  This paper outlines a simple approach to evaluate habitability of terrestrial
planets by assuming different types of planetary atmospheres and using
corresponding model calculations. Our approach can be applied for current and
future candidates provided by the Kepler mission and other searches. The
resulting uncertainties and changes in the number of planetary candidates in
the HZ for the Kepler February 2011 data release are discussed. To first order
the HZ depends on the effective stellar flux distribution in wavelength and
time, the planet albedo, and greenhouse gas effects. We provide a simple set of
parameters which can be used for evaluating current and future planet
candidates from transit searches.
