I recently repair a contraflow heater in Yelm, WA. This heater was built around 1992. It was built with a tappered throat as you would see in a traditional fireplace but would no longer see in contemporary heater designs. Over the last 20 years of heating the bricks in the throat had deteriorated and begun to debond and fall foward as shown below
The heater had in the past had a metal oven insert. This insert had been removed previously and the area around it had deteriored quite a bit. Bricks were missing, debonded and cracked. The upper porations of the inside side channel walls were also debonded.
The rebuild began with demoing and removing the throat. The throat was built on top of a skewed brick made of precast refractory that allowed the throat to built easily with a taper as the bricks were layed on the skew rather then level. I was hoping to be able to demo the throat, all the masonry in between it and the back wall, then remove the skew to lay the bricks level while corballing foward. This would further allow me to tie the bricks into the masonry more and lead to a stronger throat. Unfortunatley, the masonry behind the throat bricks was to solid to remove. I thus had to rebuild the taper with the brick tilted forward as origonally designed.
Rather then rebuild with regular firebrick, I elected to cut a 24″ tile in strips that would span the entire throat and thus be tied into by the side channel walls as shown below
I added a removable liner to the back wall of the firebox as it was taking the most abuse. The custom made skewed piece on the back wall tied all the way into the back rear wall of the heater. It had a crack in it so I wanted to protect it in particuclar rather then leaving it exposed to the highest temperatures in the heater.
The firebox was reset. I few new pieces put in and the bricks around the air intake redone.
Some of the facing brick around the door was experiencing cracking. The rear part of these bricks were exposed to the inside of the firebox so I installed some shielding.
Lastly the oven which had previously been a metal insert was bricked in to create a white oven. (meaning it is heated from the outside in as gases flow around it)
Unfortunately I did not take a finished picture. However here is one during the process. It was tricky working with such a small access. The oven was built on top of the tappering throat. I relayed the upper portion of the side channel walls. The began building the oven walls. There was not enough space to build the oven walls and then insert the ceiling tile in. So I built up the rear bricks, built half of the oven walls then inserted the ceiling and proped it up on the rear bricks, finishing building the oven walls, unproped the ceiling tile and lowered it onto the oven walls.
It was a fun but challenging job. Rebuilding such a significant portion of the heaters insides proved to be quite a challenge clearence wise. Hopefully, this gives the heater another 20 years of life. I believe contemporary heaters without tappered throats will be holding up longer, further contemporary replacable firebox liners allow for easy repair of the firebox.