  Using a full spectral scan of an active region from the Extreme-Ultraviolet
Imaging Spectrometer (EIS) we have obtained Emission Measure EM$(T)$
distributions in two different moss regions within the same active region. We
have compared these with theoretical transition region EMs derived for three
limiting cases, namely \textit{static equilibrium}, \textit{strong
condensation} and \textit{strong evaporation} from \cite{ebtel}. The EM
distributions in both the moss regions are strikingly similar and show a
monotonically increasing trend from $\log T[\mathrm{K}]=5.15 -6.3$. Using
photospheric abundances we obtain a consistent EM distribution for all ions.
Comparing the observed and theoretical EM distributions, we find that the
observed EM distribution is best explained by the \textit{strong condensation}
case (EM$_{con}$), suggesting that a downward enthalpy flux plays an important
and possibly dominant role in powering the transition region moss emission. The
downflows could be due to unresolved coronal plasma that is cooling and
draining after having been impulsively heated. This supports the idea that the
hot loops (with temperatures of 3{-}5 MK) seen in the core of active regions
are heated by nanoflares.
