Be aware everybody that just because it's a light firebrick does NOT mean it will survive in a propane forge, even one with a poor burner. A propane forge has a thermal cycle from room temperature to upwards of 2,600f in maybe 10 mins for a so so burner. 

Most standard soft fire brick aren't rated higher than 2,000f. and do NOT like rapid temp changes.

Frosty The Lucky.

Frosty is right on. Choose Morgan insulating firebricks, which are at least rated for 2600 degrees. 2800 is even better if you have a really hot burner. Then coat their flame faces with at least kiln wash, or some tougher re-radiating surface, to save fuel costs and lengthen brick life.

Morgan makes insulating ceramic refractories rated well hotter than the K-26 and that was last time I checked a couple few years ago.

Frosty The Lucky.

Yes, and also insulating bricks that have higher temperature ratings. However the higher the rating the less insulating they are. Everything is a trade-off. There are no free rides. Nevertheless, all these bricks are more insulating than standard firebricks.

Like I said above I haven't looked at HWI's insulation / refractory specs in years, it was a major PITA worming my way in to actual specs rather than marketing lip flapping. 

You're only partially right Mike, they make insulating refractory tiles (brick) up to 3,000f for inventory. They have virtually identical insulating values. However the greater the temperature differential the faster the energy transfer. This is simple physics, entropy applies to any energy transfer. 

Anyway, there's no real downside provided the Morgan product can take direct contact with molten iron / steel. No?

Frosty The Lucky.

 

On 10/25/2025 at 11:45 AM, Frosty said:

Anyway, there's no real downside provided the Morgan product can take direct contact with molten iron / steel. No?

Yes