Furnace Leaves Soot On My Walls

Furnace Leaves Soot On My Walls

When my furnace was working badly (the flue was clogged with soot, and only about a 2 inch diameter open), it got soot on the walls, especially where there were air currents and especially where the sheet rock was nailed to the wall in the big bedroom**

As suggested last year, I put cloves in the fire, but didn't smell any cloves coming out of the furnace. That is supposed to mean that the firebox is ok, a complete separation between the fire and the forced air.

So how did the soot get on the walls, especially where the hot air vents are in the walls or floor or ceiling?

Is the firebox breached even though I don't smell the cloves.

Furnace left soot on my walls