Regarding the cracking around the loading door, @
brenndatomu showed his metal heat shield in post #323, and mentioned firebrick as an alternative. I did that this past weekend.
After measuring everything, I cut firebrick to the following dimensions:
The 1st piece in the above goes on the top front of the firebox, the 2nd piece goes on the bottom front, and the 3rd piece goes on the side top toward the front. After cutting the 4 1/2” wide firebrick to 3” wide for the 1st and 2nd pieces, I had a pair of 1 3/8” wide strips that I was going to toss but they ended up fitting on the side bottom toward the front. The firebox is symmetrical, so I had to multiply all of the above pieces by 2. The below picture shows the final pieces; the pieces on the green kneepad go on the front of the firebox (as looking from inside the furnace), and the pieces off the green kneepad go on the sides of the firebox. (*note that I had some firebrick left over from a previous furnace, so I used that, therefore the burn marks.)
This is the top right corner (as seen from inside the rear of the furnace, on the door hinge side)
This is the bottom right corner:
This shows the same bricks looking sideways at the top:
And sideways at the bottom:
As mentioned, the install looks symmetrical on the other side.
I didn’t remove the baffle around the air inlet damper, as Brenndatomu did. I installed the bottom front firebrick, then the top front firebrick, then the top side firebrick, then the bottom side firebrick(s). The side bricks hold the front bricks in place. The secondary burn rectangular tube holds the top side brick in place and the top side brick holds the bottom side brick(s) in place (just like the original Tundra bricks did).
I kept to 1/16” in my dimensions and cuts, but probably could have relaxed that a bit. The 2.25” dimension on the top side firebrick left things a little tight to wiggle the bottom side bricks in below, and I could have made that 2.25” a little bigger with enough meat remaining to be restrained on the top by the rectangular tube for the secondaries.
I had fully intended to cut a single brick for the side bottom, but when I looked at the 1 3/8” cutoffs, they added up to about the right size so I used them instead. I might yet replace them with a single piece, and it won’t be a big deal to cut them if I decide to.
I have a cheap tile wetsaw from a bathroom remodel. It cut the firebrick like butter. However, the bricks were pretty saturated by the time I was done (also from blasting them clean with the garden hose), so it took them a few days in the sun to dry enough for the final install to avoid putting that moisture into my furnace.
The bottom of the loading door still is directly exposed to the firebox. I suppose I could line that with brick, too, but I’ll wait to do that. I’m thinking the bottom might not be quite as hot, and I’ll measure that this winter with the IR gun.
This spring I noticed my loading door handle is not as stiff to unlatch as the floor model at Menards. I remember my handle took some heft to unlatch when new, but not much anymore. I looked closer, and found that the firebox steel on the side of the door is warped a little to relieve the stress in the latch when the handle is closed. Just another indicator in my opinion that the front of the firebox should be lined with brick.
So, hopefully this brick will help stop the cracks in posts #101, #120, and #316 and prevent the latch from relaxing further.
