Last summer, Dan built a masonry stove to replace our cast iron wood heater.
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| Masonry stoves are based on ancient technology and are amazingly efficient. |
The gist of how it works is that the firebox is located in a large, empty space called a thermal mass. The thermal mass retains and radiates heat long after the fire goes out.
Last winter, we used it and loved how long it kept the house warm between fires. The downside is that it tends to be a bit smokey with a cold start. Until the mass warms up enough to create a good draft, smoke comes out every time the door is opened, or through any leaks in the masonry. There are tricks for dealing with this (Tests and Tweaks), and usually, people only have trouble at the beginning of the season. For us, however, in our goofy southern climate, there are times when we don't need the stove and let it go out. In a typical winter here, we might restart the stove several times, especially in spring.
Last month, Dan added a smoke by-pass to use when the stove is started up. The by-pass offers a direct outlet for the smoke created when starting a fire. Once the stove heats up and the draft is good, the by-pass damper is closed and the thermal mass can build up heat.
Here's what Dan did in pictures.
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| The first step was to take down the existing chimney pipe. He cleans the chimney once a year anyway, so that got done too. |
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| Installing the damper required drilling a 6-inch hole in the top of the stove. For that, we had to get a 6-inch diamond masonry drill bit. |
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| Here it is from the damper side, where you can see the openings and gap. You can also see how the insulation discs blocks them. |
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| Insulation side |
8 comments:
Very interesting!
I think I told you this back when you were building it, that I usually try and leave my firebox door open for about 15 minutes before I start a fire to allow time for the coldest and heaviest air in the flue pipe to settle into the house and get replaced by warmer house air. What I don't recall if I told you or not is that I usually buy some compressed sawdust and wax pellets (you could easily make them) to light and stick inside the firebox and close the door. They burn nearly smoke free and help get a column of hot air going up the flue and setting the draft. Then I just toss in my kindling and a few logs before the pellets burn out and away I go. Using this, I can get nearly a smokeless fire start every time. The few that result in smoke is always during the coldest and windiest days of winter when it is just hard to get a draft going up the flue.
What an innovative solution to the problem, Leigh! Was this something that you found as a reference or a self-designed application?
Laurie, I'm glad you think so! I wondered if it wouldn't be something of a boring topic for most people.
Ed, that is a great idea about the sawdust and wax. We have both and I think it would be worth a try. I do remember about leaving the door open. With our convoluted chimney set-up, it's a little more challenging.
TB, we were aware of the by-pass from Permies forums. But we didn't incorporate it because it added something complicated to the plans. This year I contacted the guy selling the by-pass gates and he told us about his new design using a regular chimney damper. We took his idea and went from there. He thought it helped a lot, so that was good enough to give it a try!
I am so impressed at what some people can do - i.e. you and Dan. First of all, to build such a beautiful masonry stove, and then to figure out a solution to your smoke issue - and it's attractive too!
Becki, thank you! Part of it is that Dan is a very hands on guy. He is a doer who loves a challenge.
The smoke issue was known before, from what other people who have these stoves have said. Some people say, 'it's just once a year,' others have worked out solutions. So we looked at all of those solutions and decided on this one. Time will tell how well it works!
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