I have never seen vents like this on the side of a chimney chase. Manufactured wood burning fireplace with manufactured chimney. Are these supposed to be intake vents for combustion air? There was one on each side of the chase.
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Yes… …
And it makes a heck of a difference. They eliminate the draft from pulling combustion air from the room that the fire place or insert is in.
I had to drill through brick to put mine in but it was well worth it.
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Yes, most likely it’s a fresh-air intake. Needs cleaning and looks somewhat home-brew. The screen should be on the outside so birds could not nest inside.
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Yes, Simon, I was going to say that I put a aluminum screened louvered vent termination on mine.
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+1 on that. The drafting up a chimney sucks heated air out of the room, greatly impacting the net heat gain of the appliance. It’s way better to use cold outside air for the combustion.
In some cases this is done with two pipes up to a dual chimney cap, so you won’t see vents in the side of the chimney chase (the combustion air comes down the chimney).
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I believe those vent covers are installed incorrectly. All the ones I see have the opening facing down. Also, some fireplaces have a lever on the front edge of the fire box with a lever to open and close a damper for the combustion air vent.
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That draft vent space is to keep kendling dry, Lol.
Likely done by the home owner to prevent rodents from entering.
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Larry, what kind of difference did you see. I have had a wood stove and now a pellet stove for over 36 years and I am thinking about adding the pipe to the outside.
I saw this kind of difference, Gordon:
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I often see fan ducts open into the crawl space that are for fireplace combustion air. Also, some outside vents like OP shows. Lots of times the grills inside are covered. I’d like to think it was by someone not planning on using the fireplace but fear it’s just more of the human nature thing of plugging any hole in their house (soffit vents, crawl space vents, etc.).
As for a the pellet stove question I never notice much of a draft of combustion air and ran with one for years (don’t need it in Maui 
) I think it’s because of the relatively small flame size compared with a raging wood stove. I also had a wood stove and that thing would cause some crazy drafts in my house when I really got it going.
House Wrens pile twigs into the cavities they choose to nest in, either to make a bed on which to build a soft-lined cup, or sometimes mounded up into a barrier between nest and entrance, seemingly to protect the nest from cold weather, predators, or cowbirds. Here are other birds nesting materials.
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