Here is a little tip on how to help keep your ductwork of your central heating and air conditioning plan cleaner longer, not sure if you knew, but if you hand washed all the grates of the air vents to your central heating and cooling unit, you can stop a lot of dirt, grime and maybe even pet dander from getting into the ductwork, and I learned this not too long ago plus have been trying it.
Ever since I have noticed in my case that I do not need to have my ductwork cleaned every other year like I have been. I can now break that down to just a few years if I continue to scrub the grates of the air vents to my central heating plus A/C, all it takes is soap, water and some scrubbing while up on a ladder. It can be a bit time consuming, but it will save you some money in the long run of things by not having to get your ductwork cleaned as often. I am pretty shocked that it worked out the way that it has. But it did work in my case. All I can command is to provide it a try plus see if it works for you the same as it has for me. If it does not, then just go on casually and get your ductwork cleaned every so often as usual if that is what you do, and there are all kinds of ways to maintain your central heating as well as air conditioning plan and everything that goes with it.