Question: Last month- I purchased a 21" vented gas log for my fireplace which is 28"(width in front)x19"(length)x13"(width in back). Last weekend- after burning the logs for two straight days- I was overcome by a feeling very much like carbon monoxide poisoning- which finally dissipated after I left my house and then aired it out. A certified chimney sweep- after checking the draft and examining the chimney- advised me that the logs were too large for my fireplace- thus preventing sufficient circulation of oxygen- and then creating a possible build-up of carbon monoxide. He also noted that the logs have a large build-up of carbon on them-considering the length of time that I've owned them. The retailer of course says that the size of the logs have nothing to do with the problem- that it's the drafting of my chimney. What do you think? P.S. I closed my damper while the logs were still very hot- but after I shut the gas off. Would this cause the problem? Answer: ALL vented gas logs get a buildup of soot on them. This is completely normal. Your problem is that the flue gases are not going up the chimney...either partially or totally. There are a few possibilities. 1. Down drafting/reversing chimney...Reverses when not in use....then you start logs and all byproducts come back into the home. Before you start your logs...open the damper fully and stick a small piece of newspaper up...light it with a match and make certain it goes up...this may warm the flue. 2. Lack of make-up air. Vented gas logs burn air from the home..if the room or home is fairly tight- this could cause a problem. Try cracking a window if this is the case..or opening doors into other rooms. Maybe outside air should be brought into the fireplace. 3. Flue not large enough or tall enough to vent the BTU's produced by the logs. Usually- a minimum 8" flue is required for most vented logs sets. Check the requirements in your manual. If the above does not work- getting a more efficient set- like a Peterson RG6 series - which uses 1/2 the BTU's and has reduced vent requirements- might be the answer.