Why is it that adding a volumetric heat source, in my case: a 2.067" diameter x 0.25" height cylinder set at 35 F in a 2" pipe, increases the total number of cells in the simulation by nearly an order of magnitude? I would understand some increase in cell count, but this seems like a lot.

Is there a way to reduce this increase in mesh density?

Without Heat SourceWith heat SourceRed circle = heat source