Page 1 of 1

gasifying wood boiler

Posted: Thu Sep 26, 2013 10:48 pm
by johnh
not a DB question although i do use the tractor to process my fire wood...

anyway, i wonder if any of you lads and lasses are running a wood boiler with thermal store, in paricular the newish gasifying type wood boilers.
i am thinking of getting one to replace my oil boiler and it seems that it would be economical especially if i cut the wood myself. at the moment i only use about 1000 litres of oil a year and that seems lower than average from what i read on tinternet but at the same time it seems people with these boilers (although the majority of info is mostly from america) seem to burn cords and cords of wood.
from reading the energy websites it tells me that a m3 of decent hardwood should equal 150 litres of heating oil so that would mean about 6 m3 of wood should see me through the year. that would be great but i haven't found any case studies yet that are even close to that, more like 20m3 on average is usual.
should i believe the science or not? can anyone shed light on this for me?

much appreciated,


RE: gasifying wood boiler

Posted: Thu Sep 26, 2013 11:18 pm
by mart1602
i run a wood boiler,not a gasifying one if you burn softwood you need to check it every hour cos it eats wood,15-20ton through the winter at 35pound a ton un proccessed it a lot of work to save not a lot of soon as my stockpile has run out im putting in an oil boiler!aiso wood needs to be sesoned for a year and bone dry or you loose heat creating steam

RE: gasifying wood boiler

Posted: Fri Sep 27, 2013 8:45 am
by case-ih1594
Hi, as mart says, softwood will disappear at a fast rate, so it may be a false economy in terms of how long you spend adding wood (especially if it is a smaller stove). I've seen bonfires where pallets are bunt, and 30 mins later there is just a pile of nails remaining. Again as mentioned wood is meant to be seasoned for at least 9 months otherwise it is not as efficient and will tar up the chimney/flue. Chimney or flues also are meant to be swept every 6 months regardless. With respect I would not believe too much information from an American commercial energy website, I’m sceptical of many of these statistics, such as the benefits of solar panels/windmills, as when you speak to people who have had them installed they usually tell a different story. If there is an easy or low cost way to produce energy than someone will have got there first ! Wood is probably lower cost generally, but comes with the extra preparation/maintenance/messing about.

RE: gasifying wood boiler

Posted: Fri Sep 27, 2013 9:50 am
by erkki
Hi johnh,

As a premium fuel wood requires rather much work in several steps. If you dont mind all that extra work, its ok. I use oil burner boiler, which works fine but in order to reduce oil bill we are burning wood also, 5...10 cubic metres per year. The idea is that we have a rather large stove, made of bricks, indoors and it is kept warm the whole winter time. That requires a good fire on every second day. Because the heat of the stove is emitted mostly indoors the house, the oil burner starts not that often. I like the system because if we stay out of home for a holiday, the oil system works automatically and out place does not freeze meanwhile. Also in summertime when no energy is needed to warm the house, the oil boiler system supplies warm water. Heating by wood only requires tinkering with boiler also in summertime if warm water is needed.

RGDS erkki

RE: gasifying wood boiler

Posted: Fri Sep 27, 2013 9:44 pm
by johnh
i've got a rayburn cooker in the DAVID BROWN TRACTORS ARE THE BEST. and a woodstove at the other end of the house so i am used to processing wood, about 10m3 a year usually, and that's not a big problem for me, i leave the tree trunks to dry for a while and then it takes me about 45 minutes per m3 to cut, split, put in tonne bags and put in position under cover for further drying.

what i don;t know is whether the kw/h per cord vs. kw/h per litre of oil is at all reliable as a way to estimate the extra wood required to replace the oil. and with mart1602 saying he burns 20 tonne and would get an oil boiler in the future, well i'm really not sure anymore about this wood gasifyer....

RE: gasifying wood boiler

Posted: Sat Sep 28, 2013 7:48 am
by erkki
Specific energy for dry wood kWh/kg is almost independent if the wood is birch, pine or whatever. What is important is moisture because high water content eats the energy efficiently. Where I live the wood shall stay stacked on piles under a roof for two years before its perfect fuel. The households which use chipped wood in an automatized boiler quite often have a drying storage where on sunny days dry air is pushed through a special floor to the material. Commercial pellets are very dry with compared to any wood from outdoor staorage or dried chips. That is why rather high power can be achieved by them. Nowadays price level of pellets is becoming slightly high to make a decent pay-back time for an insvestment for an automatic pellet burner.

W.B-R erkki

gasifying wood boiler

Posted: Sat Sep 28, 2013 10:09 am
by manxmac
I have quite a large quantity of demolition timber from a builder who uses one of my barns. It consists of old construction timber 4x4, 6x4 etc and some new building timber off cuts it is barn stored and dry. My main problem is cutting this into useable 1ft lengths to fit my woodburner, Chain saws don't like the odd nail or bits of invisible metal, my reciprocating demolition saw will cut it but is quite slow. Some sort of wood guillotine would be ideal but I can't find anything apart from one from Browns which is too expensive. Any ideas?

RE: gasifying wood boiler

Posted: Sat Sep 28, 2013 11:52 pm
by johnh
manxmac maybe try some sort of hydraulic shear.

erkki, i don't mind if i need the very best oak as long as that equals 1 cord of wood per 450 litre of heating oil as the science says. if i got ash or acacia then ok, i'll burn 1.5 cord per 450 litres that's fine with me too. i just don;t want to be talking about 10 cords as that is a lot of wood....

RE: gasifying wood boiler

Posted: Sun Sep 29, 2013 7:58 pm
by dj
I've just learnt something new today. Hooray for Wikipedia.
I'd never heard of the term "cord" in relation to wood, but now I know that a cord of wood is (and I quote) a unit of measure of dry volume used in Canada and the United States to measure firewood and pulpwood. A cord is the amount of wood that, when "ranked and well stowed" (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of 128 cubic feet (3.62 m3). This corresponds to a well stacked woodpile 4 feet (122 cm) high, 8 feet (244 cm) long, and 4 feet (122 cm) deep; or any other arrangement of linear measurements that yields the same volume.

RE: gasifying wood boiler

Posted: Mon Sep 30, 2013 2:54 pm
by erkki
Hi johnh,

I think your calculation is correct. 1 kg of heating oil has 42.7 MJ energy
Absolutely dry wood has 19 MJ/kg, 10% moist has 16.7 MJ/kg, 20% moist has 14.5MJ/kg 30% moist has 12.3 MJ/kg and 40% moist about 10 MJ/kg.

One year outdoors storage under a roof gives moisture about 30 per cent. One more year can reduce it close to 20%. So if you have wood boiler and oil boiler with the same effeciency, you should be able to substitute 1000 kg oil by 3,5 tonnes wood. Practise has shown that oil boilers are very effective with compared to wood boilers, so as a rule of thumb a 10 cubic metres pile of good wood is required to do the duty of 1000 litres oil. So even by an old fashioned wood boiler 10 cords of good wood should be able to substitute 3500...4000 litres oil. I have seen that happen, no doubt. Modern technology may give better results, theoretically there should be plenty of potential.

RE: gasifying wood boiler

Posted: Mon Sep 30, 2013 11:34 pm
by johnh
these new gasifying wood boilers are designed to burn as hot as possible which gets the most from the wood. you 'batch burn' so that the boiler can be fired once a day whenever you like with all the energy being stored in the thermal store which can then be used when needed instead of only when the boiler is running. this method of burning always at full power which makes the wood 'gasify' leads to pretty good efficiencies, around 90%, or so i have read, which is as good as an oil boiler.

so, if the kwh conversion is correct i would only need 2 cords or 6m3 (over here a cord is only 3m3) or as you say erkki, 3.5 tonnes dry weight. that would be great.

how are you people heating by the way, and what sort of m3 / litres or whatever are you using.?

RE: gasifying wood boiler

Posted: Tue Oct 01, 2013 6:12 am
by erkki
Hi johnh,

If the boiler works as the manufacturer promises, 2 cords will be enough in your case. I would ask for a reference from the manufacturer, seeing a working installation and discussions with the opreraror often tell more than bochures.

W.B.R erkki

Posted: Tue Oct 01, 2013 6:28 am
by philedge
Hi John. If you already have wood heating capacity and a back up oil bolier, I would stay as you are. Whilst your current woodburning kit might not be efficient you give the impression that you've got a ready supply of wood so cost of wood supply is not too big a concern?

You've got fuel diversity so have a choice in how you heat depending on fuel availability and in current world climate the fuel market including wood is going to become more volatile and costly. Even if you have your own woodland and fuel is free there is still alot of graft involved in collecting and processing enough to heat with. Also consider if you were ill/injured how would the wood get processed and the house heated?

I dont know if your Rayburn or woodburner is integrated in your hot water or central heating, assuming you have CH, but I would look at integrating the wood heating into the hot water/CH system and maybe getting an efficient oil boiler, if your isnt.

Our setup is woodburner with back boiler heating hot water and CH and an LPG boier as an expensive back up. We also have top class solar panels that do just about all the hot water for 6 months of the year.

Www is a good place to get info on your original questions over gasification boilers.

Posted: Tue Oct 01, 2013 10:39 am
by johnh
i do have central heating run from the oil boiler which works well and means the house is warm when we get up but costs 1000 a year and we have it on as little as possible. the wood burners haven't been connected to any water heating set up as it gets a bit complicated with a mains pressure hot water system.
i could buy and have delivered 2 cords of hardwood, cut, split and pretty much ready to burn for around 300 euros but while i am fit enough i can buy it standing and cut it myself for 70 or 80 euros. if the wood boiler worked as planned i'd probably have it on a bit more than the oil boiler which would probably not increase the wood consumption at all as i wouldn't need to light the wood burners until later in the day/year.