I have been offline for awhile. A Blessed Christmas to you all!
Looks like you have something similar in your old firebox to what I did.
Here is my project FWIW to you...
My Pacific Energy insert stove was $2500 delivered.
The insulated 6" dia. liner and attachments cost another $525.
And another $175 +/- in odds and ends for a total of $3200.
I used both a sawzall and angle grinder to cut a hole in the firebox at the damper (3/16" steel)
for the chimney liner to pass through:
You can see the clay flue chimney with 11" x 11" inside dimension
The stainless chimney liner was a breeze to install and cap off at the top.
The whole project was well worth the effort with the money saved but perhaps most of all the
satisfaction of having done it DIY.
One other thing I did was to make a sheet metal "blockoff plate" (this forum has a lot of info on that)
and insulated above the plate as well as the walls of the existing firebox around the insert.
I created a thermal wall to direct all the heat into my living space.
Otherwise I would be losing a lot of heat to the chimney cavity behind the firebox,
which was the original design goal of the old Heatilator.
I used fireproof Roxul mineral wool sheathing insulation 2' x 4' x 1" from $9.50.sheet).
The cheapest I found here:
https://www.zoro.com/roxul-insulation-wool-foil-backing-40260/i/G9076024/?q=G9076024
So again Here is the BEFORE:
And AFTER w/ new paint job:
(note the foil faced sheathing wrapping inside on the walls of the firebox)
This heats my whole house with very little wood.
Will not have to use the HVAC system at all this Winter to heat my house.
In a couple of years the stove will have paid for itself.
Take a couple of days off work and install your new stove and save all that money.
