Can you use a waterbed heater with thermostat turned down extra low as an UTH ?

I have been wondering about this for quite a while, but figured it would be still too hot and melt plastic, or heat glass too much.
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"There is a principle which is a bar against all information, which is proof against all arguments and which cannot fail to keep a man in everlasting ignorance- that principle is contempt prior to investigation." Herbert Spencer