Winter Sumac

Received an offer for 6-8 small "trees". I accepted but when I checked them out, two of them were Sumac(fruit cones on tips). Since there were no leaves and snow on ground so couldn't see any leave signs at all, How would I be able to tell if it was poison Sumac?
I'm not interested in it for heating since I learned that Sumac is pretty lame in the BTU department. In fact I threw it over the bank. But for knowledge purposes I'd like to know how to identify if no leaves are available. When cut the sap did turn blackish but from what I read there is also another species that will do the same thing. Any tell tale signs to know it's poison without leaves? I am pretty sure it was OK because it was not a wet area but not willing to take the chance for a low BTU output.
On a positive note, the other 5 trees were small cherry trees(I'll be confirming this with pictures in a few days) so it was not a waste of time.

Poison Sumac does not have upright clusters of red berries, instead it has hanging clusters of white berries. Staghorn Sumac is common and has big red clumps of hairy berries and hairy twigs. Smooth Sumac is similar to Staghorn Sumac but the clumps of berries are less dense and the branches are smooth.

Poison Sumac is pretty rare and generally found only in swamps. I am interested in plants, can ID most of what I see, and get out in the woods a lot but I have never seen Poison Sumac, which indicates how rare it is. Of course there is somebody somewhere that has it growing like a weed in the backyard, but in general it is rare.

The 5 cherry trees will make a nice stack & make it worth while.
Have never seen a sumac big enough to cut into firewood. Like you said , not much heat value there anyway.

I agree with Dave on those cherry. I also have never seen sumac big enough to want to burn in a stove. Have cut some for the brush pile though.

Wood Duck, Thanks for the lesson. Staghorn sounds right. The twigs were hairy and had upright clusters of red berries. The main trunk was about 8". Not big but from what you guys are saying, that must be big for a sumac.