Direct vent fireplaces are some of the most common natural gas or propane fireplaces on the market today. They provide heat at the touch of a button or the flick of a switch, with no smelly fumes or smoke back drafting down the chimney. Direct vent fireplaces do sometimes make some different noises than people are used to from a traditional fireplace.
The "Bump" Sound
Many people wonder what the bump sound is that happens a few minutes after you turn on the direct vent fireplace and a few minutes after you shut it off. Because the unit is made of thin-wall stainless steel, the metal expands when heated and contracts when cooling, causing the metal to flex and sometimes make a "bump" noise. This is a normal part of the fireplace operation and will happen every time the fireplace is used.
Whether you are aware of it or not, most direct vent fireplaces come with a blower fan that is factory set to automatically turn on at a certain temperature. The fireplace blower fan will not turn on sooner unless you physically turn it on by hand or reset the parameters of the fan. This is located underneath the unit behind the grated portion of the bottom of the unit.
Any rubbing noise is generally from an unbalanced fan that hits the fan housing in the fan unit. The only solution for this problem is to remove the fan unit and replace it with a new one.
Adam Yeomans has been writing professionally since 2010, with his work appearing on websites such as eHow. He works in the construction industry as a builder and as an energy efficiency consultant.