  We confront the warm inflation observational predictions directly with the
latest CMB data. We focus on a linear temperature (T) dissipative coefficient
combined with the simplest model of inflation, a quartic chaotic potential.
Although excluded in its standard cold inflation version, dissipation reduces
the tensor-to-scalar ratio and brings the quartic chaotic model within the
observable allowed range. We will use the CosmoMC package to derive constraints
on the model parameters: the combination of coupling constants giving rise to
dissipation, the effective number of relativistic degrees of freedom
contributing to the thermal bath, and the quartic coupling in the inflaton
potential. We do not assume a priori a power-law primordial spectrum, neither
we fix the no. of e-folds at the horizon exit. The relation between the no. of
e-folds and the comoving scale at horizon crossing is derived from the
dynamics, depending on the parameters of the model, which allows us to obtain
the $k$-dependent primordial power spectrum. We study the two possibilities
considered in the literature for the spectrum, with the inflaton fluctuations
having a thermal or a non-thermal origin, and discuss the ability of the data
to constraint the model parameters.
