Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: how to get the maximum heat of a wood stove?
pneumatician
National Hazard
****




Posts: 273
Registered: 27-5-2013
Location: Catalonia
Member Is Offline

Mood: Anar fent.

[*] posted on 27-9-2020 at 08:12
how to get the maximum heat of a wood stove?


hi,

I want to maximize the heat of the stove, how? putting radiators in the stove body?

A stove body more large with the wood in the center?

How many heat is lost by the chimney??

Also, how to "neutralize" all the smoke passing it through water or other thing making innecessary the chimney? exist something like this on sale?
View user's profile View All Posts By User
Herr Haber
International Hazard
*****




Posts: 893
Registered: 29-1-2016
Member Is Offline

Mood: No Mood

[*] posted on 27-9-2020 at 09:48


I occasionally visit friends who try to live off the grid as much as they can so wood stoves are quite common.

What's your stove heating ? Is if for cooking and heating ? heating only or for hot water generation ? (I love splitting wood 1 hour before the shower is ready)

The best stove I've seen there is built into the room. I have no idea how to call these in English. They use 2 fires for the bigger ones.
The idea is to use as much of the heat from the gases before letting them out.

First you light your fire behind or above the stove so the hot air will create a vacuum through the labyrinth of bricks that is the stove.
Then you light the stove itself at floor level. The longer the escape route, the better.

It's amazing how much heat you get from very little wood.




The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
View user's profile View All Posts By User
andy1988
Hazard to Others
***




Posts: 126
Registered: 11-2-2018
Location: NW Americus ([i]in re[/i] Amerigo Vespucci)
Member Is Offline

Mood: No Mood

[*] posted on 27-9-2020 at 10:31


Quote: Originally posted by pneumatician  
hi,
I want to maximize the heat of the stove, how? putting radiators in the stove body?

For an existing stove, put on a metal heat driven stove fan.

Quote: Originally posted by pneumatician  

How many heat is lost by the chimney??

Lots, but necessarily so, otherwise creosote condenses on the chimney walls and will greatly increase risk of an eventual chimney fire. In other words, in a conventional metal wood stove, reducing heat lost in the chimney is dangerous. But I suppose you could get sophisticated but a better approach is to not use a conventional metal wood stove, but a stove which burns at a higher temperature which also burns the creosote and smoke as fuel.

http://batchrocket.eu/en/
During startup and shutdown there will be visible smoke and poorer emissions than at full combustion out the chimney due to the lower combustion temperature. It is cleaner and more efficient than conventional metal wood stoves both because more of the fuel is burned and more heat can be retained (not sent out the chimney to minimize creosote buildup), less wood you have to chop!

In these designs high temperature insulation is used, such insulating fire brick and ceramic blanket. Metal in the combustion chamber will corrode away at these higher temperatures, so it isn't advised to modify a conventional wood stove or buy a metal stove advertised as a "rocket stove". Non-insulating fire brick may handle the higher temperature, but the startup/shutdown times will be longer (less efficient) and may be quite difficult to bring up to desired temperature, with much higher risk of backflow during cold startup. You can use non-insulating fire brick on other parts, like the exterior or mass, but not the combustion chamber or heat riser. Use fireclay or dust (from sawing bricks) as the mortar. It is easiest to just buy the brick and make the stove per a design someone had shared. There is a lot of terminology and acronyms these amateurs had come up with and lots of forum posts to dig through... it is a bit daunting to find answers sometimes. Here are a couple forums:
https://donkey32.proboards.com/thread/2215/documented-high-t...
https://permies.com/t/106480/Geeking-temperature-readings-co...

Since the creosote and smoke is burnt up, you can then pipe the exhaust piping through a large mass, which will absorb that heat and release it through time, and then out the chimney relatively smoke-free and heat-free (but still has CO2 and CO). 'Rocket mass heater' is their term for designs including such a mass, otherwise they call it a 'Rocket stove'. They have rules of thumb on how long this piping through the mass can be without risk of backflow, which is a function of chimney height, riser height, and channel dimensions. The term 'masonry heater' applies when brick is used to make the bell instead of a metal drum.

The 'Batch box' design allows more wood to be loaded at once, so you don't have to put in wood so often. There are automated wood pellet variants as well. I'm personally fond of a ceramic blanket in the riser instead of insulating fire brick due to a faster startup. All sorts of variations and experiments people have tried.

I'm sorry if my use of terminology anywhere is sloppy.

[Edited on 28-9-2020 by andy1988]




View user's profile View All Posts By User
Fyndium
International Hazard
*****




Posts: 895
Registered: 12-7-2020
Location: Not in USA
Member Is Offline


[*] posted on 27-9-2020 at 10:45


Attach a duct fan in steel tubing and make it force air into the furnace. You easily melt steel.

Open breathing fireplace? Maybe 800-1200C core temp when used in larger amounts.
View user's profile View All Posts By User
sodium_stearate
National Hazard
****




Posts: 251
Registered: 22-4-2011
Location: guard duty at the checkpoint
Member Is Offline

Mood: No mask.

[*] posted on 27-9-2020 at 16:39
good heat


Just keep the stovepipe and the chimney clean
and burn good wood or coal.

A properly functioning plain cast iron stove with nothing fancy
attached can and will throw lots of heat if decent dry
wood is used.

There is always plenty of free oak around here, and after
that dries out for about a year, it heats very well.




"Opportunity is missed by most people
because it is dressed in overalls and it
looks like work" T.A. Edison
View user's profile View All Posts By User
brubei
Hazard to Others
***




Posts: 162
Registered: 8-3-2015
Location: France
Member Is Offline

Mood: No Mood

[*] posted on 27-9-2020 at 16:53


use gas for less consequences with particles or smoke and fire in exhaust.



[Edited on 28-9-2020 by brubei]




I'm French so excuse my language
View user's profile View All Posts By User
wg48temp9
International Hazard
*****




Posts: 598
Registered: 30-12-2018
Location: not so United Kingdom
Member Is Offline


[*] posted on 27-9-2020 at 23:27


In some areas of France they use wood stoves to heat the whole house with a hot air system similar to the hot air systems that were common in the USA.

The wood stoves were/are finned, partially enclosed and connected to a ducting system to supply hot air by convection to the upper rooms of house.

These days old buildings using wood stoves tend to have there chimneys lined with a double walled stainless steel duct and the space between the duct and chimney insulated with vermiculite. That is part of building regulations in the UK.

The insulted double walled chimney ducting and recommendation of a minimum flue temperature reduces the chance of tar build up and limits the efficiency of the stove. There are no condensing wood stoves.

Even dry wood is mostly carbohydrates (carbon and water) hence wood has a low calorific value, just about 20% of natural gas. You need a huge pile of wood to heat an old poorly insulated house in the winters of the UK and northern France.

I should also add that wood stoves are much more efficient compared to an open fire. Open fires have has all that extra air that is sucked up the chimney and must be replaced by the cold air from outside.




I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
View user's profile View All Posts By User
Junk_Enginerd
Hazard to Others
***




Posts: 159
Registered: 26-5-2019
Location: Sweden
Member Is Offline


[*] posted on 30-9-2020 at 10:56


Maximize heat or maximize efficiency?

To maximize efficiency, you would theoretically extract all heat from the exhaust gas, ensuring it is at room temperature before it leaves the house. In practice, this is impossible, and you wouldn't be able to rely on the natural draft to vent out the smoke, but would have to use forced air intake or an exhaust fan. But much worse is all the crap that would condensate in your chimney; soot, tar and volatiles. All flammable, and then you'd have a chimney fire which is seriously dangerous and damaging.

To run it at peak efficiency and taking the above into account, you want the exhaust gas to be around 70°C when burning wood at the stoves rated power. Higher than that means losing efficiency, lower than that means danger.

Reaching this temperature can be done in lots of ways. If it's too high, which is most common, then start adding heatsinks. Metal fins might work, a large thermal mass works nice as well.

If you want to maximize efficiency, start by getting a thermometer to monitor the chimney temperature so that you know where you're at.

If you want to maximize the heat, well... just use oily plywood cut into small pieces. But I'm guessing that's not really what you meant. :)
View user's profile View All Posts By User
Twospoons
International Hazard
*****




Posts: 1114
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline

Mood: A trace of hope...

[*] posted on 30-9-2020 at 12:33


If there's all this combustible stuff going up the chimney, then that's a waste. How do we get that burnt too? Some kind of catalytic surface, perhaps?



Helicopter: "helico" -> spiral, "pter" -> with wings
View user's profile View All Posts By User
Herr Haber
International Hazard
*****




Posts: 893
Registered: 29-1-2016
Member Is Offline

Mood: No Mood

[*] posted on 30-9-2020 at 14:09


The word I was looking for is mass stove.
That's what some of you are describing here.

I've seen of several sizes, most of the time they're made so they can be used as furniture aswell.

Junk_Enginerd mentions that you cant rely on natural draft to get all the smoke out. That's particularly true with bigger stoves.
In the bigger ones I've seen there (3-4 meters wide) is a secondary fireplace near the exhaust that is lit at the beginning to force a draft (pretty much like a vacuum pump if you want) and solve that problem.
In any case, a mass stove should probably be rebuilt every few years because it'll eventually clog up no matter how clean and careful you are.




The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
View user's profile View All Posts By User
zed
International Hazard
*****




Posts: 2125
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Online

Mood: Semi-repentant Sith Lord

[*] posted on 17-10-2020 at 05:36


Lots of wood around here. I just burn it. Smaller diameter wood, burns hotter and faster. Sometimes my heavy cast iron stove glows orange. Slow burners create a lot of creosote. Fouls your chimneys, catches fire. Burns your house down.

Oak is sweet, if you have it. I don't have it. I have 2x4 scrap lumber. I have fig wood . I have apple.

I have compressed paper products. All cellulose.

I recently cleaned my chimney. Not bad, a little soot. Hard and dry.
View user's profile View All Posts By User
Dr.Bob
International Hazard
*****




Posts: 2299
Registered: 26-1-2011
Location: USA - NC
Member Is Offline

Mood: No Mood

[*] posted on 17-10-2020 at 16:37


just blow some oxygen into the stove, and that will generate lots of heat. But many modern wood stoves have a catalytic surface in the top of the oven to help burn all of organics and keep the exhaust cleaner.
View user's profile View All Posts By User
zed
International Hazard
*****




Posts: 2125
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Online

Mood: Semi-repentant Sith Lord

[*] posted on 19-10-2020 at 06:52


Oh, I have an old Yotul/Viking. Kinda small for my large poorly insulated house, with lots of large uninsulated windows. I'm venting into my regular chimney, which has been sealed up with a sheet of cement board. Works pretty well. Keeps the house habitable, if perhaps not cozy.

Anyway, I burn the stove hot, hot, hot. I have to. Keeps the house sort of warm, and the chimney clean.

I don't use a full 25 ft. of stove pipe. I just vent into my brick chimney. It works fine. And, as I said, it seems to burn pretty clean.

Every once in a while, my non-stainless stove-pipe deteriorates beyond repair, and I have to replace it.

5 inch pipe some of it. Can't find it anymore. Stove pipe is very expensive now. Though I was able to get exactly what I needed by ordering from Lowe's, online. I ordered it. The price was OK. And it showed up in the mail in a few weeks.
View user's profile View All Posts By User
Mateo_swe
Hazard to Others
***




Posts: 219
Registered: 24-8-2019
Location: Within EU
Member Is Offline


[*] posted on 25-10-2020 at 10:21


Quote: Originally posted by pneumatician  
how to get the maximum heat of a wood stove?


Burn it!
If it was a iron stove it doesnt burn so well.. he he...

Sorry, feeling funny tonight.
If you want hotter you must increase the airflow but the wood fuel gets faster consumed.
Some reduce the air intake then the wood lasts long time, burning slowly all night instead of burning hot and then go out.
Some let the hot air go around in pipes a bit before letting it out the chimney, that makes it a lot warmer inside.
View user's profile View All Posts By User
pneumatician
National Hazard
****




Posts: 273
Registered: 27-5-2013
Location: Catalonia
Member Is Offline

Mood: Anar fent.

[*] posted on 10-1-2021 at 14:41


well in the market exist catalitic burners with 85% efficency, and with some "improvements" is possible to get +90% efficency...

https://www.motherearthnews.com/diy/high-efficiency-fireplac...

in one of this I see a guy with a stove very large auto build very nice and, I think, suoermega efficient, but I don't rebember the video exactly.

https://www.youtube.com/results?search_query=savage+hunters

[Edited on 10-1-2021 by pneumatician]
View user's profile View All Posts By User
Hey Buddy
Hazard to Self
**




Posts: 50
Registered: 3-11-2020
Member Is Offline


[*] posted on 28-1-2021 at 05:04


Three primary factors in generating heat from a wood stove:
1) fuel source energy density.
2) harvesting heat energy from fuel within living confinement.
3) preventing heat energy escape from living confinement.

All fuel is not equal. Some fuels provide energy at a magnitude of ten in volume when compared to other fuels @ higher energy density. Some fuel would release too much energy. Like thermite, for example.

Personally, I like hedge tree. Maclura Pomifera. Grows fast (relative) in most conditions. Very hot. Can melt metal if oxygenated. Serious Spark hazard in open fire.
8.8M btu/m^3
Other powerful fuel:
Bumelia aka wooly bucket aka chittamwood
Mountain "mahogany"
Both Hotter than hedge which is

To use the heat in a living area, it has to be harvested out of the cycling stream.
Most stoves are a pipe. Heated on one side, exhausted on other. The trick to heating is to harvest the heat by using it as a load.
Masonry is a simple way. Bricks/stone pull heat like a capacitor. The simplest way to make a load in a heating circuit is to just put masonry in contact with hot surfaces. More efficient is to pass exhaust stream into a masonry hollow chamber before exiting chimney path.
For measure of efficiency, exit gasses should be just over the minimum temp to prevent stack collapse/reverse flow, obviously hotter than ambient temp by a margin, but if exit gasses are really hot, heat is pouring out into atmosphere.

Then the heat just has to be kept in the space. That's a matter of confinement materials and the temp differential inside vs out. I can tell you that blocking/disrupting wind from working against building surfaces is paramount and overlooked. Ppl focus on insulation, trying to make a big cooler, what should be done is blocking wind access to building by heavy vegetation or walls.




20210128_061025.jpg - 1.4MB
View user's profile View All Posts By User
rockyit98
Hazard to Others
***




Posts: 234
Registered: 12-4-2019
Location: The Known Universe
Member Is Offline

Mood: no mood is a good mood

[*] posted on 28-1-2021 at 05:42


two words heat exchanger.aka condensing stove. that is, it even condenses water from the exhaust to pull the last bit of heat from it. also no risk of CO poisoning and can work with charcoal.



MMH- You sure this thing won't blow up?
Silas- it won't blow up. But I can't guarantee it won't implode.
View user's profile View All Posts By User
RogueRose
International Hazard
*****




Posts: 1564
Registered: 16-6-2014
Member Is Offline


[*] posted on 29-1-2021 at 01:03


Quote: Originally posted by pneumatician  
hi,

I want to maximize the heat of the stove, how? putting radiators in the stove body?

A stove body more large with the wood in the center?

How many heat is lost by the chimney??

Also, how to "neutralize" all the smoke passing it through water or other thing making innecessary the chimney? exist something like this on sale?


One of the best ways to get as much heat out of a wood stove is to concentrate on the quality of the wood - but this assumes that the stove is fairly efficient - if the stove is not efficient than that might be something you need to look into.

As for the wood, you need to know the type of wood such as family, genus or species - so you can tell the difference between oak, cherry, pine, maple, beech, birch, ash, etc. The reason for this is woods have a fairly wide range of energy content for the same size piece. The difference in energy is based on density & it is similar to burning methanol or diesel - a gallon of each has it's own BTU value with diesel having about 2x the energy/BTU's.

If you look at all the different woods, you will see all are pretty similar in BTU value per lb or kg. There are some woods that are actually 3x the density of others. More dense woods are often more desirable (and expensive if buying it) b/c you don't have to move, split, stack, carry as much wood to get the same heat.

Another factor which is extremely important is to burn wood that is as dry as possible. There are a lot of ways that you can dry wood, and I suggest you look into this and find out the best ways - don't settle for normal, traditional methods of drying if you are really looking at getting dry wood - there are some very interesting methods out there so do some digging! One method is to use a fan and draw air through a plastic wrapped stack of wood - this will even work well in the winter as the movement of air helps pull the moisture from the wood.


View user's profile View All Posts By User

  Go To Top