Thread: Chase ventilation

Just trying to confirm 2 answers from 2 contractors on 1 topic.
Does the storm collar allow for the ventilation of the chimney chase from the gap between the chase cover hole and the vent? As well as the chase cover overlap, over the chase? Image 1
If these two areas are closed will that not choke off the chase and cause overheating? Image 2

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Sorry, I may not understand your question. The storm collar on my chimney is like the first photo. I sealed all gaps to prevent swarming ants from entering the flue chase and entering the house. The first time it happened in our house, we had about a thousand winged ants walking around the living room.
Frankly, I never considered that a gap might be needed for ventilation.

Originally Posted by Lon Henderson

Sorry, I may not understand your question. The storm collar on my chimney is like the first photo. I sealed all gaps to prevent swarming ants from entering the flue chase and entering the house. The first time it happened in our house, we had about a thousand winged ants walking around the living room.
Frankly, I never considered that a gap might be needed for ventilation.

Question is; are these or is either of these areas places which require air to enter for ventilation of a FB fireplace chase system.

I don't think so or at least, I have never heard of a need for ventilation there.

Interesting question Marc. Maybe Bob Harper will chime in and help.

My read is that air will move through the space between the inner and outer walls of the chimney, just like in a B-vent. As a result, I would assume some amount of airflow is needed.

The gap between the collar and the chimney flue pipe will allow air movement.

The fit at the top of the chase (chase cap or pan flashing) is a matter of convenience. I think the sheet metal guy will generally oversize the pan flashing in order to ensure it fits over a non-square chase. It will also provide a drip path for water instead of allowing it to flow down the trim and/or siding.

But, I have been wrong before.

Originally Posted by Gunnar Alquist

Interesting question Marc. Maybe Bob Harper will chime in and help.

My read is that air will move through the space between the inner and outer walls of the chimney, just like in a B-vent. As a result, I would assume some amount of airflow is needed.

The gap between the collar and the chimney flue pipe will allow air movement.

The fit at the top of the chase (chase cap or pan flashing) is a matter of convenience. I think the sheet metal guy will generally oversize the pan flashing in order to ensure it fits over a non-square chase. It will also provide a drip path for water instead of allowing it to flow down the trim and/or siding.

But, I have been wrong before.

Hey Gunner, wut's up buddy...
I started to question this because my friend is a chimney guy who says yes, this area(s) must be ventilated, and a few others now that say no. Honestly, being in this position sucks because IMO its black or white.
I'll hang out and wait for Mr. Bob. he'll put this away.

It'll be written in the installation instructions for that unit. There isn't a blanket answer for all prefabs. Sometimes the same unit can have 2 different requirements depending on which style cap is installed.

This is the unit...

Originally Posted by Marc M

This is the unit...

So, why would you need to have air flow outside the double vent pipe. Of course distance to combustibles around the flue pipe. but what possible good would it due to vent the framed chimney shaft or leave the collar up to vent the shaft.

I see it serving no purpose what so ever.

I will in fact check with the local chimney guy but as I stand right now I would write it up if I saw open gaps all over the place.......to vent the shaft????

Yea, to vent the chase. I did check and got multiple conflicting answers.

Originally Posted by Marc M

Yea, to vent the chase. I did check and got multiple conflicting answers.

So I guess we are suppose to write up shafts that are blocked off at each ceiling height. That heat might build up around that double walled flue pipe and burn the place down.

Just funning with you.

I see absolutely no reason to vent the shaft the double wall flue pipe is coming up thru.

Originally Posted by Ted Menelly

So I guess we are suppose to write up shafts that are blocked off at each ceiling height. That heat might build up around that double walled flue pipe and burn the place down.

Just funning with you.

I see absolutely no reason to vent the shaft the double wall flue pipe is coming up thru.

I agree, but even as Lou stated, its possible.

The chases shouldn't be blocked off at each ceiling, they should have the listed firestop for the unit which will not seal 100%. If the chimney was tested and listed with ventilation, then it requires ventilation. Factory built chimneys have to be installed exactly as described in the manufacturer's installation instructions.

Originally Posted by Ted Menelly

So I guess we are suppose to write up shafts that are blocked off at each ceiling height. That heat might build up around that double walled flue pipe and burn the place down.

Just funning with you.

I see absolutely no reason to vent the shaft the double wall flue pipe is coming up thru.

Originally Posted by Lou Curley

The chases shouldn't be blocked off at each ceiling, they should have the listed firestop for the unit which will not seal 100%. If the chimney was tested and listed with ventilation, then it requires ventilation. Factory built chimneys have to be installed exactly as described in the manufacturer's installation instructions.

So, I just rescanned the installation instructions for that fireplace and chimney.

Other than distance to combustibles (one inch here and 2 inches in Canada) I see nothing where there has to be or should be ventilation for the shaft from fireplace all the way out thru the chimney

There is no reason to do that.

Says fire stops under ceiling if there is a room above and fire stop above ceiling where there is an attic above. As far as I have ever know there is a collar that the flue goes up thru at the ceiling (fire stop). Whether it be one ceiling or a 4 story home. The idea would be to block a fire that may start below so it does spread through the entire hme and or burn the roof so it spreads over the home.

If I am not understanding this please point out where any chimney manufacturer is going to say that there must be openings in the shafts from floor to floor.

There is no reason to vent the shaft. There is a reason for combustion air as in all fireplaces of this sort and it has its on line to the exterior to draw air in.

On page 11 of the installation manual it says when installing a chase termination, refer to the specific instructions that come with that chase termination. Here's an example of instructions that come with a chase termination:
http://www.northlineexpress.com/media/pdf/rlt-12d.pdf
This particular termination requires spacers under the chase cover for ventilation.
As for firestops, the listed firestop that comes with the chimney will have the required amount of airspace around the pipe already.

Originally Posted by Ted Menelly

So, I just rescanned the installation instructions for that fireplace and chimney.

Other than distance to combustibles (one inch here and 2 inches in Canada) I see nothing where there has to be or should be ventilation for the shaft from fireplace all the way out thru the chimney

There is no reason to do that.

Says fire stops under ceiling if there is a room above and fire stop above ceiling where there is an attic above. As far as I have ever know there is a collar that the flue goes up thru at the ceiling (fire stop). Whether it be one ceiling or a 4 story home. The idea would be to block a fire that may start below so it does spread through the entire hme and or burn the roof so it spreads over the home.

If I am not understanding this please point out where any chimney manufacturer is going to say that there must be openings in the shafts from floor to floor.

There is no reason to vent the shaft. There is a reason for combustion air as in all fireplaces of this sort and it has its on line to the exterior to draw air in.

Originally Posted by Lou Curley

On page 11 of the installation manual it says when installing a chase termination, refer to the specific instructions that come with that chase termination. Here's an example of instructions that come with a chase termination:
http://www.northlineexpress.com/media/pdf/rlt-12d.pdf
This particular termination requires spacers under the chase cover for ventilation.
As for fire stops, the listed fire stop that comes with the chimney will have the required amount of airspace around the pipe already.

The one you showed and the one he showed are not the same. The one he showed only mentioned space between combustibles and the flue which is 1 inch here to combustibles and 2 inches in Canada. If you use a fire block such as metal that is non combustible then you would not need the one or two inch clearance from that metal. Just the surrounding wood. Even in yours it is just mentioning the chimney not any other chases coming from the ground all the way up thru a few floors up thru the roof. Other than space to combustibles.

Anyway, it would be nice for uniformity. In the past we would put a spacer between the cap flashing and the would (one that would no wic) to keep the wood from rotting with the metal sitting directly on it and sweating and such.

As far as any others I guess we can only go by the instructions. As far as a need I just don't see it at all. Double flue pipe, distance to combustibles, done.

If the chase top needs to be ventalated it will be spelled out with the factory chimney instructions that may or may not be with the fireplace instructions (some fireplace use varous brand chimneys).

If a vented chase top is called for then it will have noncombustable spacers with it or specified. When RSF used air cooled pipe they shipped spacers with the fireplace. Now they don't use AC and they don't ship spacers.

That said these days I rarely see this requirement except with older double or tripple wall chimney, DESA is a good example. I could be wrong but I think that 103HT chimney's don't need or use vented chases.

As allways if it is in the manual for that product, follow it, do it...

Also if the chase top has a decorative chase top/cover (vs a factory cap/termanation) then it needs to be vented (the chase top pan flashing) to comply with the decorative chase top UL standards for one off listings.
This would be true regardless of the chimney brand/type.

Lou is correct. Note figure 30 where it shows not to seal the pitched roof flashing to the chimney. As for chase tops, this mfr. provides metal spacers required for the listing to ensure the inside chase wall temps. do not rise more than 90F above ambient. Double walled air cooled chimneys usually draw cooling air from the ambient chase air. That means makeup air must be provided so the chase can respire or breath. This is one reason those listed firestops cannot be caulked as well as the chase top spacers. It also allows heated air to breath out the top.

Originally Posted by Bob Harper

Lou is correct. Note figure 30 where it shows not to seal the pitched roof flashing to the chimney. As for chase tops, this mfr. provides metal spacers required for the listing to ensure the inside chase wall temps. do not rise more than 90F above ambient. Double walled air cooled chimneys usually draw cooling air from the ambient chase air. That means makeup air must be provided so the chase can respire or breath. This is one reason those listed firestops cannot be caulked as well as the chase top spacers. It also allows heated air to breath out the top.

Up here they like to stucco them closed.