By ignoring your air ducts you are doing everything but saving your money. The thing with air duct maintenance is that quite often people associate it with elevated costs made during various air duct cleaning and air duct sanitizing procedures. Most of the time people tend to neglect the fact how these procedures definitely do not fall under the category of overpriced services and also how these services may put a stop on some serious health dangers and that is definitely something no one can put a price on. Another thing is that these procedures are in direct connection with the overall atmosphere in the terms of your indoor air quality. Learning how your air is of lower quality is also something priceless and probably something that you would like to know about no matter what is the price. Third thing is that air duct companies and air duct cleaners before actually start the cleaning procedure they first inspect the actual state of your ducts and while this inspection may reveal dirt that needs proper addressing it may also reveal eventual duct leaks and ruptures.
Revealing leaks and ruptures means discovering the reason why your utility bills have been so high lately, why your home felt stuffy all the time and why you spent your last winter dressed like grizzly. These are all very useful things to know and are definitely things that long run help you save money.
Make a decision
So to conclude, yes short run you are saving some money by not spending it on professional air duct services. Long run you are definitely not in plus since the money you will eventually need to spend exceeds by far the amount of money you are saving right now.