The first decision is how much heat you want to generate. Whilst it’s tempting to purchase the largest that will fit in your room or burns the largest logs possible, you need to be realistic. Too small and it won’t heat your room enough, too large and you’ll overheat or need to limit the flow of air into the stove – burning fuel inefficiently.
Heat output is measured in kilo watts (kw). 1 kw is the equivalent of a one bar electric heater. A normal double radiator (e.g. 600mm x 900 mm) gives out about 1.5kw. An online calculator, e.g. This one: stovesandfires.com will give you a rough idea of what you may want given the size of the room you’ll be heating. An estimate in kw is (volume of the room in meters cubed) / 14.
Stoves are available ranging from roughly 3kw to 15kw.