Many of today's stove inserts are made to put in a ZC fireplace. In 1992 I put an Avalon stove in a Heatolater ZC fireplace and it worked just fine. Heated the whole house.
What you have to do is find a reputable dealer. It sounds to me like the one who wants you to rip out the fireplace wants to make some money.
What you're going to need is a stove and a chimney liner that takes the chimney opening down from 8 inches to 6 inches.

I currently have a Regency stove. And they make a number of inserts that are certified for a pre fab fireplace, as do many other brands. Do some online looking and you'll have the information necessary to talk to any dealer.

Just remember, although you have a 2,000 sq ft home, you don't want a stove that will heat 2,000 sq ft unless the home is one big room. Otherwise you'll heat the room the stove is in too hot. Something that will heat 1,000-1,200 sq ft will do nicely.

Below is a link to Regency inserts and one that is good for a ZC fireplace. It's a good place to start.

Here is a link that might be useful: Regency Stoves

Thanks for the feedback. Been doing some reading so I'm starting to get a handle on this. Seems like the majority of dealers are against doing it but some will. My chimney is do for a good cleaning so I'm on the lookout for a good chimney sweep who could also shed some light on my current setup. Thanks again for the feedback.

i have a z c fireplace the firebrick on the back is crumbling away. i vac the ashes out when it is cool ,the bottom stone is cracked but intacked, can i replace this fire brick , if so where do i find it.

Here is a link that might be useful: uniflame fireplace

I am going through the same thing right now. The chimney sweep who just cleaned seemed to be very knowledgeable and understanding of my ZC system. He told me he could install an Insert that would be a great heater for my house. Today I visited two different fireplace stores and one store told me there was no way I could put an insert into my ZC fireplace, no matter what it would be a huge fire hazard. The other ones made it seem to be very expensive, $5500 and a difficult job. Yet, on the internet I see there are Inserts made for ZC fireplaces. Any help appreciated. (I have to talk again to my chimney sweep about his recommendations)

Firestop

The professionals who actually look at the existing chimney and are certified as a sweep are the ones to listen to when evaluating an existing appliance. Sales people will always tell you that the appliance they sell will work, or they can make it work. The individual who takes time to come out and inspect the situation and puts their name behind the repair will always be more thoughtful of your safety and satisfaction. Always look for a certified chimney sweep to inspect your system and usually they can install replacement appliances or recommend someone who can. There are several members of the Masonry Heater Asssociation located in New York who can help you find a workable solution to the problem.

yes, we had no problem installing an insert. Our insert is "rated" for zero clearance fireplaces and was professionally installed.