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rocket mass heaters

Batch Box - Condensation

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posted 9 months ago

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First Test Burn!

The fire lit very easily and it's definitely drawing. A little bit of smoke came back into the room when I loaded bigger logs. None of the flu is sealed with cob yet and barrels need fire rope/gasket too.

What I did notice was water dripping from the bend and inspection T's, a significant amount. I think it's condensation? Will cobbing the flu reduce the difference in temperature therefore reducing the condensation?

I just want to double check before I start cobbing 👍

Annoyingly I did not get a video of the water dripping 🤦‍♂️🤣

Peter van den Berg

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Location: +52° 1' 47.40", +4° 22' 57.80"

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posted 9 months ago

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Since it's your first burn, all pipes are cold and the core is still wet. Condensation will occur in this stage, the process of burning itself is producing water vapor which is turned into condensate in the cold pipes. I'm inclined to think the chimney temperature is too low, this should be 55 ºC (130 ºF) or higher within 20 minutes after lighting. Measured in the core of the vertical pipe, of course, the pipe itself is much cooler. Failing that, water condensation in the chimney will drip down to the horizontal pipes, cobbing in might or might not solve that.

Batch boxes are very picky about friction in the smoke path, those pipes create lots of that. When the gas velocity is getting higher in the system, it might pick up a slow pulse, like a steam engine. This is a sure sign there's too much friction in the system. A build that is truly to specs, using a brick bell, won't pulse at all.

I saw your video on Facebook, the total length and lots of bends of the horizontal pipes surprised me. Judging by the bricks in the core, I'd say this is a 6" system. Before you do anything else, sit down and calculate all the internal surface areas. Omit the floor of the lower barrel plus the bottom quarter of all the pipes. In case the resulting figure is significantly higher than the recommended 57 sq. ft., there's a fat chance condensation will be a normal effect during winter.

Sorry for being the messenger of bad news.

regards, Peter

thomas rubino

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posted 9 months ago

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Very common Liam.
Quite a few first/second, and even third burns have drips.
Covering the flue is very important to keep the cooling air traveling out of your chimney.
Exposed pipes radiate too much heat.
The wood you are burning can also be a source of moisture.
Tape your pipe joints with metal tape, cob over all that should be.
If you used a mortar and had wet bricks, all need to be dried.
How about some pictures of your build.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com

Liam Alderdice

Posts: 13

posted 9 months ago

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thomas rubino wrote:Very common Liam.
Quite a few first/second, and even third burns have drips.
Covering the flue is very important to keep the cooling air traveling out of your chimney.
Exposed pipes radiate too much heat.
The wood you are burning can also be a source of moisture.
Tape your pipe joints with metal tape, cob over all that should be.
If you used a mortar and had wet bricks, all need to be dried.
How about some pictures of your build.

PXL_20240329_133926439_exported_5588.jpg

thomas rubino

rocket scientist

Posts: 6320

Location: latitude 47 N.W. montana zone 6A

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posted 9 months ago

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Hey Liam;
Very clean-looking build you have there.
Peter thought it looked like a 6" system, I think it looks larger like maybe an 8".
I would like to see the transition area better. Is that one continuous pipe or two legs?
How much pipe do you have, not counting the vertical rise?

At this point before cobbing, you could easily change from pipes to a bell system.
Bells are so much easier to run than a piped system.
I have an 8" piped system that started with an 8" J-Tube feeding it. Worked great!
That same piped system is now fed by a 6" batchbox, it also works great, but only once it is completely warmed up.
It does need to use its 4" bypass anytime it is not warmed up.

If you are happy with your draft then start cobbing over those pipes, they are a part of the condensation issue.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com

Liam Alderdice

Posts: 13

posted 9 months ago

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thomas rubino wrote:Hey Liam;
Very clean-looking build you have there.
Peter thought it looked like a 6" system, I think it looks larger like maybe an 8".
I would like to see the transition area better. Is that one continuous pipe or two legs?
How much pipe do you have, not counting the vertical rise?

At this point before cobbing, you could easily change from pipes to a bell system.
Bells are so much easier to run than a piped system.
I have an 8" piped system that started with an 8" J-Tube feeding it. Worked great!
That same piped system is now fed by a 6" batchbox, it also works great, but only once it is completely warmed up.
It does need to use its 4" bypass anytime it is not warmed up.

If you are happy with your draft then start cobbing over those pipes, they are a part of the condensation issue.

This is a 6 inch system with just over 6m of flu in the bench and around 4m of vertical flu out the roof. The top couple metres in the loft will be insulated. I've installed a Y inline with the vertical flu incase I need to preheat it (Venturi?)

I understand how the system works but calculating surface areas and knowing what I need to subtract confuses me so would love some help there!

Unfortunately I can't really afford to buy new materials right now so if the cob doesn't work I'll have to build a bell system. Or install a bypass if that'll work.

I'll add some more images

Liam Alderdice

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posted 9 months ago

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Here's a few more images of the system

PXL_20240328_163013609.jpg

PXL_20240328_144735868.jpg

Liam Alderdice

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posted 9 months ago

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Liam Alderdice wrote:

thomas rubino wrote:Hey Liam;
Very clean-looking build you have there.
Peter thought it looked like a 6" system, I think it looks larger like maybe an 8".
I would like to see the transition area better. Is that one continuous pipe or two legs?
How much pipe do you have, not counting the vertical rise?

At this point before cobbing, you could easily change from pipes to a bell system.
Bells are so much easier to run than a piped system.
I have an 8" piped system that started with an 8" J-Tube feeding it. Worked great!
That same piped system is now fed by a 6" batchbox, it also works great, but only once it is completely warmed up.
It does need to use its 4" bypass anytime it is not warmed up.

If you are happy with your draft then start cobbing over those pipes, they are a part of the condensation issue.

This is a 6 inch system with just over 6m of flu in the bench and around 4m of vertical flu out the roof. The top couple metres in the loft will be insulated. I've installed a Y inline with the vertical flu incase I need to preheat it (Venturi?)

I understand how the system works but calculating surface areas and knowing what I need to subtract confuses me so would love some help there!

Unfortunately I can't really afford to buy new materials right now so if the cob doesn't work I'll have to build a bell system. Or install a bypass if that'll work.

I'll add some more images

I forgot to add that this is one continuous flu, the burn chamber is raised above. 2 45⁰ bends to creat the shape of the bench

Peter van den Berg

gardener

Posts: 1054

Location: +52° 1' 47.40", +4° 22' 57.80"

447

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posted 9 months ago

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Liam Alderdice wrote:I understand how the system works but calculating surface areas and knowing what I need to subtract confuses me so would love some help there!

So you need some help, OK then.
I did a rough calculation for the two barrels and the 6 m (19.7') of stove pipe plus multiple bends. Assuming the two barrels plus core would be about the same as two whole barrels this would be 3.26 m² (35.1 sq ft) of surface area.
The 6 m (19.7') of pipes would be equal to 2.12 m² (22.8 sq ft), omitting the bottom quarter of the pipes. This is done because of the hot gases will predominantly in the upper part of the pipes.
Then there are 5 x90º bends plus 3 x45º bends. I calculated these as being equal to 3 m (9.84') of straight pipe, together 1.06 m² (11.4 sq ft) of surface area.
Keep in mind, his is a very conservative calculation.

Now, together you have 6.44 m² (69.3 sq ft) of surface area, while the recommended maximum is 5.3 m² (57 sq ft). This is 1.14 m² (12.3 sq ft) too much, being equal to 3.22 m (10.6') of pipe length, according to my calculation. So I would recommend to shorten the total length that 3.22 m (10.6') anyway.

More friction in the system could lead to more problems, though. Like the slow pulse as a steam engine, for example. If at all possible, I would recommend to buy a 6" to 8" reducer and mount this between the barrel and the start of the pipe. Due to the larger opening in the barrel one possible pinch point will be not there anymore.

A lot of numbers, I know that. Let it sink in and see what (and how) you could do.

regards, Peter

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