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Is this moisture an insulation issue?

Hi there,

We have been dealing with moisture in the ceiling around our chimney, below the attic. We thought the roof was leaking but it only seems to happen when it's colder outside than inside and doesn't make a diff. if it's raining or not. I'm guessing it's condensation, but what do I do about it? I did check up there and there seems to be blown-in insulation (reminds me of old furniture stuffing) several inches around three sides of the cement block chimney, and those are def. the places where the water damage is the worst. The rest of the attic has fiberglass batt throughout. One side of the chimney has fiberglass batting flush with the chimney - the side you can't see from the 17" poor-excuse-for-an-attic-access hole.

I live in a 1920's bungalow in Michigan. When we first bought the place 15 years ago, we had the old, gigantic furnace replaced with a new, gas forced air furnace. From what I've read in other posts about insulation and chimneys on this forum, it sounds like some of you are saying that, aside from code requirements, maybe the amount, type, and method of insulating the area around the chimney might vary depending on the method of heating because older type furnaces made the chimney hotter and were more fire hazardous??

I don't get it. I'm so confused. I just want the moisture to cease and desist. Any tips you can give me for fixing this problem are greatly appreciated.



Re: Is this moisture an insulation issue?

I'm a little confused too. Is this chimney just a fireplace chimney or is it also used for the furnace exhaust? If it is used for the furnace exhaust, then you can get a lot of water in the chimney from the combustion process of the furnace.

If this is a masonry chimney used as the exhaust for a modern gas furnace of around 80% efficiency, you could be getting a lot of condensation inside the chimney, which would migrate through the old masonry. If this is the case, you will need to get your chimney lined with a stainless steel flue. an alternative would be to upgrade the furnace to one of the super efficient furnaces where the condensation occurs within the furnace and goes down the drain into the sewer/septic system. I would get quotes for both and consider potential savings in the equation.

Insulation should be kept 3" away from a masonry chimney on all sides.

Re: Is this moisture an insulation issue?

No, this isn't a fireplace chimney, it's for the furnace and hot water heater.

Thanks for the info about moisture inside the chimney. I had no idea about that at all. That never would've even come to mind. I'll check into the things you said, and I'll probably cringe while checking because it doesn't sound like it'll be cheap, but hopefully it will save my ceilings and walls.

Thanks again!

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