How does wood compare to coal in terms of home heating efficiency?
A quick search yielded this:
http://www.reddit.com/r/Banished/comments/20b7gi/firewood_vs_coal_heating_some_numbers_or_wtf/
The essence of the post there is that there is no difference between coal and firewood heating, except coal being harder to obtain, of course.
Keep in mind that this was 4 months ago.