loose perlite insulation around flu pipe?

[ckdickerson]

I will be starting the construction of my oven in a few days and I have a question regarding the installation of loose perlite that I will use to fill the area on the sides and top of my oven. I will frame around the oven with hardybacker and metal studs and fill the void as I have seen and read in the plans but I can't find any clear pictures or instructions on how to deal with the area surrounding the flu. I will be using 8" double wall stainless for the flu which of course will be inside the hardybacker with the oven itself. Do I just fill the entire void with perlite and let the loose insulation fill in around and contact the flu itself, or is it best to section off the area around the flu with another piece of hardybacker and leave open air space around the stainless pipe? Thanks for any help you can give me.

[dbhansen]

I don't think there's any reason to cover the flue pipe with insulation, especially if it's an insulated (double-wall) pipe. Mine has no insluation around it and the hardibacker that's in front of it doesn't even get very warm. On the other hand, there shouldn't be anything wrong with having perlite touching the pipe, if you want to use that much perlite.

[dmun]

You can section off areas where you don't want perlite, like the corners of the square enclosure. You can also use your hardibacker to partition off the flue, but there's no harm in having insulation there. These tactics are mostly to save on the expense of perlite: There's no harm in just dumping it in if you have enough. Be careful to police your enclosure for leaks before adding the perlite. It can get through surprisingly small holes.

[Tscarborough]

You have that right. I sealed my sill plates and the casing bead on the stucco and STILL had to pop a tube and seal some areas once I started pouring perlite into the enclosure.

[ckdickerson]

Thanks for the feedback. Do you recommend applying a coat of perlite concrete to the outside of the dome before back filling or just fill it up?

[dmun]

Do you recommend applying a coat of perlite concrete to the outside of the dome before back filling or just fill it up?

No need: if anything the perlite works better loose than mixed with the heavy portland.

[ckdickerson]

My concern was that the perlite might find its way into the oven with no barrier of any kind especially around the flu or through a fine crack that I have heard tend to develop after a few firings. Should I be concerned about this or am I overthinking?

Craig