[viper]

Per my understanding, double wall pipe from the ceiling line all the way through the attic and out is code? Can I assume it is then safe to blow cellulose insulation right up against the pipe in that case? I have an 80% furnace and demand HWH (separate flues of course) and just get a little nervous about that I guess.

 

[josall]

You'll need to check the pipe manufacturer For sure but I would guess you will still need 1" or 2" clearance from any combustibles.

 

[viper]

How is that typically done in new homes? Do they use a triple wall or something or slip a larger single wall pipe around as a sleeve before filling with insulation?

 

[josall]

This may explain it better, http://www.northlineexpress.com/Images/Pdf/5-8DuratechInstallationInstructions.pdf

Its called an attic insulation sheild.