I have a Biz fireplace. Every year I need to replace the firebricks; back, sides and top. Why do they warp and crack? We have electric heat, which we supplement with the fireplace. It heats nicely and reduces our electric bill immensely.

Our woodstove is 28 years old . When new it wouldn't put out much heat. I replaced the firebrick with 1/2" steel plates 10 " x 30". Heat output increased at least 25%. and shows no sign of wear.

I assume you mean a BIS fireplace. Replacement of bricks every year can be caused by several things, but the most common being overfiring the fireplace. Which is boring the fireplace too hot for too long. Possibly loading wood too aggressively could also cause the fire bricks to break, such as tossing or dropping g wood I to the firebox. Using wood loading leather gloves everytime would help with that. Also if when you replaced the brick, if you did not use the correct brick that was recommended by the manufacturer.