Yes, they can reline it, but we have a 2.5 story house, and relining would cost roughly $4000. I have higher-priority fixes, and there just is no room for that much of a cost. I probably could do up to $1000. I'm just curious about why all the fireplace vendors we talked to led us right over to the inserts, even after I told them that I wanted to use the original fire box.

I'll have to see what's up with local codes.

Fireplace retailers are leading you to the inserts because inserts are your best option if you don't want to get the chimney cleaned. The risk of a fire is very real with an open flame - I would question the integrity of any retailer installing a log set in a chimney filled with creosote.

Of course most retailers would love to give you exactly what you want, but not at the expense of your and your family's safety.

Thanks for your informed response! The problem is that lower edge of the liner (which I'm sure was installed in 1922) is a little too high (if I understood correctly) letting creosote build up between the liner and bricks on the back of the chimney. We had the liner and firebox cleaned anyway. Is there some way to seal up the gap? Maybe a (bear with me here) kind of metal funnel that would cover the entire outlet of the firebox and direct the heat and smoke into the part of the liner that works? Sorta like just the top panel of an insert. Or would it still not mitigate the temperature enough?

I wish I could find an insert that doesn't rob me of 30% of my firebox's volume.

Yes, they can reline it, but we have a 2.5 story house, and relining would cost roughly $4000. I have higher-priority fixes.

If you're set on a gas log set, then you need to make this a high priority fix.
Even if you could find someone to make you a custom funnel for your chimney that will meet safety codes, you'll be spending more than the cost of just cleaning your chimney and making it safe.

Just in case you are wondering, this is the illustration of a fireplace in the current code book.

https://codes.iccsafe.org/public/document/IRC2015/chapter-10-chimneys-and-fireplaces

It seams very much like what you are describing.

Rumford fireplaces are awesome!

If you can get the area cleaned that is the problem then I don't see why a high temp cement could not be used. But you still need to pay someone to clean the chimney, that should run about 400-500.