This is Turtle.

i will use the words of what type thermocouples are loosely to say the
least. ALL per say 24 volt thermocouples will work in all applications
just fine. Now there is a difference in the types of thermocouples that
you may buy on at stores 7 wearhouses today. all will work but some are
made to last longer and some is made to put out just a little more mill
Volts for the gas valve to hold it open.

The HVAC type is made to put out about 27 to 29 Mill-volts and then the
Hot water tank type is made to put out 24 to 27 Mill-volts service.
anything 24 volts or over will work fine but the higher volt
thermocouples seem to last longer.

TURTLE