I usually burn about 4 cords of seasoned hybrid poplar a year in an airtight Quadrafire 5700 stove, burns cleanly with a moderate to generous amount of residual ash. The glass in my stove door stays cleaner with hybrid poplar than burning with other wood species. Pound for pound when dry, it releases about the same energy as other hardwoods, but since it usually has a dry density of about 23 lbs/cubic foot, it burns quickly. I usually don't split very small pieces.
Hybrid poplar is a cross between two types of poplar, for example known varieties of Populus Deltoides and Populus Nigra (a DxN cross) or Populus Tricocarpa and Populus Deltoides (a TxD cross), etc. Poplars have been hybridized for many decades and there are quite a few clones in existance which have a unique name like "15-29" or "op-367" etc.
Like native Poplars and Aspens, hybrid poplar can have a high moisture content when first cut. Where I am located, I let it dry for a year. I like it because the trees grow about 10' per year in height, unfertilized, and provide me an abundant source of fiber for firewood and utility grade sawtimber.