Miles Teg

https://plumbingsales.com.au/pex-gas-water/water-pex-pipe.html

hmm pex piping is about $120 for 50m, but for wood floor I think I might need quite a lot of 50m lengths, maybe more than 10... starting to look like it's just not feasible with Aussie prices, at least for me.

Rico Loma wrote:Give it a try, I agree with T Rubino.  Not familiar with Aussie prices but in US Pex tubing can be under 50 centavos per foot. 200 feet for 90$  If you decide on heated floor with Pex it won't be thousands of dollars, have retrofitted 70 year old  house and it wasn't hard or expensive.  Good luck with it.  

i will take a look, but I think prices in the land downunder for such things are inflated beyond belief, I have a feeling that what may cost a few hundred eagle bucks will cost me thousands in dolleroos unfortunately, but I will take a look after work tonight and see if it's viable or not. Then my biggest concern would be leaks etc.

Oh side note: I bought a stick welder yesterday, haven't welded since high school many years ago, but my other friend is a qualified welder, so if I forget anything I can just ask him, and I think I remember the basics pretty well, I will have to get some scrap steel to practice fillets etc on now, but hoping to get some welding skills up on this job too if needed.

Cheers.

thomas rubino wrote:Not many folks have experienced mass-heated homes.
It is hard to comprehend how well it works until you do.

Mass heating does take time, to start to share its heat.
At Miles's location, he might not like a mass heater indoors, as I suspect it warms up quickly outdoors once the sun rises. (having never been down under, what do I know?)

Having a highly insulated batch outdoors and utilizing fans and the existing ductwork (perhaps brick-lined) might work well for him.
He is excited to try experimental rocket science!
We can all learn from his success or his failure.
As long as we can guide him to build his core to published dimensions, then everything beyond is playing with fire.
Something all good rocket scientists love to do!

Thank you all for the carefully thought out replies, i will just reply once rather than make 4 posts:

My pad for the heater is about 4m from the house, at the end of the decking at my back door. So the heater itself will still be useful for winter days and nights when it's not raining to make it more comfortable on the deck, and in summer I can still use it to cook a pizza, while not heating the house if i don't turn on the fans.

I would like to use water, but at the moment that is going to be cost prohibitive, I am trying to use existing fittings in the house, water and floor heating means thousands of dollars in refitting the whole house, and I just can't do that.

Also, building in the house is not ideal, as it's a wooden house on stumps, I would have to do some major foundation work, and then insulate the walls against burning from the radiated heat, I have watched enough videos of people doing the build and then scrambling to put aluminium etc between the heater and their wood wall to know that is not the best idea unless you really insulate the area the heater will be in.

And, as someone said, it does get cold here in winter, but we don't get snow, I usually only need to heat 10 or 20c max to be comfortable day and night here, and I do still have the reverse cycle for really cold or rainy days when the rocket may not work as designed etc, though of course the goal is to not have to use it in winter at all if possible, save myself about $100 a month on my power bill for about 6 months of the year, nothing to sneeze at if I can use scrap wood from my fruit trees etc!

If this doesn't work,  I will still have a pizza oven, or I can take it apart and re-design it, at least I'll have the materials on hand to try something new if this doesn't work, but as far as I can tell, most who have asked the same questions here never actually went ahead with the build, so if I'm the first, and it fails, at least I tried and we'll know exactly why this isn't a good idea, and if it works, I'm happy to leave plans here for others to follow if they want to do something similar in milder climates.

I totally get that you guys have to balance the advice with proven theory, but still try to encourage innovation, it can't be an easy line to walk, and i appreciate you all for chiming in where you have.

I am currently working on the redesign based on all of your inputs, I will post in the next few days when I have something I'm happy enough with.

Cheers.

Glenn Herbert wrote:If you must go with an outside combustion core and heat exchanger, I would second the water idea over air to get the heat into the house.

Splitting air ducting for more surface area sounds sensible, but you would have to greatly increase the total cross section of ducting to get good results. Air flowing in ducts generates friction from the duct walls giving a relatively stagnant zone next to the surface. This effectively decreases the size of the duct by an inch or so, meaning that you need much larger small ducts to allow sufficient flow. Going from 6" to several 2" ducts would probably need 2 to 4 times the nominal cross section. Friction increases faster than airspeed, so the duct with the easiest flow would speed up until flow and friction balanced between the ducts, and one would not take all of the flow, but it would not likely be evenly split. Basically, you would get better results with a large flat surface on the heat exchanger than a bunch of little ducts.

My only issue with water is 1. that I then have to somehow exchange that heat again to get it into my house, and 2. that the double exchange will be more wasteful than just pumping the air through the mass above the rocket.

Wondering if you have any ideas on how to exchange the water back to the air ducting in the house? And what you think of the double plate "U" shape with fins idea.

Rico Loma wrote:Yes, I think you are right about building something now.  Let us know when you are producing heat as you desire.  Perhaps that time gap could let you firmly grasp the next step, i.e., transfer of heat to the house.  If you have time, look at two tiny designs: the micro RMH at the Love Shack, and Cyclone by Kirt Mobert. If you could live with that idea it might be easier and foolproof, and give back your back yard space.

One last plea Miles go with a proven design, then use water circulation into your house or under the floor. Water's specific gravity gives it an edge over ducting the hot air.  As a man dealing with an old house with 12 inch crawl space, I would suggest avoiding the idea about using your crawlspace as a strat bell.  Like comparing apples to oranges, the two are not equals i think, and this idea might have you breathing some unhealthy air

Thanks for the advice, I think I will be going with a proven design for the rocket itself for sure, Peter of the P channel seems to have the best rocket ever made, so I will likely go with his design based on some of the cast ones people have made, but fashioned out of firebrick and clay.

As for the heat transfer, I have an idea to max out the heat transfer into air, my only worry with using water is that I then have to get that back into the house, into radiators and fanned around the rooms again, pretty much negating the ducting under the floor which I want to use if possible.

I am still planning though, water may still be on the cards depending on how this all goes, I'll see if I can draw what is in my head with some kind of accuracy to demonstrate it properly.

I may just start building then, and post pics, then test it and see how well I went when it's all done. Even if it doesn't work well as a house heater, I plan to have a pizza oven in there, so it shouldn't be a total loss

Thanks for the reply

Cristobal Cristo wrote:Miles,

If tinkering then here you go.
I would do the following:

1. Build an 8" J-tube from insulating materials, the entry opening from hard bricks.
2. Build a heat exchanger, let's say eight 2" pipes in parallel joining into a 6" pipe. I would insulate the 6" pipe VERY WELL on the portion between the bell and the building. The total cross section of the small pipes would match the cross section of the large pipe, but later on a different ratio could be tried. Also a different configuration of pipes could be used, but that would be a start of the journey.
3. Position the exchanger at the top of the bell above the firebox exit.
4. Build a small bell from insulating materials. It would be like a ceramic kiln, so most of the heat would be staying inside and heating everything to quite a high temperature, but the blowing air would be cooling it and extracting the heat.

I would experiment with blower speed so the temperature of the exhaust leaving the bell would be low enough to maintain efficiency. It could require changing the design of the exchanger - for example using higher number of small pipes, positioned horizontally and also vertically, so the cross section of the pipes would look like this when looking towards the front of the bell:

o o o o o
o o o o o
o o o o o
o o o o o

Actually, the more I have been looking into it, I have been thinking of something a little different to maximize the air mixing and surface area of the air to medium contact.

Thinking of getting a couple of steel plates, having one close to the bell, but probably still behind a layer of fire brick so it doesn't pit and rust over time, or at least to delay it somewhat, anyway that one lays flat over the bell and the other one sits maybe 2cm (or about an inch) above it, with some bolts to space it out, and then keep building up on top of that, seal the whole thing inside a nice thick masonry top to the whole unit, and run the air ducting through the strat chamber, up through the plate in one corner, maybe have some baffles like a radiator but not all the way floor to ceiling, so the air always has one basic path to take along the flat plate, separate the thing in the middle leaving a gap over the bell, so the gas has to rush past the hottest area on the way through the plate, and then drain it back out and into the house through the ducting.

I was thinking on the one pipe to many idea, but I did manage to find some short threads on here of others who did have my idea, but either got talked out of it or gave up, because the threads just stop after a question or two.

One of those threads mentioned that splitting the air up will guarantee that only some of those tubes will get the majority of the airflow, while the rest get almost nothing, so getting the air into a flat plane with some fins for extra area and push it around a "U" shape made of metal plate for good heat exchange from the masonry, and back out again through the strat chamber to keep the pipe warm when it's cold outside. That can then be dug underground and insulated over to the house, and hooked up to the existing system I have under the floor after I have inspected it all and probably repaired some of the duct that is likely in some form of disrepair.

This, to me seems like the best approach, after researching heat exchanges used in hvac systems, double skinned pipes etc appear to be the order of the day, keeping the surface area as big as possible and making the air turbulent inside the plate seems like the way to go to me.

Can you think of a reason I should still go with the split pipes design though? If you think that might be better than the plate with fins idea, please let me know and I'll listen.

Cheers.

Just so I'm covering all bases, my own research told me that this would be the best way to go with the existing constraints I have:

1. I have a ready supply of small sticks every year that I can dry out, but getting larger wood will cost me money every year and I might as well just use the reverse cycle and save the time and effort of lugging it all over the place, so I would like something that burns the small stuff as efficiently as possible.

2. I have existing ducting under the floor and it's on stumps and a fair gradient (front of the house is walk under, back is crawl) so putting something like this inside is not going to work for me, I would have to stump down the whole mass etc, and I'm not willing to go that far with my foundations! But I would like to use the existing ducting

3. I don't have infinite backyard, so I have cordoned off a 2mx1m area to build in, and I would like to keep the height in the 1.5m area so as to not give the neighbours an eyesore out of their kitchen window too. The area I have is close to the house to allow for the ducting to be as short as possible. I have not done any actual building yet though, only digging so far.

If there is a way that anyone can think of to convert my small sticks into hot air to pump around the ducts in my house that is not a rocket mass heater with air ducting through it, I am absolutely open to hearing about it. This is just the best idea I could come up with after a lot of looking into it.

Cheers, I'll happily end the thread right now if there is another way to do this and not cost me more than a couple of grand or so in aussie dollerydoos.

My intuitive idea that sparked all of this was thinking about how much warmer the house got when I was a kid and we had one of those huge wood heaters in a very large room, with the fan off, the area around the fire got hot, but the other end of the house stayed cool, but turn that fan on and the whole house would be toasty in a few minutes. There has to be something to running air over a hot fire and heating a space with it, doesn't there?

After a fresh google search, these guys are doing essentially what I want but with an existing fireplace, they just place the hot box against the hot chimney and duct the rest of the house up with a fan running the whole thing from what I can tell:
https://chazellesfireplaces.com.au/fireplaces/hot-air-ducting-system/
I want that, but contained in a rocket mass heater if that is possible, but once again, if there is a reason no-one does this, I am absolutely all ears, if it's just that no-one has tried it, I am willing to try.

Sorry for the edits, but the ideas keep coming. Since hot gasses rise, I could theoretically do away with the ducting and seal up the whole gap under the house to use as one giant strat bell, with the top being the floor of the house being constantly heated and the gas escaping from the front where the hill is lower naturally.

It would involve making the under house gap airtight though, which may cost more than the heater build in the end... but ideas are still coming.

Cristobal Cristo wrote:Miles,

I understand that you would like to use the existing ducts, but the principle of heating with masonry heaters is radiation of the mass heated by hot exhaust and by radiation of the burning/burnt fuel. Radiation constitutes 50-70% energy output of wood burning. For this reason heating rooms in which with the masonry heater is not located is either difficult or just impossible if the walls are masonry. That's why in part of Europe where masonry heaters were (or still are) popular, each room had a separate unit. It is partially possible if using water as the medium. That's why you can not find anything that would meet your idea. Like I said before - in theory it would be possible, but you would have to develop such system.

Hmm, I may end up going with something that is at least sound in design for the heater, like a bell for example, and work with that to start with.

As I have said in another post, this place was built on tinkering, and it seems like no-one has done this exact thing before, so testing is very limited. I might just build the damn thing so I can test how well it actually works! You never know, it might surprise us all and become a new design, or it might fail miserably and be taught as a reason not to do this in the end. As long as it doesn't explode and I get some kind of use out of it, I would like to try something a little new.

Not too out of the box, fitting as many of the principles already learned into it as I can, but unless someone has done the testing to say this is not a good idea, I am willing to be the one to do that testing and find out.

I am now thinking a double masonary bell as the mass could be a better idea, maybe even run the air direct through the gap between the bells to maximise contact with the hot bricks, I do have a physics background, but doing calculations is never the same as seeing something in action.

I may take what I have and go with it, but I'd rather work on the design as much as possible before I go ahead, unless someone here gives me a good reason to stop of course.

So far though, just being something new is not reason enough for me, so I'll keep drawing for now.

Cheers.

Rico Loma wrote:Miles, with respect, you might consider following a proven, basic design that has worked well for a decade or more. Then a later attempt could be for quirky,  esoteric ideas that pop into your head.  Folks here are trying to help ensure a quality heater for you, but cannot build it for you.   For the sake of your safety and your happiness long term, please consider this idea and ignore various Youtubers and fly-by-night TMH builders.   Experts on Permies are legit and generous.  

In the name of Prometheus,
Rico

Thanks, taken with the good will it was intended to have.

A little on my thought processes before coming here:

I bought a house, realized I have ducting in every room and no ducted heating system because someone blocked it all up with renovations, and my only heating/cooling is the reverse cycle aircon in the loungeroom which does nothing for my bedroom and the rest of the house, as well as costing quite a bit to run as a heater for as long as I want the house warm.

So, I looked up other options, found rocket mass heaters and started watching all of the videos on the subject... and I mean all of them, I think I've actually watched 90% of what is available on youtube now, and I assume that some of the fine folk here are also some of the ones making a few of those videos I watched, but for one thing, everyone has their own special way to do the little things, and also I cannot find anything that is exactly fit for my purpose (having the mass outside and running the air through to utilize the existing ducting in the house) in any of those videos, or anywhere else. The closest I could find was the batch oven mass heating devices from russia, but here is my problem:

I have a backyard full of trees that I will be pruning every year, leaving a large amount of small sticks not really suitable for a batch heater as they would burn a little to quickly, at least going by the people mostly throwing a couple of logs at it and leaving it like a normal fire box. I don't really want to spend money or days cutting and lugging firewood, so I figured the J tube would give me the best bang for my existing fuel buck.

But no J tube mass heater that will fit in the footprint I have for this project, so the shape of the thing has to be more like the batch heaters, though I figure as long as the airflow is still there, it will work the same way, and this whole place was built on people tinkering, so I am here in that spirit, trying to make the best of the constraints I have, and I don't want to spend the world on this either, I have a budget and a footprint, and the fuel ready to go, I just have to make something that fits.

If anyone has a design that matches those specs, I am more than happy to copy it, but so far I have come up short in that regard, so this is my only option, and this is the best place I can get advice so that my tinkering is not just random stabs in the dark, which is why I am very open to suggestions from the crew here.

I hope that clears it up a bit? All due respect to yourself as well.

EDIT Also the decision to use brick comes from the fact that I know a mason who as built some very nice brick and even stone pizza ovens, and I'd rather have something that lasts 10 seasons than replace a barrel 5 times in that same period, I even purchased a barrel to use but decided it was going to be too much and I don't want the radiated heat, I want it directed into the air in the ducts if that is possible.

Cheers.

Cristobal Cristo wrote:Miles,

The finer aggregate you use, the higher total surface area the particles will have and you will have to use higher clay ratio to make it stick. The general rule is to use particle size to be no more than half the joint height, so for example if your joint is 10 mm then grains up to 5 mm are acceptable. When laying firebricks, small joint of 2 or even 1 mm is desired and in this case the particles should not be larger than 0.5 mm which would be equivalent of US mesh 35. When I prepare the mortar for adobe bricks, or rooftiles I use the ratio of 2.8 (coarse sand):1 (clay), but the same clay when mixed with mesh 18 sand has to go in ratio 2:1 and for mesh 35 the best strength is when I mix 1.5 (sand):1 (clay).
Fine silicas from the ceramic supply store are used to prepare glazes or engobes, coarser ones are used as grog. The finer silica will help to develop lustrous glazes and the coarser will not quickly melt and will help to develop matte effect. For glazes I purchase mesh 325 - it's like wheat flour.
For cob it would be most efficient if you just dug some soil (without top organic matter) on your property and amend it with clay if needed. Some samples would have to be done first to determine the best ratios.

Regarding the idea of blowing air in pipes through the mass I doubt it will work. Air has 4 times lower heat capacity than water, but 1 m of air weighs only 1.2 kg, so the same volume of air has 3400 less heat capacity than water. Forced air heating systems also use air, but it goes through heat exchanger and multiple torches. It could potentially work if the exchanger was closer to the fire, but at the same time it would lower the efficiency of the wood combustion, which is not a problem with gas torches. Nonetheless I believe that it somehow could be developed.

Thanks for the grain info, that does help with selecting the size now that I know the basics.

As for the air movement, it was my best idea to use the existing ducting that came with the house, but if there is a better way I am all ears, maybe water running through the mass with copper tubing, running into a radiator to blow the hot air into the system? I'm not sure that would be more or less efficient, however.

This is going to be an ever changing design until the build happens, and I want it to be as good as I can get it, so please let me know if that would be a better idea.

EDIT: My other option to heat my house this winter is a reverse cycle aircon, I don't mind running it in bursts to cool the house in summer, but running it all day in winter is a little cost and pollution prohibitive, so anything better than that is fine by me. Just for context of what I'm trying to do better than, a heat pump.

Thanks.