Glenn Herbert wrote:I checked the specs and the customer Q&A at Lowe's, and these are not "concrete" as the title says, but standard firebrick. The 3000 degree spec is contradicted by an answer in the Q&A that says they are good for 2000-2300 degrees, which is good enough if not spectacular. 3000 degree firebrick are a specialty high-performance item, not likely to be standard at a consumer big box store. Kiln supply companies offer 2300 degree and 2600 degree firebricks, with the 2600 version distinctly more expensive.
The upshot is that this would be a typical material for a J-tube and heat riser. You might want full thickness firebrick (4 1/2" x 9" x 2 1/2") for the bridge over the burn tunnel, as that shape might be more durable than the equivalent in splits on edge; I haven't seen comparison tests there.