ductshvac
Most of the duct dampers don't provide 100% seal from air flow. The below picture might be. I have collar with damper, But its just not enough to stop/bypass the air flow.
what is this called in the picture highlighted, Fiber stripping, what kind of it is ?
It seems the strip is glued to the metal.
thanks!
Don't use duck/duct tape on HVAC ducts, use foil tape. Duct tape isn't designed to take the heat variations in duct work and will lose it's adhesion over time.
More than likely you can unscrew this section of duct work and remove it instead of cutting holes. With it removed, you can either fix the damper or replace the section with a new damper. If the damper itself is fine, the problem may be a clog in the duct itself which is easier to clean with the duct opened up. I've used the dryer vent cleaning brushes from Gardus which would work well for this job:
When reassembling, use self taping sheet metal screws to attach the ducts, and then cover the seams with the foil tape.
There are a few ways to accomplish this. On the cheap DIY side, you could cut a few pieces of tight fitting cardboard (stack them and tape them together) to create a plug. I would punch a couple small holes in it and make a rope handle to pull it out.
On the more convenient side, you could get a expanding plug. The link shows a 6" plug... perhaps that's the size of your damper?
On the industrious scale, you could locate the duct and install a couple more dampers in series. Having a few dampers should effectively restrict air flow.
You could also potentially build a plug from from a bag and a can of expanding foam. Here's a video about a commercial product (instapak). Obviously you can do this yourself... but you might need a couple of practice tries to get the amounts right. Essentially, you would put the bag in the area that you want to seal and spray the foam in the bag and tie it off. You don't need or want air in the bag when you add the foam. Most cans of expanding foam come with a nozzle. You just want to insert the nozzle into the bag, spray it, and tie off the bag. Then you could set a board or something on top (or in front) of the damper so that the foam doesn't expand into a muffin shape.
Best Answer
It may be a simple weatherstripping that was added.
It is rare to completely block a trunk line. In fact I have seen trunk lines split open because they were blocked off. The home owner did not understand what he was doing when trying to convert a multi level home from 60-40 to 40-60 and split a large duct in the wall.
In another case the blocked both main trunks with the fan on and it split the duct from the Y to the furnace.
The few times I have done this is for garages or basements not normally conditioned so a more positive or complete seal is made.
To do this I have used weather stripping. I have used silicone, but have found metal riveted in place with a compliant rubber stays in place and seals better.
The quality of the seal and how well it is installed can seal close to 99% and self adhesive sponge rubber seals can do as good but don’t last long and can blow out with higher duct pressures.