  We extend the method of Flow Equations to the Effective Field Theory
framework of inflation, in order to investigate the observable predictions of a
very broad class of inflationary models. Focusing our attention on the
gravitational-wave sector, we derive a general expression for the consistency
relation for effective models and provide a numerical implementation which
allows to study how the generated models populate the $(r,nt)$ plane. We
analyse $5 \times 10^{4}$ realizations of inflationary scenarios that respect
the Null-Energy Condition ($\epsilon > 0$) and $5 \times 10^{4}$ realizations
that violate it ($\epsilon > 0$). In both cases, 90% of the viable models are
below the most recent upper bound on the tensor-to-scalar ratio from Planck and
BICEP2/Keck Array BK15 data: $r_{0.002} < 0.056$ at 95 % CL. We find that
general EFT inflationary models with $\epsilon > 0$ are typically characterized
by $n_{t} < 0$, whereas the vast majority of NEC-violating models presents a
blue-tilted spectrum ($n_{t} > 0$). Since a blue tensor spectral index implies
more power on small scales, this result is of considerable interest in view of
a possible direct detection of the primordial gravitational-wave background.
