Home & Garden

What is/was this duct for?

  • Last Updated:
  • Dec 15th, 2020 3:51 pm
Tags:
Deal Fanatic
User avatar
Sep 27, 2006
5969 posts
2754 upvotes
Not so easy there Ma…

What is/was this duct for?

I discovered this insulated duct above the dropped ceiling in the basement. It stops above the washer and dryer in the utility room where the furnace also is. It runs to the back of the house but there's drywall up there so I can't see any further. A full bathroom was added by the former owner below where this duct runs. As far as I can determine it is not in use for anything. I "think" it may have been hooked up to the exterior vent that the basement bathroom exhaust vent is now connected to? Any other thoughts?
P_20201213_201708.jpg
The opening on the end is 3" and I believe the diameter of the insulated duct is also 3"
P_20201213_201638.jpg
It's very clean inside as per the photo
P_20201213_201647.jpg
The bathroom has another duct for its vent fan that exits the back of the house and runs parallel to this one along another floor joist about 2 feet away. I don't know the diameter of the bath vent duct.
P_20201214_222337.jpg
The furnace has an insulated 4" fresh air vent duct running to it that goes out the side of the house.
P_20201214_130147.jpg
13 replies
Deal Fanatic
Mar 17, 2004
5580 posts
1106 upvotes
Toronto
Get a long piece of string and tie a small metal washer to one end of it, then attach the other end FIRMLY to the inside of of the duct or end of a shopvac hose. Put the hose into the "blower" part of the shopvac, Stick it inside the duct. Use a plastic bag with holes on two sides and some duct tape to create a seal between the shopvac house and the duct. Turn on shopvac and then walk around the house to see if you hear rattling anywhere or look at the outside vents to see if you notice any warm air coming out if it's winter.

Other than that I've got haven't got a clue.
Deal Guru
Jan 25, 2007
12695 posts
7861 upvotes
Paris
Looks like my parents air exchanger hose.
Deal Fanatic
User avatar
Sep 27, 2006
5969 posts
2754 upvotes
Not so easy there Ma…
Jerico wrote: Looks like my parents air exchanger hose.
There's no air exchanger but that makes me wonder if an air exchanger was an option when the house was built and that's why the hose is there? As the builder cheap-out alternative this house has the switch on the main floor near the thermostat labeled as "ventilation fan" that turns on/off the upstairs bathroom fan.
Deal Addict
User avatar
Feb 25, 2004
1915 posts
1501 upvotes
Longueuil
It looks similar to what I have in my house. In my house that duct in the basement is an intake. The builder installed a thermostat switch in the middle of the house that starts when the humidity level set is reached. Once it happens, it will start the bathroom fan and open this intake flap so that air exits from the bathroom fan and enters in the basement. If I use the switch in the bathroom it will start the fan without opening the intake in the basement.
Try not! Do or do not, there is no try...
Deal Addict
User avatar
Sep 22, 2005
4047 posts
3277 upvotes
Ottawa
Do you feel cooler air coming from this duct? Could be an outdoor fresh air duct for the furnace. I have a similar one hanging just above the furnace's intake pipe and it comes directly from outside.
Deal Fanatic
User avatar
Sep 27, 2006
5969 posts
2754 upvotes
Not so easy there Ma…
Oni-kun wrote: Get a long piece of string and tie a small metal washer to one end of it, then attach the other end FIRMLY to the inside of of the duct or end of a shopvac hose. Put the hose into the "blower" part of the shopvac, Stick it inside the duct. Use a plastic bag with holes on two sides and some duct tape to create a seal between the shopvac house and the duct. Turn on shopvac and then walk around the house to see if you hear rattling anywhere or look at the outside vents to see if you notice any warm air coming out if it's winter.

Other than that I've got haven't got a clue.
The shop vac was among the things I gave away or sold before I moved. I ended up selling that for less than $10 complete with bags and accessories.
Deal Fanatic
User avatar
Sep 27, 2006
5969 posts
2754 upvotes
Not so easy there Ma…
gumby wrote: Do you feel cooler air coming from this duct? Could be an outdoor fresh air duct for the furnace. I have a similar one hanging just above the furnace's intake pipe and it comes directly from outside.
It does look like it could be a fresh air vent but no cool air ever seems to come out of it. I do have a fresh air duct for the furnace, it's just like yours and it's in the fifth photo.

Edit: fifth photo
Last edited by fergy on Dec 15th, 2020 2:03 pm, edited 1 time in total.
Deal Guru
User avatar
Mar 10, 2005
12349 posts
5403 upvotes
OP

That could be an old furnace vent. Older furnaces were vented through the roof. Look at your roof from the outside... Is there a short vent sticking out around that location?
"If you want to improve, be content to be thought foolish and stupid." - Epictetus
Deal Guru
Jan 25, 2007
12695 posts
7861 upvotes
Paris
blexann wrote: OP

That could be an old furnace vent. Older furnaces were vented through the roof. Look at your roof from the outside... Is there a short vent sticking out around that location?
That is a plastic wrapped flexible line, not solid double walled b-vent. There either was an air exchanger and it was removed, or it was installed for a future one.
Deal Guru
User avatar
Mar 10, 2005
12349 posts
5403 upvotes
Jerico wrote: That is a plastic wrapped flexible line, not solid double walled b-vent. There either was an air exchanger and it was removed, or it was installed for a future one.
Makes sense. I have something similar but without the plastic piece.
"If you want to improve, be content to be thought foolish and stupid." - Epictetus
Deal Fanatic
Mar 17, 2004
5580 posts
1106 upvotes
Toronto
fergy wrote: The shop vac was among the things I gave away or sold before I moved. I ended up selling that for less than $10 complete with bags and accessories.
Use the blower end of the vacuum cleaner?
Deal Addict
User avatar
Feb 25, 2004
1915 posts
1501 upvotes
Longueuil
fergy wrote: It does look like it could be a fresh air vent but no cool air ever seems to come out of it. I do have a fresh air duct for the furnace, it's just like yours and it's in the fifth photo.

Edit: fifth photo
You need to have air exit to have air enter. Start your bathroom and kitchen fans on max speed with all outside doors and windows closed, you should feel air coming in if it is an intake.
Try not! Do or do not, there is no try...
Deal Fanatic
Jun 24, 2015
8524 posts
2944 upvotes
0 downvotes
if its not hooked up, maybe they should have capped it off too instead of leaving it open so critters and stuff can crawl in?
Supermarket worker at Fortino's
I'm Not a Wise Guy but more of a Good Fella~!
Drive an Escalade

Top