HOTBLAST FURNACE FIREBRICK WITH THINS ?

I have a hotblast hot air funnace.It came from the factory with thin firebrick 1.25 ins.If you look at the way they fit it looks like the firebrick should be twice as thick.When I first got the furnace 3 yrs ago I replaced the thins with full size firebrick and ran the furnace.It didn't seem to run much different so I put the thins back in. I didn't know what I was doing but looking at it again it just looks like it should have full size firebrick,so I put them in and seems like the ash won't have as much space to sit in the firebox.The bricks end right at the teeth of the grate so to speak.Has anyone else tried using full size firebrick in their hotblast furnace?These are the cheap ones from TSC.
DON

Don
I have the clayton 1600 and put in full sized fire bricks,really they are refractory bricks from a glass furnace. Because of their size 9X12 aprox. they eliminate a good part of the taper in the firebox. I also used regular firebrick to add to the height of the firebox. Mostly seeing if a deeper bed of coal added benifit in this unit. I just got today more of the standard firebrick from TSC with the idea of makin a wedge for behind them to stand the stock ones with less taper. I feel I had better heat output from the thinner ones. The furnace itself works fine for the $$$ you spend. Working on getting a stoker furnace or boiler for the house and then put this unit in the barn.
Bogie

Bogie,
I know by using thicker firebrick you will reduce the volume of coal you can get in the furnace.But you're going higher up in the chamber to make a deeper fire,interesting.I'm going to try the full size brick in the fall,I may have to change them in the winter(back to thins).I don't have any trouble with mine with the thins just thought I'd try something different.I've been very happy with my hotblast,you just have to learn what it likes.GOOD COAL.And shake the h#ll out of it.
Thanks DON