You need to slide that handle over to the larger slot and then pull it down or push it up.
Ok, good you got it. It was hard to tell from the picture which way it operated. You could try some WD-40 but these dampers are pretty cheaply made and don't have a precision fit. You should try working it back and forth to loosen it up a bit.
What are these copper pipes and do I need to do anything to them
before covering them with a wall?
Since they have been open behind a wall for nearly 40 years without an issue i think is is safe to assume there is no problem.
If you do not want to try and figure out where they come from and re-purpose them then just solder caps on them and build your wall.
Consulting with an HVAC technician advised:
disconnect the left duct from the fireplace just below the first floor subfloor
disconnect the right duct just above the wye on the first floor
route the furnace + water heater duct to the left duct using 6" round B-Vent. The technician pointed out that it's key to match the existing brand (I have Ameri-Vent) ...
You can cap it with a chase cover if its not functional, your local sheet metal shop can probably make one at a low cost, here's an example:
https://www.kmsheetmetal.com/shop/Chimney-Chase-Cover-p195969014[![enter image description here]1]1
What I did. I purchased a new flexible elbow and borrowed a five blade HVAC crimper from my local Tool Library.
I carefully spray painted the transite asbestos flue pipe, just to make it a bit less powdery if touched. Then crimped the standard 5" pipe down to about 4.5", and sent it home with improvements to the straps holding the entire pipe up. ...
You are likely correct with your analysis.
All the properly capped chimneys I have seen have an air vent top and bottom to allow slower air movement compared to the original chimney.
When people have "hidden" the fireplace but not capped the chimney, they sometimes just put a mesh over the top end of the chimney to prevent birds getting in and an air ...
To properly seal the fireplace flue, I’d 1) Install a flue cap, 2) put a cement “wash” between the flue and fireplace bricks for positive drainage, 3) Install a clear sealer on the fireplace bricks, 4) Install flashing between the fireplace bricks and the roofing material, 5) verify that the roofing around the fireplace isn’t leaking.
If the flue only ...
To answer your question I suppose it could although I have never seen it. I doubt your vent cap is too restrictive unless you have or have had in the recent past a bad sooting problem. I rather suspect the B-vent is not being kept warm enough. It has to be in a warm space basically all the way to its termination. No drafts. No cold spots. Warm. It ...