To be considered, an "appliance" must use the burning of biomass fuel to heat an existing principle dwelling, or to heat water for use in the dwelling.  

The appliance must have an efficiency rating of at least 75%

Installation is covered, as long as it is a requirement for the appliance's proper and safe functioning.

The tax credit is 30% (up to $1500) for the purchase and installation in 2009 or 2010 - not a seperate credit for both years

The credit is an aggregate,  i.e., the total amount can include other energy efficient items.

Manufacturers must provide a cerificate of qualification to qualify, which must be retained by the taxpayer.

The IRS has not claified whether fireplace inserts (units inserted into existing fireplaces) are covered, but they are assumed to be included under the broad definition of a "stove" by the EPA.