Could smoke odor be originating from the HVAC system of an adjacent townhome?
I'm not sure about the codes in your local, but to my knowledge it's not legal in my area for townhouses to share anything. With that in mind, your smell is most likely residual in your ducting. Even if your cleaner did a very good job cleaning it, there's probably still some soot hiding somewhere. 

If you have an actual furnace (gas, oil or electric) you could also have something hiding in the furnace that's being burnt. Inspect there when you have it manually shut off and see what's happening. If you're system uses a heat pump the. Noting should be getting hot enough to cause that. If it is has the gas pressures checked cause that could become dangerous.