Brick oven - General maintenance questions, particularly during winter

[Motrendo]

Hello oven folk,

Two years ago, during the first COVID summer my family and I decided to build a pizza oven. I picked up a lot of info on this site, and we’re very happy with the result. (Although it does show that none of us have any experience with masonry.

The oven is built by a mountain cabin in Norway, so the winters are pretty hard up here. I have a few questions regarding maintaining an oven in this kind of climate. We don’t really plan to fire it during winter, but we’ve been struggling with humidity getting into the oven. The first year we covered it with a tarp. This seemed to cause a lot of condensation on the inside of the tarp, which we figured weren’t great. The second year we left the oven uncovered, which also ended up letting a lot of humidity in…

This leads to q nr. 1: How do you guys minimise humidity getting in to the oven during the winter? And how do you handle it if the oven does get fairly humid?

Unrelated question nr. 2: We always brush the floor bricks with a steel brush, but we still seem to have a build-up of old, damp ash on the floor. Do you guys ever clean it with a wet cloth or something? This seems to limit the temp of the floor quite substantially.

Q nr. 3: We’re rebuilding the pipe this summer. There is no flute in it, it’s only bricks. It kinda works, but we figure it has to be taller to reduce smoke coming out of the front. How much taller to you think it should be, and is it okay to build a chimney without an internal flute?

Sorry if these are common questions on the forum.

[david s]

We live on the other half of the planet in the tropics so our hot months are the most humid. There's no way to stop humidity getting in, a roof might prevent rain getting in but won't stop humidity. Simply drive out the moisture gently with fires. You never have to go right back to the really slow gentle fires required after building a new oven, but long prolonged fires are required. As the underfloor moisture is the most difficult to remove, providing an exit by a few holes through the supporting slab into the underfloor insulation helps enormously. These can be drilled from underneath even after the oven has been built. Likewise, some kind of hole or holes in the outer shell that can be blocked off with a cap will help remove the moisture from the dome.

Don't use a wire brush on the floor as there have been more than a single case of ingestion of wire pieces that have caused serious intestinal damage. A blowpipe is a far safer and more effective tool to clear the floor of ash, but just remember to blow not suck.
I think perhaps the cross sectional area of your chimney is inadequate leading to smoke out the front. Not sure of your oven size, but typically ovens up to 36" (100cm) internal diameter require a 6" (15cm) diameter flue pipe. That's a cross sectional area of 27 sq in (177cm2). Ovens over a metre internal require an 8" diam flue pipe. The cross sectional area of the flue or chimney is the most important factor. A chimney does not require an internal flue, but a round flue with a smooth surface is considerably more efficient than a square chimney with mortar joints that disturb flow. Adding extra height may only help a little and has the disadvantage of adding considerably more weight over the entry arches.

[Kvanbael]

You speak of damp ash, but after a long proper firing, one would expect every last bit of moist to be out, even the nastiest greasy food stains should have burnt off, leaving a clean oven with only dry dust & some embers. I get most of it out with my metal pizza peel + blowpipe. Before cooking anything directly on the floor, I would *always* do a final pass with a damp cloth, wrapped around my peel. If the oven is properly hot, and the cloth isn't soaking, then that shouldn't drop the floor temperature in any significant way.