These seem to run quietly, but do not seem to work well, even in a small room. They will make a sizzling sound after a while and no idea why they do that. They are much smaller than expected and I have both of them in the same room. Even that is not as good of quality as an older Hunter brand I have that I was hoping to replace due to its age. Car ionizer does not seem to do any good in the car. Way too expensive for the quality of item purchased.