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Jerry
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# Posted: 29 Feb 2012 10:07am
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I'm converting an old round, double walled wood burning stove to make it a sauna stove and have a question that is being debated between me and my friends. The stove is double walled allowing for water to circulate around the inner wall and exit for a heating system. The smoke pipe originally exited out the upper back but I rerouted it out the top and welded a big box around it to hold sauna rocks. I made the smoke pipe out of 1/4" walled steel pipe so it should be good for the life of the stove.
Our debate is, after positioning the stove in my future sauna should I fill the space between the stove walls with dry sand to act as a heat sink to retain heat in the sauna at an even level, or would that take so long to heat and transfer to the sauna room that I'd regret it? If it were in a living space I could see doing it, but a sauna is usually a place to get heated up, use it for a short time and leave. Then again maybe if it was filled you could keep the sauna somewhat warm for the weekend and it would be easier to bring it up to heat for the next use.
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PDK73
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# Posted: 29 Feb 2012 10:44am
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Hi Jerry, sand in the cavity will add thermal mass but make sure that you have good air flow for pressure changes. I'd be against filling since it would mean a longer wait for warm up and unless you were going to use it a few times a day that much thermal mass probably wouldn't make a big difference heat retention wise. A better option might be to drill/cut holes through the outer jacket around the top and bottom to create convection. In a small space it might not make a difference which way you go. The amount of stove pipe inside definitely will, increasing the radiant surface.
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MtnDon
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# Posted: 29 Feb 2012 12:56pm
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One thing people sometimes notice about the newer wood stoves with EPA approval is that they take longer to warm up and start heating the room. That is because many (most?) new stoves have fireboxes lined with refractory brick (fire brick) to make for a hotter burn in the firebox and less unburned gases escaping up the chimney.
So, IMO, I would not fill the stove voids with sand as it could likely slow the heating up of the sauna. That's the theory anyways. Of course the trade off would be the stove might retain heat longer and perhaps even out the temperature in the sauna.
How easy is it to fill and to empty? You could always try it w/o sand, then with sand to see if you have a preference.
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Jerry
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# Posted: 29 Feb 2012 04:01pm
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MtnDon,
To fill it with sand would be relatively easy - the original fittings for water in and water out are still there. I'd fill it in position and shake the stove to get the sand to settle. To empty it would be more difficult. By then it would be connected to the chimney, very heavy and I'd have to take it out of the sauna to turn it over. It would be a job. I think I'll try it first w/o the sand and see if I'm satisfied with the performance. Come to think about it, I might drill, tap and plug some holes on the bottom and maybe I can experiment with creating some convection as mentioned by PDK73 above.
Thanks for the input.
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Martian
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# Posted: 29 Feb 2012 05:52pm
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Jerry, are you going to give the stove it's own air supply? Depending on how big your sauna is, something to think about. Is your sauna going to be wet or dry? If wet, you might plum a steam system from the water jacket.
Tom
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Jerry
Member
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# Posted: 29 Feb 2012 11:34pm
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Martian,
Hadn't thought about giving the stove its own air, but that's not a bad idea. The sauna will be dry. I didn't know there were "wet and dry" saunas until I asked about a building permit for the building. I was told if it's wet you need to connect to an approved septic system, and if it's dry, you need no permit at all. The guy said you can bring in a bucket or two of water and that's still "dry". That's what I've always done anyway, so dry it is.
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