You should be worried the chimney air kit was not installed. It is what keeps the air between the walls of the chimney cooled. It is mandatory with the SL300 pipe, and the SL300 pipe is the only pipe authorized for use with this fireplace. I even asked HeatNGlo, because this unit is so similar to the Quadrafire 7100 whose manual says can take triple wall Simpson Dura-plus chimney pipe, but HeatnGlo said, nope, SL300 and thats your only choice for the NorthStar (Quadra-fire and HeatnGlo & Heatilator are all under Hearth&Home;technologies company).
So effectively it is mandatory and is somewhat dangerous without it. I'm not sure if its related to your heat output woes, but you should call whoever installed it and demand they fix it immediately, which won't be such an easy task with the chimney already installed, and at their total cost. Read the manual, it states at least twice that the CAK4A air kit is mandatory and must be installed. There is even a sticker on the box saying that as well, and if you saw the fireplace when it was unpacked, there was a hanging laminated piece of paper inside the unit saying it again. You should also report that dealer to HeatNGlo. And also check to ensure your installer used SL300 pipe (there are stickers on the pipe if you can get a look it, you should see part numbers like SL348 or SL336 SL324 SL312)
I know, I'm in the
middle of a retrofit and am installing a North Star right now.
And this is exactly why I'm installing my fireplace myself. After 1 dealer told me he wanted to install simpson dura-vent (not the same as dura-plus), and another dealer was trying to line my existing chimney with a liner to the northstar (not sure how either of these guys would have connected to the northstar because the collar on the unit will only connect to the SL300 pipe), it became obvious to me that alot of these dealers don't know what their doing and can't read a manual. I reported these dealers to HeatnGlo and actually got a response from a regional rep asking me for more info. I'm no expert for sure, but I can read, have done smaller remodling projects and built pole barns, and looking at what some of these dealers do, they aren't right.
Another example, the unit I just tore out, didn't have ember strips, didn't have the required clearance in the back ,didn't contain the insulation in the chase, didn't have the firestop installed properly in the chase, didn't have the requied hearth extension, rolled up 20' of romex right next to the fireplace...and the list goes on..so many bad installers it seems. I'm sure there's good ones, but you have to watch these people like hawks. That goes for almost anything though, car repair, home repair...you name it...