This is like having a few watches and never knowing what time it actually is. My own DHT 22 sensors I have found to be within 0.5 degrees F. To actually check (calibrate) your temp sensor you will need a temperature measuring device more accurate then the DHT 22. You can't rely on any unknown device. Whatever you check your sensor with you want it to be at least 4X to 10X more accurate than your DHT 22. Having a good known accurate standard is the only way you will know what your sensor is really displaying. You also want to test your sensor over the range it will be used in.
Also, forgot to mention, if you have any concerns as to humidity you may want to start looking at saturated salt solutions.
Ron