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RMH elbow exhaust entrance  RSS feed

 
shadrick wilsons
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Greetings. After fiddling with my first RMH build after much research it (kind of) works! Perhaps my oder of operations is screwing me a little bit though. Anyways it draws mostly so far without exhausting above the same plane as the rest of the system once I vent outside. Now so far I'm at about 40 feet of pipe just to make it outside. Can I add 15 or 20 feet of vertical exhaust without consequence? I messed up in my burn tunnel dimensions also. It's 7 wide by 5 high and I know it should be taller rather than wider. Is it possible for my burn tunnel to be too short however? Also the smoke seems to be going where it should be but I noticed in someone else's thread they have an elbow to ease transition into the mass. Is this necessary? Also, as the outside of my fire brick heat riser heats up over time and (assumingly) matches the inside of the heat riser will this cause problems? Gracias!

Shad
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allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Shad : At 40' you would be in trouble with a 6'' system, and marginal with an 8'' system. We also have to calculate every Elbow in the system as adding the equivalent
drag as another 5' of pipe*. The good news is what you lose with a very long horizontal run you gain back with a very Tall Final Vertical Chimney ! **

I am sure that others will find fault with my ratio but if the Feed Tube is 1 unit deep the Burn Tunnel should fall in the 1.5-2 units of length with the Heat Riser needing to
be at least 3-4 units Tall 1 : 1.5-2 : 3-4 Also with some of the other compromises you have built into your system a 2'' gap between the top of the Heat Riser, and the
Underside of the top of the barrel seems called for !

We speak of the area where the Cool(er) Exhaust Gases fall down the outside of the Heat Riser and turn 90ยบ to flow horizontally through the Thermal Mass as the
Transitional Area - This should be as large as possible !

Without insulation wrapped around the outside of your brick Heat Riser to isolate the two different temperature streams from each other, you will have the potential
to lose some of the strength of your draft as the two streams blend their temperatures, this will be late in the burn and by then you may have a strong enough 'draft'
to carry you through to the end of your burn cycle , 1 hour of burn for 12-24 hours of heating from your Thermal Mass

You have laid your bricks the way a mason builds a house, this takes up a lot of the room that could be used for improving gas flow AND also for a blanket of insulation

Most Experimenters lay their Heat Riser bricks on the other side of the brick making a Tall Heat Riser with fewer brick, and compensating with the Blanket of rock wool
or better ($) insulation- You do not appear to have the necessary room to add any insulation. You have Created a system that has a few compromises, but like all wood
stoves the colder it is outside the better Your rocker should Draw, ( I Think,Probably) most of your problems should be draft on marginal days when you need a little heat
(I Think )

While not really timely I hope this helps! For the Good of the Crafts ! Big AL

* one of your last two elbows at your vertical chimney should be a 'T' with a clean out !

** Please tell me this IS an 8'' system ! A.L.


 
Glenn Herbert
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Location: Upstate NY, zone 5
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I would add an observation that you appear to have soot deposits everywhere inside your system. Some sooting is to be expected during startup, but once the fire is burning properly, the surfaces inside the feed tube and heat riser should be hot enough to burn up all soot. It looks like you have soot inside the riser, which indicates that you are not getting high enough temperatures for complete combustion. What temperatures do you get at the top and side surfaces of your barrel?
 
shadrick wilsons
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Thanks for the replies guys! The system is 8 inch. What do you mean it is appropriate that the barrell is 2 inches away? I'm going for more immediate heat for cooking since I live in Michigan in in a concrete house with lots of access to wood. The most I've ran the system is about 20 minutes so far. Maybe 2 good handfuls of wood. I haven't cooked on the barrell yet but it's too hot to touch lol. What factors effect the combustion efficiency? As far as insulation I will look into rock wool but I don't want to make the gap at the side of the barrell too narrow. How thick of rock wool will do the trick? And the side gap should be like 1 to 1.5 inches on each side of the barrell right? Thanks!
 
Glenn Herbert
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The side gap should be at least 1 1/2", or you will get too much friction. A larger gap allows easier airflow.

As you have only burned for 20 minutes, I retract my comment about soot. Keep an eye on it when you actually use it and see what it looks like.

You can find magnetic stove thermometers (made to stick to a woodstove exhaust pipe) that will give reasonable measurements.
 
shadrick wilsons
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Now looking into insulation there seems to be no simple solution to insulate the fire bricks... I'd like to use ceramic fiber but I can't think of a way to get it tight around the bricks. Rockwool doesn't look reliable either. What's the best option for my situation?
 
allen lumley
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Shad : A simple wrap in chicken wire or hardware cloth in a lite non-Aluminum gage will be sufficient as a wrap to hold your layer of insulation in place-

don't try to use fiberglass !!! For the good of the craft! Big AL
 
shadrick wilsons
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Genius! Thank you! Is it necessary to be air tight to be sufficient? Tucking in all the corners in the odd spots to prevent hot air from escaping through the sides if that makes sense? And I should expect the metal to melt over time and the fiber will hold its place? Also I just realized will that fireplace steal a significant amount of heat if left unsealed?
Mucho gracias!
 
allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Shad : Turn about is fair play ! This time you have confused me ! Your entire system should be air tight, but definitely your Heat Riser and your Barrel Both Have to be air tight

The chicken wire should be just tight enough to hold everything snug against the barrel, wrapping it up tightly reduces the Rockwools Efficiency as insulation - BUT you really

need that 1.5'' air gap all the way down to the Transitional area ! Just do the best you can ! For the Good of the Crafts Big AL
 
Glenn Herbert
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Chicken wire as a wrapper for the insulation will not see the super high temperatures that cause deterioration. It reportedly lasts a long time. It won't matter if there are spaces between the brick and the fiber blanket, but keeping the fiber blanket continuous will make a difference.

If the fireplace is solid brick and connected to the outdoors, it will be a constant heat sink. If there is insulation or even an air gap between the fireplace itself and the exterior shell, it may be an asset as a thermal mass. Does the brick around the fireplace get quite cold in winter without a fire in it? The chimney flue will be a constant heat loss if it is open, so if you are not using it at all you should definitely seal it up, preferably at the top as well as above the fireplace.
 
I agree. Here's the link: http://stoves2.com
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