Sunday, March 4, 2012

Rocket Mass Re-Build

We've had a freakishly mild winter this year. Works for me. Although surviving through multiple week stretches of -40 weather is kind of a badge of honour many Canadians are proud of, I hate that shit. It's almost over anyway, and the season for building things and growing stuff is so close now. Today was a beautiful, sunny +5 C day with no wind. Mrs. Mud and I went wandering around the acreage looking for scavenging materials that we've probably seen a dozen times but still hadn't figured out what to do with. As new projects develop there is often something laying around that seemed to have no good purpose until just right now. Also, today I cleaned one of the guns, went outside and put 25 rounds through it. Wandering around the property with the old lady in beautiful weather and then some shooting adds up to a pretty wonderful day.
I have nothing to complain about. Well, except that my government (and probably yours too) is filled with a bunch of peckerheads bent on turning the country into a corporate free-for-all while 'real persons' struggle to survive and pay the politicians lucrative salaries and pensions.

My rocket mass heater is acting weird. I'm thinking of tearing it apart for a complete rebuild. That certainly doesn't cause me to complain. On the contrary. How many people with 'traditional' heating systems in their 'traditional' homes can just rebuild it themselves? That's why I love owner built homes using mostly natural materials. I'm in control. I don't need some overpriced furnace guy or electrician to come into my home, do some weird voodoo I don't understand and leave me with a huge bill. (I don't mean to rag on plumbers or electricians in particular, I'd understand if they felt the same way about some overpriced GIS dude handing them a bill for something they didn't understand or need and could have likely done a different way themselves for free.)

When I first fired up the mass heater it worked great. And has since, but not consistently. Sometimes it will reverse. All of a sudden, the airflow will change and blow smoke into the house. Then it reverses again, sucks smoke back into the feed tube and makes that satisfying rocket sound, just like it should. I have some ideas why this is happening. One is that the vertical stack at the end of the run within the mass is just not getting warm enough. There isn't enough heat left by the time it reaches the stack to combat the push from the column of cold air fighting against it. That's one possibility anyway, I'm not sure if it explains the 'pulsing' motion of air flow though. Another possible issue may be that my bell chamber between the barrel and the beginning of the run the mass might have too much volume. Another problem may be that since winter got here before the thing was completely finished there may be minor air leakage around the bottom of the barrel. All these problems can be easily dealt with in a rebuild. I will go with a shorter run through thermal mass. Also reconfigure the layout so that the final vertical piece of pipe that leaves the house would be positioned right against (or darn close) to the heat exchange barrel. Both these things would increase the temperature of the gasses in the vertical stack, thereby increasing the 'suck' at the feed tube.

As much as I wish no changes would be required I'm glad to learn this now instead of after moving in this fall only to be smoked out in the winter. I don't want to be pondering improvements to the system standing outside in January watching smoke billow out the windows.


  1. Nothing beats having a system you built yourself and can rebuild and repair if you have to.

    I'm thinking your stove might have some air restriction. Ash build up? Call it a wild guess.

    Good luck, and have fun with it.

  2. Sixbears,
    I've taken apart and removed the entire unit a few days ago. Ash wasn't the problem. The entire length of 7" pipe as well as the insides of the heat exchage barrel were actually pretty clean. This leaves me certain that the problem was that the gasses were getting too cool before exit and that was causing the reversal. One thing for sure in my new design is shortening the length of vertical rise at the end of the run. Then there won't be as much 'push' required, fighting that column of cold air.