wood burners - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 01:37:35 pm
content: I know this is not strictly electrical (until someone raises the control system) but. As I cut down and shred a large tree I wonder about the practicalities of having a woodburner that feeds in pellets or shavings to burn. What really turns me off wood burners is that usually they are just furnace boxes that burn wood and like a regular fireplace still send most of the heat out of the flu. What I would propose is a burner that can feed in at the correct rate for the energy demand and be fanned by an electric fan that will push the exhaust through a heat exchanger that exchanges with air or water. Does such a device already exist ? are they stupid money or something worth considering.I grew up in italy where people used olive pip burning furnaces to heat their homes much like i am hoping to do although I have no idea how they did the heat exchanging and they were big units.

author: dr.diesel
author_rank: Super Contributor
timestamp: August 26, 2017, 01:43:29 pm
content: Those things are all over the place in rural US, commercial units run about $5k, but doesn't include the plumbing and installation costs. Most of the units here are an outdoor unit with a glycol system to carry the heat inside.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 01:58:52 pm
content: Ah right, so they are quite efficient ?

author: dr.diesel
author_rank: Super Contributor
timestamp: August 26, 2017, 02:12:53 pm
content: Not at all, for the most part. I've not read anything recently, but a typical non catalytic burner was somewhere in the 50% range, but varies depending on load. But also spews tons of particulate matter into the air, smoke like crazy.These things are regulated by the air inlet, when the inside gets warm and the burner gets choked off, they smoke/smolder even more, at a super low combustion efficiency point.They do make some fancier units, that once up to temp can burn the particulate/smoke in a catalytic chamber in the upper exhaust, but I've never seen one of those in action. Probably 3x the cost as well.

author: mib
author_rank: Contributor
timestamp: August 26, 2017, 02:54:50 pm
content: A typical wood burning stove should be roughly 75% efficient. 75% of the potential heat from the wood should end up heating your home.That sort of efficiency does require it to be installed and used correctly, something that many people fail to do.You can also get very efficient pellet boilers here in the UK that will burn any biomass that is cut into small enough pieces and appropriately dried. They are 2-3 times the price of an equivalent gas boiler - mostly due to the much smaller market. They are a little less efficient than a condensing gas boiler due extra losses in the fuel loading and ash removal systems. But they can be 85-90% efficient.The biggest problem with pellet burners is the physical size of the unit plus space for the fuel, which rules out their use in most homes here.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 03:47:38 pm
content: I see, well outside I have plenty of space and I shred any wood matter that I need to dispose of as I generally allow it to compost but I don't have the sort of supply that might make it worth while. I don't really see why they can't be made very efficient by simply passing the exhaust through a heat exchanger. This idea comes from an article i read about a guy that used an oil burner to generate electricity with peltier cells and then fed the exhaust through a radiator and effectively achieving near 100% heat recovery.I am currently cutting down a rather large apple tree hence my interest, again not worth getting a burner for but i wonder if there is a market for my shredded chippings.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 26, 2017, 03:54:15 pm
content: Quote from: Simon on August 26, 2017, 01:37:35 pmLike someone else said depends how there used and installed, I am lucky that my flue runs up the middle of the house and also passes one side of the airing cupboard so heating the brickwork is very useful. I inherited the burner 13 years ago and immediately knew something was wrong as it had no internal baffles meaning as you say most of the heat went up the flue. I made some heavy gauge baffles to force it into a serpentine path and now so much better. Proper control of the top vs bottom air also works wondersMy only wish is that it had a back boiler but cannot have everything

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:12:04 pm
content: To be honest I can't see anything not passing the exhaust through a proper heat exchanger as efficient. It is just a fact that most heat is carried away by the fumes so you have to recover it from there.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 26, 2017, 04:21:15 pm
content: Your right but I didn't want to restructure my building and I would be very concerned about tar buildup, as the gasses cool then tars in the wood condense so your heat ex changer efficiency may well drop off rather rapidly, however I am sure someone has done it. I guess it also depends what you want to burn, in my case it's multi-fuel meaning anything I can get for free

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:23:47 pm
content: yes that is true I suppose hence chimney's need cleaning. Maybe there is a way of burning the tar off by injecting some sort of liquid and highly flammable fuel.... kind of reminds me of the soot burning off that diesel cars do (or are supposed to in the case of VW)

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 26, 2017, 04:31:28 pm
content: Burning the tar off (aka chimney fire) is what happens here when city dwellers light the woodburners in an old house for the first time, they seem to think the more it roars the better then cannot understand why it roars and roars without any wood!! Many fine thatches have been lost that way too

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:41:32 pm
content: Well clearly not something I should go dabbling in, if anyone is interested in some of the finest apple chip fuel let me know, I'll be storing it up nice and dry and hoping to shift it to someone that can use it as it will be too much for me to compost and the council aint having it.

author: Ian.M
author_rank: Super Contributor
timestamp: August 26, 2017, 05:03:25 pm
content: It looks like good clean dry apple wood chips go for about £10/Kg for barbecuing and home smoking.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 05:13:31 pm
content: Wow, I've cut down a gold mine . Do you think it has to be leaf free or does that add to the taste? I once sold a small quantity of apple for 40 quid I think I know why now....Sent from my Moto G (4) using Tapatalk

author: mib
author_rank: Contributor
timestamp: August 26, 2017, 05:35:15 pm
content: You'll be disappointed in the value of your prunings...I have a large garden, and I do maintenance on a number of neighbour's equally large gardens. I can easily produce 20+ cubic metres of shreddings over the next few months. So I made some serious queries about whether they had any value. The simple answer is my idea of a large quantity is industries idea of too little to bother with.If you can provide 10 cubic metres or more of green waste all at once then you'll probably be able to find a local company that will take it away for free (actually they'll usually pay you a token £1 for it or something like that so it's not taxed as waste). That's probably the best you'll find. They only start paying when you can provide 100s of cubic meters on a regular basis.If you're cutting down an apple tree then the wood does have value. Larger pieces can be sold to wood turners as long as they aren't rotten in the centre, which is rare with an old tree. Failing that any bits larger than 2" diameter cut into 8" lengths are worth £20-£30 per cubic meter as firewood. You can at least double that by storing it in a dry place for a couple of years and selling it as seasoned firewood.To sell it as chips for smoking you'd need start with the bigger bits, remove all the bark, leaves etc, then kiln dry it and chip it - you're not going to make any money doing that on a small scale.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 05:41:39 pm
content: Oh so I won't be buying solar panels on what I make out of the tree .yes there will be some nice size pieces for wood work but no I'm not going to that effort for the chippings.Sent from my Moto G (4) using Tapatalk

author: Ian.M
author_rank: Super Contributor
timestamp: August 26, 2017, 06:17:58 pm
content: If you are keeping the wood for turning, you need to dip the ends in melted paraffin wax to prevent rapid moisture loss causing cracking. For the rest of it firewood sounds like the best option.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 06:25:54 pm
content: ok, is paraffin wax readily available, there will be a few nice pieces and the trunk is really thick, the house was built in 1947, I am guessing the land was an orchard and this is one, or the only remaining tree, would be nice for it to be turned into something nice (pun intended?) instead of just going for firewood. The small branches bub 30mm will be shredded, still good as fuel and too much to compost so will see if anyone wants it for burning.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 26, 2017, 07:34:04 pm
content: I didn't see this thread until now. I happen to have a wood burner for "auxiliary" heat in my home. It is an outdoor version.The burning unit itself is a large double walled boiler. Fire is in the inner chamber and that heats water (400 to 500 gallons) in the supply between the two walls. The water in the outside boiler is at atmospheric pressure, and the burner operates at somewhat reduced oxygen.A circulating pump brings the water to the house. There is a neat little heat exchanger in the house that heats the water used for domestic heat. If the wood burner is off, domestic heat is provided by a propane boiler. It is probably a bad idea to use a single water supply. I have not seen that done.Efficiency is of little concern as the fuel is waste wood and would probably be burned in a pit outside just to get rid of it. No non-commercial individual I know actually buys the wood used. He have a real surplus of dead ash at present.The circulator motors are quite small, usually 1/25 hp to 1/4 depending on the BTU. My propane house furnace is 100,005 BTU and uses a 1/25 hp circulator. The circulator to the wood burner is 1/4 hp, but the pipe is larger (1-1/4") and the distance and water volume greater.A medium size home will go though several cords of wood in a Winter, so wood from a single tree would hardly make a dent. Maintenance is minimal, except the larger circulator pumps are expensive when they need to be replaced.As mentioned, they are quite popular in rural areas that otherwise depend on propane for heat. One downside it that the propane dealers are allowed to charge more, if you have a wood burner. That additional charge is in the form of disallowing certain discounts. Nevertheless, a home that might take $2000 to $3000 to heat all season, will get by with less than $500 in propane. A neighbor says his propane bill is only $100.The other downside is the need to add wood on some miserable days.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 07:45:57 pm
content: In italy they burn olive stones that are available by the sack after the olive pressing season ends. they are usually installed in a cellar of rural houses (mains gas has arrived to most places). they have a big funnel shaped tank with an endless screw in the bottom so you can fuel up for an amount of time and leave it running like any other boiler.I know what you mean about oh it's only scrap wood who cares about efficiency but meh, people in the UK think that installing wood burners is being green but ultimately they amount to boxes with pipes out the back and up the chimney, they are slightly easier than a fire and in my opinion just as inefficient, if we all installed them in the UK how would we fuel them all sustainably?

author: G7PSK
author_rank: Super Contributor
timestamp: September 03, 2017, 05:13:29 pm
content: https://www.stovesonline.co.uk/wood_burning_stoves/Pellet-stoves.htmlEasily available in the UK complete with subsidies.

author: Towger
author_rank: Super Contributor
timestamp: September 03, 2017, 05:57:59 pm
content: It is better in Northern Ireland where there are big subsidiaries. People with empty warehouses heat then just to claim the subsidiary. Google Ash for Cash for details.

author: Simon
author_rank: Unknown
timestamp: September 03, 2017, 06:06:45 pm
content: Quote from: G7PSK on September 03, 2017, 05:13:29 pmOh god not another solar FIT scam ? I'd struggle o fuel one really where I m so probably not worth it.

author: Delta
author_rank: Super Contributor
timestamp: September 03, 2017, 06:23:13 pm
content: A wood burning stove is nearly an order of magnitude more efficient at heating a room than an open fire. Do not be deceived by the simplicity and old fashioned-ness.I assume you are using renewable energy to power your garden shredder of course...

author: Simon
author_rank: Unknown
timestamp: September 03, 2017, 06:39:00 pm
content: Oh I assume they are very good, but I don't have a consistent supply of fuel and frankly the idea that using these is classed as renewable is ridiculous, yes renewable is a few thousand people lived in the UK, not a few million, when we gobble up everything we have what do we burn then ?Well when my powervault arrives I could be running my shredder off 50% solar, maybe 100% if i do it when the sun is out so I have 1.6KW from a powervault and 1KW from my solar but that would take some timing and weather.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: September 03, 2017, 07:23:26 pm
content: I have been really interested in the homestead scale pellet mills, feed in all the chips off your land, get feedable pellets out. In some areas it is sustainable, a couple acres in a temperate area produces a LOT of manageable fuels.http://www.ebay.com/itm/like/182286174995?chn=ps&dispItem=1

author: Simon
author_rank: Unknown
timestamp: September 03, 2017, 07:30:04 pm
content: so a couple of acres per household ? the UK has i think 65m people, assume 4 per home, thats just over 15m households or 30m acres required, there are 640 acres in 1 square mile, so that is nearly 47'000 miles, or an area of about 220x220 miles, hm that's a decent chunk of UK land me thinks. we cant grow our own food and have to import it already.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: September 03, 2017, 08:27:37 pm
content: Population density is one of our more obvious challenges globally. Largish chunks of the rural US have low density and high rates of biomass production.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: September 03, 2017, 09:10:39 pm
content: Here in Germany, modern wood fueled (wood chips, pellets) heating systems are outfitted with so called "Brennwerttechnik" that might translate to "condensing boiler technology". These systems are available from around 4kW to 20kW thermal output as stand-alone units and the condensing boiler recovers most of the heat from the exhaust gases. The final exhaust temperature is around 30-40°C.I am not too deep into the matter myself, but maybe this gives you some interesting pointers

author: tautech
author_rank: Super Contributor
timestamp: September 03, 2017, 09:57:25 pm
content: Quote from: Simon on August 26, 2017, 04:23:47 pmThere's ways to manage chimney tar build up, an old wives tale is to burn your egg shells in the fire but of course your choice of fuel has the greatest effect on chimney build ups.How you manage your fire can help, it's a good idea if you know the state of your chimney is to let her roar for short periods from time to time. AFAIK there's no other ways to keep them clean other than getting them swept on a regular basis. We run a small kitchen log fire continuously (~11 KW) with a wetback for ~4 months of the winter and the wood we mainly use is quite tarry so ongoing management of flue deposits is needed. This winter (nearly over) has been good, we've had more of a mix in the shed than normal but the flue will still need some decoking come summer.

author: eas
author_rank: Frequent Contributor
timestamp: September 12, 2017, 06:04:38 pm
content: When we bought our house, we had a chimney sweep come to clean the chimney and check it for safety. When he was done, he handed me a singled sided xeroxed page from a chimney sweep industry magazine that explained how to build the cleanest burning fire practical in a traditional fireplace.It's simple, and it works. Rather than piling up your logs, putting the kindling and tinder below, and igniting them, you invert the arrangement. The principle is to have the hottest part of the fire at the top, so the hydrocarbons in the smoke are hot enough to combust fully. Radiant heat from the fire on top is enough to start decomposing the unburned wood below. A bottom up fire is great for making lots of smoke, by getting the wood on top hot enough to smoke, but not hot enough to burn well. The inverted fire isn't smokeless, but it is dramatically cleaner. Inverted fire arrangements also works well in an outdoor firepit.The disadvantage is that its difficult to refuel and still maintain the clean burn. What I usually do is push any embers and partially burned wood to the side, put new logs on the bottom, and then shovel/move the remains of the old fire to the top of the pile.Traditional open hearth fireplaces are horribly inefficient on three fronts: they don't burn the fuel efficiently, they don't recover heat from the fire efficiently and because they draw heated indoor air for combustion, and then a lot more of it in order to ensure a good strong draught. There is an old design called the Rumford that improves things, by, in part, reducing the amount of air pulled from the house to maintain a strong draught in the chimney. A glass door and an inlet for air from the outside reduces the heat pulled from the house further. Adding a heat exchanger improves heat recovery. Some people have built "dragon stoves" that are good enough at recovering heat that condensation and poor draught become a problem (much like an ultra-high efficiency gas furnace.As for the rant about heating with wood not being "sustainable," or "renewable" the answer is simple: Language involves ambiguity, particularly when a single word substitutes for a much larger concept. Assuming that everyone else shares your definition is not wise. As is often the case, the robustness principle (aka Postel's Law) applies: "Be conservative in what you send, be liberal in what you accept."To that end, in this context I'll suggest that for something to be "sustainable" or "renewable" it doesn't have to scale to support everyone in the world (or in a country), the status quo alternative certainly doesn't. In my urban neighborhood of mostly single-family detached homes, some people heat with kerosene, others with vegetable oil, others with heat pumps powered by electricity (mostly hydro, though our utility also uses as much wind as it can, and a lot of people have added PV solar) others with resistive electrical heat, and a few, with wood.Don't get me wrong, I hate how insufferably smug and clueless some people can be once they start using some renewable energy that can't possibly scale to meet a significant portion of energy demand (like biodiesel made from food waste).Still, its clear to me that burning wood or other biomass is viable enough in some regions as to be economically sustainable as well. I think most often, the feedstock are byproducts of other industries, primarily sawdust and wood scraps from lumber mills. On a small scale, people practice "coppicing" to improve sustainable yields from wood lots.

author: Simon
author_rank: Unknown
timestamp: September 12, 2017, 06:34:21 pm
content: I am afraid that the only efficient chimney is a blocked up and unused one. I can't see how you can make a chimney more efficient unless you manage the exchange of heat with modern heat exchangers and ensure proper airing that does not take hot air back out of the room, put the wood on in any order you like, the vast amount of heat will still be going up the chimney. Yes your separate air intake is a good idea.Indeed some methods will work well for some people but it sounds like woodburners are being pushed by my government with financial incentives, when clearly it is not suitable for wide scale deployment. We don't have the level of agriculture in this country to fuel these things on any reasonable scale and they won't make a big difference to our CO2 output so why is the government incentivizes them? it's clearly for the smug middle classes that can afford the investment up front and will then smugly claim their rebate while telling the poor people that they just need to work harder. We went through the same farce with the solar feed in tariff that see those who could afford the investment earning 4 times the rate that electricity is actually worth. Muggins is running solar on the cheap and not making a penny but doing it because it is the right thing to do.I'm sure larger countries like america with a much lower population density can grow the biofuel they need and in that situation the wood/pellet burner makes sense, but in the UK for us all to run these systems we would cut down every tree quite quickly.

author: Zero999
author_rank: Super Contributor
timestamp: December 24, 2017, 06:10:12 pm
content: Old thread but interesting, so I thought I'd bump it.There's been talk of tighter regulation of wood burners in the UK, as they emit more dangerous fumes than diesel and engines. Burning wood emits, various toxic and carcinogenic compounds, including: benzene, formaldehyde, acrolein and polycyclic aromatic hydrocarbons.https://www.epa.gov/burnwise/wood-smoke-and-your-health

author: WastelandTek
author_rank: Frequent Contributor
timestamp: December 24, 2017, 10:08:26 pm
content: Quote from: Hero999 on December 24, 2017, 06:10:12 pmModern catalytic stoves burn very clean, but what we really need is fewer homo sapiens.

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2017, 01:58:46 pm
content: Quote from: WastelandTek on December 24, 2017, 10:08:26 pmI didn't know about catalytic stoves. They sound expensive. I thought the cleanest wood burning technology was gasifier. The wood is first superheated and emits gasses, which are burned very cleanly. No expensive catalysts are needed.The trouble is in the UK, people tend to get crappy wood burners, which kick out all kind of crap.

author: Simon
author_rank: Unknown
timestamp: December 26, 2017, 02:38:01 pm
content: a wood burner simply being a fireplace in a box

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2017, 06:56:24 pm
content: Quote from: Simon on December 26, 2017, 02:38:01 pmThat's the usual design, which is very inefficient.Better, more efficient designs exist.http://www.appropedia.org/Wood_gasification_stove

author: Delta
author_rank: Super Contributor
timestamp: December 26, 2017, 09:02:30 pm
content: Quote from: Simon on December 26, 2017, 02:38:01 pmYou are being very dismissive of a proven and very mature technology. Wood burning stoves as significantly more efficient at heating a room than an open fire.Don't be such a technology snob!

author: Tomorokoshi
author_rank: Super Contributor
timestamp: December 27, 2017, 06:53:16 am
content: I've dabbled a bit with burning wood and pellet fuels. Here is my view of it:Traditional fireplaceThese are neutral at best for getting heat into the house. Negative with the door open and in colder weather.Fireplace with woodburning insertThe range of inserts is fairly large. A good insert will restrict overall airflow through the firebox and otherwise limit leakage flow through the chimney. Pretty much requires a convection fan to circulate air around the firebox. Possible to heat a house with it. Need central air recirculation venting for best distribution. This will dry out the house. 4 cords of wood per year is possible in colder areas when used most of the time. It's a lot of work.Woodburning stove (potbelly stove)On par with the efficiency of a woodburning insert if constructed properly. Heating is radiant only due to lack of convection fan.Pellet stoveRequires electrical power for basic functionality. Efficiency can be quite high. This is offset by increased fuel cost. Mechanical and electrical maintenance can also offset efficiency gains. Some are able to burn other fuels such as corn, be tuned to burn grass pellets, etc.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 27, 2017, 08:55:02 am
content: I heard of a unique approach to improving wood burning efficiency. Step one change you home address to a postal box for all important mail. Next answer all junk mail with interest saying you like their product and you want to make an order as soon as you have their literature , especially those high BTU magazines. With the fuel being delivered to your door step for free who cares what the wood burning efficiency is ?

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 02, 2018, 01:00:48 am
content: http://www.mha-net.org/visit-with-peter-van-den-berg/http://donkey32.proboards.com/

author: ikrase
author_rank: Regular Contributor
timestamp: January 02, 2018, 04:17:40 am
content: Among the sorta crunchy / wilderness-farm-homestead community, a popular scheme is something called a "rocket mass heater". It starts with a "rocket stove" in which the fire is made to burn sideways, and convection draws the flames upward into the stove, developing a high enough temperature to burn up all the creosote (and also to annihilate any but the very best refractory material). Sounds like a jet taking off.In the rocket mass heater, the flue gasses are then piped horizontally through a large heat storage mass -- traditionally this is adobe masonry in the shape of a bench, but can also be water or something. Alternatively the mass is sometimes used to store heat for hot water, with the actual output water going through a heat exchanger.No moving parts, and usually uses small sticks and kindling but people have made them pellet-fueled. With a combination of a servo-controlled air damper, a way to dispense chips/pellets, and a blower to get the fire going sideways, I can imagine you might pull something off.(Edit: I see the previous poster mentioned rocket stoves)

author: james_s
author_rank: Super Contributor
timestamp: January 04, 2018, 06:42:53 am
content: A guy I know in England built a woodburning boiler that uses a small firebox with a forced air induction fan. It burns a relatively small fire at high temperature, resulting in relatively complete and clean combustion, heating a large water jacket around the unit. The water is circulated through radiators to heat the house. Additionally there's a conventional gas fired boiler connected to the system so it isn't necessary to fire the wood boiler all the time, it's a supplementary heat source that can be loaded with scrap fuel whenever it is available.

author: f4eru
author_rank: Super Contributor
timestamp: January 13, 2018, 07:07:07 pm
content: Hello,Wood burning can be very efficient, with wood gasification, and a second flame.I have a water heating stove like this one :http://www.kuenzel.de/produkte/kamin-holzvergaserkessel-hv-w/It's very efficient, about 92% efficiency, and it burns very very clean, because it's always at full power, so it doesn't smolder, and emits less particles and NOx70-80% of the heat goes into the water side, so it dosn't heat up the room too much.Also, it's combined with a 1500 liter water storage, so it can run full power for many hours, and we get heat for two days.Some wood burners are even more efficient, up to 115% with condensation(And just to clarify, no, it's not overunity, it's just that it condenses water back in the exaust, and gets the latent vaporisation heat, which is not counted into the normal wood burning efficiency)Conclusion : get a modern wood burning system, with good efficiency, and always use it at full power.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: January 13, 2018, 08:35:38 pm
content: Quote from: f4eru on January 13, 2018, 07:07:07 pmthanks for the link, that looks great!I wish they had translated versions of their site...no spreken

author: f4eru
author_rank: Super Contributor
timestamp: January 14, 2018, 08:36:44 am
content: Yes, Künzel does not seem interested in selling outside the german speaking zone.I got one in France though.Just for info, Germany is at top of technology for efficient wood burners, because the law mandates clean burning, even old ones have to be retrofitted now.