Michael writes:
> I find that my KS10radiator is just a little bit more (in)efficient than
> my VAX radiators. Those extra four bits help a lot. The RP06radiator
> also does a good job with air circulation but it is a bit noisy.

Any of those should be very very close to 100% efficiency.  Just about
the only loss would be due to noise or radiated RF energy that actually
escapes from your building.  Noise and RF that is absorbed within the
building will heat it.