Direct Vent: Insulating Exhaust Tubing Only, or Both?

[PLohr]

We are installing a direct vent Napolean Roxbury GDI-30 insert in a masonry fireplace. The instructions are not clear about insulating the two vent tubes (pipes / piping). On page 9, the manual says to insulate the exhaust tubing. On page 10, it says to insulate the "vent lengths". I assume this means both tubes but can't be sure.

From Page 9 of the manual:

From Page 10 of the manual (probably the referenced TROUBLESHOOTING section):

I saw some posts on this forum suggesting:
1. The top (below cap) and bottom (above damper) of the chimney be packed with insulation.
2. The entire chimney be packed with rock wool insulation. This could be difficult to remove if propane prices increased significantly and we had to go back to wood.

Anyone want to take an educated guess at why Napolean doesn't suggest #1?

Is one of the goals of the insulation to keep the intake tubing as cold as possible? Since cold air holds less water vapor than warm air?

Thank you for any help.

 

[DAKSY]

When I install DV Gas inserts, I ALWAYS follow the #1 method. It will create a dead air space between the cap & the block off plate. That dead air will also act as insulation. You want to prevent cold air from dropping down the chimney & creating a draft from around your insert when it’s not in use.

 

[PLohr]

Daksy - thank you, that makes sense.

I did some reading on insulating the exhaust / intake tubing. For anyone interested, Duravent makes two products particularly for this: ProFoil and ProMesh. Both products are expensive. It will be much cheaper to find the thinnest regular insulation (R13 / 3.5" thick?) available at Ace Hardware, etc., compress it as it is installed, and use some hardware fabric (galvanized steel mesh) to keep the insulation compressed and protect it while sliding the vent tube assembly down the chimney. The hardware fabric can be held on with metal wire, such as rebar tie wire.

Rockwool / mineral wool seems to be the better choice of insulation materials.

The insulation assembly will not be installed beginning where the tubing needs to bend through the damper to the connection at the fireplace insert. Two reasons: first, the tubing plus insulation and hardware cloth won't fit through the damper; second, it would not be flexible enough to make the turns.

 

[stoveliker]

When I install DV Gas inserts, I ALWAYS follow the #1 method. It will create a dead air space between the cap & the block off plate. That dead air will also act as insulation. You want to prevent cold air from dropping down the chimney & creating a draft from around your insert when it’s not in use.

Huh?
A single large dead air space insulates far worse than the millions of small dead air spaces in insulation...?

 

[DAKSY]

Huh?
A single large dead air space insulates far worse than the millions of small dead air spaces in insulation...?

True, but if there is no air movement between the upper & lower insulation, then why waste the money, time & material to fill that space? I installed DV units for 10+ years & never had an issue …

 

[stoveliker]

But there will be air movement; convection in the dead space.
This is detrimental to insulation value, and precisely the reason that double pane glazing is sometimes sold with heavy gases in between; to minimize heat transfer.

Anyway it may be sufficient for functionality, it is not better than fully insulated. The reason to go for sufficient here is not performance as you seemed to indicate, but cost.