I have the wiring configuration for a RHEEM thermostat Pictured Below. On it, there is a "V" wiring connection which according to the manufacturer is for "Pulsed width modulation" type heating. On the other end, the furnace, it connects to a "V/W2" connection which I have verified is pulsed width modulating.
Initially, Nest showed that I was incompatible due to the "V" wiring but learned that it was because they thought it was "milivolt" designation. However, after talking with them and researching, I learned that this was not the case and should be able to connect the V/W2 into the Nest "W2".
Will this accomplish the same thing? I learned that W2 is for 2nd stage heating which doesn't seem to be exactly the same thing as Pulsed Width Modulating heating.
Edit - Found in manual: From Manual
To set the furnace for operation with two-stage thermostats, set switches 1 & 2 of SW2 to the “ON” position (See Figure 56). Note that these switches should be in the “OFF” position from the factory. With both switches in the “ON” position, the furnace can still recognize a “V” signal present and will still operate with a modulating thermostat. However, with both switches of SW2 in the “ON” position, the furnace is set to operate with a two-stage thermostat as well. With a two-stage thermostat (installed as shown in Figure 50) and switch settings configured as described above, during a call for heat, the furnace will operate as follows:
So it is currently operating in "modulating" thermostat mode but is able to operate with Nest in a "2-stage" mode by simply flipping a dip switch. Then the "V" wire will act as "W2" wire.