Hi David
 
there's a lot of useful threads on wood boilers here and on Green Building Forum. Can you post a drawing or picture of your existing system? Or decribe wht you have? We can then comment on how you might add / change it.

It's a very old Franco Belge wood-burning range with a back boiler, (under-)powering six radiators and providing HW with occasional assistance of an immersion heater.
 
I'm going to insulate the house to current standards (which includes replacing two concrete floors) and convert two outhouses into guest bedrooms with en-suites.
 
The total floor area (both floors) is 142 sq.m., and internal volume is a shade over 600 cubic metres (I'm assuming two air-changes/hour, which I know is a little high, but I'd rather have an over-sized system, than under-sized).
 
I'll be adding another nine radiators, and there will be a fall-back wood-burning stove in one of the rooms, just in case everything else fails.
 
I intend to replace it with a 25KW wood-gasifyng boiler which I will batch-burn to heat an accumulator to provide DHW via a coil and CH directly (I've been advised that 1500L is probably about the right size for that).
 
I may add a solar collector later, so I'll have a second coil fitted ready for that.
 
'Atmos' and 'Attack' both make gasifying boilers of about the right size, and perge supply reasonably priced accumulators, although if I can get a good price for an Akvaterm one, I'll probably go for that.
 
That's all I can think of, but I'm more than happy to answer any further questions.

Hi David
You seem to be well prepared. CAT do one or more booklets on wood fuelled heating which may be useful.
I have an Atmos DC25GS and Akva 2000L accumulator. The boiler comfortably heats the store so you could go for a larger one. I decided against a DHW coil because I put in a Gledhill solar cylinder. The thinking was that even in summer the accumulator was too large for the solar to heat so solar goes to the cylinder. But if you put in a big solar collector and smaller accumulator as you propose this could work for you. We have only 3m2 of tubes which will easily heat the 300L cylinder when the sun shines.

How about doing some insulating and draft sealing first?

Julian, thanks for the CAT recommendation, I'll take a look.
How are you getting on with the boiler?
From what you say, it seems I may have to go for a larger accumulator than I was originally planning, especially if I want to add solar later. I'm not sure I follow your point about the separate cylinder - my understanding was that if all the heat sources feed into the one accumulator they all contribute to it.
 
Tony, I'll be insulating everything, including the roof, to current building regs (or better, if it's not too expensive), and draught-proofing too, as well as fitting glass and wooden shutters so I can have, effectively, cheap and cheerful triple glazing.

Good for you
 
Much better than building regs will pay for itself over and over during the life of the building so the house can afford it even if you cant!
 
This should also allow you to use a smaller heat source. I have no boiler, rads, ufh etc and I live in the Thames Valley

Hi David
 
the boiler is largely good. It is hard work storing and processing the fuel, cleaning and de-ashing the boiler and loading and lighting it. But we couldn't have gas or oil (road too narrow) and even with the extensive refurb and insualting we have done we find still need some heating. 25kw heats the (2000L) accumulator very well so you could think about a larger store. However, the point I made about solar inputs is that ours was deemed too small to heat the accumulator in summer. That was what we had originally planned - with DHW on a coil in the accumulator and no hot water cylinder. This wouldn't have given us our hot water so we put in a 300L solar cylinder instead. There is a pumped circuit to the cylinder from the accumulator.
So if you have either a smaller accumulator (as you propose) or larger collector area than I have then it could work for you. If you can I would get some sound professional advice as to sizing the accumulator:solar area - or ask on here or on green building forum. With hindsight I would have put a coil in the accumulator and used it as a pre heat for the hot water cylinder.

Thanks for the information Julian. Sorry to keep bothering you with questions, but there's no substitute for actually being able to speak with someone who's got real life experience of something.
 
How long does a "typical burn" last? I've seen figures from four to ten hours for various boilers, and it's that which will determine how big an accumulator I will buy.
 
Also, how often do you need to light it? Again, figures I've seen vary, but typically people seem to light it once per day in winter (sometimes twice), and once every two or three days in summer.
 
How much ash does it generate?

Hi David
No problem - ask away. Happy if any of it helps. Have you looked at this (mammoth but useful) thread on GBF
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=660&page=1#Item_0
If you go to the search facility and put in 'gasification' there is a lot of stuff.
The burn is one of those how long is a piece of string questions. As you'll understand from your log burners, fuel quanlity, ambient temps and all else are factors. At present in this cool weather I light it at between 11.00am and 2.00pm. It burns about one filling plus a half filling added when first has burned down. That gets the store to 80 degrees by around 10.30pm, heats the house from when kids come home from school and heats the DHW if the sun didn't come out so it has more to do than if the accumulator isn't being used. In the coldest weather however, we had the heating on all day. The boiler was lit around 8.30-9.00am and ran all day, keeping the accumulator topped up to around 80 degrees and using about 2.5 fillings of logs. I have had a lot of people telling me that they burn as many logs on their wood burners in a day as go into the boiler. It really is efficient. So in all but the coldest weather a half day burn is the average. In summer it is not lit. The solar can easily get the 300L cylinder to 60-80 degrees top to bottom. This autumn was the first time the boiler was on and we went from lighting every four days, to every three, then two and finally every day. It is surprisingly easy to adjust but you need to forecast your demand a day ahead. For examle if you're going away for the weekend, you can burn the boiler the night before you go. That way it will give you heat the next morning with some left for when you get back. But it isn't gas or oil and sometimes - if you go away for several days for example - it doesn't get lit and you have insufficient heat stored away for you needs. Very, very little ash. A handful of small lumps of charcoal. You don't need to de ash avaery day and I gave it a good 30 minute hoover out last weekend for the first time in four months. Lighting routine is scrape off creosote with shaped poker (1 minute), sweep ash into burn off chamber (not every day if you choose not to but around a minute again) add paper, cardboard and kindling to fuel chamber and light (1 minute). When lit add fuel (2-3 minutes). If you add in five minutes that gives you some idea of what is involved. Getting a barrow full of logs takes the longest. Once it is lit it needs checking periodically but you could fairly safely then go off to work once you were sure of the two very simple thermostat setting positions. We are in E Devon W Dorset so if you're passing or local and want to have a look you're welcome. julian
PS Re store size - in some ways I wish I had oopted for the next size boiler up - think it is 34kw - as that would have meant shorter loading times i.e. shorter firings. But what we have is actually excellent for what we need. I was told to get the biggest accumulator we could so we went for 2000L then worried the boiler would not heat it. But is copes easily. In your case you'll need to feel sure that the solar:accumulator ratio will work to give you hot enough water.

---

Another thing to try David is the yougen website. This page shows biomass installers (equally you can search for solar or whatever else) who work nationally. There is a firm listed in the Scottish Borders (sorry...of course you're not local!) who do solar and solid fuel, and a firm in Peebles who work nationally. You can select to look for firms out of your area who will work in it. Getting them there might be another matter however but maybe worth a look.

Thanks Julian, I've read that GBF thread (I found it when I searched for Atmos initially) - it's actually what made me realise that I don't know as much as I need to, hence my post here.
 
The yougen site was very interesting, I've bookmarked it for later perusal.

Hi David
without seeing your existing it is difficult to know exactly what is needed. If you imagine the accumulator (store) acts in place of a traditional boiler to heat radiators etc. So where your current FB stove has a flow pipe from the back boiler to the rads, the store will have a top tapping to connect (via a circulator) to this pipe. It is important to have a mixing valve (eg Acaso Automix) add cooler return water into the flow so you don't have scalding hot radiators. The store will also have a lower tapping for the cooler return water. This will have a leg of pipe running up to the mixing valve on the flow. On the other side of the store (depending which store you choose) will be another high tapping which will take the boiler flow and a lower tapping for the cooled store water to return into the boiler. Another valve bridges these two (you may already have a loading valve eg laddomat) on you currrent set up. This recirculates the boiler flow until it is very hot and then slowly mixes in cold from the store. this keeps the combustion in the boiler hot, reducing creosote, helping efficiency and preserving the life of the boiler. I can email you some diagrams if you like.
julian

Thanks Julian,
 
I believe I understand your description; so I won't trouble you for a diagram, but thank you for the offer.
 
One "refinement" I haven't mentioned yet is that I'm considering using the current immersion tank, which I won't need, as a "pre-warmer" for the DHW. I really hate the idea of wasting the heat stored in bathwater, so I thought I'd feed it through the immersion tank (filling, and emptying from the top) with a coil inside through which incoming cold would feed before going into the DHW coil in the accumulator.
 
Not very easy logistically, so I'm not sure it'd be worth it.

David...going to the start of the thread i may be able to help on a couple of points.
I am a director for Eco Angus and speak as a supplier but hopefully you will find a couple of points informative.
Schematic drawing for installations....
I am not sure whether you are on an open vented ot pressurised system but please see;
http://www.ecoangus.co.uk/ecoangus_images/Heating_Systems/Principal_drawing_for_standard_AKVA_accumulator.pdf
 
This gives you all the possibilites on an open or closed system taking into account a back up gas or oil boiler/solar connection/UFH etc.
 
Julian gave an excellent response on the working of his Atmos boiler.
3 things i would add...the rated heat efficiency of the boiler,the volume of the loading chamber and the weight of the boiler vs kW output are important in your decision making process.
If these are higher for one 25kW boiler against another 25kW boiler then you will get a longer burn time and projected life cycle.
Heat dissipation of the tank is also important. Some tanks have better insulation than others so aid longer burn times as the boiler will spend a greater percentage of the time in wood burning rather than gasification (down burning) mode.
One point i would like to ask to Julian is cleaning of the heat exchanger tubes.
0.5mm pitch on the heat exhanges can reduce heat transfer by 30% form the combustion gases to the water jacket.
How ofter do you do this with the Atmos and do you have to rod them out with a brush.
This is important as this maintains the efficiency of the boiler along with burning wood of the right humidity (usually 15-20%).

Thanks for the information, I've actually looked at the Eco Angus site before.
 
One question I have for you directly, is this: I notice that you sell both gasifying and non-gasifying wood boilers.
 
I had been looking at a gasifying one, but non-gasifying ones are much cheaper, and seem comparable in terms of efficiency (for example, 83% vs 84%).
 
So I'm a little baffled as to why anyone would choose a gasifying one.

David
 
I am in much the same situation but may be a bit aahead of you in that I have found a number of useful local resources (installers etc). There seem to be a number of people in the borders who may be able to help . I am also not that far away in Dumfriesshire. If you want to contact me to talk about this further you can whisper me in the green building forum (I use the same user name) and I will send you backmy email and phone number.
 
Cheers
 
Jwd

I don't know if this may be useful to you but there is an alternative energy system quite new to my knowledge that runs on a perpetual motion system (so it creates free clean energy). I found the info recently. can tell you more if this is something you're interested in.

That would be useless --- even it did perpetual motion you wouldn't be able to take any energy out of it..
 
we call things like that "snake oil" and give them a wide berth.

Hi David
 
If you visit www.heatweb.com you can use all sorts of online tools and calculators which will help you produce an bespoke multi-fuel heating system.
 
Our advisors are also always happy to help - contact details are on the website. Although we're obviously biased our free online resource is second to none.
 
Good luck with your project!
 
The Heatweb Team

Hi jwd,
 
Sorry it's taken me so long to respond to your post, I'd stopped checking the forum.
 
Thanks very much for your kind offer - I'm having an attack of the stupids, and can't see how to whisper you, but I'm happy to post my e-mail address, and risk the spam, and I'd be grateful if you would contact me.
 
It's: david.robot.mitchell@googlemail.com
 
Thanks.

not possible to whisper hear.