have you looked at :

http://www.oilstoves.co.uk/shopdetail.php?AP-THERM-200

http://www.beacon-stoves.co.uk/tile/interview.shtml

http://gloucestershirestovecentre.co.uk/stovecentre/index.php?page=shop.browse&category_id=11&option=com_virtuemart&Itemid=2&vmcchk=1

http://www.ecoenergydepot.co.uk/product_info.php?products_id=32&osCsid=15501d55218f28e6aa8b4a1fde35fe44

milo

AndyinHawick:

Not sure where you heard about wood burning balanced flue. The only references I could find were for gas stoves. Once I found out what was meant by balanced flue, however, I don't see why it wouldn't work with wood also. It may, however, lead to more soot and creosote build up in the pipe due to the extra cooling effect. I suppose if a catalitic converter were fitted to the stove or the stove had one built in already then you'd be alright.

You probably already know about Clearview, but here's one that can be fitted with a balanced flue.

http://www.clearviewstoves.com/pioneer400.htm

According to this manufacturer (UK) a balanced flue may extend 4 M horizontally, or 10 M vertically. You should check your local building and safety codes, however.

http://www.drugasar.co.uk/balanced_flue_system.htm

Here are some wood burners that can be fitted with an external air supply.

http://www.fireplaces-oldham.co.uk/Barbas_Woodburning_Fires.htm

You probably won't find many wood burners using a coaxial flue/air-supply, because wood smoke leaves deposits of creosote that interfere with free breathing.

This company offers several wood burners that are "approved under EC 13240 specifications".

http://www.sussexwoodstoves.co.uk/stoves.htm

I lived with wood heat in western Oregon forty years ago. It was dirty and smelly, but cheap, since our fuel was waste wood from a local sawmill. Good luck finding a better solution!

I see that DRU is well supplied with hubris...

"DRU engineers from the Netherlands invented the (balanced flu) system in the 1930s."

such counter current heat exchangers have been used on furnaces since the 1880's in many industries. Marketing and design leads to such lies

Creosote(condensed tars from the destructive distillation of wood) buildup would be an even worse problem with wood in a balance flu system. The logical way to deal with creosote is to have a periodic creosote burn-off by using inside air. This would use the outer flu/inner flu air space as an insulator to get fast heat buildup to burn the creosote. All such exhausts need to be made to tolerate the high remperature (stainless comes to mind) and to be well and permanently sealed because melted creosote can run like water and catches fire like gasoline if it should exit the flu into the room

Thanks for all those excellent links. I'm not convinced that the Drugasar balanced flue system extends to their wood-burning stoves, the page is entitled "balanced flue gas fires" and these are standard enough.

The problem with tar/creosote build-up in the flue is significant but the secondary air that most of these stoves introduce to the flames above the fuel is intended to burn off that (and any CO produced) but the regulations seem to insist on a much more robust flue for solid fuel ... unless there's exemptions for certain, well-designed systems.

There's also talk of boilers reducing the temperature and quality of the burn. This need not be the case if the the boiler is heated by the flue gasses and not in contact with the burn area itself. A decent control system with adjustable vents and variable-speed pumps and fans should be able to control the burn thoroughly enough to ensure complete combustion and maximum heat flow to the water and maximum extraction of heat from the flue gasses ... but does anyone make such a unit yet?

The technology has come along nicely in recent years and the pressure is building for nicer units that people can use instead of open fires or gas or electric heaters. What we need is a bit more inter-disciplinary involvement to add a robust, fail-safe control system to an enclosed stove to get the best out of it and reduce the downsides. Burning hot enough gives a very clean flue output but that needs to be thoroughly cooled before it exits so as to get the most heat out of it.

There's certainly some nice units around and it's helped me trim my spec'. I'm looking for an 'inset' or 'insert' type, about 4-10kW, with boiler and balanced flue of 3m horizontal length (with up to 2m vertical within that if necessary).

Does anyone have experience of similar units?

Hi Andy, Look at this one http://www.gflame.co.uk/products.htm This system is one of the few I know of with a powered flue - it's not a balanced flue as you are looking for but maybe good enough for what you want. The problem of the exhaust is more of an issue usually than the combustion air needed. So long as you don't have a sealed room for your boiler room you are OK. The additional benefit with this boiler is that they make a dual furnace model that burns logs and/or wood pellets. Not sure if you have wood pellets in the Borders but first plant in Scotland is not far from me at http://www.hotstovies.com/index.html . Keith will charge you £130/tonne bag or you can buy in small 15 kg plastic bags. Seems that with oil cost now fuel cost using pellets is between 35% and 50% compared to using oil. My friend in Sweden has a log only c/h boiler which he has just installed - it's incredibly efficient and also has a powered flue but I guess you know how these need to be used - you need about 3 tonnes storage capacity of hot water and a fairly sophisticated control system. Have that and only light the boiler once a day in winter with a single fill and you are done. I will go for the dual pellet/log one - been waiting for years for that system to be available! By the way I see no problem now with pellet availability here - plenty guys building pellet plants as we speak so no worries about supplies in future

Andy - another thing - you really don't want incoming cold air cooling your hot outgoing exhaust and thus condensing any unburnt tars within the exhaust tube so from a design perspective I would steer clear of a true balanced flue as we know them for gas fires.

Alf

Thanks for your good link. I know Kingcraig somewhat from holidays there in my youth; it's good to know that they're producing efficient solid fuel boilers there now!

My preference would be to burn off all the tar and extract the calorific value from it before it ever gets to the flue. Even the soot should get burnt to CO₂ before leaving the combustion chamber. I see that some of the Green Flame units have automatic heat-exchanger cleaning, which I presume ensures that any deposits get burnt off from time to time. I see that they're using an oxygen sensor to monitor the thoroughness of the combustion.

Cooling the exhaust gasses shouldn't result in any condensate other than water and perhaps some inorganic compounds from sulphurous and other impurities. Forced ventilation will be a necessity.

I can see that my desire for an open fire or stove that is highly efficient, contains a boiler and is 'inset' wall mounted is still a while away. I'm not yet ready to instal it, so that's OK. Maybe in five years time they'll be available on the market.