How to Temporarily Block The 2nd Chimney That is Not in Use

[tathspts]

this old house I bought had two masonry fireplaces, one in the basement and other in the living room. Both fireplaces have terracotta chimney liner with separate chimney flue.

I know chimney flies are separate becaue I looked up from my living room firebox and could see only one opening. I can't see anything by looking up from the basement firebox. My guess is flue is curved there?

I noticed both of the liners were left wide open, there is no cover installed. During rain or snow water would come in but it was not enough to cause any concern, maybe few drops here and there, little bit more when it is pouring rain. I wanted to know if that is normal? In my neighborhood I rarely saw any chimney liner left opened like that.

Now I recently had a wood insert installed in the living room, where installer installed 6 inch flexible chimney liner and there is a cover on the top. But the 2nd chimney for the basement fireplace is still wide open. I don't currently have any plan or budget for installing another fireplace in the basement. But, goal is to have another one installed in the basement sometimes down the road.

That bring me to the question what should I do with the chimney liner that is left open? I plan on temporarily blocking it by putting roxul insulation and cover it with some sort of metal plate and silicon. What you guys think of this solution?

If you recommend some other way, please do. Any other solution or product to tackle something like this?

If you think my method will do it, can you please recommend me silicon product for this purpose and type of metal plate and a way to keep the plate in place so it doesn't blow off with heavy wind flow?

Thank you.

 

[jatoxico]

So you're certain there is no damper/flue closure in the basement flue? Are you getting cold air coming in from the unused flue? If not you could just cap it to keep the rain out or throw a few bricks over and call it a day. I understand there are balloon type devices that inflate to close off the flue if a good seal is needed which is easily removed. If you want to seal it with a plate any quality silicone would work.

 

[tathspts]

There is a damper in the basement fireplace, I do not feel much cold air is coming in when the damper is closed. I am more worried about deterioration of internal chimney than cold air coming in. That is why I am exploring this.

Although I have a very strong cold air draft coming into the clean out which is right by the basement fireplace. Ash dump for that clean out is stuffed with roxul insulation when the insert was installed upstairs. For the life of me I cannot figure out where that strong cold air draft is coming into that clean out.

So you're certain there is no damper/flue closure in the basement flue? Are you getting cold air coming in from the unused flue? If not you could just cap it to keep the rain out or throw a few bricks over and call it a day. I understand there are balloon type devices that inflate to close off the flue if a good seal is needed which is easily removed. If you want to seal it with a plate any quality silicone would work.