The niacinimide is the non flushing B3. It will be labelled as such on the bottle.
It has been my experience that the degree of flushing is an indication of the degree of niacin deficiency in the body. The niacin deficiency may be a result of a high toxin load in the body. The flushing subsides as the niacin levels increase in the body. For those who are chronically toxic it may not be unusual to have to use 1500 mg a day, of niacin for a year, as I had to.
It is adviseable to gradually increase the niacin levels. Dr. Max Gerson and L.Ron Hubbard in their detox protocols use high amounts of niacin, so it is one of the key vitamins for detoxification, although not the only one.