Mysterious smell / asthma from DIRECT VENT unit. Please help!

I have a direct vent unit from Travis / Fireplace X - the 34GSR. This is a direct vent fireplace insert, installed into an existing masonry chimney.

It's making me sick.

I have asthma, which is why I got a direct vent unit. The unit has been run for more than a year, and ever since it arrived, I noticed an increase in asthma symptoms. For a while, I dismissed it as unrelated. Now, however, it's reached the point where if I sit for a few hours in the room with the direct vent insert, I will get asthma that night. Last week, I had to go to the hospital to get nebulized, which is why I registered here. I don't normally have severe asthma, and I have no problem at my friends house who has a normal wood-burning fireplace.

This is a direct vent unit, so my understanding is that it's basically a heat exchanger - air from the combustion chamber should be going up the chimney. Room air should presumably be circulated through it and heated up. There should, in theory, be no issues - in theory, this is basically the same as my house's gas furnace.

There is slight burning odor when the fireplace is running - you distinctly notice it when you walk into the room that has the fireplace. Since this is a sealed unit, I've tried to look around the stove to see if the stove is touching anything outside that could be melting / causing the smell, and I've found nothing. The odor is not the issue per se, it's the resultant severe asthma that's the issue.

Could someone please advise what could be causing this? Again, this is a direct vent unit, so combustion products are going straight out the chimney. Where could the smell be coming from?

Here's a link to the 34 GSR site: http://www.fireplacex.com/ProductGuide/ProductDetail.aspx?modelsku=98400108#Documents

And here's a link to the user manual: http://www.fireplacex.com/TravisDocs/100-01236_000.pdf

Any suggestions on what could be causing the smell would be much appreciated.

Sounds like a bad install, or perhaps a crack or leaky gasket in the heat exchanger.

x3 this is not right for a DV unit. We have two at our old house and aside from the dust burn off for the first use or two every year and the original curing, there is no smell.