Lots of services in my vicinity flogging these type of clean-ups – “clear out your clogged air conditioning ducts! Save energy! Avoid allergies! Avert lint-induced fires in your clothes dryer vent!”
Necessary/not necessary but useful and energy saving/pointless?
Had a thread on that not too long ago. The process gets mixed reviews.
I have to comment on dryer-vent cleaning. Ours (at our old house) was totally clogged. As in, no air was getting out. This turned out to be the result of our having put mesh over the outlet to prevent birds from nesting inside (as they had from the stove exhaust).
So a large portion of the vent was full of soggy lint. Cleaning it out worked wonders.
As far as fire hazards, it’s hard to say. If there’s enough lint in there to be a fire hazard, chances are it’s pretty damp from the moist air that’s being pushed through the duct, so not all that flammable. Ours was damp enough that we had water damage to the drywall!
In hindsight, the birds would have been a better choice!
The dryer-vent cleaning can be very helpful. The benefits of cleaning air ducts are less obvious. Lint builds up in dryer vents very easily and can block airflow, meaning the dryer runs hotter and takes longer to dry your clothes, and clogged dryer vents do pose a fire hazard.
On the other hand, I asked my allergist once about whether I should clean out the air vents, and he said not to bother. Whatever dust has stuck to the walls of the ducts, he said, isn’t going to get back out and bother you.