I have a brick fireplace with approximately a 23″ round opening. I would to put an insert in, can I have the opening extended and made square and still keep it safe? If so, what type of contractor would do this type of work?
There are several sources for fireplace inserts. I have included a link to one of the many sites where you can find information on these inserts.
There are dealers that sell and install these inserts. Make sure to use only qualified and licensed installers since incorrectly installed inserts could lead to some severe consequences, such as a fire outside the fire box.
Another option is to hire a mason that has experience in modifying fireplaces. These types of projects normally require the issuance of a building permit which ultimately will result in an inspection of the modifications a by city official.
You may be able to find a qualified mason by checking with a local supplier of masonry products. Make sure to check his/her references.