Air gap top plate

[Ctwoodtick]

And you are right there can be an issue with multiple flues at the same height. But honestly in my experience those problems are pretty rare[/QUOTE].
If I put a flat paver stone or something similar covering up the flue that is not in use, would that pretty much eliminate any issues with this?

 

[bholler]

And you are right there can be an issue with multiple flues at the same height. But honestly in my experience those problems are pretty rare

.
If I put a flat paver stone or something similar covering up the flue that is not in use, would that pretty much eliminate any issues with this?[/QUOTE]
Yes

 

[webby3650]

His is dura liner so there is a layer of insulation. But we use high temp silicone at the top all the time if you are over 650 at the top of the liner you are running way to hot. But we do not seal the gap between the top plate and liner it just isnt nessecary. We do seal the storm collar but in this case with a multi flue cap it foesnt matter.

I can't control the temps people run. If there's silicone on a single wall liner, it's almost always baked off. Anyway, I was referring to the gap between the liner and the top plate like the OP had asked about. Evidently wasn't the area in question anyway.

 

[WoodyIsGoody]

If there's silicone on a single wall liner, it's almost always baked off.

Try the Rectorseal Hi-Temp Silicone, it costs almost double the Rutland brand but it stays flexible to 650F. Rutland is 100-150 degrees less. the Rectorseal lasts a long time, even at the top of single wall liner.