Every two years. If you have never had it done there will be a lot of fuzz/lint/dog hair etc. And change furnace filter annually. The whole system will be more efficient.
my dryer heating element just crapped the bed, did some reading on it and the ducts not being cleaned make it so the coils can get too hot with not enough air flow.
Had ours done in a rental after about 6 months of living there. We were sick on and off for a majority of that time. Had the management company bring in someone to clean them out. No issues after that.
I just take my registers and return air grills ( where most of the crap settles) off and take a good shop vac and stick the hose in there and vacume them out real good.
Dryer vent , depending if it's the floppy flex stuff or hard pipe. If it hard pipe you can get a long 4 inch brush and run it in and out of the pipe also. If it's flex, and easily accessible I just replace it.
its main benefit is to those cleaning the ducts. For the most part if you have dust settled in your ducts it’s going to stay there, unless you disturb it by trying to clean it. I think it’s a scam BUT the dryer vent is a completely different matter, it can be a fire hazard and needs to be cleaned. https://www.epa.gov/indoor-air-qual...never been,necessarily enter the living space.