And I’m rather relieved to see that it can be done, given my nearly identical setup.  I had sort of resigned myself to needing to pull out the prefab and either replacing it with an EPA ZC or building an alcove in its place.  I had actually figured the R-value underneath would be the harder issue.

Of course, I really wish I had gotten into wood heating before I built the house and paid for the current setup, but such is life.

What about the chimney? Are those pre fabs approved for a stove or do you have to reline with a class A?

I’m not sure about 8’s, but my WMC42 (prefab) has a HT2100 chimney (8” ID triple-wall air-cooled).  I don’t know if it is “approved” to do either a direct-connect or a relining, but both should be safe.

I had a 6” stainless rigid liner put inside of the 8” pre fab.  8

Nice set up!!!  The rock rocks!!!!!