Rocket Mass Heater tested with a Flue Gas Analyzer

[matt walker]

Well gang, I think I mentioned getting the Testo flue gas analyzer. I finally got around to doing a full test run a week or so ago, then procrastinated making the video. Partly because it's not the best run, but, after thinking about it a bit, I think that's great. This shows pretty normal use, not an ideal situation. One thing that would make the efficiency go up is cooler stack temps. I could fake it and do a test run after letting the heater cool for 24 hours or so, but that's not how I actually use it. I also loaded it with fuel that was cut a bit small, and that spikes the CO in the beginning of the burn. Again, I could have tuned the load for a test, but I think it's great that it shows the quirks. As for the heater itself, I'm inspired by the tester to try to keep more heat in the house, stack temps are surprisingly high after going through all that mass. There may be another bench extension in my future this summer. Maybe. Anyway, it's kinda boring, but maybe someone will find this useful.

[pa_friendly_guy]

That is a great tester Matt. It gives you a wealth of useful information and seems to work really well. I enjoyed the video very much. keep us posted with other tests and your other out door stoves when the weather turns warmer.

[mannytheseacow]

Great video, Matt. Thanks a lot for sharing that. I found it pretty fascinating. Considering my tankless water heater is only 84% efficient, I think there is a lot to be said for what is going on there. I found it particularly interesting that when the fuel load drops and the CO level rises, the efficiency has no significant change. I wouldn't be getting very much done if I had a device like that. I'd love to run tests on all the different kinds of wood that I burn and use that kind of information in planting, thinning, and other maintenance on my forest, planning for a long-term dependence on wood burning. How much wood do you need to run a test? I'd be willing to send you a little variety pack of species if you'd be interested in running the tests? How differently have the other heaters performed that you have tested?

One last request (for today )- You mention the MHA website and a 90% efficient batch burner on there... I looked all over the site and found it about as loopy as donkey's board. Can you post a link to that?

[matt walker]

You callin' me a heater nerd? Hahaha, kidding. Here's the article I was referring to:

http://www.mha-net.org/documents/visit- ... g-part-ii/

I believe a large part of that 90% number is the fact that they can start from cold with relatively cool water to pull tons of heat from the heater, thus making a very cool exhaust temperature. I am certain that my core burns as efficient if not better than a batch, but in the winter if I'm using it for heat there's no way I'm ever going to have a super cool exhaust since my bench internal temp is never much below 200°F. If I had a 50° bench to start with, I believe my efficiency numbers would be on par with those.

I'm pretty excited to share this real world performance, since I'm starting to realize I've never seen tests like this. The others are always testing in a shop, or a new build, but not a warm working heater. Like you, I think the numbers I get are very encouraging. Much better than that and I think I'd be gaming it to get there, which isn't what I want to show. Honestly though, there's been so much hyperbole about these things that I have kinda been cringing since I put that up, waiting for the inevitable "so and so said theirs is 98% efficient!"

I've tested two other heaters so far, 6" J tubes, and both of them performed pretty much the same. I think the J is just a very stable burning design. Dead simple and fairly forgiving.

As for wood, a test is one full load, and my feed is about 6"sq., so that much. 16" long fuel works well for my heater, but a little shorter or longer is fine. If you do want to do that, don't send me your finely split stuff. I'm afraid a full firebox of 2" hardwood would make my whole barrel glow!

I sure wish I had this when I visited, I bet your heater is in the 90% range with your low exit flue temps.

[mannytheseacow]

I had an immediate case of heater envy looking at that thing. How come those Europeans make everything so shiny?

I get what you're saying about batch heating the water and starting from cold. RMHs can for sure be as much a heater as an insulator. It makes a lot of sense to store that heat in water and use it hydronically. Still, I just love the warmth of a big wood fire.

I won't constipate over numbers too much here, but it is interesting that his CO levels are more than twice what you were running. Admittedly, 10 and 20 is kind of moot when you're talking parts per million, but still...

[matt walker]

I suspect the CO numbers are a function of how much wood is in the thing. Like, I have 4lbs making 8ppm, he's got 12lbs making 24ppm, or something like that anyway. Yeah, shiny, also, crazy expensive, even if it was built by the owner. That's one thing most, not all, of the European RMH guys seem to overlook about this technology. A big part of the reason this technology is a winner to me is because I am able to build it myself for a few bucks. If I was ready to drop thousands of dollars on a heater, I'm not entirely sure this is what I would choose. There's a lot of good wood heat technology out there.

[mannytheseacow]

For sure, for the cost of one of those things a person could get a 1 way ticket to somewhere warm, and probably live there for a year to boot!

[solarguy]

I used to be a natural gas pipe fitter.

In that capacity, I worked with gas appliances.

Until you graduate to high efficiency furnaces that condense the water vapor in the flue gasses, it is impossible for a furnace to exceed 82% efficiency.


I suspect that some rocket mass heaters do, in fact, condense some of the flue gasses, and may very well exceed 82%.

It's kind of a win/win or lose/lose situation, depending on how you look at it.

If you are actually condensing the water vapor, you may exceed 82% combustion efficiency. BUT then you get condensate somewhere in the system. It tends to be acidic and corrosive.

If you don't condense the flue gasses, you are less efficient, and you don't get the gooky corrosive acidic condensate.


Finest regards,

troy

[4seasons]

[4seasons]

I am still trying to grasp some of the concepts and ideas surrounding rocket stoves so I have a hard time following some numbers that a computer spits out and relating that to what real world performance shows. From reading on Donkey's board particularly in Peterburg's builds I see tons of technical information and Testo charts but I have yet to see any information on why some numbers are bad and some are good. I am still not even sure what the efficiency number means. Is it referring to the BTU's being extracted? If so how does a computer sensor know how many pounds of wood you packed in to your stove to know that you left all 6200 BTU's per pound of heat in your house? I guess my main concern is getting the right amount of heat in my house for the least cost or amount of work. Therefore I don't see hours or dollars on these readings which leaves me wondering what the point was. Now don't get me wrong, I am not saying that these test are pointless, only that I have not been able to tie these test to real world results. Now if I am completely off base here feel free to slap me around a bit. I am only the new guy that has been reading everything I kind find on RMHs for the last month and some of you guys have been doing this for years.

I really do appreciate all the work Matt and others have put into these designs and test. Also I am grateful for the willingness to share what they have found so that we can avoid mistakes and build on success.