Fire or storage heater bricks

[chrisa]

Hi, quick question. I'm ready to start on my base/cooking surface. I have a 4" vermiculite "mortar" underbase,with other insulation below that. On top,as a cooking base, I have the option of using firebricks, size 200x62x50, or storage heater bricks, Size 230x190x50. What in your considered opinion, would be best in order to hold the heat. They're both 50mm thick.
Many thanks !!

[oblertone]

If you've already got them use the firebricks, if not then the heater blocks will be considerably cheaper.

[chrisa]

I have accumulated both types, do can use either. However,I'll take your advice and use the firebricks.Many thanks !