@JohnD
Yes, JohnD, "mainitan" is similar to "antukin" in the sense that they are more often used with the object that initially might look like the actor instead.
Ako ay mainit. = I am hot. - In Filipino, "mainit" is warm or hot and is only about temperature. So, "ako ay mainit" would be understood to mean as "I have a fever" or "I am warm-blooded" if the discussion is about biological categories.
"Maiinitan" is "to be affected by heat" and therefore, you might feel warm or at least, uncomfortable as a result. "Maiinitan ako" would mean "I would be affected by the heat" and the "doer" is going to be that which transmits the heat to you.
>>I think I would end up with 'I am being heated by (unnamed actor)'
That is, therefore, correct.
"Maiinitan ako ng araw" = The sun will make me feel warm/hot.
"Maiinitan ako sa araw" = I will feel warm/hot under the sun.
In English, the actor/subject is different in these two sentences. In Filipino, because the verb is object-focused, the one affected (heated) by the verb will be the object/subject and the sun will be the "actor" in both instances.
Since human beings are physiologically warm, we can transmit heat, too. We can, therefore, be the actor and someone or something else is the object. "Maiinitan KO ang kamay mo kung hahawakan ko sila ng dalawang kamay ko" = I can warm your hand if I'd hold it with my two hands. "Ko" (I) is the actor in this case.
We can also say, "Aantukin ko ikaw (kita) sa pagkanta ko." = I will make you sleepy with my singing. "Ko" (I) also becomes the actor there, but in reality it would be the song or singing that would induce sleep. With "maiinitan", it is the heat of the actor itself that produces the effect.