rusted out firebox and moisture

[KrisP]

My current old 70s heatilator is pure rust from 30 plus years of no chimney cap, i plan to install an insert and liner. I also had the flashing fixed, crown sealed, stainless crown cover, and chimney treated with water repellent. All previous water leaks are gone after many hard rains and me testing with hose. 2 questions
1. Sometimes i notice small amounts of condensation in the rusty old firebox... is this normal?
2. Can i leave the rusty firebox when i install the insert ? its VERY very rusted and i beleive there is just raw masonry behind it

 

[begreen]

This sounds like a heatform style fireplace with a masonry chimney. Is that correct? Some condensation may be due to high humidity with AC on.

 

[KrisP]

yes it is, it is also in the basement. Just making sure that can actually happen and i dont have to try and find a super tiny leak. Is an insert okay to put in even though the existing firebox is toast ?

 

[begreen]

Yes as long as it has a full insulated ss liner too. But the condensation problem (or ground water?) may still be present. If so that will also rust out the insert jacket eventually.

 

[KrisP]

Can this angled section of the firebox be cut out or even the entire back section and still be okay to put insert in? I assume it’s just raw masonry behind it?