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Getting more from solid fuel

Presumably, having read this far you are reasonably persuaded by the merits of solid fuel appliances as a heating source for you home, workshop, premises etc. Or maybe you just like staring into a fire?

In terms of bang for buck not much beats a dry burner installation, and the majority of installations are just this. The next step is often seen as a wet installation, namely using a solid fuel burner to heat water either indirectly in a water storage cylinder to provide hot water or directly into a sealed central heating system to provide heat in multiple rooms.

Some manufacturers have the facility to have a boiler installed at a later date such as Aarrow and Villager but most are intended to be wet from the outset. The traditional way of linking a burner to central heating was via heat exchangers and heat store. The new way pioneered by Broseley allows the burner to be an secondary input into a combi boiler system with not much more than a low loss header (a custom made pipe with multiple inputs and outputs such as this one). At present I do not know if burners other than those supplied by Broseley can be connected to such a system, but cannot see why not.

There are two other methods of getting heat from a dry installation spread around the house.

  • Firstly a flue boiler such as that made by Charnwood, which is a wet system added to an existing flue pipe.

Charnwood flue boiler

  • Secondly there are convection burners.

Convection burners at their most basic pull in air around the firebox, warm it, convect it out a vent in the appliance. Burners such as Grey Metal's 'Cube' operate like this.

The next step up is an appliance with built in ports for hot air ducting pipes to be attached. Popular in France but rarely seen in the UK.

Hot air ducting for convection wood burner

A third option is a dry flue boiler not dissimilar to that made by Charnwood combined with dry ducting, another French innovation. Ducting has the advantage that a dry installer can complete the task and less involvement with Building control officers. However the Charnwood system probably has the edge as regards performance.

How hot air ducting systems work with flue boilers

 
Ways to get more from dry installations
1. Don't line the flue Unlined flues allow more heat to be conducted into the masonry providing more heat into the room above, too much heat loss can however cause the gases to condense and create the conditions for a chimney fire. When installers cite flue 'efficiency' as a reason for lining ask them exactly what they mean!
2. If you have exposed pipe work fit a Charnwood flue boiler Charnwood manufacture flue boilers with outputs up to 3.4kW. Charnwood claim that these boilers will provide enough heat to power 3 radiators or most domestic hot water requirements with minimal effect on the dry burner or chimney. From £300ish via Bradley Stoves near Horsham. www.charnwood.com
3. Hot air ducting Popular in France, I've struggled to find a UK supplier. Usually powered by a small electric motor 40-70W, often connected to an inset burner with three 'exhaust' ports. one for the flue gasses and the other two for cold air in and hot air out. Ducting is usually 5" (125mm) or 6" (150mm). Capable of having multiple ducts.
4. Burner fans Never used one myself and I can't decide if they are a gimmick or really rather clever but £100 seems to buy one. www.bhl.co.uk
5. Insulate Stop or slow heat transfer to unwanted places. Generally speaking around a solid fuel appliance use not just a non combustible but a flame retardant such as Rockwool or vermiculite. That said I have seen Rockwool singed by an inset appliance over many years use.
6. More energy dense fuels Mineral fuels routinely have kW per kg of over 8. Some smokeless fuels reach 9.16. If wood is your thing certain species of tree provide significantly better fuel than others, see this link. Eco logs have a kW per kg of near 14, a usual burn time is approximately 3 hours per log.
7. Sealed air intake Burley amongst other manufactures offer a room sealed air intake system for their burners, I don't understand how this makes burners more efficient, but it does and Burley currently hold the crown for the worlds most efficient solid fuel appliances.
8. Fit an efficient appliance Not wishing to sound like advert for Burley or Broseley but fitting an appliance with an efficiency over 80% puts you into the premier league of solid fuel appliances. See this link for more information.
9. Use dry fuel Wood at 0% moisture (kiln dried) wood gives 100% or close to of it calorific value in heat, when burnt. However at 20% moisture only 81% and at 50% moisture (green) as low as 62%. Similar figures apply to coal and anthracite. I sell moisture meters for measuring these figures.
10. Match the appliance to setting and use A few rules of thumb, inset appliances take longer to warm the rooms they are in but retain the heat for longer. Convection appliances generate heat faster. High mass burners can often take a long time to warm up due the mass of the appliance, steel generally has less mass than cast iron, the 12kW Firefox is notably slow to warm-up.
I appreciate that most of these options have to be considered at the moment of installation, and are difficult to retro fit