fire bricks v old bricks

[h12rpo]

OK so I can see that cost aside, fire bricks would probably have greater insulating properties so the oven will get hotter quicker, but does that same insulating property mean that the firebricks will retain its heat longer than an old house brick ?

Or is the difference so small it doesn't matter ?

[tonyb]

Firebricks are designed to handle high temperatures and heating cooling cycles, ordinary bricks are not. If you use ordinary bricks for a wfo there is a risk that the bricks spall, ies small bits break off. 'Old' bricks were generally fired at higher temps so more able to withstand wfo duty.

Incidentally, I've never considered standard firebricks to be insulating materials. Industrial use is more about there ability to withstand thermal and chemical attacks, for wfo use its also about thermal mass.

There are a number of builds on the forum using old bricks and no reports that I can recall of problems. As to whether the difference is material, we don't really know, there is no 'standard' old brick to test against. As in many things, it is about design compromises and your approach to risk.

[cannyfradock]

h12rpo

Can't add much more to Tony B's perfect response. As he says...it's down to compromise.

Even on a shoestring build, a fire-brick hearth should be considered to make the oven function.....as an oven.

Terry