To bring this thread back on topic to the topic that it originally derailed from the first off-topic topic,
The Pri Toar writes regarding a kli that is not for food use at all (his case is scissors), and one wants to use it sometimes for a food use, that it does not need to be toveled. Similarly, Rav Elyashiv and the Ohr Yitzchak permit using room heaters for heating up food (even when directly touching) without tevila.
This clearly appears to apply to something that is not a food tool at all. R' Chaim Kanievsky does say that you would need to tovel a blech (without a beracha) if you warm challas on it directly, even every once in a while. R' Elyashiv makes this distinction explicitly, saying the problem with a "sakin shel klafim" is that it is still called a "sakin." However, the grates on your stovetop would not need tevila because almost no one roasts eggplant (that was the case) directly on it.
I will not discuss the apparently horrible hygiene in almost every case above, but I will note that not everyone holds tinfoil is considered enough of a separation to consider the food not to be touching for the purposes of avoiding tevila.
Pri Toar: YD Kuf Chof sk 11
Ashrei Hoish YD, Tes, Os Chof-ches
Ohr Yitzchak I YD 23
RC Kanievsky from a teshuva in Ohel Yaakov, B'Nesivos H'Halacha 46 p 413
The distinction from R' Elyashiv is brought in Avnei Yoshfeh I Siman Kuf-Mem-Zayin p43.
