Insulate Chimney Chase....correct?

[mtj53]

Hi everyone, I would like to ask you guys this question who have been through this many times before. I did a site search, believe I know the answer, but want to be sure. I have found some conflicting information on other sites. My dealer will be installing an RSF Opel fireplace soon. It will have the required 7" ICC Excel Insulated chimney. My chase is only currently insulated against the living area of the house. Here are the questions:

1-Do I want to insulate the entire chase, all the way up and on all 4 sides?
2-Insulate under the cap as well?
3-If the answer is yes, is there a special type of insulation that should be used? Or just regular, unfaced fiberglass?
4-Assuming yes on the insulation, should I also install plastic vapor barrier over insulation, as well as some type of fireproof material like drywall?

Just want to be sure I do this correct. Dealer is doing removal of old and installing new fireplace, but I agreed to do this part to help out. I wasn't sure about vapor barriers and where they should be located against outside walls vs against the interior of the home wall...sure don't want any condensation or draft problems if I can help it. I also didn't know if it was possible for the chase to be "over insulated". There will be plenty of room to maintain clearances whatever I do. I always appreciate the help, Thank you...Mark
here is a photo of the chase:

(broken link removed to http://i405.photobucket.com/albums/pp135/mtj54/home2007f-1.jpg)

 

[jtp10181]

I assume that picture is of your house....

The exterior walls of the chase that are below the attice should be insulated and drywalled the same as the rest of the walls in the house. This should be sealed up with the main wall envelope of the room. This maintains the envelope seal and prevents cold air from coming in behind the fireplace. At ceiling height you should have a false ceiling in the chase made out of 1/2" OSB or better. Pipe should go through this with a firestop and attic insulation sheid. Above the OSB it should be insulated the same as the rest of the attic. The rest of the chase is "attic" and could be left as is.

If you want to go nuts you could put another false ceiling in the chase up higher and then insulated that again and the walls of the chase all the way down. For this to be of any use the chase would also have to be blocked off from the attic so its basically a big dead air space.

 

[SmokeyStover]

I assume that picture is of your house....

The exterior walls of the chase that are below the attice should be insulated and drywalled the same as the rest of the walls in the house. This should be sealed up with the main wall envelope of the room. This maintains the envelope seal and prevents cold air from coming in behind the fireplace. At ceiling height you should have a false ceiling in the chase made out of 1/2" OSB or better. Pipe should go through this with a firestop and attic insulation sheid. Above the OSB it should be insulated the same as the rest of the attic. The rest of the chase is "attic" and could be left as is.

If you want to go nuts you could put another false ceiling in the chase up higher and then insulated that again and the walls of the chase all the way down. For this to be of any use the chase would also have to be blocked off from the attic so its basically a big dead air space.

I agree with this completely. Just wanted to add that you should check with your local CEO first. Some jurisdictions will require the dry wall to be 5/8" firerated.

 

[mtj53]

Thanks very much for the replies guys, very much appreciated. The photo I put in was of the back of my house showing the chimney chase. I don't think this matters, but I will add, the chase doesn't go up through an attic, there is a flush wall inside and the chase is seperated from the house by the 2X4 wall which is drywalled. I'll add a photo here of what is inside, this photo is from 20 yrs ago when the fireplace and brickwork were just about finished. What you see in the photo is what I just tore out--but once the new fireplace is put in, it will be quite similar except the fireplace itself. The contractor installing the fireplace does plan on putting two firestops. The 5/8 drywall just sounds like a good idea so I'll just go ahead and do that over the insulation. Thank you again...
(broken link removed to http://i405.photobucket.com/albums/pp135/mtj54/fireplace2.jpg)

 

[jtp10181]

Sometimes even though its an outside chase it is connected to the attic by a hole cut in the side of it. Doesn't matter much anyway. Regardless, make sure the upper most "ceiling" of the chase is insulated like an attic, R-38 or whatever they are doing these days. The goal is to make the chase at least as well insulated and sealed as the rest of the house, if not better. Otherwise it will be a weak spot and you will get cold drafts.

 

[mtj53]

I'll make absolute sure that it is insulated very well. I messed up the first time around when the house was built by not paying enough attention and asking enough questions. I never could use my current fireplace because there were always draft issue's. We tryed absolutely everything you could think of to remedy the problem, and from what I have read on hearth.com here, I am thinking much of my problem had to do with a combination of three things, tall chimney, air cooled chimney which was hard to warm up, and the uninsulated chase sure couldn't have helped. A large part of the house has always been cold as well, and now that I opened the chase up, only half the existing fireplace has insulation tucked along the edge so there were very large gaps just behind the brickwork. No wonder it was always cold in the house...It will sure be a great upcoming winter! I'm going over later to look into having the chase done with the spray foam insulation---no experience with that but the way my chase was built it will be hard to seal up with fiberglass and get it good and tight. Thanks again!

 

[oconnor]

While it may be implied, I will add this - make sure you leave any required air gap around the ICC flue and the insulation/combustibles that make up the chase. Most prefab flues aren't zero clearance installs, and need an air gap inside the chase as well. That includes the top caps and other penetration points.

When in doubt, read the instructions - they will specify what clearances are needed.