chimney - boiler question?

Monday I got my adobe cleaned out, one heck of a job. I cut the back open and removed about 2 gallons of ash and soot. I made a new back side for it hopefully it will come off easier than the old one should I have to do it again. The adobe has worked well the last two days, although it is hard to tell as it is now 40* (where's the cold weather when you need it). My new chimney (12' insulated outside, 6 'single wall inside) is drawing at .04-.05 seems to be OK. I am contemplating putting on another 3' of chimney to be sure, either that or a draft inducer. What do you think? Also now that it is going to start to rain, should I put on a rain cap or will that also screw up the draft.