They don't burn as hot, but I don't think they burn any slower. Cold smoking on a Drum without any modifications will be tough. One other thought, how much wood are you using? It won't burn as well if you are using too much and this could put you out. You just need three or four chunks to do the job.
Hey its not a cold smoker...really cant do that.....you would really have to modify it to make it work and it would take a second barrel that would accept the smoke from the first one.