The wood that gives off the highest BTU rating is called madrone wood. It gives off around 30 BTUs per cord.
Madrone wood is rated as having a high heat output, although it is not easy to split when dry. In order to get the full effect from madrone wood, it is important to make sure the wood is sufficiently seasoned and dried. Properly burned madrone wood does not give off heavy smoke, making it excellent for indoor wood-burning stoves and furnaces.
Other woods that produce high BTUs include white oak. Birch black, beech blue, birch grey, hard maple and hickory shagbark. Each of these types of wood has a BTU of over 25 per cord.