  Context. Flare Hard X-Rays (HXRs) from non-thermal electrons are commonly
treated as solely bremsstrahlung (f-f), recombination (f-b) being neglected.
This assumption is shown to be substantially in error, especially in hot
sources, mainly due to recombination onto Fe ions.
  Aims. We analyse the effects on HXR spectra and electron diagnostics by
including non-thermal recombination onto heavy elements in our model.
  Methods. Using Kramers hydrogenic cross sections with effective Z, we
calculate f-f and f-b spectra for power-law electron spectra, in both thin and
thick target limits, and for Maxwellians, with summation over all important
ions.
  Results. We find that non-thermal electron recombination, especially onto Fe,
must, in general, be included together with f-f, for reliable spectral
interpretation, when the HXR source is hot. f-b contribution is greatest when
the electron spectral index is large, and any low energy cut-off small. f-b
spectra recombination edges mean a cut-off in F(E) appears as a HXR feature at
Photon energy = Ec + Vz, offering an Ec diagnostic. Including f-b lowers,
greatly in some cases, the F(E) needed for prescribed HXR fluxes and, even when
small, seriously distorts F(E) as inferred by inversion or forward fitting
based on f-f alone.
  Conclusions. f-b recombination from non-thermal electrons can be an important
contributor to HXR spectra and should be included in spectral analyses,
especially for hot sources. Accurate results will require use of better cross
sections than ours and consideration of source ionisation structure.
