How about the moisture produced by the RMH!?

I knew water was a by product, but I didn't really "know". We have a stalagmite and stalactite situation outside(see picture), and we have a bit of seepage from some cleanout joints inside.
We are adding some heat return pipes to our bench, and may add some domestic water pipes later.
There was too much smoke for our J tube arrangement, so we shifted to front feed with a door.
I am amazed that it heats the whole house. We haven't had to really test it at sub zero, because we have had the mildest winter I can remember.

In order to avoid those stalactites, you'd better mount the chimney pipes all with the crimp ends down.

Linda; Nice looking build ! Wonder why your J tube smoked back on you ? Maybe your mass was not dry enough at the time. As far as your moisture problem , mine had a similar leakage but it lessened as that winter progressed and this year I have almost none ! I think moisture in my mass & wood played a part last season. This year I got all my wood partly split and in the shed by july (unlike last year!) and even with a core rebuild, with my mass completely dry I have not had any dripping issues at all . Unusually mild winter here in NW montana also.

Peter and Thomas, thanks for the help.
We were pushing into winter, and I was thinking more about the mass than the stack...also cut most of our wood after July (super rainy summer!).
It will be interesting to check the performance when it is really fully complete, and wood has had a year to dry.

daily burner durham nc rsm heater/waterheater first winter

also getting lots of clear water condensate with black creosote looking streaks took apart the last leg leaving mass to window exit no ash whatsoever though after burning from mid october

i moved the last leg of flu pipe nearly horizontal radating heat as it leaves and it is dumping more waterwhich i catch with a coffe can on a wire

i have been plugging the fire box after burns have gone completly out to trap the heat in the house if you dont have a door on the stove and some mass built up feel how much drafting heat goes right up the chimney out the house drafting cold air in behind from out side

Thanks Derek,
it's nice to hear that there wasn't a lot of ash. Do you have a picture of your can set up?
I know a couple of folks in Fairbanks that have already had stack fires with their wood stoves this year. Do you think there is enough creosote in the exhaust liquid to be flammable? Have you ever hear of a fire caused by buildup in a RMH?

If an RMH is burning decently hot there will be zero creosote, as that burns up at much lower temperatures. Black soot or stains would indicate poor combustion, or maybe a lot of cold starts which deposited bits of soot.

posted a pic on the rocket stove rocket stove forum 6" l feed in the subject

Linda Cozzini-McKirgan wrote:We are adding some heat return pipes to our bench, and may add some domestic water pipes later.
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Going by the pictures, that is a nice looking setup . . . the one thing I keep in mind, is that the more heat you pull out of the stove, the less heat goes out the chimney. . I wonder if you are removing too much heat and the steam is condensing on you too soon . . I know that with my rocket stove, I have alot of dripping out of my chimney as it hits the colder metal but I have not had any moisture problems indoor for a while now (at one point it was running out a couple of places) . . . How would you like to do a bit of a test run ? Cover the mass with blankets and give it a good test burn (don't take away any heat) . . by holding more heat in - you may get more steam going out the top of the chimney taking the liquid with it. . .

Just a suggestion . . . keep them pics coming . .

Edit : I was going to put in 4 rows of copper tubing inside the mass of my stove when I was building, but was worried about condensation - really interested in what happens...

I had the same thing as little Santa under my chimney pipe. WOW. All my crimps were already down. But. then I put a Tee to replace the ninety. That did not help much at all. So I put in a Tee with a 30 inch leg going down . Open on the end but it sits on a block. Not airtight but pretty good. That was it. It worked GREAT. Solved all of my moisture running toward the house. Actually it cut out most of the moisture . It seems to have better draw. PM me if you have any questions.
Thanks

Update about water output...
We get a much better burn because we put up a taller outside stack (8ft to 16ft). And pre splitting the wood smaller (dries better than quarter split) as kindling brought the moisture down quite a bit.
Our interior Alaska winter has been mild, and we heated our 1000 foot cabin with only a bit of help from the boiler November-February.

Is there any easy way to measure stack particulates?

I don't think that's creosote - I think it's ice with a little bit of soot stains. But it's darker than some of the other ice I've seen.

The chimneys where I've seen this happen are in cold climates (obviously), but they also have another thing in common: LONG runs of exposed pipe after the bench. We saw this on one of Paul's wofati projects, where there was a nice normal-sized bench and then 20 feet of near-horizontal pipe inside the building, then another 12 feet of insulated pipe outside to get around the roof eaves. That's almost triple the recommended length of pipe as would be used in the heater itself - and most of it is either too horizontal, or too cold, to be making any positive contribution to the draft. Cold, exposed, or non-vertical chimneys make the draft work in reverse.

There's also an issue in one of the projects above where the bench is a little longer than I'd recommend, and the addition of water pipes could potentially remove more of the exhaust's heat before it reaches the chimney.

... Chimneys, Water, and Mass Heaters ...
As Peter pointed out in 2014:
When you burn wood, if it starts at 15% moisture (ordinary, responsible, dry wood), then you get something like 62% of the wood's weight in water (steam) in the exhaust. My numbers say that if the wood was impossibly dry at 0% moisture (not going to happen in any reality, as some of the moisture is actually trapped in the resins and structure of the wood itself), then you would still get over 50% of the wood's weight in water in the exhaust. Hydrocarbons and carbohydrates contain hydrogen; hydrogen and oxygen burned together makes water.

The masonry heater boys try to keep their exhaust above 200 F, to avoid the dew point of water in these concentrated, steamy exhaust environments. They aim for 200-300 F during normal working conditions - not necessarily the outside surface of the pipe, which might be down around 150 to 180 F, but the stream of gas inside should mostly be above 200 F.

In our rocket experiments, we like to lower the exhaust temperature a little further for efficiency, in buildings where we can pull it off. But Ernie and I know we can't afford to do this in 2-story buildings, and that a chimney that is mostly outside the building will be highly vulnerable to over-cooling and chimney stalls. It doesn't even need to get colder than outside air to start stalling or flowing backwards - it just needs to get colder than the dew point of water, and the exhaust becomes a dense fog that won't rise up the chimney, and plates out water or ice on the chimney walls instead.

So your batch box might just be allowing a lot more air and heat through the system, diluting the steam in the exhaust, while at the same time raising your stack temperature to workable levels.

If you will burn dry wood in the system (no more than 15 to 20% moisture content), then we aim for an initial stack temperature on a wet, cold, new project of at least 100 F on the outside wall of single-walled pipe. In practice, this pipe will get warmer as the mass dries out and reaches operating temperatures - ours, with a relatively short run, operates between 150 and 180 F at the surface in the coldest winter months.

If you will burn wet or green wood, all bets are off. Not only do you have a lot more steam in the exhaust, but the process of boiling off that steam robs heat from the fire, and the steam expanding in the firebox displaces air. You can end up putting out creosote, regardless of how well-designed your stove may be, because you're basically running your fire with a fire-extinguisher continuously streaming into the firebox along with the fuel. Putting more wet wood on the fire can literally extinguish the flames. And then you don't have the heat you need to run the draft, which means everything is sluggish and prone to smoke, and the sluggish, cool exhaust has even more time in that cold chimney to deposit condensation on the sides, which runs down to the warmer parts where it came from, where it evaporates, robbing more heat, and goes back up for another ride down. You can make the exit chimney completely stall, certainly at temperatures as warm as 100 F regardless of the outdoor temperature, if there is enough water in the exhaust.

Emergency operation: If you notice that the exhaust is falling as it leaves the chimney, you're close to neutral, and could be prone to a chimney stall soon. Some heaters have a lower cleanout at the base of the chimney (we do this on all of ours now if we have anything to say about it); you can open this cleanout and "dump" the cold exhaust downward, clearing the pipe for warmer, drier exhaust, or even priming it with a propane torch or burning newspaper to re-start the chimney draft.

However tempting it may be to have this option, it's not worth putting the chimney outdoors to make it more convenient to dump. You want the chimney to stay warm, to have as much advantage as possible. The warm house is also creating draft, and can induce negative pressure in the lower third of the walls (or anywhere, in various wind conditions and considering modern ventilation fans). So you want the chimney to be warmer than the house, taller than the house, and to be sheltered and supported by the house, as much as possible. And you want to balance the amount of heat extraction with the basic needs of the fire and chimney system, for the right heat and air to maintain successful draft.

Even if you install the chimney right-way-up (so it collects any condensation inside instead of running down the outside of the pipes), it is not going to pump cold exhaust through a block of ice, or even drain water properly if the weep hole ices up. This is a problem that needs to be prevented in the design and planning stage, and by diligent preparation of dry fuel.

This is a very common mis-understanding that is reinforced by Ianto Evans' book, and by YouTube users who live in mild climates and unusually forgiving house designs.
We cover it in 4 different places in our new book, because it's such a critical thing to get right in the climates where heat is not a luxury, but a survival necessity.
That's the Rocket Mass Heater Builder's Guide, coming out in June of this year (2016).

And now a tiny self-promotional plug:
Our new book is now available on Kickstarter for pre-sales. As are a bunch of other useful resources. Please spread the word. We have until the afternoon of April 11, PST, to make the most of this opportunity.
https://www.kickstarter.com/projects/rmhbuildersguide/the-rocket-mass-heater-builders-guide

Good luck with the icicle factory!
You will definitely see improvement when you have time to put up drier wood - I am going to celebrate the first day of spring by posting some woodshed designs on our blog. ernieanderica.blogspot.com

Thanks for your lengthy reply Erica.

Our ice monster was defiantly under control with the birch that was 12% or less.
I don't mind putting up with a bit of moisture knowing that all the heat is staying in the house (exit temp is about 120f). The only time we get a smoky start is when the system is cool or we get a chunk of wet wood.

Also, this summer I am going to finish my cob work and put a finish coat on the bench. Does your new book cover finish work?
Thanks !

Wow loads of info there thats important. I would love to see my system if i followed all those points, i think i would have a bigger monster than i have. I think failed all those with a smaller chimney than my roof, 100F exhaust or lower, the tarp flew off my wood pile during a 3' snow storm and i had to stuff the wettest, punkiest, snowiest, funkiest larger than 8" into my system and it didnt flinch chewing it up. Theres a reason or combo of reasons why my set up got such draw. I have only speculated a few guesses as to the reason of its strength. I do know that my system no longer collects moisture after I Insulated my 6" pipe with thin layer of yellow fiberglass roll on and a 8" pipe slipped over the outside and it works perfectly... no weeps no icicles.

the chimney is upside-down?