Jotul Oslo 500 Maintenence questions

[acesneights1]

Hey newbie here. I have a Oslo. It's about 3 yrs old and been used heavily. I bought it new. It doesn't seem to be burning as hot as I feel it should. The damper does not seem to have alot of effect on the flame. I have it sitting in my fireplace with about 5 ft of 6 inch flex going into a 12x12 masonry chimney that is about 15ft high. The guy at the stove dealer said I need to run a liner all the way up because the stove is not getting enough draft. I spoke with a chimney guy and he said(now this is a chimney co , they love to sell liners) he doesn't think it's my problem from what I describe(he did not see the stove). He thinks I have an air intake problem with the stove itself. The Jotul manual says nothing of cleaning it or where to clean. I took off the thing inside with the 3 holes and vac'd it out as best i could. Anything else I can do and where should I be checking. The stove burns better if I crack the ash door a little bit but I know that's a no-no. I am burning 1 yr old red oak.
Thanks.

 

[The Dali Lima]

Have you had the chimney cleaned in the last 3 years? If not, I would have a sweep come in and clean it up and then look at your setup. From what I've heard here and other places the liner is a must in a masonry chimney to get these stoves to really burn efficiently...

 

[acesneights1]

I clean it every year. It's spotless.

 

[acesneights1]

I basically just want to make sure the air intake is not restricted but I don't know where to check. I just ordered a liner from Chimneydepot. I am going to line it anyway because I want to move the stove out in front of the fireplace.