Hackberry is a great firewood and is comparable to oak firewood however I can easily get more Hackberry firewood easier than I can oak firewood so while it's not exactly the same as in BTU ratings for heat output Hackberry does make a great Firewood if you can get plenty of it.
Just be sure that you let the Hackberry firewood dry and season for at minimum of 6 months and it'll burn okay but I find if I let the Hackberry or any other firewood dry and season for a full year then I get more heat output from firewood and it burns much better and is easier to get lit.