I purchased a Marley S1504TB kickspace heater to replace a similar older heater (Nutone 9112NT). The older unit had been controlled by a separate thermostat - Honeywell T498. In the instructions for the new heater it states:

'If wall thermostat is used: a double pole wall thermostat of the type where both poles cycle on and off by temperature change cannot be used with this heater. Only one pole may cycle and this pole must cycle heating element only, not motor'

Does this describe ALL double pole thermostats? Are they all 'this type'? If not, how do I know if my thermostat is 'the type where both poles cycle on and off by temperature change'? Aren't double pole thermostats required by electrical code?

The wires running to the heater are black, white and ground. Here are the readings I have taken to try to figure this out:

Thermostat OFF - 0V white to ground, 0V black to ground, 0V white to black
Thermostat ON but thermally OFF - 106V white to ground, 115V black to ground, 0V white to black
Thermostat ON and thermally ON - 115V white to ground, 115V black to ground, 230V white to black

I've taken these reading multiple times with the same results. Kind of confusing to me. Why does the one hot wire jump from 106V to 115V when thermally on but not the other hot? How can I have a 106V hot/ground and a 115V hot/ground that measures 0V across each other?

Any help would really be appreciated. Thanks!

New heater: http://www.marleymep.com/en/multimedia-library/pdf/qmark-pdf/products/specialty-heaters/qts/5200-2329-004.pdf
Wall thermostat: http://www.gogeisel.com/geiselonline/support/Honeywell/T498A_B.pdf