Gravity Venting Options/Alternative?

[NHBuildBuddy]

Running Gravity Air Venting Kit into Insulated Ducting?

I am currently in the process of building a new house and am planning on buying and installing the Valcourt Mundo II food fireplace. My question is about Gravity Air Distribution/Venting kits. The installation guide clearly lists that the Gravity Kit Vent requires 12" of clearance to any combustibles. Our first floor has 10' ceilings and the maximum duct length of the kit is 10' so having the vents come out of the wall as described in the manual is not possible. My original thought was to install the vents 12" below the first floor ceiling and then simply put a collection vent directly above them which would run between the 2nd floor joists and terminate in floor grates. However it would be so much more aesthetically pleasing to have the whole apparatus enclosed, so I want to know if it would be possible to have the Vent (vents in the case of the Mundo) terminate into a Rockwool insulated duct running between the second floor joists which would then be connected to floor grates? Does anyone see a reason why this could not be done? I've attached some Sktechup diagrams to further explain what I'm on about.

 

[begreen]

The first thing to do is get a code review. It's very unlikely that using a joist space as a hot air plenum will be permitted. It would be better to have the entire fireplace enclosed in the room envelope so that it can directly vent to the room above.

 

[NHBuildBuddy]

The first thing to do is get a code review. It's very unlikely that using a joist space as a hot air plenum will be permitted. It would be better to have the entire fireplace enclosed in the room envelope so that it can directly vent to the room above.

Are you suggesting that we move the chase inside the living room? If so, given the location that would not work for our project. As for Code review, we live in a town with no building inspector so this is more or less a question of why can/can't we do this. If I am mistaken about the chase location change, I would add that the design right now is for the chase to essentially be part of the building envelope constructed and insulated in the same way as all other exterior walls (2x6s with Rockwool insulation batts).

 

[begreen]

Are you saying you can build a house with no plan review for septic, water, electric, etc? I am talking about national fire and mechanical codes, not local code. If the chase is well insulated then why not bring insulated gravity vents up the chase and into the 2nd floor room via wall vent(s)? Note that there will also need to be a firestop in the chase at the 1st floor ceiling level that the gravity vents will need to pass through.

 

[NHBuildBuddy]

Are you saying you can build a house with no plan review for septic, water, electric, etc? I am talking about national fire and mechanical codes, not local code. If the chase is well insulated then why not bring insulated gravity vents up the chase and into the 2nd floor room via wall vent(s)? Note that there will also need to be a firestop in the chase at the 1st floor ceiling level that the gravity vents will need to pass through.

So the gravity vents are only supposed to run 10' including elbow total, and the number of elbows cannot exceed 2. Because of the floor plan of the Second floor this is essentially undoable. There are obviously building codes that we must adhere to, however the decentralized nature of their review and enforcement means that this would likely never come up. If I did not mention it previously, my thinking was that the Gravity Vents would terminate inside of HVAC rated metal ducting which we would then surround with Rockwool.

 

[NHBuildBuddy]

So the gravity vents are only supposed to run 10' including elbow total, and the number of elbows cannot exceed 2. Because of the floor plan of the Second floor this is essentially undoable. There are obviously building codes that we must adhere to, however the decentralized nature of their review and enforcement means that this would likely never come up. If I did not mention it previously, my thinking was that the Gravity Vents would terminate inside of HVAC rated metal ducting which we would then surround with Rockwool.

NFPA 90A code book states that this is acceptable as long as the materials have a 1 hour fire resistance rating and the heat delivered to the plenum does not exceed 250F. To the best of my knowledge this appears to meet all of those criteria.