in the warm, humid summer weather, when the ducts are cooled by the air conditioning. This same issue can occur in the attic, but may have been more manageable in the past due to much more space for increased insulation.
Regardless, the best option after removing the chimney and chase is to relocate larger ducts to an interior wall or walls on the main floor. This will be most easily accomplished if one or more of the bedroom walls is common to other rooms upstairs. In that situation, the new ducts may be run horizontally inside the bedroom floors. These could be connected to the existing ducts at the bottom of the old chase, or new ducts run through the main floor walls. The location of these will be reliant on the existing conformation of the main floor and will likely require modifications to some walls on both floors. Also, removing a portion of the upper floor in the bedroom with the chimney will be needed, but that will have to be patched anyway, after the chimney and duct removal.
Because of this, plans for new floor coverings on the upper floor rooms should be included in the renovation plans. That way, any floor sheathing that is cut for installation of the new ducts can be easily patched. That will also allow for installation of floor level heating and return air registers, which will be a much better location than in the ceilings. The existing ceiling registers should be removed and the attic ducting either abandoned and well sealed, or taken out altogether, to prevent any future issues.
Relocating poorly installed heating ducts and registers, along with a nuisance chimney, is a good plan when upgrading your furnace. It will involve some removal of wall and floor coverings, possibly on both floors of your home, but should be worth the effort. Moving all of these to the warmer areas inside the living space will prevent possible condensation and moisture issues possible with the current duct location.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.