I'm new to these forums so firstly, hello 
I've been using the DHT11 humidity and temperature sensors. I'm not interested in the temperature side of the sensor.
Although, I have found that the sensor gives unusual results when being powered off 3.3v compared to 5v?
The readings I get with the 5v supply, are higher than the 3.3v supply. I was under the assumption that this sensors operating range was 3.3v - 5v or am I missing something here?
And "hello" back....
I've got the DFRobotics one, and here it mentions only 5V.
edit... but here it says 3.5V minimum.
So who knows?
my experience is they work reliable at 5V
you could patch the lib you use like I did here - DHT22 sensor experiment - not reading all bytes => Fast Humidity sensor - Libraries - Arduino Forum -
(no code as it was a quick experiment only)
fetching only humidity would be twice as fast on a DHT22
Shame. 
Was hoping I could use this with 3.3v so I wouldn't need a second supply.
Using the 3.3v as the AREF so I get better accuracy. But hoping to put this onto a permanent board and didn't want to add an extra regulator if I didn't need to.
Thanks for you help.