Gas Furnace Chimney
All natural gas venting systems should be examined regularly. Cleaning of these chimneys and vents is generally not required unless deposits due to malfunction or animal nesting. The cleaning is then similar to that of a wood stove.
Wood Furnace Chimney
All wood/oil burning furnaces - including combo furnaces (with natural or propane gas) should be examined regularly. If the wood burning unit is used frequently, it may require cleaning more than once per year.