Fiberglass insulation touching flue?

[knottshawk]

I had some professionals install a new fireplace insert... basically it's a wood stove... well, to seal around the flue (a flexible flue) going up my chimney, they packed unfaced fiberglass insulation. I know it's noncombustible, but it tends to melt at high temps. Is this plan okay?

How hot can the outside of a flexible flue get?

[chandler]

If it is triple wall pipe, the outside won't get hot at all. In fact, the space adjacent to the outer layer is actually your combustion air intake so there is a rush of cold air running down to the fireplace.

[knottshawk]

Oh, on the contrary... I tried the insert out a few days ago and, after a few hours, the flexible flue is blazing hot. The only question is whether it gets hot enough to melt my insulation. The only way I can think to test this is to put some insulation in a pan and see how hot it has to get to melt.... then, using a thermometer, test the flue temp.

[chandler]

Then it isn't triple wall pipe. You say "flexible". How many chambers does it have? Is it going up a brick chimney or framed chase?

[knottshawk]

It's going up a brick chimney...

How hot will the outside of a single wall flue get?

I tested by cramming some insulation up against a 100 watt light bulb, which is supposed to get a surface temp of 450 degrees fahrenheit and it didn't melt or anything...

[chandler]

Single flue will get as hot as your fire. Why is the insulation there?

[knottshawk]

As hot as the fire? Not to be belligerent or anything, but I'm not sure how that's possible...

The insulation is there to seal my existing chimney from coming back into my living room....

[GBR in WA]

Ignition temp of various woods 190°-260° F

Keeping glass fibers molten to make fiberglass insulation 2500*F
They do not burn or ignite.
Be safe, Gary

[chandler]

Knottshawk, no problem, but where do you think the heat of your fire goes? In your room? Hardly. Most of it goes up the flue and creates heat in the pipe. That was my concern.
Gary, you are comparing apples and oranges with the combustion temp of wood and fiberglas. It isn't the combustion temp of wood, but the BTU output of the burning wood that creates the heat, and it can be quite hot. Maybe not up to what you call the melting point of fiberglas, but hotter than the 260 degrees you say. Just wanted to be clear on what we were talking about. Knottshawk should be fine with the fiberglas packed around the flue, but I would have preferred a metal air break to be installed, caulked with heat resistant compound.
Just thinking out loud here.