butch burton wrote:
Now are there differences between tube type HX's from manufacturer to
...
Are there differences in types of HX tubes - if so which brand(s) are

Don't know which specific model/manufacturer is better, but it would be
reflected in the overall reliability of the model. Newer models use
different designs and materials (stainless, "Tufsteel", etc.), so the
reliability may vary year to year. As a homeowner, I don't think you
need be concerned about this aspect, and instead concentrate on a good
installer and warranty.