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The fireplace

The floor is one row of lower half-slabs, the back of that wall is entirely flat, the underside of it is dug out, now if you look closely you'll see that the birch logs are placed diagonally form the fire block.

Fire spreads diagonally though, so why is it not doing it here? Is this really a safe setup or is it only a matter of time before something burns? (I tested this for over 30 minutes without anything burning)

Why does this work? Is it really safe or just a fluke? I've seen similar fireplace designs fail.

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According to the Minecraft Wiki on Gamepedia, fire can spread to any air block in a 3 by 3 square, up to one block under the fire, or 4 blocks above it. It can only spread to air blocks and only if they are next to a flammable block.

Using this information you can easily check if your fireplace is safe by using this command (if you don't have cheats, then you can rebuild it in a world where you do):

/fill ~-1 ~-1 ~-1 ~1 ~4 ~1 minecraft:glass replace air

It will turn any block that the fire can spread to into glass. If there are any flammable blocks that touch the glass produced by this command, then your fireplace is not safe. In your fireplace it looks like this:

enter image description here

There are no flammable blocks next to any glass blocks, so your fireplace should be safe.

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  • Ah, guess I forgot to mention the floor was made up of lower half slabs, and there's nothing underneath it but air. Seems like the same deal I guess. So the answer is that fire can only spread to surrounding 3x4x3 air blocks and only ignites flammable blocks directly if it is parallel to them.
    – Cestarian
    Jun 23, 2019 at 12:39
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    It should be fine anyway. The area it can spread to is 3x6x3: 4 above the fire, next to the fire, or one block under the fire
    – user232393
    Jun 23, 2019 at 12:43
  • Yeah got confused a bit. But doesn't the 1 block under the fire really just mean the netherrack it's on + adjacent air blocks to the netherrack?
    – Cestarian
    Jun 23, 2019 at 12:51
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    It's still a 3x3 area under the fire, so the netherrack and the blocks next to it, in this case your stone slabs, and part of the wall behind it. None of those are air blocks, so you should be fine
    – user232393
    Jun 23, 2019 at 12:52
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Fire can only spread to air blocks that are adjacent to flammable blocks. A block can burn out only if there was fire next to it. From the screenshot it seems you have flammable blocks in range but you do not have air block next to them in range of the fire, that is why the fireplace is safe. You can check out this question as well for more details on fire spread: Minimum safe spacing between lava and flamable materials?

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  • But it could spread two blocks to the side, to the other side of the stone brick wall, right?
    – Fabian Röling
    Jun 23, 2019 at 10:19
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    @FabianRöling No the fire can't spread that far: it spreads only +/-1 horizaontally and +4/-1 vertically. There is a screenshot in the question I linked that hopefully makes it more clear
    – Kcats
    Jun 23, 2019 at 12:34

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