Can I "Thermosiphon" Hot Air?

the size of the duct is just one factor. I don't think insulated box is the key. what is the elevation change between the garage and the back of the house. a fan speed control is nice if the blower is overkill. random thoughts

Draw a diagram and you'll see why this won't work....

it already works, without the big insulated box in the attic, without the blower going. i was hoping the box would make it work better.

You must be patient with us non-genius types, I thought you were trying to transport hot air from one building to another, and make it then flow downhill....If I might ask, why would the 'big box' make it work better?

the hot air will rise up beside the box, then "pour" into it from the top side. As the air cools a bit, it should fall down the pipe going to the back of the house. A large box would have more air mass falling inside it, theoretically helping to push it along down the pipe. that is how rocket stoves work anyway, pushing air thru 30 ft of vertical stovepipe before going up and out. Just expanding on the thermodynamics and boyles law that make rocket stoves work in the first place.

A vertical pipe and a horizontal pipe are vastly different with how air moves.

Did you not read the Wiki article on the "stack effect" that I posted?

rocket stoves can run with enough force to run a horizontal exhaust 40 feet, with no "stack". Adding a stack to them does increase the volume and velocity of the exit gasses tho, certainly. look up, if you havnt seen it, a solar chimney, or stack. the effect is so great you can stick a turbine power generator at the top to produce electricity, with no fire heating it up,lol.

To get a reasonable air flow though ANY piping in the loft, you need a large (as possible!) inverted funnel, where the hot air is.

This will gather a large(r) quantity of warm air, forcing it into the smaller pipe, thereby increasing its speed due to the stack effect (or use a fan, pedal power?)

Not having a large funnel/collector, will seriously slow down air speed.

The box you envisage will make that even worse to my mind, turbulence and the like.....

Just a thought!!

The biggest issue is getting air to return back to your garage with little to no restriction.

If you have that problem solved then it may be possible to get it to work but over all your energy savings wont add up to enough to worry about given you will have a considerable reduction in airflow which means less total heat getting to the back of the house where you want it most.

It works like an electrical circuit. The amount of air flow is proportional to the driving force (difference in density times difference in elevation) and inversely proportional to the resistance to airflow. There has to be a complete circuit of airflow.

So to minimize the resistance, you would have to have two air ducts, one to take hot air to the house and one to return cooler air. If your return is via "outside air", then you have to vent your house to let air out and the garage to let air in, and this would be complicated by outside air temperature and wind conditions.

I would stick with the blower.

i am familiar with the air circulation principles, somewhat anyway. the stove drawing in air already creates some airflow thru that duct. i was hoping by rigging an insulated box in the attic, that it would increase the airflow

hot air already makes the loop. hot air upup to the attic duct, then cooling a bit and falling into the house, then thru the house, and out the door to the garage. i was hoping adding a big insulated box in the attic would increase the airflow.

Of course convection will work--look at the difference in temp between the floor and ceiling in a tall room or industrial building. BUT, the hot air flow has to go uphill all the way, or have enough pressure to get it thru other sections. And there has to be a return. Stick with the existing fan; it's less headache and $$$.

Use the fan and don't quit your day job.

Or use the heat to heat hot water and circulate it or replace your water heater.

Looking at the various differences between air and water should convince you of the lack of feasibility.

water is already solar heated, via an old truck camper top tilted toward the sun with the old water heater inside it, and old sliding glass doors mounted over what was the bottom of the truck topper. Water thermosiphon system to back of house is next, as soon as i buy and install a 250 gal water tote. pex tubing is already imbedded in the thermal mass heat bank

The video in the link you provided leaves me wondering how well segregated the CO and CO2 are from the air in your garage and home.

all the exhaust from that stove goes thru stovepipe buried in 10,000lbs of clay and rock, heating that all up as its going. the exhaust then does an "elvis" and leaves the building thru an exhaust stack, 5ft above the roof peak. the stove is self aspirated, no blower, and is quite safe. the folks protesting at standing rock are now building similar heating systems to deal with the low temps, while the opposition freezes,lol

Are you working on a way to enable the president-elect to solve all our energy problems?

Sadly, our energy problems, and nothing of any tangible value at all will ever be solved by tweeting.

The P.E. is incapable of anything constructive.

A few quads of hot air could help heat the northeast this winter.

That requires Congressional action and we all know they are dysfunctional and incapable of any coordinated, intelligent acts.

thermal mass rocket stoves burn about 25 percent of the wood a "wood stove" does, for the same heat output. the emissions are way lower than any air quality codes too. Plus, with a large mass, they continue to release heat for a few days after the fire is out. the thermoelectric generator i built for the top of the stove will charge anything from a cell phone to a deep cycle battery, while its running a series of led lights thru the house. My energy problems are about solved. The govt already knows how to turn heat to electricity with thermoelectric generators, its 1870's tech.... the voyager spacecraft has been powered by one for over 40 yrs now. god gave us fuel, greed gave us gas,lol.

A well insulated pipe (stops losses to a great degree), that always rises, will soon have large quantities of hot air going through it.

Its called the chimney effect and allows fires to blaze well, as it sucks in lower colder air, into a fire, and has done for millions of years.....well since mankind has had fire at least!!

Yours will not have smoke in it, the main difference!!

There is no need to return the colder air back down, that some here seem to believe, just exhaust it low down, up where the heat is used when the warmth is gone from it and take fresh air from below- You may want to have a damper to control just how much hot air gets delivered.....

A siphon does not return water either, many forget that!!! You do not need to return the air, that is simply misleading!!!

See here:-

Chimney or Stack Effect

So if the hot air is entering into the room at the ceiling and the cooler air is exhausting the room at floor level isn't that in a basic sense an air return system being the air has to travel in a complete pressure loop from the heat source to the room at the end of the house and back to the heat source to complete the convection circuit?

Also given the formula in your link and basic rough estimates form it for air flow what do you get for total BTU's that could be transferred in an ideal condition though various common sized ducting that someone such as the OP would use in his house?

I get 'It ain't much compared to a basic fan and a 6" duct' in my estimations.

I think this was to be for home heating. Therefore, the "cold" air in the system will be warmer than the outside air, thus it should be returned for reheating, to keep colder outside air from being sucked in.

Perhaps you have a method without fans that you could mention here, I am sure the OP will be grateful for good usable ideas.

The saving of electricity, if I understood correctly, was more important to the OP.

Maybe I'm simply wrong on that point!!

I personally have never seen a warm air system that returned the cold air back, but I also bet that somewhere its been done....

But you should consider that if the fire is fed from a cheap fuel source (free wood?), the extra work and parts to return the cold air may or may not be worthwhile....

I personally feel that a delicate/correct control of the speed of burning/heat produced will bring far more savings than returning the cold air....but that's just my opinion.

Having constant fresh warm air, will also be healthier than cycling the same old air round and round I feel.....

Tell us your feelings....

Uh what?

My point is if you need to put warm air into a room it had to have place to go so where are you thinking the air its displaced is going and being that warm air that went into the room had to come fomer some place what fills the void from the area it came from?

By my reasoning that constitutes an air flow circulation circuit and thus the need for a viable low restriction air return path from the room being heated to the source where the warm air comes from and to do so and get enough volume of warm air moved from point not point either large passive air ducting with very low restriction or a smaller ducting with actively move air flow is required.

Hence my question for you using the formula of your own link on what numbers you have to show the what an how you find a passive system viable for any arbitrarily described theoretical home application?

I as others have no suggestions for a passive system being the rough numbers for any reasonable degree of warm air circulation by shear passive flow from a garage location to the far end of any average size home requires unreasonably large air ducting and return passage sizing or substantial floor to ceiling thermal gradients to be practical.

Especially so if even the most basic ROI analysis of the cost of install time and materials Vs energy saving in electricity are factored out. I mean, what's the point of doing a multi hundred to thousands of dollars house renovation to put in huge duct work just to save pennies a day on electricity?

What are you talking about?

Do you need to be a trollish ass about things when you have some sort of misunderstanding about what the OP is talking about or is there some sort of language issue where what the Op has said and is wanting does not correctly translate in intent and context as you are reading it?

So far I and several others here are seem to have no problem reading things as the OP is talking about capturing the warm air rising off his fireplace system in his garage and transferring it to another part of his house through overhead ductwork. Not taking house air and sending it up his chimney as you seem to be fixating on that so far he has given zero indication of concern or relevant need of advice on.

As for my heating system engineering credentials about 15 years ago I designed and built my own boiler system that burned most any solid fuel that would hold flame and not just burned it burned it efficiency at that by using a digital contorl system of my own deign and contracting as well that also seamlessly integrated the hot water heat produced in a boiler room off the side of my shop with my standard forced air heating system in my house which is now ~350 feet away.

In fact I not only built that one I have built several custom units for people over the years as as well that are also seamlessly integrated with their home heating systems as well and a few of them have been in reliable service going on a near decade now.

On top of that as of this year my old system has been retired and a new mini boiler dedicated to operating as a used oil only fired system has been my personal and primary home construction project the last few weeks.

As of a few days ago it's been plumbed into my work shed floor heat and has been keeping the building at a nice 55 F even though it does not yet have the oil burner systems or electronics systems in place or is it fully hooked up to my old house either. (I'm waiting for a second pump to show up so I can get that plumbing done this week)

Here's where it sits as of a few hours ago. I have been heating 2 - 3 times a day with my big propane torch to keep the shed at a workable temperature as I deal with fabricating and assembling other parts of the system and dealing with other higher priority projects like this week big snow storm.

So do I know heating system related engineering and design among my other engineering and technical fields? I don't know? What do you think?

no basement in the place i am heating with the thermal mass rocket stove, its all one level basically. Garage slab is 3 ft lower than house floor tho. From all i have read here, i think i will go on and try the "box in the attic" to boost the airflow i already get to the other end. I will try to draw it out if it works later on for any interested folks. I wont have to spend much on it, i have materials laying around here for most of it. I will also finish up the water transfer system, because the pex is already in place under the tile on the heat bank. I will use the air while the garage is hot as the stove runs, and turn on the water flow after the garage cools off between burns.

i will double the hot air intake area to try to increase the hot air rising into it, hopefully helping to push the air a bit as it cools along the pipe to the back. Heres a pic, for anyone not following my rambling idea

That's basically how I envisioned your setup but with the garage on the left, not right.

Why not use your thermoelectric power to run a few common DC fans lie the ones found in computers (especially the compact high speed high air velocity ones) to work as draft boosters in the ducting?

If hung at a rough mid point in the cross sectional area of the duct they can produce a pretty decent venturi effect greatly boosting the overall air flow rates with very little electrical energy input.

Also if you are truly bringing your burner exhaust temp down to ~150 F how are you combating creosote and other condensate related build up issues being water vapor and micro particle production from wood burning is as I have ever understood it a unavoidable byproduct.

With my first boiler design I had very high heat transfer efficiency even at full burn due to having a very large flue surface area that gave me similar low exhaust temps but the downside was even when running the hottest cleanest burning fires possible the was no way to avoid the water condensation and related micro particle collection issues that went with it.

Because of that I had to redesign the boiler flues to have far less surface area in order to get my stack temps up into the necessary 600 - 800 F range for long enough periods of time and often enough to burn that condensate and related microparticle build up out otherwise it would eventually turn into basic wood tar creosote that had to be deliberately burned out in a controlled stack fire 2 - 4 times a winter depending on what grade and type of wood I was primarily running.

Good clean dry Ash and Oak had very little problem but the majority of the wood I had to work with here was old dead Elm and other natural deadfall material we have to clean up around the farm regardless and old assorted lumber and wood shipping pallets that tended to be rather punky and damp a lot of the time.

i didnt realize those little fans would help any, so i may stick a few in. The core of a properly built rocket stove goes over 2500f, and is made from refractory firebrick, backed by light insulating firebrick. so basically it cracks the tar and creosote into hydrogen and whatever else and burns it all, even the smoke. most of the time you can not see any smoke exiting, and when you think you see smoke, its mostly water vapor, like a gas furnace produces. My exhaust stack leaves the stove, travels 15 ft, then makes a u turn back toward the stove, then rises out the exhaust stack. On the run leaving the stove, the exhaust is slightly tilted back toward the base, so any condensation runs back and gets reheated. After the u turn, it slopes down slightly, allowing any condensation to run into a drain pan just under where the pipe turns to go up. the stack pipe going up is built in reverse manner, allowing any condensates to run out the seams in the pipe joints and down the outside of the exhaust stack into the catch tray too, which has an overflow line leading to a collection pan, that usually evaporates it all. So yes, condensation has to be dealt with, but is not a problem if you use a bit of foresight in your build

i also replace the lower elbow and the bottom few feet of the stack every year, because i just use cheap normal 6 inch ac ducting for that part of the flue so far.heavy triple insulated stainless stack still goes up thru the attic, from the previous regular wood stove install that came with the place. Next year, i may upgrade to more expensive normal black stovepipe, to avoid replacement every year. i have seen rocket builds that use drier vent tube, so the cheap ac ductwork is safe enough. exhaust temps never get hot enough to burn off the galvanizing. i actually duct tape a sheet of paper onto it so people can visualize the low stack temps, without having to touch it, which i always can, because it stays so cool.

hey, at least im not running this one in the house,lol.

Firstly, your drawing has cleared up a lot of questions about the shape and sizes, many thanks.

But I am at a loss as to how the box will help you. Just coupling the garage to the room with no box will work better, well insulated will reduce losses.

With the box, once the warm air gives out in the garage for any reason, the rest of the warm air in the system, will only come out of the box as it cools.

Due to its shape, it will also further slow down the warm air and allow some extra heat loss, depending upon the standard of insulation.

Actually, the same will happen with the pipe alone, but the quantity of warm air in the pipe will be far less than the box....

That is, "the warmest air will remain in the box until it cools below the temperature of any incoming air!!"

To get it to work well, you will need large sizes of trunking when designing for no fans, large volume, low pressure.

As any hot air balloonist will tell you!!! The hot stuff is always at the top!

That is my projection, but please build it so that you can find that out for yourself, thats far better than just believing anyone else......

Some years ago I performed tests with transferring some hot air near the ceiling from our kitchen, wanting to spread it into the lounge. My tests showed that it was possible, but even with a fan moving the air, the gains were minimal. I dropped the idea completely.....

It just struck me, it was very similar to what you are attempting.....but with a fan!!

I wish you a great day.

the rocket stove design acts as a pump. hot air rising in the center riser hits the barrel, begins to cool, becomes heavier drops to the outlet and can be pushed along 40 feet of horizontal uninsulated stovepipe, before making its upward exit turn. I was hoping building a box in the attic, similar in design to a rocket stove, it would help to "push" air along. rising hot air pushes the cooler falling air along, as it cools and condenses a bit more, it becomes easier for the rising hot air to push it down the pipe. sticking a small rocket stove under a 50 gallon gas water heater i have on hand out back and thermosiphoning that into the house may have greater results for less effort tho,lol.

Hi,

Excuse a stupid question, from someone who knows nothing about the subject.

Isn't it a bad idea to feed oxygen depleted exhaust gases into the space where you live?

Thanks,

Mike

Yes

Why and how do you figure would he be doing that?

From the drawing it looks like the flue gas is being transferred from the stove in the garage to the house.

What do all the OPs posts say about what he is doing and how he has it designed?

no. the flue gasses go out the chimney, 5 ft above the roof peak. i just didnt combine both pictures. One was diagramming how a rocket stove worked, and the 2nd was a diagram of how i am hoping to get the hot air to circulate thru the house, using the same thermodynamics and boyles law that drives a rocket stove.

its a thermal mass rocket stove out in a drafty garage. Plenty of o2 to go around. But i will probably add in a line to feed it outside air directly before long. If it doesnt cool the fire too much, or add too much humidity to it. 2nd year with it, so its doing good as is. There was an old 2 barrel wood stove out there for years before i took it out. With all the time and fuel i was going thru hauling, cutting and splitting "firewood", i might as well have just burned all that fuel for heat,lol. Woodchips for the rocket stove get delivered free by the dumptruck load, and just have to be raked out onto plastic and dried a few days, instead of 6 months, and they are ready to burn.

right. thank you. it already works a bit without the blower on. i am hoping a big box in the attic will help the air flow a bit better. hot air into the top of the box, then as it cools a bit, down the duct to the other end of the house. the air temp at the garage ceiling gets to about 150f. so even if it drops to 80f on the other end, im happy,lol.

the air makes a loop now already, because i have a air grate at floor level back to the garage. So it rises from the garage ceiling, goes thru the insulated duct and out into the back of the house. I was just wanting to increase the airflow without running the blower. why pay some corporate fat cat, war monger or harrem humper for electricity, if i can get it to circulate naturally thru the house? And believe me, i dont spend hundreds or thousands of dollars on my projects. Most of it is "roadkill" ducts and such i have scavenged from demo jobs,etc. the woodchips my heating uses are happily delivered free by a local tree company. God gave us fuel, greed gave us gas....

For the most part, rocket stoves have one speed, wide open. the fire burns hot enough to destroy titanium rods i was using for a grate, now i am up to ceramic grill rods, that seem to be lasting. I actually put a 45 degree bend into an "arkansaw stone" ceramic knife sharpening rod,lol. It burns so hot, no smoke comes out the chimney, and beats all epa standards. i just hate spending money unnecessarily,lol. i can get dumptruck loads of wood chips delivered free, so why waste time, money and enough fuel to probably heat the house toting, cutting and splitting firewood? the stove already makes a bit of electricity with the thermoelectric generator i built to put on top of it. about 3 amps at 13.5 volts, not much yet, but slowly adding to it. Some people build or buy these firewood sucking outdoor boilers to heat with, then run pumps to circulate the water. why pay to pump water, when, if built right, it will thermosiphon free. i am hoping to do the same with the air. God gave us fuel, greed gave us gas,lol. The biogas plant is the next project for the back yard next year. And this house is pretty old. quite enough fresh air comes thru the cheap windows and outlets,etc, so it never gets "stale"

I pump water being it's a liquid thermal mass that can be located outside my house some distance away and tapped into as needed.

The old boiler was ~350 feet away and ran at better than 90% efficiency at idle and could burn anything that was remotely flammable that was under 4 feet long and 12" dia or of less weight than I could lift.

As far as tree hugger emission concerns it's a BS scam perpetrated by the same greedy "some corporate fat cat, war monger or harrem humpers" and far worse people in our own country (still can't believe you enviro hippies fell for the scam as well as you did and persist in following it plus are actually willing to spend the outrageous cash to keep it up just as the fat cat war monger harem humpers want and profit heavily from to keep their scam going just the way they want you to, but hey, it's your imagined problem and money going support them, not mine) and I don't buy it and never will and have zero issues with burning plastics, tires, railroad ties, coal and used oil to stay warm for free. God put the stuff to make that on earth to and made it flammable for a reason.

Now as for free electricity and having it in a form that user friendly like your common 120 VAC outlet power but sourced from thermoelectric, wind photosolar or whatever or whatever this may be of interest to you.

DIY pirate Grid TIe Inverter design. ( literally wrote that 'Pirate GTI for dummies' book myself) With minimal electronics components you can take you variable DC power off whatever you have that's making it and synchronize it with your utility AC power and supply your free self made power to your normal AC line powered equipment including things like your air duct fan cutting your utility supply power usage down without all the wasted money on materials and wasted runaround setting up independent low voltage systems.

i have a water line thru a cooler part of the stove, 300f or so, as well as lines thru the heated mass. I plan to do a water thermosiphon setup before long. I just have to get some more pex and at least a 250 gal ibc water tote, and figure out where to put it,lol. for making my own power, i am slowly adding teg modules to the setup. they are a lot smaller than equal power output from solar, and run 24hrs a day, if my stoves hot. Right now i am just charging one battery, to run my shaker on the rocket stove, and some led lights. occasionally when powers out, i hook up an inverter to the battery, but normally just hook it to my truck, throw the main house breaker, and backfeed into the house wiring. The tegs are actually cheaper than solar, for the same output. but it will still cost a few thousand to totally offgrid or zero out my power meters usage. i would be interested in purchasing a gridtie inverter in the future, because my knowledge of constructing electrical components is quite limited

last year i fed the rocket stove plastic drink bottles, used motor oil, food, etc, but i overheated things, and cracked my ceramic glass i watch the fire thru,lol. So this year, only woodchips and food leftovers are going into it. Properly built rocket stoves can burn plastic, motor oil and probably even anthrax, to epa standards. They run over 2000f in the core...it already ate the titanium rods i was using for a grate, and warped an "arkansas stone" ceramic knife sharpening rod to a 45 degree angle. the ceramic cooker rods i got next seem to be holding up tho.

My old boiler system used a combination floor draft and top draft system and had no problem melting most stones with dry woods and I had to make my bottom draft box plate out of 3/4" steel plate with 1/4" hoes on 1" centers to make it heavy enough to stand up to the heat without warping. Same operating concept of the rocket stoves with the high volume clean air flow through fire but controllable for long duration burn times.

Being able to load near a million BTU's of wood at a time and have it regulate its burn rate to keep the water jacket temp constant for up to 12 - 15 hours at time made it easy to work with.

Hot fast heat is okay for showing off but when a guy has better things to do in life that baby sit a fire, load and walk away is so much easier to work with. Especially when all the mess of that fire, its fuel and it 's relate thermal mass is out where it doesn't intrude into the house and unlike yours there isn't one room that runs at ~100+F while the others are way below that with the furthest ones to the point of being uncomfortably cool in comparison.

I know a big family (used to be, most are all grown up and have kids of their own now) that are good friends with a buddy of mines family and they did the home built large mass high burn rate fireplace (early rocket stove variants of some sort I suspect) thing for a while like you.

If you talked to them for the first few years it was the world's greatest device ever made and everyone should have one. Then about 3 - 4 years later I saw them again and they were then running a large central boiler system that could eat logs that took two people to carry and it was plumbed into their main heating systems for their house and shop.

When asked why the change, being they were so thrilled with their super fire place contraption that 'everyone in the world should have', the dirty little secret came out that it was a huge time and work investment that made one area of the house way too hot to live in while the rest was too cold and the shop was unheated and intolerable to be in in the winter.

But the change over to their boiler made everything related to heating so vastly much easier and with far more stable heat spread out over the whole house plus the shop too that what ever efficiency was lost it was far outweighed by the time and effort savings simply due to being able to load it with largely unprocessed wood in a high volume and being able to walk away for a near full 24 hours before loading it again.

I could totally relate to that concept being I grew up in a house with a fireplace where everything had to be under 16" long, 3" - 4" dia and reloaded every 2 or so hours. Making trees into pieces that size was a huge investment in time and labor compared to my boiler that could eat anything small enough for me to carry.

And to be honest even with that minimum wood dimensional requirement feeding my boiler got old after a decade or so and I went to my now present used oil burning system.

i do have a feed system on the stove now that feeds it for 3 or 4 hours. After it runs that long, it puts out heat for another 20 hrs or so. But i do want to use a water system, but my "boiler" will just be an insulated ibc tank of 150f or so water, thermosiphoning or uggh, pumping water to a few car radiators and probably 12 volt fans to draw out the heat. I would run a whole radiant floor, but the construction of this old place makes it difficult. It would be easier to blow hot garage air under this place than to run pex under the floor, unless i redid the floors, with tubing under it as it went down. This home is an old doublewide mobile, with an attatched garage on a slab, and the mobile raised on a block foundation, with a 2nd roof and attic directly on top of the old trailer roof,lol. I am sure someone will soon mention to watch out for "overdrawing" from my stove room, causing the stove to leak or return co into the garage and ductwork. I am watching that carefully. If i set a cigarette on the top of the feed chamber and smoke rises from it, i am overdrawing the room. If the smoke sucks down into the feed, its all good,lol.

An interesting and very informative post, many thanks.

Getting the old air back down would simply not work, too many leaks. Be happy for them.

The Norwegians and in some other cold places, don't try and move hot air around, they run the stove piping around the room/house to deliver the heat in the smoke to various places, always at an angle, but always going upwards. The longer the pipe, the more heat gets taken out for the house.

Some put a "short circuit" in with a damper, to help to draw the fire when first lit. Closing the damper when that part of the chimney is warm forces the hot gasses to circulate through the longer piping..

Is something like that any help, maybe "after" the thermal mass?

I looked around for some pictures and stumbled on this, which has some really good tips. By the way, I have nothing to do with the company concerned, but they do give a knowledgeable impression!

eight-tips-for-burning-wood

If you are on Instructables (you should be!!), you can see a great DIY heat exchanger for getting more heat from the stove pipe. They can also be bought on ebay already made.

Woodstove-Heat-Exchanger/

A friend of mine has added a similar one to his old Franklin wood stove and complains that it makes the big room TOO hot! He has to learn to run a smaller fire!!!

They must be kept clean though so as to not cause a creosote chimney fire, a smaller hotter fire is best and more economical generally.

Using such a heat exchanger, means getting your warm air via the exhaust smoke, with only the exchanger added, not piping!

Have a great day!!

what i dont like about those heat exchangers is as soon as a little hole rusts thru them, you are blasting co into the living area. The exhaust from a rocket stove is already quite cool anyway, about 150f, after 30 ft of stovepipe goes thru 30 feet of rock and clay bench, heating it all. If i cooled it any more, it wouldnt get out the chimney stack,lol.

Nowadays, for any such installation, a CO and CO2 sensor is as good as being mandatory for any serious burning of any fuels....anything else is simply too risky....but sadly, not against the law and many just ignore the possibilities.

I have several CO sensors (one in the gas central heating boiler), but no CO2, maybe I should update!!

People die quite often from CO poisoning!!

Here are a few ways to detect it from ebay USA:-

Sensors and alarms for CO and CO2

Furthermore, if your stove smoke piping is only pushed together, there is always a risk!! You still should have an alarm!!! No matter how well they are put together....

i did seal all the seams with heavy foil high temp tape. except for the first 6 ft of heavy black stovepipe that gets to around 250f, but it is buried in the rock and clay bench. the condensation still manages to drip thru the tape a few places, to the catch pan, but just at the upright part, where it looses enough heat to condense. past those first 3 joints of heavy stovepipe, everything else was taped off. But the co sensors are next on purchase list

That's my thoughts as well. Any air that leaves the garage has to be made up from some place just as any air that is displaced in the room the warm air is going into has to go somewhere as well.

If x cubic units of air go out of the garage and X go into the room they have to balance out somehow and doing so by recirculating the air inside the house is way more energy efficient than using cold outside air as part of the circulation loop.

The rest is just the logistics of how that air will be moved and by my estimations to get any decent heat transfer fairly large volumes of air need to be moving and to do so passively over any distance with very little elevation change from thermal source point to sink point it takes a lot of ducting cross sectional area with very little restrictions for the whole circulation loop to even begin to work let alone work well enough to justify itself.

"Really all very, very simple, provided you understand it!!"

Arrogant German say's what?

in deinem Gesicht ?

Little do you know!!!

At least I don't contradict myself and what stand for from thread to thread.

Wood heating.

right. the stove exhausts out the roof, above the peak. the garage ceiling air gets to around 150f or so, then goes up into the duct and cools a bit, then "falls" out the other end, at the back of the house. it already circulates some air without the blower. I was hoping a big insulated box with hot air drafting in would give it a bit more airflow without the duct fan being run

thank you. the insulated duct thru the attic is already working a bit without the blower going already, apparently to many members disbelief,lol. i was just wondering if adding in a box would increase the natural draft any.

Remember when the coal furnaces used to located under the living room floor? They functioned entirely by convection. The hot air would rise out of the middle and the cold air return was around the edges of the grate. Later on they morphed into the "octopuses" to channel the warm air to the nether regions of the house.

Coal furnace heat exchanger repurposed as yard art.

WOW!

Great picture, thanks.

(Spoken in a whisper, so as to not disturb the fans)

"Score tied now, tcmtech (5) tied with Andy Germany (5).

Tech served first but Germ was in the game soon after that.

Lots of word count and and parrying, but no clear winner yet.

This contest is NOT over yet, folks. Stay tuned for more action."

LOL! Some days you do make me laugh for good reasons!

As an apparent impartial third party what do you get out of the OPs post and implied intent?

Chimney draft and make up air related question or how to move hot air from one area to another inside his house by passive methods.

If he comes back and states it's a chimney and makeup air related problem I have no problem with admitting I misread the original post.

However if it's not chimney and make up air related but a how to move hot air from his garage to another part of his house though basic passive thermal convection through ducting I am expecting some OT point readjustments out of this!

Sorry, I must remain impartial in this contest.

^{_{My take is he wants to move (circulate) inside, warm air around without using a fan.}}

the intake air comes from the garage floor currently, so the ductwork thru the attic already loops a bit, from the stoves draw. heated garage air goes up into the duct, then is drawn thru out the other end of the house, then back to the garage. I am hoping putting a large insulated box in the attic helps it thermosiphon better than it already does, by reducing air drag, and by cooling a bit in the box, and falling thru the duct at a greater cfm. makeup air gets drawn in from outside a bit, because my garage doors arent totally sealed airtight, and house air gets drawn in too, because i have a return vent from the living room to the garage. it will blow out a candle when i shut the door from the living room to the garage if you put it in front of the return vent...

The box and the down-sloping duct are unlikely to provide benefit to flow or heating of the house.

You would probably be better off with a well insulated horizontal run or a well insulated slightly ups loping run.

Natural Circ, will mainly be driven by difference in height between inlet and outlet and average difference in density between path and surrounding. Any down slope hoping to take advantage of cooling losses decreases overall difference in height.

If you simply must build a hot air box, put it over the area you want to heat. Insulate it well on the top and sides, cover it in a radiant barrier, and line the upper inside with a good radiant absorber//emitter.

LOL!!

Good one Lynn!!

I don't think a siphon will work with air like it does with a liquid. I don't see the point of a box in the attic. Hot air will rise into it, but won't flow well into the house unless the pipes are sloping upward, and that's not practical. Then the hot air will not want to come down into the house, so a fan would be desireable. You want the hot air to come out at floor level. If your garage is attached to the house, just open the door between them for the return air to flow into the garage.

Have you given any thought to adding a small sterling engine and fan as a passive booster blower? I suppose if you were into steam punk, you could add a passive twin cylinder steam prime mover on a flash boiler to provide motive power to the air.

I was also wondering what you do in your house to avoid stratification of the warm air at the high points in the house. Destratification in the house would work against the efficiency of thermosiphoning, but essential for comfort.

i love stirling engines. But for my machining skills, thermoelectric generators are easier to slap together and stick an old drone motor fan onto to move heat off the stovetop,lol.

Maybe its worth to gamble for your luck, but some says skill is forever.

[Again, in a whisper] Well folks, after a grueling 24 hours of back and forth action, with the germ overpowering the tech with word count, it seems to be still too close to call.

The germ threw the "chimney effect" at tech and that was skillfully deflected by citing the "air return system" strategy, but that was countered by the germ's "delicate/correct control of the speed" ploy with no mortal wounds inflicted, so far.

Well now, that "circulation loop" thrust seems to have hit home with germ being penalized for his "that you are not an Engineer in any way shape or form" rebuttal, resulting in a yellow flag penalty of 4 OT being assessed.

Finally, with a pictorial display of " heating system engineering credentials", tech may have put this match away for good.

That concludes tonight's coverage. Tune in tomorrow for more exciting, no holds barred action right here on CR9 Sports.

So you quit your day job, Lyn? Well, Happy Holidays in advance to you and CR4. Nice to be back around here, it's better than the news as always.

I wouldn't call it much of match. Heck. I didn't even know I was in a game until you pointed it out in post 24 and even then I along with several others, including yourself, had the OP's system pretty well visualized before my suposed opponent stepped on the field.

I cite posts 3 - 6 as proof and pretty much all appear to be within reasonable range to consider them as having some degree of viable understanding of what the OP is talking about.

So if there was some sort of game going on regarding who understood what the OP was saying and who didn't he pretty much managed to take the bat and ram it up his ass all on his own with his first post.( while most everyone else stood around wondering what he was doing.)

Now that said and given his apparent obliviousness and the evidence of his overall poor sportsmanship attitude as seen beginning in post 15, to which I didn't bother with a reply to him on that specifically until post 23 where he then claims at post 46 it was me who insulted him in post 13 by asking him what he was talking about in post 12.

Game wise after that I rather just gave up and went home being the next posts he made pretty much looked like he was trying to shove the bat up his own ass then sit on it and spin to everyone's apparent distaste given the quantity of OT scores that resulted. (German game play rules perhaps?)

I had considered doing a few professionally written and numbers backed posts to explain myself and what I know in more defined detail but I doubt he would take them for what they are and what they represent anyway and it would just lead to him discrediting himself and whatever it is he does or has done for a living even more.

Not to say I may not later but at this point I see no reason. I clearly can't make him look any more unprofessional and childish than he already has done on his own so far.

(This ends my game perspective interview.)

You missed your vocation! You should do commentating FAR more often!!

Not many threads rise to the level of being commentator worthy.

Nice one Lyn,

not many videos come along either..

Ohhhh, he's right, Lyn. You should do the commendation for the Man-Roo bout.

'Commentation'

Ridiculous know-it-all spell check.

I read a story about giving an oil furnace a fresh air supply directly from outside and I thought "Why wouldn't this work with my wood stove?" My roommates thought I was crazy cutting a hole in the wall until the whole house suddenly felt a lot warmer. And that was before I had assembled my home made heat exchanger from steel ductwork.

We now have a free standing gas heater. The first thing I did was give it a fresh air vent. I repurposed a dryer vent by removing the flapper and directing the duct under the burner.

Thats very common over here, why "burn" your already warmed air!!

I believe I also mentioned this earlier in this blog in one of my posts....

And its often very simple to do. I ran a 2" pipe from the cellar, directly below my pellets stove, you cannot even see the pipe!! I can shut it if needed, but I have never had a need in 10 years.

Oldhouse, the cellar is probably not perfectly sealed, though the rest of the house is when we insulated 10 years ago.

The pellets stove takes what it needs of course from the kitchen air just below it, and I have never ever tried to find out if that pipe is large enough or if a small percentage of kitchen air is still used.....

In the cellar, I also take the air from the lowest point of the cellar where the air is at its thickest....the stack effect "may" make a difference, certainly placing your hand over the hole demonstrates quite a draught when the burner is running and next to none when its not!

But it may also be due to slight differences in air pressure in the kitchen, due to the fan that a fan drives air through the whole pellets stove by sucking air through it (no "over" pressure air in a good pellets stove, just in case a leak develops, only air is sucked in, not gases of burning blown out), thus the kitchen has every so slightly less than normal air pressure in comparison to that outside. I have never tried to find out what the difference in pressure might be.....

(Good) Pellets burners, due to the exceptional electronic control and tiny but very hot fire, need far less air than say a big woodburner with a relatively huge fire of course...AND they produce NO SMOKE = NO FINE PARTICLES in comparison to ANY wood burner (one without an electrostatic smoke scrubber that is). More than 100 x less in tests.

A colleague last week, told me about "Industrial Snow", which has nothing to do with "Snow Cannons" as I thought at first!!

Its actually snow that develops in the air as normal, but from a tiny fine particle, from say cars, trucks or wood stoves exhaust, hanging in the air (call it "smoke" for simplicity!). It takes on a tiny drop of moisture from the air, particularly when its misty. By taking on the moisture, its temperature drops slightly, and when the temperature is just right, it causes that moisture to freeze, attracting further moisture and building up a snow flake in a very short time!! = Industrial Snow!!

I did look for a better explanation online, but found nothing useful.....

A long read, but a good thread. I only have a few points.

Cold air falls because it is denser, and gravity pulls it down, displacing hot air.

If the house is leaky, air flow to the garage will draw cold air in through the windows/leaks. Better to have the air flow going out the leaks.

Forget the box, move that hot air to the house, asap.

My house, like many others with central heat recirculates the same air, over and over. A filter is all you get.

My house is quite tight, so I will have to bring in fresh air to a wood stove I'm installing in the basement. I plan to pipe it as close as possible to the air intake of the combustion chamber. No need to allow cold air into the basement unnecessarily, so I'll have a shut-off on it.

A final thought, you may consider a fan in the exhaust coupled to a fan in the duct, like the turbo in cars. Only one moving part.