Woodburners are usually bigger than multi-fuels because, er, people are expected to burn big bits of wood in them. Our multifuel has a grate about 14″ x 12″ but it doesn’t half knock out some heat. The best advice we were given when we bought ours was to err on the side of a smaller stove, which would mean that we’d be burning it a bit harder and hotter and the flue gases would be hotter and cleaner with less tarring of the flue and the inside of the stove. It’s all about combustion temperatures and oxygen.
On the other hand my cycling buddy has a woodburner and I have to admit that nothing looks more welcoming than the big window and a couple of logs glowing nicely on a bed of hot embers, fully seasoned wood gives off gorgeous irridescent flames that lick lazily around the grate. Wood gives off less heat than coal so you do need a bigger grate to achieve the same output.
My advice would be to find a good stove supplier (Milligans of Burnley if you’re in the NW) and ask then what to do. Maybe they can advise on fitting some bits of refractory lining to make the grate smaller, they will have all kinds of bits in stock for different stoves.
Alternatively flog the huge woodburner on Eblag (it will fly) and buy something compact and multi-fuel like our Dovre 500. Here:http://www.dovre.co.uk/html/woodburning-stove-500.html