hi, building my first new rocket mass bed/forced air system. any oneelse ever did this?

ok , i have an old church i just purchased it is a huge living space at 1900 sq feet. I'm half way threw the construction and realized the bench even though its a queen sized bench in the middle of my living room might not cut the heating needs for my home and we had this cold front come in early. so i'm working on a forced air solution and have it figured out (I think) but was wondering if any one else had ever tried it before, if so what did you learn? I'm running the duck work for the air, threw the bench starting with an intake on the barrel and with one side exposed to the barrel then to an inline fan, then into the cob all the way threw it diagonally to a heppa filter out onto the floor. my riser is a full 6ft high and i'm using all 5' internal piping it burns great by the way fast and way efficient. Any way like i said this is my first one and i'm only half way threw. any suggestions comets concerns? Just figured i would ask.

On a side note i have to thank you Paul for the information and insight i got from all your online stuff, i am planing to buy all your videos if i can ever afford them. If you ever need a place to stay or some one to kick an idea with I would be honored to be at your service.

Any way questions comments concerns.. attached are some pictures of my project.

Howdy James, welcome to permies!
Are you saying that you are exhausting into the room through a filter?

LOL I'm crazy but not that crazy..lol.. I am creating a fresh air venting system separate from the exhaust of the stove. With the intake Attached to the barrels (outside) with an open face to start to heat the air and the exhaust of the separate air flow tube (running threw the cob) attached to an air filter to clean and heat the room. Sorry if i was unclear. I was thinking of going with a 6" or 8" tube flatish and split so i my out flow of air could be directed in two ways. I'm not sure I might do two airflow tubes depending on how it works with one.

Here is what I did today, tomorrow i work on finishing the cob. I'm probably going to use some bricks and rocks in the cob to make sure the non insulated air duct doesn't go flat with use. (I have a 3 year old and a 5 year old) So if i don't do something to support it I know they are going to get crushed. lol.. Any other suggestions out there? I could use an extra mesh and/or maybe a few croquet Wickets at intervals? Hmm I'm sure i could get those. I'll have to experiment. How can i get more support from the cob? here it is. fans work and it blew a little warm air so a win for the day, yea. I couldn't resist testing a little already with a 25 min burn. . So I'm hopeful. Had a few cracks come up but i'll fix them tomorrow. Any comments any by one else ever work with a forced air threw a dragon? Well advise is always welcome from any one. after all its the reason I'm here, to learn. On a personal note I'm beat but am having a great time.

for more pictures see my face book page at https://www.facebook.com/greenenergyadvisors or my dragon album at https://www.facebook.com/greenenergyadvisors/media_set?set=a.498351920262611&type=1


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OK thanks James. Sounds like a cool idea. I will look forward to hearing more about your project!

just an update filling in cob and my bench the past three days. Had a bit of a health issue so I'm down for a min but will be up soon. It happens. Any way here is where I'm at.

Just to let every one know I got frozen out with this unusually cold weather with the cob still wet. So Ive been delayed in my experiments. more updates as I can work.

It looks like the ducks in and around the bed in the picture goes out the dryer vent covers? I thought the pipes were suppose wind through and go to a vented chimney or riser out side I may be wrong just asking. David

I don't know how cold you get in your area but why not run a HRV to ensure you're getting clean air into the building? Then you could just run the duct from the HRV to the barrel area and then to the rest of the house. It would be simple but allow you to think more long term with your system.

Well guy's,Thanks for chiming in it's good to get some dialog. So I have two separate types of "piping" and the one with the air going threw it is a sort of HRV,(that I made) collecting heat directly from the bench and barrel threw the hose. I used a thin non insulated set of pipes (hoses really) for the air and its pulling heat from the outside of the barrel slowly with two small inline fans close to the end pulling the air threw. The exhaust is running slightly below the air system and out the chimney to harness the heat in the bench and from the rising exhaust heat. The drier vets on the barrel are the intake of air, the other ones at the foot are the exhaust of the air. I used a curving flex tube to snake up and down and back and forth into the cob heat battery. If I did it right once it goes above freezing (were living at 40 degrees below normal here in IL right now and it went from 70 to 0 with in two weeks so I got caught with wet cob and then got sick so I'm stuck until I can get the house above freezing so I can work. Once I get it all dried. it will no longer (or should be) no longer a problem no matter the outside temp. (I hope) I also right before getting sick made a miscalculation on my burn chamber (the inner pipe) and built a fire too hot trying to get it to dry so I melted it.(just the inner pipe of the burn chamber not in the riser) So I have to replace that too. Anyway that brings you completely up to date and I think a good explanation of whats going on, I'm hoping to get back to work this week to fix that and get back to burning it to get the ice out as the temp is supposed to go back over freezing. It's all good, I'll get there it's my home and this is my off grid in a city (well small town) to prove I can. So I have a lot riding on it. I have a 1900 sq foot area to heat and I wont stop until I can get it to 70. My wife has a disorder that makes her unusually unsuitable to cold so I will make it all work. As soon as I get this done, I'm putting a large pocket rocket in the center of the basement to keep the chill out of there and heat my water. I think the two (since the water heater stove will be directly under the cob bench, should do the entire job, once I'm all done. Is that a clearer picture of what I am trying to do?

btw, I had to look up the HRV so its not exactly what I've got going one but its close in principle I think.

here are some more picture i took while filling in the bench.

Do you have some sort of battery backup? This arrangement of coils of rough inner surface pipe has so much drag, that you won't have heat without electricity.

I don't understand the question/comment. My power source for the blower part of the system is my home power source which is from my solar/wind and batteries on the blower part of the system. Now I did use a flex pipe for both the blower part of the system and the exhaust part of the system, the stoves I saw, some of them, used it and it was much cheaper so I went with that and considering my limited budget it fit better than trying to use the strait pipe. Are you saying it wont heat the bench?
My temperatures at the end are none existent so I figure it is going into the bench. Of course I'm still sick so i haven't been able to work on it in over a week. Please clarify. Thank you.

I'm sorry you have been ill.

Temperatures under 140° in the exhaust are problematic. I asked the question because the whole system won't draft without the forced air. You said you are working off your batteries, so you are covered.

You may find that the barrel will take so much of the heat out of the exhaust that you don't have much left over to heat your bench; in order to get the bench warm, you would need to put cob on the barrel. In other words, it could take days to heat the bench with a bare steel drum. We are doing some testing on this issue at the moment and when we have complete results, we will publish them at our blog.

Yes, I was actually going to cover the barrel and the air draw completely with cob, I got stuck in the middle of finishing. But that helps, I think you got it. from looking at it. I didn't realize you could loose so much heat in the barrel. I have the air part of the system separate from exhaust part of the system however, the fans and electric are on the air duct work only. My heat riser ratio is longer than the plans stated to increase the draw, it was working before the meltdown and freeze and flue. I got white ash out so it was burning well for three days. Thanks I'm feeling better finally, I think. Anyway, communication is not my strong suit (I have a degree of autism) so maybe what I am doing is unclear. but the idea was a standard rocket mass heater with a stronger draw created by a higher heat riser and a separate system pulling heat from the cob into the room with blowers. I own an old church so its a large living area I'm trying to heat. Once I can fix my burn chamber (which I melted) I will be able to look at it again. If I need to completely change out my piping, well that's a mess I would rather avoid if I can.

These are the last pictures I took before i had to break. I still have to level the bench and build up the cob on the barrel. I was going to leave the very top open as a cooking surface but i could build a cob stove over it to keep more heat in.

Maybe, it's in the book somewhere, but I'm wondering where the idea came from that you could get a stronger draw with a longer heat riser?

You have to choose what you are going to do with the heat. There are only so many BTU's in the amount of wood you are burning. So, if you add a radiating cook surface to your barrel, you will decrease the amount of heat in the bench.

No that was me its not in the book. by increasing the heat riser ratio, I increased the rate at which the hot air moves by increasing the distance at which the hot air moves up. Hot air rises at a constant rate, my hypothesis was to maximize the draw by giving the air more room to travel up and increasing it's speed. The further straight up (obviously its not absolute there is a point where its no longer effective but i think I maximized it.) the faster it exits. there by increasing the draw from the system. Allowing it to use all the fuel in the wood. that part worked. Almost too well. I got white ash out and the draw was strong enough to feel the suction and burn the fire hot enough to melt the 30g steal inner lining on my burn chamber. This was my first experiment and so I know I was going to make mistakes, I could not afford the book or most of this I have been working as best as I could with no budget and very little information I could not figure out for myself. Most of this is clay from my yard. So I had to do things unconventionally because of my budget. Unfortunately I live in IL where everything is expensive and no one has any thing for free. They even want me to pay for garbage. it seems. Any way if I completely screwed it all up it wouldn't be the first time but I will make it work I have to.

As Satamax Antone is found of saying "Metal is doomed". He means specifically in the combustion chamber.

i still think you nailed my problem, The way i made it, I need to insulate the barrel. but time and experimentation will tell. I will let you know as soon as I can work on it again. Thank you for your time and the advise it is much appreciated.

he is right..lol.. I was thinking of using the cob to encapsulate the burn chamber on the outside, I used the two pipe method originally with vermiculite as the insulator the inner one burned up. I need the circular construction to get the fire to burn with my design properly but I need to make it stronger. I was thinking about a double or triple walled inner pipe to replace the one I burned up. Any thoughts.

Cindy Mathieu wrote:As Satamax Antone is found of saying "Metal is doomed". He means specifically in the combustion chamber.

Have i said this?

Oh, or heat risers

Well i will understand the damage better once I can get home and take the barrel part off and get at the heat riser to see how bad the damage was. I think it was just the burn chamber that burned up but I got sick right after and haven't been able to start on the rework investigation. I will take pictures and share my folly as well as what I do to fix it. Thank you all again for all the dialog and help. I'm basically on my own here so it's nice to talk with others that are doing this.

I'm no expert on RMH but at the basic level it looks to me like your really trying to push and pull the design I some ways it wasn't meant to be.

The bed has a ton of surface area and the flex tube creates a massive anoint of resistance to flow at that length probably we'll over double that of standard round pipe. This to me is an area of major inefficiency. I doubt it will ever function safely without the fan.

The extended heat riser and barrel might make it initially draw better but is probably also consuming more energy that you want to transfer into heat in the process. So I'm wondering if this is a net loss of usable BTUs rather then a net gain? The thing is a RMH is designed to be about as close to maximum efficiency of a wood stove in its basic design. I'm doubtful there is room to make it any better and still have net gain?

The forced air aspect to me looks is like adding a turbo to an engine and considering a RMH is already close to max efficiency all the turbo is gonna do is suck up more fuel meaning you'll be feeding this beast like crazy. This may mean more heat as we'll but RMHs at their basic level already operate at close to the maximum limits of the materials so this could be why it's eating itself up on you. So what happens when it's the middle of winter and your peer system fails for 3 days? You have a RMH that doesn't work and a cold house.

Finally the cheapest energy is the energy you don't use. I'm assuming you've already upgraded the building envelope to be more efficient? Typically churches are not efficient structures and need a lot if insulation and air movement to be comfortable and healthy places to live.

I know it all sounds negative but maybe issues your going to have to deal with to be successful. Good luck and enjoy the journey.

Well Sean, your right I am trying to tweak it as far as it can go, further than any one has, I think. (and maybe too far but nothing ventured is nothing gained) Yes I know my old church is a pain to heat too. It goes back to budget on everything of which i have none. That's why I need every bit of heat I can get into the battery and room. Your insights are appreciated negative or not. This is all new to me and I had to fly blind, we are very low income, I have a sizer condition and haven't been able to work in three years outside of the home. So I had no money to buy any plans or videos or supplies. I have had to do this with the free information on my own researching what I could find and from teaching myself. So there are a tremendous amount of gaps in my knowledge. I'm trying to make up for with experimentation. Now Just for a need for clarification. The forced air system I built is threw the bench only, I have a slow draw of air from inside the room, the intake vents are pulling heat into the air in the air duct from the outside of the barrel, to circulate the air threw the heat battery ( in theory) heating up the clean air as it moves threw, then out into the room. That part of my design will only work once I can get the bench to heat up. I have not put any fans inline with my exhaust so it has no effect on draw. I can if I can get another one. All the draw I was getting was from my heat riser and that part was working. My area of expertise is in electronics so my home power system I have made so electricity to me is free. The thing is, the amount of waist in an electrical heating system and the wear on the system using heaters on it are tremendous so this was my alternative. (you can blow inverters like crazy and the overpowering required to protect them makes the ones that will work unaffordable for me.) I could put a fan inline with the exhaust, I suppose, on the side by the chimney pushing out but I want to see if I can get it to work with out one. In fact I thought it was. We will see. I finally got rid of this fever after two months now its below zero outside and by extrapolation in my home. I just don't get it, the planets warming up and in my little neck of the woods its colder this year than in a long time. I figure the goddess is testing my resolve..lol.. anyway thank you again, Sean all information I get is more than I have so it's good.