I just tested my c-pap(Respironics c-flex with heater.) using my clamp on amp meter and a little amp test cord i have and it draws one amp with the heater.
1 amp x 110 volts = 110 watts.
Some thing i have found very handy is my clamp on amp meter and load test cord.
With it i can test all my 110 volt plug in items and know just what they draw.
For the load test cord take a male and female three prong plugs and wire them together with about 6 inches of wire and tape the ground and neutral wire so that you know what ones they are and leave the hot (black wire) separate so you can clamp one the clamp on amp meter.
CLAMP THOSE AMPS
I plan to put a small deep cycle battery and 200 amp invertor back in the bed room area of my Bounder just as a dedicated c-pap power supply
i will wire it to both a small solar panel on the roof and through my regular battery system by way of a battery isolator.
This way it will even work if i lose power in a RV park and i can sleep through the night.
I can even plug my alarm clock into the circuit.