Condensation between double wall pipe layers

I am trying to figure out why water would condense between the layers of a double-wall flue pipe. Condensation in significant quantities requires moist air. Where does the moist air come from? Why is the outer layer cool enough to support condensation and freezing of the moisture? I can understand how you might have condensation between the layers IF you had a supply of moist air, but where is the air supply? If it is outside air it will have a low absolute humidity content because it is cold. When it gets in between the layers of flue pipe it should warm up because the inner layer of flue pipe should be pretty warm/hot. That should drive the relative humidity of the air down, so even if the outer layer of pipe is cold there shouldn't be a whole lot of condensation, and I definitely wouldn't expect the water to freeze. Maybe I am wrong about this, but I imagine the outer layer of a two-layer flue pipe warms up above freezing when you are using the fireplace. Even if the outer layer is at or below freezing, how is a supply of air getting into the space between the layers? This space should be protected from air movement so that it provides the insulating effect it is meant to provide. Is the sapce between the layers on double wall flue pipe hollow?

So, I am wondering if you are sure that the water you see is coming from the space between the two layers of the double wall flue pipe.

So there is an open space btween the inner and out flue layers, and this space pulls air from inside the house and presumably vents the air outside? Does this space draw air from inside the fireplace or from outside the fireplace but still inside the house? This seems unusual to me, but I really don't know much about flue pipes. The moving air would cool the outer flue pipe, but this seems to represent a large loss of heated air from inside your house to the outside. I don't think this is how most flue pipes are designed. Lets hope somebody else can comment on this - it doesn't seem right to me.

Sounds like a typical air cooled flue to me. We put chimney air kits on all ours, so they pull outside air and not from the chase. That might help if desa makes one. This is self installed I assume? Or what does the dealer say about this?

I thought an important reason to use insulated flue pipe is to keep the inner layer of pipe hot to reduce accumulations of creosote. Wouldn't an air-cooled flue negate this benefit?

air cooled is mostly used for open fireplaces, hot fast burns. Also if you have a hot fire with good wood, you have a hot flue, air cooled or insulated. The insulation or air chamber is also to keep the outer wall cool so it can pass testing and get listed, the benefits of the insulation is secondary.