Boy it sounds if you and swissmiss have issues with zero clearance fireplaces. With yours though there are several things that could lead to what you are expiriencing. 1. Down draft from the chimney pipe. This is indicated if the room smells of old burnt wood or creasote when the draft is noted. 2. Air leaks from the framing around the fireplace. An easy check for air leaks is to take a lighter, long match, or candle and move it slowly around the outsides of the fireplace where the construction materials meet the face of the actual fireplace if there is an air leak it will either blow the flame to point into the room or if it is sucking air it will draw the flame toward the wall. 3.When a fireplace is installed on an outside wall of a house there is a cavity that the fireplace sits in and the pipe for the fireplace passes through that extends above the roof area called a chase. This cavity in what we refer to as extreme climates such as winter conditions in the northern US the chase should be insulated from the slab all the way up to the point of termination above the roof. This would eliminate the draft or cool air coming in around the fireplace to a more tolerable level. Any questions at all feel free to contact me at maverick_75457@yahoo.com

Sorry to bring up an old post but I'm having the same problem with a Kingsman. Did you ever resolve this? I found this information (posted below) on another site but it doesn't really help. I have several floors in my townhouse, the fireplace is on the 2nd floor and everything is insulated very good on the floor above. The only other place I can feel some cold air is by the front door which is below the fireplace on the first floor (basically just the door and garage). Do NOT insulate the fireplace directly! This is a fire hazard! Clearances are air spaces. You fireplace uses cold air to insulate the inner flue. This cold air dumps into the chase at the starter collar at the top of the Fp. The chase will always be full of cold air. The answer is not more insulation or sealing but physics: If you open a window, will warm air exit the house or cold air infiltrate in? How does it know? Physics. For cold air to infiltrate in, there must be either a higher pressure outdoors than in or a negative pressure inside With Respect To(WRT) outdoors. If cold air is manifesting at your fireplace, it means you have negative pressure and the rest of the house is relatively tight leaving the Fp as the path of least resistance. How to minimize it? First, reduce the negative pressure. Seal the top of your house like Tupperware. Next, provide a dedicated source of fresh air elsewhere in the house. Next, seal & balance forced air ducts. Provide makeup air for any exhaust fans.

Most, if not all, wood burning prefab fireplaces are fitted with an air intake in the firebox to bring air in from the outdoors to feed the combustion, so that opening a window to bring in fresh air to replace the air used up by the fire would not be necessary. I would be surprised if inserts are not similarly equipped.

For those folks in similar situations the problem with gas inserts is that most manufacturers only make about 3 sizes of inserts - small medium and large. Since an insert has to fit various sized fireplaces they are generally short in height and don't adequately fill the opening hence the outer surround panels to cover out to the existing surface. The largest inserts rarely exceed 24" tall so in a 42" x 42" opening as shown in the sketch above, the gas unit does not fill the opening,and has way too much black surround. Valor Gas Fireplaces makes 4 Insert specific units, but their 7 zero clearance fireplaces can also be used as Inserts if the fireplace is large enough. If your F.P. opening is about 53" W x 54" H you can fit a 50" Linear inside. This means that Valor has 11 inserts, more than any other manufacturer. A Valor H6 fireplace is 42-1/4" w x 34-1/2" H which would fit if you have more than 42" If anyone needs more information contact me. Here is the Valor website for more information www.valorfireplaces.com