Masonry Stove: Tests and Tweaks

After stove construction was complete, it was time for a breaking-in fire to test for leaks. And this is where the adventure began. We knew from Permies (my go-to place for information and questions), that first fires in these stoves are smokey and full of surprises, so we picked a mild afternoon where we could open windows and doors if need be. 

Dan got the fire started and long story short, the room was so smokey we had to run out onto the front porch! It wasn’t bad enough that there were billows of smoke rolling out of the open doors and windows, but bad enough to crank all our fans up to start to exhaust it. 

Since the experienced stove builders on Permies all knew about this, their advice was to keep the fire going. This is because part of the problem is that the stove is cold, and the chimney is cold, so there’s no draft yet to pull the smoke out of the chimney. I learned this has to do with positive and negative pressure. As the bricks heat up negative pressure is created which assists in getting the draft going. This is a typical problem at the beginning of stove season and why people sometimes heat the chimney before starting the fire.

The second reason is that the bricks and mortar aren’t completely cured yet. Not sure how that works, but we did notice that the back wall of the thermal mass (bell), the wall that was originally part of our woodstove alcove, didn’t leak at all.

Lastly, there are often tiny spaces and cracks in the mortar that allow smoke to leak. If the stove is properly built, these leaks stop as soon as the draft gets going. The biggest culprit for us was around the doors, which needed more mortar for a better seal. We also took note of a number of seams that could be pointed with mortar to seal them. 

Once we got a good draft going, all the smoke leaks disappeared, which meant that the stove was functioning properly. We kept a low fire going for the rest of the day and the bell gradually heated up. We were pleasantly surprised that even a small fire heated the bell and heated the house. We would often keep small fires in our soapstone stove on cold days to preserve some coals, but we never got any heat out of that and the house was cold when we built up the fire again for the evening. So, already, we were getting more out of our wood!

The other bonus was that by the next morning, long after the fire had gone out, the brickwork is still very warm and the house was comfortable. 

After the stove cooled, Dan set about to seal the doors and obvious cracks. I have to admit we were both a little nervous about that second fire. However, I heeded the advice on Permies and used one of our space heaters to warm the chimney first. I wanted a good draft from the git-go! 

Space heater to heat the cold chimney. Heating the chimney is only needed when the stove is cold.

This worked beautifully and between that and Dan’s pointing the mortar, our second stove fire was smoke free! No more smoke leaks and even the roof chimney exhaust was clean.

What a relief.

We’re still in the breaking-in stage, and still learning about masonry stove and fire management. With a conventional wood stove, a fire must be kept going as long as  heat is wanted. With a masonry stove, only two fires per day are typically needed. Since the stove is already warm there are no more draft problems for the season.

I’ve been monitoring the temperature near the chimney flue . . .

Remember, the heat is retained in the bell so that the coolest air exits out the chimney.

Source: https://www.5acresandadream.com/2024/11/masonry-stove-tests-and-tweaks.html