I saw a label on a Westinghouse 175 watt MV bulb that said H22 or H39 ballast type. I know what H39 is but I have never heard of H22... is there such a thing?

 H22 was par of an old rating system . Just as the modern 400w H33 was originally called H1 .

Correct, I think MV were the only HID lamps that received a new ANSI code though. 100w used to be H-4.

Interesting, I didn’t know this. Does anyone know the reason they changed codes?

I believe it happened around the time that the US mercury lamps changed to use the newer Osram emitter material for the electrodes.  Since the lamps started more easily during life it was possible to make smaller and cheaper ballasts with lower open circuit voltage.  But those could only start the newer lamps and not the original types having thorium emitter - therefore the ballast codes were changed, to indicate that older lamps would not work on the newer ballasts - however the newer lamps could function reliably on the older ballasts, and were therefore marked with both ballast codes for many years until the original ballast types had been mainly replaced.

 Interesting ! I didn't know that .

Ok, going on a limb here, would the old H22 ballasts work at least somewhat reliably with M57 metal halide lamps ? I believe the difference between H39 mercury and M57 MH ballasts is that the MH has a higher OCV, but maybe the H22, while higher than the H39, might not be enough.