I had a friend who had a real bee in his bonnet about wood burning stoves. He wanted me to write a web page, and I wanted to validate the info first, some of what he had said was true, to burn without particular emissions the stove needs an after burn and the flue gases have to reach a set temperature, at least until wood is transformed into charcoal or coal into coke. To get to this temperature the unit has a very small window of output, so 4.5 kW to 5 kW in your case, and in real terms we normally want to run the unit likely 1 kW to 5 kW so only way is to have a back boiler which can remove the excess heat and store it for latter use.
The other was what type of wood, some people said mixture, some said hard, others softwood, so again looked into it, and all wood including coal which is only compressed wood has around the same calorific output per unit weight, however what controls the burn is volume on the fire bars not the weight, seen this problem with steam trains where trying to convert from log burner to coal burning, there needs to be a way to alter size of the fire box.
Clearly burning enough coal to pull 100 tons of steam train 8 miles if fire box not set correct it would cost a lot of money in wasted energy. With wood and coal burning stoves we look for a flue temperature of around 150°C, over and wasting heat, under and the flue can soot up and go on fire.
However if like me you light the fire once a year, does it really matter? If the fire is there for ambiance, when you have visitors to impress, then being set up spot on does not really matter, if however it is going to be regularly used, then needs to be set spot on. However this is for wood and coal, charcoal and coke is a very different story, the process ovens have already removed the nasties, but to burn charcoal or coke the fire still needs doors, and the whole idea is ambiance, and doors closed there is not so much ambiance. However there is not so much a problem with getting the chimney swept or varying the output.
I was brought up in a steel-working town, to make iron in a blast Furness it needs large lumps of coke, and the small stuff was sold off cheap to the workers, so we had all coke burning fires, and bunkers at rear of house to store it all, there was a minimum delivery, however once we had to pay full price, very quickly the coke burners came out and gas fires went in instead.
That friend of mine was right with one thing, unless you have a cheap supply of fuel, solid fuel is not cheap to use, the main problem is it causes draft, and you seem to have realised this and are fitting a burner which draws combustion air from outside, this was why most of the old fires were so bad, it is why we had high backed chairs to stop the draft.
However the price for a wood burner from B&Q is quite low, under £300, but it will not really comply with any regulations, but a condensing stove
with a plastic horizontal flue pipe, looking at a few £1000 pounds. OK that is not a normal stove but this one
is more a normal stove for every day use, note the water cooled jacket, which in turn needs a method to store and use the stored energy
now your looking at £10,000 to install, personally can't see how it would ever pay for its self, my brother-in-law had it in his last house, and yes it worked, a fire in evening was enough to keep house warm all day, plus heat from solar panels, but I just get oil delivered twice a year, the cost to install a proper multi fuel fire is just far too much.
Main point is what will the building inspector allow?
