Converting wood burning fireplace with top damper to gas

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Jul 14, 2008
Northern Virginia
Our house has two fireplaces, upstairs and down. Both were functional wood burning fireplaces.

We did a renovation that involved extending the chimney so the chimney and flues were made taller. Our contractor did not finish the job and so we have flap dampers at the top of each flue, but the chains are not connected, so they're both wide open.

We plan on continuing to use the upstairs fireplace as wood-burning, but will install a vented gas log in the downstairs. For the upstairs fireplace it's easy, we just need to add a damper cord and connect it to a handle and we're good.

I am trying to figure out what to do about the damper for the downstairs fireplace. Currently it has only a top flap damper and no damper in the fire box. So like if you stick your head in the fireplace and look up, you'll see all the way up to the bottom of the flue cap.

I understand that for a gas log set you need to make sure the damper remains open at all times so gas and carbon monoxide can escape. This is my first question. Some people say that the damper has to be all the way open (like, others say it can be blocked partially open with a clip. Leaving this damper completely open would be a problem since cold air really pours down this chimney when it is open. If it has to be left open I would prefer it is open as little as possible. Glass doors for this fireplace is an option but I would like to avoid that expense if possible (I've been quoted $800 to $1500 for glass doors).

Second question is how to ensure this damper remains partially open. All of the damper clips that I see (products and instructional videos) are made for a damper that is in the fire box. I have not seen any clips that go on top-flap dampers. I had one guy tell me he could ensure that the flap would remain open by making the damper control chain a little bit shorter. This does not make sense to me because I close the damper by pulling down on the chain. Making it shorter would only ensure that it is closed. Perhaps he could make it a bit longer but there would still be the risk of someone pulling too far down on it. So I don't like this solution.

Last question, it says here: that top-flap dampers are not supposed to be used for gas logs at all because vented gas logs can generate some moisture and this moisture can damage the chimney structure.

So at this point I'm pretty confused. Thanks to anyone who can straighten me out.

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