Using an electric bed warmer on Shabbat

Can one use an electric bed warmer (a mattress pad with a heating element) on Shabbat?

Taken from: ERETZ HEMDAH

Our understanding is that nothing you would do on Shabbat would affect the operation of the warmer (including that it works at a set level of heat and does not work based on a thermostat.) Therefore, there would be no problem with using it even on Shabbat, with a timer. It doesn’t seem to be any different than an air-conditioner or electric heater on a timer, which is commonly used on Shabbat.