Condensation

My Rocket Mass heater is up and running, which is wonderful. I have a similar design to the heater that was constructed by Erica and Ernie, in their DVD. The bench that is about 10 feet long, and nicely painted. Mine is not yet nicely painted.

Everything seems to be going good since the bench has dried out. However I am having some issues with condensation. I have a through wall Chimney, double walled stainless. ( the expensive one). But am experiencing water in the interior pipes of the mass.
Is there a fix for this issue?
Any advise would be greatly appreciated.
kathy

Kate : A couple of things, yes at 6 weeks your stove should be Dry. lets look at your wood, As this is your first year with a Rocket Mass Heater RMH, I have to ask
where your dry wood came from, and how dry is it! How is it stored, What kinds, how long has it been stored, and how much of that is split ahead !

Bark is not good fuel though we all burn it. It totally stops water vapor escaping that way, most water vapor escapes out the cut ends of the log though splitting does
help. The wood splits you feed your fire should always have more area of wood fiber showing than bark !

So just to cover the basics Short, very dry ,fine split Wood!

Now about the Condensation, Up too 20% of your woods weight is water vapor and the three major products of burning wood well is Carbon Dioxide, H2O, and Fly
ash, that should feel like talcum powder, with only a lithe grit and almost no charcoal in the combustion core! So you are still dealing with lots of water.

Now here's approximately what happens when you bring all that water up above the temperature 212ºF. Here All that water is suddenly changing into Water vapor!
There is a Phase Change *point where a lot of additional energy is removed from the burn, to push this phase change event.

With conventional wood stoves all this energy Trapped in the water vapor in our exhaust stream and vented outdoors with the EPA required 500ºF exhaust! In our
case the water vapor that cools and condenses releases all that latent Heat of Evaporation to Your Thermal Mass ! This is not only a Win-win, its like getting money
from home without even writing !

* when I went to school they only knew about 3 states or phases of matter Gas Liquid, and Solid! (Now there is 5? ) Anyway many materials have these Phase
changes or changes of state. Here Liquid (water) to Gas (water vapor) that requires additional energy to make this happen. The important thing is we get most of
It back during condensation.

If you are trying to combat dry air in your home by having a pot of water on top of Your RMH, and you find that the houses windows are covered with Condensed
water vapor that latent heat is being released to the glass, and flowing to the cool side, so don't simmer water unless you can see NO Water vapor on your windows,
and every pot should have a lid ! There thats all I've got, mostly good news !

For the good of the Craft ! Big AL

Thank you for your speedy and scientific explanation.

The wood is yellow birch and was split around 16 months ago, into firewood size pieces. Last month I had it re-split into RMH pieces. It is probably around 15 percent moisture content, and stored indoors. The stove is in a newly constructed greenhouse with not much moisture in the air at this point.

I was thinking the condensation was a result of cooler outside air entering the stove the following evening/day, and condensation being formed when the cool outside air travels down the chimney and comes into contact with the warm inner pipes during the cold evenings. ( 15 degrees F)

I do not have a damper installed, and saw no mention of it in the construction details.

The majority of the water is at the end of the RMH run. before it exits up the chimney. I have a clean out there that I can look in. So I was not thinking that the moisture was coming from the wood........but I could be wrong.
Kate

In further reviewing my question, I guess the bottom line is.........How do we deal with the condensation?

Kate : No damper ever with a J-bend Rocket Mass Heater, the j-bend acts simulator to the way your 'P' trap under your sink does The 'P' trap prevents Rising sewer gas
from coming up into your House *

the J-bend stops Thermo- Syphoning after the fire is out !

How much beaded moisture or frozen moisture do you have on the Greenhouses skin !

This is part #1 Big AL

Well quite a bit of moisture on the outside skin........although it is double walled poly carbonate panels with 6 inches of space in between. Virtually no moisture on the inside..

Kate ; In our greenhouse rmh, we place two bricks to close off the feed tube at night after or as, the last fire is dying out. Depending on how large your mass is ...you could still be drying it out, mine took 6-8 weeks to really get everything hot % dry and I built it slowly in the late summer!

Thank you Thomas. When I have placed two bricks over the feed tube, there was a lot more condensation in the pipes. So you think that maybe it is still not completely dried out?
and if that is so, how does the moisture get to the inside of the pipes...
Kate

Kate; The temp difference between the hot air in the pipe and the cooler moist cob around it , similar to condensation forming on the bottom of a sheet metal roof. My condensation mostly went to my ash pit and evaporated but... not before showing me any little spot where pipes joined... I used a full roll of metal duct tape on each and every joint and bend in my vertical chimney! By the middle of winter last year I had no condensation issue at all. But it sure took a lot longer than i thought it would.

Thomas R. : Thanks for the update ! That settles it, I will have to do another one in the spring! I'm getting rusty ! :[

Kate D. : You can try a small 1/4'' hole in the vary bottom of your Final clean out 'T', to see if the water is condensing in the vertical chimney or in the Horizontal run!

If most of your water is coming from the horizontal run your Thermal mass Has not dried out yet, Sometimes people are in a hurry to seal their bench and rush through
the Structural Cob shell with wet straw and then wonder why their Finish coat will not dry out as most of your drying is still from the bench surface in you have a similar
problem except yours shows up as water on the inside !

THe good news is you should notice a drop in the amount of wood you use !

For the Good of the Craft ! Big AL

I don't know much about RMH but in most high effient gas heaters we install condensate drains to catch all the water. I've have wondered how people were not having issues with rusted ducting.

These are called condensing units, overwhelmingly they are Condensing Boilers, (this may be regional) and the additional costs are easier to hide in the Nat. Gas Boilers
than in the Forced air units > I Think

4 the Craft B.AL

Thank you ....all of that information helps. The good news is that it should lessen, yes I was in a hurry to get it finished before the snow fell, and did not dry out the cob as much as I would have liked. So it probably is damp in areas. Also happy to hear the wood consumption will lessen.

Upon reflection, possibly the condensate is at the end of the bench simply because that section is the last to dry out. The air it receives would be cooler that the rest of the pipe.
I will give it more time.....