FYI, the have inserts for both masonry and Zero Clearance (prefab) fireplaces. We had a Avalon stove installed in our Heatilator prefab unit many years ago. It was certified for such an installation. And as a result, we turned off the heat in the house. The insert heated the entire house with no problem.
As far as the glass doors go, what will happen to the fire if you close the doors. In some units, unless there's an outside air source, when you close the doors, the fire goes out.

Thanks for your responses. Now I have new questions. What is an insert? What does it look like? Thanks again.

Google "fireplace insert".

An insert fits into the existing fireplace opening. It is a metal box with firebrick, glass doors, fan, and a flue opening at the top. It can be considered a wood-burning furnace since it can make significant heat. Depending on your chimney, you may need a stainless steel liner for the insert that runs the length of the chimney.

If you have a "pre-fab" fireplace, you are limited in your type of insert. You will need a "zero clearance" insert. A pre-fab fireplace is what most new homes have.

Masonry fireplaces are made of brick or stone and have a brick or stone chimney with a clay tile lining. If you have a masonry fireplace, the inserts are much heavier and can produce serious btu's.

The glass doors for inserts are made of high temperature ceramic glass so they don't crack due to the heat.

If you don't care if you get a lot of heat from your fireplace, you can always buy a set of glass doors with openings for air intake and/or heat flow. With these doors, you have to make sure that the burning logs don't lay against the glass or the doors will crack because they are tempered safety glass (not the same as the inserts). Glass doors are good for preventing smoke back-flow into the house when the fire dies down. They also help keep odors out of the house when the fireplace is not in use.

Take care.

If you actually want to supplement the home heating system in my opinion you need an insert. If you want picturesque sit in front of the fireplace a few times a year leave it open or get a screen or cover of some sort.

Want warm and cozy heat that nothing will ever compare to being around... get an insert.

Thanks for your responses. Now I have new questions. What is an insert? What does it look like? Thanks again.

An insert is a woodstove. Or gas stove. But instead of freestanding, it fits inside the firebox of the fireplace. They have glass doors so you can see the fire. And most woodstove manufacturers have inserts for prefab fireplaces. They are actual home heaters. A woodstove has a surface temp of between 500 and 600 degrees when in operation. The radiant heat warms the home. We live in Vermont where it can go to minus 40 in the winter and we love our woodstove.

I suggest you look for a fireplace/stove store (NOT HOME DEPOT!!!) and go look to see what's available. You want to have a LOCAL person doing the installation and be there in the event you need service.

Below is a link to just one of many brands of fireplace inserts. But you can see what they're like.
I currently have a Regency freestanding woodstove in my home. The Avalon was in my last home. I like the lifetime warranty Regency has and I had it installed by a local shop so in case I need anything, I have local support.

Here is a link that might be useful: Regency fireplace inserts

What if you just want a good looking fireplace? Don’t doors take away from the look? This is a current debate with my hubby? What looks better?

It depends on the fireplace and room decor, and greatly depends on the type of glass doors you consider. Glass doors tend to have a more modern look about them, although there are some very specialized designs that can look more traditional or rustic.

Below is a perfect example of a fireplace where most people might think glass doors would not look good. As you get to Fig. 3, you can see how they might work. Of course, every fireplace is different in the context of the room, but proper treatments can be made with glass doors in most styles if you stay away from the home centers and look for something more custom.

I am not completely advocating for glass doors as there are some other very attractive ways to treat a fireplace and protect from sparks. Yet, in many cases, glass doors are required by building codes, or are necessary to keep out a very cold draft. If they are custom made to fit the fireplace and room decor, you might be surprised at how nice they can look.

Fig. 1: Typical custom made glass door. This is a little too stark and modern for this fireplace if it is in a more traditional setting. I personally am not a fan of this look, but this is a very popular custom made door due to the simplicity in design and somewhat narrow frame. In this case, the finish can make a big difference. This is a dark classic bronze.

Fig. 2: Solid Brass glass door with a casting trim in an antique brass finish. This looks much better, particularly with the andirons visible inside.

Fig. 3: This is the same solid brass glass door in Fig. 2, but with wire mesh inserted in front of the glass. The mesh minimizes the reflection in the glass, so it literally disappears. This softens the look giving it a more traditional appearance. So your husband can have the glass, but you don't have to see it.

Fig. 4: This is a very Traditional treatment with a framed mesh curtain and andirons. Quite in line with the period style of the mantel. If glass doors were not required in this application, this would be a treatment I would recommend.

Email me some pictures of your fireplace and I will show you how some well thought out treatments will look on your fireplace so you and your husband can reach common ground.

Follow the instructions here for sending pictures: Free Fireplace Design Service