I have a wood/oil furnace with a fire box lined with fire bricks, and some of them have started to fall apart and need replacing. It turned out to be easy to take them out, but I can’t find an appropriate replacement. These bricks are 4-1/2x9x2.5" but the only fire bricks I can find locally are 4-1/2x9x1-1/4" (half the thickness).
I’m pretty sure these from home depot are the right thing but they seem to be out of stock everywhere. Other local building suppliers can’t even order the larger size. These from Amazon appear to also be the right thing, but at $15 each that seems a bit steep when the half-size ones are only $1.99 at the local store.
So tell me, can I just buy twice as many half-thickness bricks and double them up (I compared against an old one and two together seem to be just exactly the right thickness)? Would I need some sort of mortar between them if I did that? Is there another kind of local store I should be checking?
The ones that are 1 1/4" thick are called splits. They’re commonly used in wood stoves and similar heaters. You need to find a local masonry supply or general materials supply. They’ll have the full sized bricks. Any business that carries bricks might have these or be able to order them for you. $15 is very high, probably how they’re covering the free shipping. Do what you can to find those locally before thinking about doubling up splits. You’ll need some refractory cement also, should be available where you get the bricks. Mixing it from powder gives the best results but for the amounts you’ll need you may as well get the pre-mixed stuff. That seems to be what the furnace repairmen use all the time. The pre-mix costs a little more but you might not find the dry stuff in less than a 50 pound bag.
If you’re sure it doesn’t use cement now then I don’t see why you would have to have it. But if you have any trouble keeping the bricks in place then you should use it. You may need it with splits if bricks are stacked on their sides. I don’t know where the bricks are used in your furnace.
They are stacked 10 to a side around 3 sides of the fire box (there’s a door on the 4th side) with 5 on the bottom row and 5 on the top row, each one standing on end and held by metal strips at the top and bottom. They each came out completely clean with no evidence of mortar anywhere, but yeah, if I went with splits I might need to cement them together so they don’t pop out in the middle where the top and bottom bricks meet.
I have a few more local places to call today and see if I can find the right thing.
I don’t know if this is helpful, but just make sure that you have the kind of bricks that were fired at very high temperatures. Otherwise, you’ll probably have to replace them in the future.
Prior to the industrial age, there was no technology that made it possible to fire bricks at the high temperatures we use today. These higher temps make the bricks stronger. Regular bricks will eventually crack and shatter in intense heat. Just make sure you have the right ones for the firebox to avoid repairs later on.
On the other hand, chimneys are different. An inexperienced handyman replaced some of the soft bricks on our chimney with standard hard bricks, and they had to be taken down and replaced. I’m not sure exactly why, but the chimney guy said it was not good. You need to check that if you ever need to work on the chimney.
All fire bricks are fired at high temperature. Almost all regular ‘red’ bricks are also, they just transfer heat a little faster than the fire bricks. What you call soft bricks are probably the lower density but better insulating type of bricks. I don’t know why it would make a difference in an ordinary furnace or fireplace chimney.
Another local building supply store claims to have them, in two colors even. Somehow I’m skeptical, but I guess I have to drive over there after work today and see for myself.
Thanks, yes, that seems to be the technical term for “Fire Brick”. Maybe I’d have had less trouble with folks thinking I was looking for something to burn if I’d used that term. But $17 each is a bit steep.
I forgot to come back and update that I had, in fact, found a local building supplier that had the full sized bricks in stock. I had to drive a bit further, but they were $4.25 each, I think, and I bought 12. Not enough to replace all the bricks, but more than enough to replace the severely damaged ones and any more I might break in the process of replacing them.
‘Fire Brick’ is well known as a name for ‘Refractory Brick’. It’s doubtful anyone who actually knows what they are would be confused. $4.25 is a pretty good price. I think I was paying around that much more than 5 years ago.
Folks on the phone regularly thought I mean BioBricks: Product Line
I assume they’re getting lots of calls about those, and not too many calls about actual Fire Bricks, and so just assumed I was part of the majority. If I had said, “Refractory Bricks” they might not have known what I was talking about either, but would have at least stopped long enough to figure it out. Or their computer might have not given them the right answer. I got pretty good results with some variation of, “Fire Bricks, for insulating a furnace”.