Kevin is now the official Archivist for you thread

I like the water vapour solution for the reasons you indicate. However you need to build a custom system to generate enough vapour to get decent blasts of "exhaust". The well tried and integrated oil systems work well and are deservedly popular. The tips below apply to both up to a point.
a) For water vapour systems. Reduce condensation in the pipe run by employing plastic and PVC fittings rather than metal (eg copper plumbing pipe). This may also apply to oil systems but clearly plastic components would need to be kept away from the heater element.
b) Arrange the pipe run so that condensate droplets run back into the reservoir and do not form pools or traps in the pipe work.
c) If possible avoid 90 degree bends in the pipework to maintain energetic and unrestricted vapour flow. Same issues as full size exhausts, gas flues etc.
Kevin will now probably point out that I have already shared all this gen on p24!
Kind regards
Fabrice