The flue is very hot, why?

Hello everyone

Hope you would help me with this new issue.

As you have helped and I am done with my RMH and thank you very much. My RMH has been serviced my greenhouse nicely. Every morning the greenhouse is 60 degree and outside is 35-45 degree these days here in northern CA. I have not used the electric heater at all this year so far, and the water pond is at 68-70 in the morning. I am very happy with that. I burn every day for couple of hours in the morning and couple of hours in the afternoon. I don't have problem of building up the red charcoal, neither dripping... But lately the flue got very hot

I just have a new problem: For the last few days, my flue got very hot, too hot to touch. After 2, 3 hours stop burning it is still hot. After 2,3 hours stopped burning, I can touch the lower outside barrel without withdraw my hands immediately, but the flue , kinda hotter than that. Why? Only for the last few days. I don't have this problem before.

May I ask what is the reasons causing the flue too hot? I need to know the reasons then recheck if I did something like that lately causing the issue

You may have the draft in the chimney pulling hot air through the system. Do you cover the feed tube when the fire is out? Can you feel air being sucked in at the feed tube when it is cold and the flue is hot?

It could be draft, different wind direction, or firewood that is more dense.

Glenn, I am not the one who do the burning, my dad is. The last few days I saw my dad running into the house watching TV during the burn and he covered the feed tube completely when he left. I opened to look and I saw that it still burning even it is covered. He did that may times during the burn, running out to fill the feed tube, covered it, and running in watching TV

And I think my dad enjoy burning the RMH, someday he burnt for 4 hours straight morning and afternoon. Maybe that the reason it made the flue hot, because he burn to long


S Bengi: No I use the same kind of wood, the wood stud I pick up near home, they building houses and give me scrap wood, about 1 feed long, I have been using it for quite some time. I don't know about the win

Oh Glen I forgot to answer your question: Yes, we always cover the feed tube when finish the burn. Should we cover it or no?

Bacon Lee : I think we are going to have to scratch our heads awhile before we come up with the right question to ask. Be patient with us.

Now about covering The top of your feed tube- Yes, at the end of your burn when you can look in there and only see a small amount of embers

That is the time to cap off the Feed Tubes Top.


The other day I saw someone who was using a short piece of wide board as a temporary cover substitute - please do not do that !


We also partially cover the Feed Tubes Top when we are burning less than a full load of fuel in our rocket, without some restriction of excess air

it will have a cooling effect on the fire potentially reducing clean combustion . As always your ear will tell you if you are 'running' your rocket

correctly.


I am very concerned about your dads habit of covering the Feed Tubes Top while mid burn !*

The last few days I saw my dad running into the house watching TV during the burn and he covered the feed tube completely when he left.

Because he is leaving a Fueled and Red Hot Combustion chamber** behind -the person that next uncovers the Feed Tube can be in for a nasty surprise!


Because the Red Hot Combustion Chamber is still converting your solid wood fuel into unburned and highly flammable wood gases -with no oxygen

to ignite them or any flow of air to carry them away they can -and have- built up into an explosive cloud of gases needing only oxygen to Flash to Flame

This is will occur just as ones face is close to the Feed tube as its cover is removed. Any time a Rockets Feed Tube is covered Tightly the rockets

fire should be allowed to go out and Not be lit again until the rocket is cold !

This condition often seen by Fire fighters is called a 'Flashover' and is scary !


It is likely that if this practice is continued someone is going to have to explain why grandpa has no eyebrows, lashes or hair on his head ! Also this is

a bad practice for any 3rd party to see and think it is O.K. to use .

I hope this is timely and useful, for the good of the Craft! Big AL


* this also will cause your rockets burn to be Temporarily very inefficient, and possibly sending wood gases down stream to collect on the interior walls

of your Horizontal piping. This coating will reduce the efficient transfer of heat energy from the hot exhaust gases to the Thermal Mass and even deposit

enough creosote there to potentially cause a chimney fire-

It would be very interesting to stop covering a Red Hot rockets Feed Tube Top and see if this condition goes away after a day or two ! A.L.


** While initially hard to see in a well lit greenhouse, the firebricks in the Burn Tunnel should start to show a red glow after about 15 minutes into your

burn, this can be clearly seen in the twilight of early morning or late evening ! This is what I mean by Red Hot Combustion Chamber . a.l.

If the burns the last few days have been significantly longer than before, that would be enough to explain the hot flue. The mass can absorb heat only so fast, and when the interior is already hot, it absorbs less heat (the transfer rate is slower). This means more heat left in the air as it reaches the flue.

The covering mid-fire can also contribute to this, as if you have good draft and the cover is not perfectly airtight, you may still get enough air drawn in to keep the fire going, but no extra, and all of the gases will be superheated combustion products instead of some unburned "ballast gases" mixed in and cooling it a bit. If you can keep your father from covering the fire completely (mostly covered, like 3/4, may be fine), and reduce the length of burns closer to your previous practice, I think you will see flue temps decrease to the usual level.

Is the greenhouse getting a lot warmer than it used to?

Allen,
My dad already has no hair. I might be the one who end up with no hair or no eyebrow, because would open the feed tube and look into, so thank you for your explanation. I already told my dad early this morning do not closed the feed tube. But I still see the flue is hot. He burns for 3 hours this morning. Let wait for in couple of days to see if the problem go away.

I covered the feed tube with a brick. However I still wonder what is the wide board? you mean the wood ply?

He normally stop his burn in the morning about 10AM, and in the afternoon he start again at 2PM. I don't think the rocket is cold yet. It's still warm. What is the negative effect if he start his afternoon burn when the RMH is still warm? Should we better off not to closed the feed tube at all after finish the burn?

Glenn,
I will tell my dad do not burn for too long. Sometime the greenhouse is so hot, above 80. My dad took off sweater only had a tshirt on and he is sitting there burning the RMH. My goodness, I will tell my dad to stop when the greenhouse reach 80 degree.
But I scratch my head a bit, the last few days when my dad started to cover the feed tube, the flue got hot hot, but the greenhouse is not as hot as it normally should be. Today when my dad doesn't cover the feed tube, I see the greenhouse hot as normally should but the flue is not normal yet, it is still hot

From your description, I think covering the feed has reduced the burn rate, so you are getting a slower fire and less heat output per hour, but the flue gases are nothing but hot hot air moving slowly through the system, no cool air mixing with it.

The mass will hold heat for a long time, and I think it is still hot from yesterday, making it quicker to heat up the flue. See what happens in a couple of days of shorter burns.

Also, as it takes time for heat to move through the mass, the hottest mass surface temperatures will be some hours after the burn is finished. The barrel gives instant heat, the mass gives slow heat. So I would not be surprised to see the greenhouse get hotter for a while after you stop burning.

Bacon Lee ; Yes I actually saw it here in a photo sent in a wide wooden board, as this site attracts especially green neophytes*, Little things like this could create

the false impression that this was ever an acceptable practice.

For the good of the craft ! Big AL


(* at sometime we all started there )

Bacon, speaking from experience. Often when you have a hot spot, that because there's a restriction at that spot.

Bacon Lee ; After some thought I too have come to the opinion that you are over-firing your RMH; if you allow 1 hr for the time that it takes the Heat Energy

To spread through each Inch of Cob, that means that if you have 5'' of Cob over the top of your Horizontal piping in Your Cob Thermal Mass Bench it will take

5 hours for the Heat Energy you are transferring to your cob to penetrate To your benches surface !

This is a great benefit in green houses as that heat can be planed for, allowing it to 'kick-in' couple of hours After you have Finished working in the greenhouse

for the Day

I think that giving your dad a daily quota of wood to burn and explaining to him that it is the time between 2am and 8am that we are storing heat for-

your problems should Go away, i expect that it is still hard for Your Dad to accept even now how little amount of wood he needs to burn up every day !

For the Good of the Crafts ! Big AL

Hello,

Allen, my dad already cut down on burning RMH for three days already, since Glenn said that 2 hours morning and afternoon. In the morning he burns 7 to 9.30 AM, and in the afternoon he starts again at 4-6 (for the last three days except yesterday didn't burn in the afternoon due to thanks giving dinner).

It has been 3 days since my dad leave the feedtube open and not to close it. This morning after he burned for 3 hours, I checked, the flue is 167 degree, still hot. The top of the cob bench is only 82 degree, and the GH is only 70. So three hours to bring the GH from 54 to 70. It was cold last night 32 degree, and my dad didn't burn yesterday afternoon due to the Thanks Giving dinner. Today my dad finished his burn this morning at 9.30AM, at 1.30PM I measured and the top of cob bench is 87, so it increase only 5 degree. And there are 9 inches from the horizontal flue to the top of cop bench.

This is not effective, right? It was different before. The room is hotter and the flue is not that hot. Now it is opposite

Shilo said something prevents the heat to get out, so I opened the third clean out to look inside. I can see up, nothing in there. I can't see down because it was so dark. But I put the shop vac hose in there and vaccumn.

Please see what's going on

I forgot one thing important. Now with burning 2 hours morning and afternoon, the GH temperature is around 70-75 when burn, over the night it would be down to 56 ti 58 in the morning, so it is ok for the GH, but not enough to heat up the 2 ponds water of 400 gallons and 275 gallons. This morning the water temperature is 63 degree. I have 2 coils of copper on top of the barrels to heat up water for 400 gal and coil slip in the top layer of feed tube to heat up water for 275 gal. I know we already talked about steam burst, to avoid steam burst, I made the coil detachable on top of the barrel and slip in to the feed tube. When power out, my dad can just lift up the coils and hang it on the wall. It is safe but then it is not enough to heat up 400 gallons and 275 gallons of water in just 2 hours morning and afternoon. Now I have to deal with hot water!

I think I know what's going on with my RMH. Before, my barrel radiates a lot of heat, so the heat remains to go to the bench is less after much radiation, so the flue is fine and my GH is hot.

Before, I didn't paint my barrel. But then I saw my barrel rusted and ugly so I decided to spray it with high heat pain (sustain up to 1200 degree). Now I recalled, the flue start getting hotter and the GH is less hot since then. I can tell when I walk around during my dad burn RMH, I don't feel the heat radiate from the barrel as much as before. Less heat radiate from barrel so more heat to go to flue. Even my cob bench big, the horizontal flue is very short, only 12 feet total. I recall someone said should be 20 feet flue horizontal, right?

Why would we paint the barrel then then it is less radiate the heat, I don't know. But I remember I paint two very thick layers.

Sorry I didn't tell you everything so you can have all facts to consider the issue. Now what choices do I have to fix this problem? Should I have cob around the flue to get some more heat?

Bacon, if you rebui_ld your flue, use this system

http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/#/user/mremine/library/NYC%20Rocket%20Stove%20Build?sort=3&page=1&_suid=1448725833656018334711587980834

More exchange surface, so more heat gathered.

Satamax, it's a great idea. Here are my questions for this system:

1) The barrels to be in place for the flue, they are half barrels or full barrel?
2) Is this system retain much heat, I am afraid because I see little cob, since the barrels are big already.
3) I like the idea of wood box, it is much easier than bricks, should be safe right?
4) They use concrete step stone on top of the bench, how come we don't do that to avoid the terrible work of plaster with cob and wheat and straw.

My dad's falling asleep during burning RMH

Working hard!

Theses are half barrels. I don't know much more than that. The only time i've used this, it's with concrete. With a single half barrel. And i've never warmed the mass. Since i lacked time. It's siting in a pile of junck for the moment.

Well, seeing your mas, you could just replace the pipe with thoses, set up as few bells. And keep your brickwork. Reuse your cob around thoses. And may be add a little extra height if you want more mass.

My dad can't stop burning. This morning he burn for 4 hours again. The flue got to 210. I can't redo the flue, it's just too much work. What other choices do I have to fix the issue, please advise.

I mentioned you use feet and inches. Temperature is in Fahrenheit? When the answer is affirmative, I fail to see the problem. This is a quite normal temperature for a vertical exhaust and much needed to keep the draft going and preventing condensation inside the bench.

Peter, now I am confusing. I remember I read somewhere in the website that the flue should be around 120 degree F. If we put our hand on it and it is comfortable without immediate withdraw and it is ok. Too hot to put our hand on is not good, not safe and something is not right. But you said 210 degree F is ok. Are you sure? Would you please give me the normal range for the flue?

That 120 F is regarded as a minimum in order to avoid condensation. I my opinion it is hardly realistic to expect the chimney temperature will be the same after several hours of running the heater. The living space, barrel and bench are warming up and so is the chimney stack. When the temperature of the stack is still 120 degrees F after 4 hours of firing I'd expect you have a hard time to start it from a bit warm, let alone from cold. In masonry heater land, the stack range could be anything from 200 to 400 Fahrenheit, even higher is not uncommon. Mind you, a rocket mass heater is depending on quite some draft which is provided by the chimney stack, otherwise the thing wouldn't start.

Well, if you find thoses 210f° too hot.

May be you could do an experiment.

Make a barrel bell at the end of your bench.

Satamax, Can I make a square wood frame around the vertical flue and stuff cob into it. I pounce the cob down tight until they dry off then I take out the wood frame. Look at the photo my dad falling into sleep, the flue by the wall. I want to do wood frame and cob from below the clean out to the bench. Would that reduce my draft or do something negative effect to my RMH?

Well, you can always try, if it doesn't work, you crush the cob again!

I would go further up. Like 6 to 8 ft. But i wouldn't put more than 8 inches of cob around.

I added cob around my vertical flue, only 2 feet, I want to try to see how it goes before adding more, but it turns out good: after my dad burns for 4 hours the flue is 130-150 and it still has good draft. I think this is good. I don't want to add more cob afraid too much cob would reduce the effectiveness of the draft, 130-150 is ok.

My dad is still burning for 4 hours morning and 4 hours afternoon. He likes his job and I don't want keep asking him to burn for 2 hours only, so add cob to the vertical flue solves the problem of the flue got too hot due to burning for long hour and thick paint to the barrel.

Thank you all for your helps!

By the way, my dad no longer cover the feed tube completely during burn. But I realized I have more ashes now compare to the time my dad covered the feed tube completely. Somehow cover the feed tube leaves no ashes at all. Why huh?

Bacon Lee.

I think you're spot on. Actualy, having cob around the vertical chimney insulates it a bit. And keeps a bit more temperature when the stove is cold. Which helps lighting it. It keeps a bit of draft, if the mass around the chimney is above ambient temperature.

Bacon Lee : An elegant solution that uses the materials at hand both efficiently and wisely, it will be interesting to see how your system works in early spring and fall.

It is probable that the RMHs Thermal Mass Will function to Help stabilize Your greenhouses Temperatures in summer, cooling during the day, and resisting cooling at

night !

When You have more time it would be interesting to have you take enough pictures to allow us to see and understand the layout of your plumbing, and your technique

for monitoring and controlling water temps ! For the good of the Crafts ! Big AL

I know long hours burning and thick paint to the barrel are two issues can't be stop so we have to add more cob to the vertical flue to deal with the too hot flue.

Now talking about cover the feed tube completely during burn, which I already had my dad stop doing so since Glenn and Allan said don't do that, not safe. But during the time my dad cover the feed tube completly, I remember I have no ashes at all compare to now I do have some ashes.

When we has no ashes which mean we have a lot of oxygen to burn everything completely right? Here is what I didn't tell you: the coil has many big slots between the rings, before I didn't make the coil tightly fit into the feed tube like the photo you see here. At the beginning, I took out one layer of feed tube with full size firebricks and replace it with that skinny coil, so a lot of loose space from the coil to the cob. When my dad cover the top, actually it would draw more oxygen through slots in between the rings and burn better. Would that make more sense to you? If you agree so then I rather take the cob around the coil out, give it some space around and then cover the top like before so the RMH will burn better and have no ashes . Please advice

Daft me!

I didn't pay attention!

Bacon, remove that coil straight away!



This is cooling your burn, and that's why you have ashes!

Satamax, you forgot. Here, let me remind you:

At the begining, my RMH has many problems: First problem is burning up. To fix burn up problem, I keep breaking the burning tips of the firewood to bring the flame down. Breaking the burning tips then created the problem of accumulated a lot of red charcoal. I could only burn for an hour, and then my burning chamber was full of red charcoals and I couldn't burn any more.

My other problems are: my bench did not store heat at all due to too much sands. Also, I have dripping water on my flue and at my clean outs, and my RMH is not that hot... many problems.

After and consulted with permies, many people gave me advises. I considered all advises with problem I had and I did some fixes, includes redid the bench to put more clay so it store more heat, increased the chimney to 5 feet to increase draft, added one more layer to my feed tube to slip the coil in to help eliminate burn up issues (because my feed tube was so hot that the minute I drop the firewood in, most of the length of the wood ignite and burn, the coil with cold water was cooling down the feed tube).

With all those fixes, my RMH is now good: My RMH is now hot to heat up the GH and my thermal mass storage a lot of heat, no more burning up, no more red charcoals building up, no more water dripping... My dad can burn for 8 hours a day, no problem.

But I do have some ashes. I remember other people said they take ashes out one a month. I take ashes out every 2 - 3 days. For bad wood and for my dad keep dropping burning left over into the burn tunnel, then I have to take ashes out every day. Which my RMH is not that good, right?

The clean out I don't have much ashes. But feed tube and burn tunnel, I do have to take ashes out twice a week or more often with bad firewood or bad burning habits.

My question is, Is this true that you only take out ashes at the feed tube and burn tunnel once a month?

Maybe firewood is not so dried give me ashes. Because for a period of time I had no ashes at all. Those days I used real dried scrap wood from some manufacture, I had no ashes at all. But I don't have that kind of dried wood that often. I get my firewood from people who cutting down their trees, most of them are totally green when they were cut. Even I had them in sunny area for a few months (since April this year until Oct then I storage them to use now), I don't think they are that dried yet. I heard it need 2 years.

But I would want to learn. What are the reasons produce more ashes in the RMH please

sorry I don't read all the thred
if you block the feedtube when burning then over the time you start to be in risk of chimney fire.

sorry I don't read all the thred
if you block the feedtube when burning then over the time you start to be in risk of chimney fire

What are the reasons produce more ashes

less temp
less o2
less mixing

Shilo, My dad covered the feed tube during burn for a while and then my chimney got very hot. Glenn and Allen said stop that right a way, and my dad already stopped cover feed tube while back. There are two issues can't stop which are long hour burning and thick paint to barrel, which I have to add cob to the flue. The flue is now ok


May I ask why cover feed tube causes chimney fire?

less o2 cause dirty burn.
dirty burn cause (more ash and) soot build up at the flue.
soot is flameable.

To follow what shilo said, you're heating up the feed tube more when covering it. There's less air to cool down the fire. There's less air to burn either. A compromise of the two should be found imho. Usualy you cover the feed at the end of the burn, but not completely. Leave 2cm or so for the air to enter.