Interesting stuff on measuring wood heater performance

If you are not interested in numbers this will be really dry (boring) but i found it interesting at least on how small things affect measurements. This particular webpage is about measuring the effect of using a flue damper or not after a bell for heat harvesting. It also tests the effects of leaving the air intake open as well.

I found it interesting that the flue damper had no noticeable effect, except when the air intake was open. This would not be the case with a standard RMH mass bench where the flue slants up from barrel to chimney.

I found it interesting that even though these are people into high mass heaters and bricks, they felt a steel chimney would be better in this case because the chimney effect would stop sooner with a thin metal chimney than with a high mass masonry chimney.

I also thought it was interesting that having a lab built for testing stoves was a handicap. The graphs show things such as door openings quite clearly. Getting good measurements was not easy and required clear understanding of what was being measured. They were seeing the heater take 5 days after one firing to reach room temperature (after that five days the room temperature had changed too). Paul's office may actually be a better place to measure things in because of the extra size and a large door that can reset the air temperature and cool the mass down quickly.

Please note: this is not meant to hold up one kind of heater over another as better or worse. I personally appreciate the effort that is being put into both RMH and the masonry heaters.

The particular masonry heater in this test is made from many premanufactured parts, but is probably still quite expensive... at least the way I count things. It is meant to be code-able and so would require a second skin.

Len, I found your summary more enlightening than all of their graphs were. I agree that putting a lot of mass in a chimney would cause greater losses through "the chimney effect". Surface temperature tells us something about heat delivery over time but doesn't address efficiency of the system.
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When it comes to testing the efficiency of RMH the only test that would matter to me is the one where a given weight of wood is used to heat a given weight of brick, cob or water. This sort of test is less prone to being misinterpreted. We know how much energy is in the wood and we can simply determine how much that energy would raise the temperature of the mass if all were stored. Simple math would allow me to figure out the efficiency if it hasn't already been done. I've looked at many wood stove testing sites and they all dance around a problem that I could have figured out for them when I was in grade six. They seem to think we're all stupid.

Dale Hodgins wrote:Len, I found your summary more enlightening than all of their graphs were. I agree that putting a lot of mass in a chimney would cause greater losses through "the chimney effect". Surface temperature tells us something about heat delivery over time but doesn't address efficiency of the system.
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When it comes to testing the efficiency of RMH the only test that would matter to me is the one where a given weight of wood is used to heat a given weight of brick, cob or water. This sort of test is less prone to being misinterpreted. We know how much energy is in the wood and we can simply determine how much that energy would raise the temperature of the mass if all were stored. Simple math would allow me to figure out the efficiency if it hasn't already been done. I've looked at many wood stove testing sites and they all dance around a problem that I could have figured out for them when I was in grade six. They seem to think we're all stupid.

Measuring the temperature of a RMH would not be easy I think. The fun thing with any Mass Heater is that the mass does not heat evenly and so there is no "temperature of the mass", but rather a set of temperatures of the mass. To complicate things farther, The RMH (and to a lesser extent a masonry heater) gives off a lot of heat up front in the barrel that is never stored in the mass. On top of that, before the load of wood has finished burning the mass has already given up a large amount of heat to the room. So to measure efficiency the exhaust temperature at flue flow rate probably gives a better idea... assuming the burn is getting everything out of the wood it can... which changes depending on the wood and water in the wood.

Anyway, The particular test I pointed to, was not trying to measure efficiency. These guys have done the math as you have long ago. They are more interested in the quality of air that comes out the stack and that is what the setup was built for. The page I showed was along the lines of "hey we have this set up here, lets test some other things too".

My summary was really a summary of things I learned, many of them passing comments. Their comments made more sense to me than the graphs as well, because they were there and so knew what had caused sudden dips in measurement.

This thread deals with RMH efficiency testing. I posted here--- https://permies.com/forums/posts/list/16/3249 --- on the day I joined the forum. In the last 2.5 years, I haven't thought of a simpler or more accurate way of taking those measurements. My tenants will soon leave my cottage and I will build a system without a barrel that should be easy enough to run this test on. I'll create a test thread and publish results regularly. Since the cottage is vacant much of the time, there will be times when a very large temperature rise is needed. I'll run it on a variety of fuels that are weighed and moisture tested.

Dale Hodgins wrote:This thread deals with RMH efficiency testing. I posted here--- https://permies.com/forums/posts/list/16/3249 --- on the day I joined the forum. In the last 2.5 years, I haven't thought of a simpler or more accurate way of taking those measurements. My tenants will soon leave my cottage and I will build a system without a barrel that should be easy enough to run this test on. I'll create a test thread and publish results regularly. Since the cottage is vacant much of the time, there will be times when a very large temperature rise is needed. I'll run it on a variety of fuels that are weighed and moisture tested.

That will be one to watch. Thank you for taking it on.