Generally, the side bricks go in first, and the bottom bricks hold them in place. Find your stove’s certification plate on the back of it, then download the manual. The parts diagram often shows the layout. More on reddit.com

The trick with wood is that while it starts to burn around 450F, it burns really, really inefficiently at that temperature, and instead sends a lot of unburned particulate up the flue. Insulating the fire does a couple things: More complete combustion = more total heat available Holding the heat = less active combustion needed to maintain the temperature = slower but still efficient burning Less active combustion needed = less airflow = less hot air going up the chimney Basically, if you get the firebox up to complete-combustion temperatures (1000F), you still get plenty of heat coming out to the surface of the stove to warm the house, and you can limit the rate of hot air going up the chimney to keep that heat in the stove and being released at a more helpful rate (no one wants 500,000 BTU/hr for just one hour). As an added bonus, the firebrick protects the surface material from the crazy hot firebox temperatures, which means the steel or cast iron frame will last much longer. Older stoves often didn't have firebrick, but they were called smoke dragons for a reason - they would burn at lower temperatures without secondary combustion. Adding firebrick and secondary combustion roughly doubles the amount of heat you get from the stove. More on reddit.com

Just some info from my recent experience that at first was frustrating to me.

I searched google for fire bricks, and refractory bricks. Even Wikipedia wasn't much help.

There is more than one kind of "fire brick." My city has a brick manufacturing plant. I called them and asked if they sold fire bricks. They said that they did but they didn't sell to the public. I spoke with the guy a little while asking questions and once he knew I only wanted 5 or 6 bricks he said he would just give them to me. They ended up being bricks for the inside of a fire place. They are hard and heavy, but I guess they can take the direct heat of being in a fire, where as regular bricks will crack and spall when heated and cooled in a fireplace environment.

So recognizing that these were not the brick I was looking for, I called a local ceramics/pottery store that has classes and sells supplies too. I asked for "bricks that go inside of a kiln" and they said they had them. They sold for $5.99 ea. They called them "soft fire bricks." I ended up with 6 of those and I'm using them for my small propane forge.

For anyone else looking for these bricks I hope to save you some time and frustration. You are looking for SOFT fire bricks.

The hard ones would be good for making a pizza oven though, which is another of my projects.

More on reddit.com

I've had 40 years of fire pits built out of regular bricks. They've never "exploded", or "shattered". They do eventually​ crack. More on reddit.com