I recently moved into an older house with a natural gas-burning forced hot air furnace. There are no records of the ducts being cleaned, and based on the layer of black grime I can see, they are quite dirty.
It seems that having the ducts cleaned would increase the efficiency of my system (by improving airflow), but is this true? If so, what is the impact?
I assume that hiring someone to clean the ducts would cost at a minimum $200. My monthly heating bill is about $70.