air sealing chase

[Charles2]

So I've got a Supervent chimney passing through a bedroom and attic. Before I frame a chase around the part in the bedroom, I'd like to seal off the chase from the joist cavity below and the attic above. I propose to do this with rings of galvanized steel. The rings would be silicone caulked to the chimney pipe and screwed to the combustible subfloor and ceiling framing.

Is this safe to do? IOW, could the rings transmit enough heat to the surrounding combustibles to start a fire? If so, is there any other way to achieve an effective air seal?

 

[Oldman47]

I am going out on a limb here since I don't really know the codes but I would venture that you do not want to seal that space. If you do it will act like the space is an extension of your chimney. With no place for the heat to escape it will end up the same air temperature as the outer wall of that chimney. That seems like a recipe for disaster to me.
Have a look at the chimney manufacturer's literature and I am pretty sure they specify exactly how to treat penetrations through floors and ceilings. Those guys know exactly what it takes to keep the liability lawsuits away from them so you can bet their recommendations will be safe to use.

 

[Charles2]

If you do it will act like the space is an extension of your chimney. With no place for the heat to escape it will end up the same air temperature as the outer wall of that chimney. That seems like a recipe for disaster to me.

Since the chase will not be insulated from the outside, there's no chance that the chase as a whole will reach the same temperature as the outer wall of the chimney. However, since the rings will be in contact with the chimney, they could get hot. Question is how hot the metal would get 2" away, where it meets the combustible material.

It raises the question, is there a rigid, noncombustible material that does not conduct heat? Ceramic comes to mind, but would be difficult to fabricate.

 

[Oldman47]

Standard components are made specifically for your application. Why don't you use them?

 

[begreen]

The ceiling support box should seal off the area below and the attic insulation shield should establish a fire barrier to the attic. If you are concerned about about heat buildup in the chase, put a vent grille in it at top and bottom.

 

[Charles2]

Standard components are made specifically for your application. Why don't you use them?

AFAIK, Supervent does not make any components specifically for air sealing. They do make this, which helps, but is not airtight: http://www.menards.com/main/heating.../universal-shielding-insulation/p-1323376.htm

The ceiling support box should seal off the area below and the attic insulation shield should establish a fire barrier to the attic. If you are concerned about about heat buildup in the chase, put a vent grille in it at top and bottom.

The area below is a living room which does not need isolation. The intervening joists are trusses, so lots of leaky exterior wall sheathing is exposed to the chase. I am not concerned about heat buildup within the chase, but do want to add the vent grilles to draw off some the heat to the bedroom.

 

[kennyp2339]

You need a firestop box, they make a kit, basically its a big round pipe that goes over the all fuel chimney, the pipe has (4) flanges on the side that het hammered into the floor joists. My setup goes like this..from the basement, out the stove collar single wall pipe to ceiling support box, then from support box, triple wall pipe through the ceiling into the attic, in the ceiling I installed the fire stop box, in the attic installed insulation shield, went through the roof and installed the roof flange.

 

[bholler]

Read and follow the instructions that come wit hthe chimney system generally you only want to use listed parts in a chimney system like this and if it doesn't say you can do it in the instructions you generally cant. But really these questions should be sent to the manufacturer they are the ones that have designed and tested the system so they are the ones that can answer your questions. But it is not normal to use anything to seal the chase more than what can be ordered from the manufacturer.

 

[Don2222]

Hello
IMO , I would much rather insulate the chase from top to bottom using100% fire proof ROXUL insulation!
Windy Cold air blasting in from the outside can really make the house cold especially when the fire is out!

 

[begreen]

The chase is interior, in the bedroom.

 

[Charles2]

Hello
IMO , I would much rather insulate the chase from top to bottom using100% fire proof ROXUL insulation!
Windy Cold air blasting in from the outside can really make the house cold especially when the fire is out!

I can't imagine why you'd want to insulate the entire chase from top to bottom, but Roxul seems like a good choice in contact with the chimney pipe. The problem with any kind of batt insulation is that none of them are air-tight.

 

[Don2222]

I can't imagine why you'd want to insulate the entire chase from top to bottom, but Roxul seems like a good choice in contact with the chimney pipe. The problem with any kind of batt insulation is that none of them are air-tight.

Simply because the chase has very cold outside air in it! If all the other outside walls are insulated then this sure should be too! Even if it is not on the outside of the house the air whipping down into the chase can be just as cold!
I have a customer with the coldest chase I have ever seen! It takes the igniter 5 more minutes to light the stove on cold days! If you do not use the stove on a cold day it is soo cold and drafty the whole room which is open concept to the kitchen is too cold!

You will never regret insulating a big chase like that just as I do not regret insulting my shed floor!

You can criss cross the insulation to be more air tight but it is still 100 times better than nothing and better fire protection than dead air. Air is fuel for a fire!

 

[Charles2]

the air whipping down into the chase can be just as cold!

Doesn't the airflow in a building or chase generally go from bottom to top, not downward?

 

[begreen]

I think someone has the wrong perception of this interior chase. Unless I misunderstand the construction details there will be no real airflow in it unless it is vented into the room. Otherwise it's a sealed chamber within the bedroom with a cap at the bottom and top by the ceiling support box and the firestop of the attic insulation shield. This is not like a pellet stove vent. The class A pipe in the chase is already well insulated.

 

[Don2222]

I think someone has the wrong perception of this interior chase. Unless I misunderstand the construction details there will be no real airflow in it unless it is vented into the room. Otherwise it's a sealed chamber within the bedroom with a cap at the bottom and top by the ceiling support box and the firestop of the attic insulation shield. This is not like a pellet stove vent. The class A pipe in the chase is already well insulated.

In theory that is correct. I have an older home with an inside chase around a block chimney. It was not insulated. The snow always melted on the roof around the chimney. Yes it was not air sealed properly around the flashing but the heat from the basement as well as the sound travelled very easily up to the Attic and put the gable vents.

Since the chase is not built yet these things should be considered could be easily added at this time.
I am sure it meets code but making the house warmer by being less drafty is not part of the fire codes

In this case if you are just sheet rocking and not building a chase then it would not matter.

 

[begreen]

Not theory. Look at how a class A chimney going through multiple floors is installed. What is described is typical for a masonry chimney. Masonry chimneys need to have an air gap around them to keep clearances to combustibles. This is not the same as with a proper class A chimney installation as the OP has described because of the previous detailed fireblocks.

 

[bholler]

Also most masonry chimneys with a chase around them or not will melt the snow due to the heat transfer through the masonry. It doesn't have much to do with the air space.

 

[Don2222]

Ok so if the op is just sheet rocking not really building a chase then insulating to prevent heat loss would not matter .

 

[begreen]

It is a chase, just interior as noted in his first post.

 

[bholler]

Ok so if the op is just sheet rocking not really building a chase then insulating to prevent heat loss would not matter .

Yes it is all internal so the only spot for heat loss would be at the attic insulation shield which will loose a little bit of heat i am sure but not enough to make much difference at all

 

[notshubby]

im new here but one of the things I have heard is that the chase cannot have vents in it to scavenge heat as it is a fire barrier. correct me if im wrong but nfpa 211 chapter 6.1.4 requires 1 hour fire resistance in under 4 stories and 2 hour over 4 stories. seeing as how the supervent described in the first post is a factory built chimney. putting a vent in would negate the fire resistance.

 

[bholler]

im new here but one of the things I have heard is that the chase cannot have vents in it to scavenge heat as it is a fire barrier. correct me if im wrong but nfpa 211 chapter 6.1.4 requires 1 hour fire resistance in under 4 stories and 2 hour over 4 stories. seeing as how the supervent described in the first post is a factory built chimney. putting a vent in would negate the fire resistance.

No you need fire stops between floors but the chase it self does not need to be fire rated

 

[begreen]

My understanding is that the chase is primarily for accidental burn protection and to enforce the 2" clearance. The chase stops people from putting something up against the pipe and kids from touching it. Locally I saw one installation where the inspector approved a protective sleeve made of perforated stainless steel that surrounded the class A as it went up through the second story. It looked pretty cool and did the job well.

NFPA 6.1.4 appears to cover day-care requirements.