Insulating a Fireplace vent?

[that_guy]

So... I wasn't sure where to post this since it's related to insulation and HVAC and fireplaces ... but anyway, here we go.

I'm installing a direct-vent gas fireplace and doing most of the work myself - except the gas line installation, having someone licensed do that. The question is, does the gap (hole) between the vent and the outer wall of my home need to be insulated. If so, I would guess I need some special type of insulation because it would come in contact with the vent. If not, I guess the fact that I've installed a vent cap and caulked it, should be enough??? The only problem is that I feel a draft coming in when the fireplace is off.

Questions? Comments?....Thanks.

[that_guy]

Anyone?!?.... Anyone!?!

[Rich]

With a direct vent most likely you'll have a B vent which is double walled to keep the outside wall cool.. or cooler anyway. Exhaust goes out the inner wall and air intake is the outer wall.
You'll need to keep the insulation 1" away from the vent pipe - but shouldn't have to be any special kind. Your installation manual should cover this.

[that_guy]

Exactly right... you got it Rich! (as usual)... so I guess, if I understand this correctly, there is currently only 1" clearance between the vent and the brick (since it's non-combustible .. as the manual says... ) and therefore, I don't need any insulation - because why would I make a bigger hole and then just insulate that same hole. I just have to caulk the vent cap and that's it, I'm done...right?

[Rich]

Yep. I would get some firecaulking to do it. 3M makes some pretty good stuff. I should clarify - 1" clearance between vent "pipe" and brick. Your interior and exterior pipe flanges should ..umm.. how to say.. straddle the brick. That's where you'll want to caulk.. then the exterior flange will accept the vent cap. I can't remember if the exterior or interior flanges have a heat shield but it should be on the top of your vent pipe.

[that_guy]

Okay...thanks again for your help Rich.

[roger g]

Well......not exactly. A direct vent fireplace does not use B vent. A direct vent fireplace uses a double wall vent system . The innermost pipe is the hot exhaust gases and surrounding that is a larger diameter pipe that is bringing in the outside combustion air. A B vent is a double walled pipe which is really a thick insulated pipe. The two cannot be interchanged as they fit on two totally different types of vented appliance.
You say you are doing the venting and getting someone to do the gas piping. Far more people are killed through impropper venting that poor gas practices though explosions definitely make for better copy.
The termination kit properly installed makes a good seal and should not allow outside air in. Read the installation instructions othewise get some help.


roger

[Rich]

You are right roger... I use the B-Vent term loosely. I've installed Myson instant water heaters for years and I've just always called it B-Vent - it's easier than trying to explain to homeowners the difference - as if they cared to begin with.
I would imagine that the whole kit was sold to that_guy with the piping included.

[that_guy]

Thanks again...to both of you. I was wondering about the term B-Vent - I didn't know why it would be called that. But regardless of what it's called, I understood the message and yes, it came with the unit, so I'm not worried about having purchased the wrong vent.

Regarding the venting instructions that came with the fireplace, I followed them but they don't say anything about insulation, nor caulking for that matter - that's why I thought I'd ask here.

But this has helped...so again..thanks.

[roger g]

I hate to be niggly but you still haven't said what you have. Is it B vent or direct vent.? B vent cannot be vented horizontally through a wall and terminate there that I am aware of. B vent can go out a wall then go verticle and vent in the verticle position.
Diect vent can terminate in the horizontal position as well as the verticle position but direwct vent are usually limited to a specific length.
There is"A" vent and "C" vent if my memory serves me. I believe A vent is really thick single wall vent.


roger

[that_guy]

Well... I don't know what the vent is actually called, but it is a direct vent (rear, not top) fireplace that I am venting straight out (horizontally), there is an interior vent and an exterior (one inside the other) - like you described but neither vent is insulated nor is either very thick.

[roger g]

Okay, it's probably direct vent. Because the hot gases are in the inner pipe and cooled by the incoming air on the outer pipe, the outer pipe doesn't get really hot but probably hot enough to burn skin. There is no insulation ina direct vent venting.Where the vent (chimney) ends outside you will have a termination kit which looks like an aluminum box with maybe some protective mesh. That is screwed to the outside wall and siliconed in place. I believe even direct vent venting still must have 1 inch clearance from combustibles so when you go through interior walls (drywall, wood, etc) you end up with a helish big hole. How do you fix this hole you ask? There is a piece of sheet metal that is called a firestop. This piece has a hole just big enough for the vent pipe to go though(really tight fit) and then you screw the metal piece to the wall which suspends the vent and prevents it fron touching anything. Sometimes you can get a fancy collar which does the same thing. Most times theyare painted black and after awhile no one notices it. I don't think I would silicone against the pipe. There is a high temp silicone but it is a bright orange and I guarantee you won't like that.

roger

[that_guy]

Roger... you got it....that's exactly the way I've done it. I ended up with a large hole. For the interior wall, I built a 2x4 'box' and the fire stop is attached to it. For the exterior wall, again you're right, the instructions say that you must have 1" clearance.

...So

1. I don't mind caulking between the firestop and the vent... but should I?

2. Shouldn't there be high-temp caulking to seal the inner and outer vents?... That is, where each vent attaches to the f/p?

[roger g]

For the first question :Try runnning the fireplace and see how hot the pipe gets. Try putting a blob of silicone on a place you can't see so you can see and smell what happens as a test.
The instructions usually say to use hight emp sealer ( sometimes a small tube comes with the kit) where both pipes attach to the stove plus at each connection. What I mean is that depending on your application several lengths have to connect to each other and we used to put the high temp stuff on the inner connections and then we screwed them together. Each company has their own design. Some companies have a very flexible inner pipe with spacers that keep it centred inside the big one. Another had two solid but separate pipes with spacers. Another one has two solid pipes one within the other and are welded together as one piece.
We didn't always use the high temp stuff because it can cause one unholy mess but the idea is to stop the combustion gases from escaping into the other pipe and your fireplace would be trying to burn gas with dirty air.
I guess you should follow whatever the instructions ay and I would imagine they would say to use the silicone. Follow instructions because it could void your warramty. ( I used to be paid to say that)

[that_guy]

Okay...thanks yet again Roger.