I don't know either.
An open fire is very inefficient though. A stove burns much hotter and cleaner, and more of the heat goes where you want (not up the chimney).
Installing a log burning stove in our house was one of the best investments we ever made. Besides heating the place, there are, as RT says, many other benefits.
The price of logs has gone up, though, in the last couple of years.
We've semi-seriously considered buying a bit of woodland so as to be self-sufficient in firewood. There isn't enough forest in Britain for us all to heat our houses that way, though.