The HD806 is, like most DLP projectors, on the high side of noisy, among home theater projectors. Those who are very noise conscious will generally not consider the HD806 to be acceptable for movie viewing, when in full power or Auto iris modes. Noise levels are better, though in low lamp mode. And for many, the HD806 has plenty of brightness in low lamp mode.
The real problem, however, is the noise the dynamic iris makes. It's a gravelly clicking sound for several seconds, which happens perhaps only a couple or three times a minute, due to the slow iris design. It is far more distracting than the fan would ever be. As a result, for movie viewing, most may want to not use it. I don't mind a little noise, but it's too much for me.
Bottom line: The Optoma HD806 is one of the noisier projectors for home theater, but it shares a lot of company where it is, most being very similar. For a family room environment, it's probably just dandy. Make your own call, regarding using the dynamic iris, if it bothers you.