Are we confusing Silver Maple with Red Maple (Swamp Maple) ??? They are both on the softer side of the Maple family, especially compared to Norway Maple or Sugar Maple. I think Silver is a little softer and grows faster/larger, and often has multiple trunks (if you will).
Silver Maple leaves have very distinctive deep teeth, Red Maple has relatively shallow teeth, and generally just turns Red in the fall. I have heated a lot with Red Maple, is is very abundant around here. Does not last as long as the harder Maples, but it will put out good heat, and has less drying time.