I think I know what my problem is, but I thought I'd ask before ripping things apart. I'll explain my issue. I'm helping a friend build a RMH in his new place. It all started out on a bad foot since he lives on the second highest hill in our county and the only practical place to locate the stove was on the wall that receives the prevailing wind.
The entire core is firebrick. My feed tube is 7X7, as is the heat riser....but, I screwed up and made my burn tunnel low, only 4 1/2" high by 7"wide (a bit of a bottle neck right off the get go). So I know that's a problem. But here's the thing, when the clean out is open, the thing runs famously...it roars. But when we shut up the clean out and make it vent outside, it runs for a bit, but not efficiently, then stalls out after a bit and smokes up the house. Exhaust tube through what will be the bench is 8" and runs 26 feet which includes seven elbows before it goes out the wall. Fortunately they're not living there full time yet, but they need to soon.
At first I thought the problem was just the fact that we were facing the prevailing wind, but after trying all our possibilities for preventing back draft (except for a tall chimney), it is still performing the same.
so is my burn tunnel being small not allowing enough air in for a good burn plus restricting the unit so that it can't get enough velocity to push the exhaust through the bench? Is the added resistance of the exhaust tube the reason why it runs well with the clean out opened, but not with it shut?
Location: AR ~ozark mountain range~zone7a
posted 6 years ago
if it roars, I don't think I would be changing the burn tunnel size, if you feel the barrel heat is substantial, don't change the stove. if the clean out CAP, or a crushed pipe does not restrict the exhaust flow...I would go with your gut feeling about the outside wind preventing good exhaust discharge, I hope a smoke stack is all that is needed. Hope ya update with what worked and what didn't.
posted 6 years ago
Well, the burn tunnel was enlarged, and it definately runs better, but the wind is still affecting it.
My concern about running the chimney pipe all the way up(two stories) is that with the exhaust being as cool as it is, if the wind isn't blowing and making draw, will the exhaust cool down too much and not be able to climb out, effectively back the thing up again and smoking the house out anyway?
Maybe if we put the chimney up, but where the exhaust penetrates the house wall we can put a T fitting in with the vertical chimney pipe on top of one side of the T and the let the other side of the T face down and leave it open. Perhaps that way when no wind is blowing the exhaust will fall down and out, but then when wind blows, it will suck it upward?
Another thought is, could the fact that I used 8" for the exhaust duct be making a situation where there is not enough push generated to overcome the wind? My thinking in using it was that since the bench is compact(only 8' long), but deep (more like a bed than a bench) and uses 7 elbows in 26' of run, that the larger diameter would decrease resistance created by all the elbows.
posted 6 years ago
Oh my, just listened to Ernie and Erika's podcast. what never dawned on me is that the roof in the second story is not buttoned up. The whole house is a chimney. How many years have I been doing this? DOH!!!
I had the same problem last year when I went to exhaust my bench to the outside.
Wind or no wind there was a positive pressure outside the house where I wanted to exhaust.
So I hooked up the old 21' of triple wall chimney left over from my old wood stove and it runs fine.
If the stove is cold (like it is when you fire it up right now every other day or so) we have to light small fire in the last clean out to push out the slug of cold air in the chimney, after that she roars to life no problems.
posted 6 years ago
Well, that was it. We buttoned up the stairway to upstairs and problem solved except for some wisps in a quite sitff breeze. Very windy day today. I'm confident a little work on the outside will resolve that nicely.
I've been away from building appliances for a few years due to hometeading and growing veggies for market....I guess my brain just got a little rusty.
Actually, this was about as easy as it gets really. I'm confident that I can put the next core together in no more than an hour or two max.
This is so quick and easy in comparison to a masonry heater. I've put a couple masonry heaters together as well as built a couple of "poor man" heaters using old flap damper style fireplace inserts and creating a secondary burn chamber above it by enlarging the smoke chamber and making it out of fire brick and putting in a sliding steel shut off in the chimney to close off after the burn was done and accomodating expansion just like in a masonry heater. But heck, we built this with new materials and I don't think there is 400 bucks in it yet. Even the "poor man" units I built ten or twelve years ago cost a few grand, so no comparison and much more total energy harnessed for butt warming.....sweet.
Now I'm going to break my books back out and do a refresher on wood burning appliance info and combustion just to get the cobwebs out.....and then I'm going to get one started in my own house, then the greenhouse and likely the home of another friend.
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