I have heard several times in the past that heating a cold block/tile chimney too fast will crack the flue. I have never heard of this actually happening. I am curious if anyone else has knowledge or experience with this? How cold is too cold/how fast is to fast?
Seems like the heat would warm it up gradually as the fire started. But this is just my logic, and it has been known to be flawed!
I don't think you could heat up the chimney fast enough without an accelerant and A LOT of it. It's not like you're taking a flamethrower to it...or are you..
I was a volunteer fireman for several years when I was a younger man . The best place for a block chimney is in the middle of the house it is easier to warm and the creosote build up will be less. A block chimney on the exterior of the building is alot harder to keep warm. Most flues with normal burning Temps in the stove will be 200 to 400 degrees up a few feet from the stove. If the creosote build up on the inside of the flue ignites Temps can soar to 1800 to 2000 degrees in a few seconds causing clay flue liners and unlined block chimneys to crack and be destroyed
I have a double cinder block chimney with orange clay tile flue; brick faced somewhat center of my home. In my opinion and experience it is not the heating of the tile that causes the tile to break. It is the introduction of moisture. My parents home had similar chimney outside wall when converted to natural gas it passed inspection. Parents furnaces never shut off did heat and hot water with 7 kids showers and dishes kept it warm in the summer and moisture out. Minor earthquakes and vibrations from traffic cause tiles to move add humidity next to Lake with freeze and thaw cycles that kills the clay liners. most pottery kilns are clay lined and heat a lot faster with more heat than a woodstove
About the only good thing about a masonry chimney is that on a big one you can hang an insulated stainless liner. I was at the masonry yard today buying firebricks and there were pallets of new clay chimney tiles. Hard to believe they’re still installing them.
We had a block and tile chimney. Probably installed ~90 years ago. Capped only for the last 20 years, or so. It's used to vent oil furnace and propane water heater. No wood fire. We recently had it inspected and the tiles were found to have started shifting. Long story short, there's now a stainless steel flue in there.
I was told in my youth it wasn't the heating of the tile that cracked them exactly, it was moisture soaked up into the tiles from poor chimney caps or exterior cracks soaking the tiles with water. Water changing to steam inside the brick and tile cause significant spalling and cracking.
40 years as a mason. Yes if the chimney is cold enough and the fire fast enough you can split a block chimney right up. I’ve seen it done. We built an outside block chimney with 8x12 flue on a new house. Gave instructions to owner let it cure a couple weeks then low and slow fires. Got a call from the owner, chimneys cracked from thimble height straight up for 6 feet or so. It was unusually cold for Ct. He decided to burn all the cardboard waste from home construction in the stove. Worse yet,,, I did it on my own fireplace throat on my new construction home. Was 5 degrees outside when I started putting on the cedar board siding. Freezing my butt off, no gloves because I had a jig to keep all the stainless nails perfectly straight and evenly spaced. Then an old drinking buddy stopped by with some beer. No heat in the house but the fireplace was done sans stone face. Lit a fire and the throat cracked right in the center from lintel to about 4’ high. Instant idiot award. Masonry expands. When the temp is too fast it cannot expand fast enough in conjunction with the colder parts of the mass. Water in masonry/cement is another issue. That’ll create little explosions as water is turned to expanded steam and cannot escape. Done that too LOL How cold is too cold? I doubt there’s any set standard on that. Nothings created equal like water freezing at 32* Inside masonry chimneys with heated homes you’d have a hard time pulling it off. Masonry subjected to outside temps then blasted with heat,,,,,,,different story.
