Tes Shvat 5774
Rabbi Yitzchok Hutner A"h lived in a complex that was heated by a centralized heating system managed by a non-observant Jew. The Jew would frequently turn on the steam on Shabbos to counter the cold New York winters. Was Rabbi Hutner allowed to stay indoors or was it necessary for him to leave the house, as staying indoors meant he was deriving pleasure from a forbidden melachah on Shabbos? At the very least, was he required to shut the heating vents to prevent the forbidden steam from warming his home?
Rabbi Hutner posed his dilemma to his esteemed colleague, Rabbi Moshe Feinstein A"h. Rabbi Feinstein addressed the issue by comparing this case to a dispute between Abaye and Rava in Tractate Pesachim (25b). The two Amoraim debated over a case where one finds himself exposed to a forbidden source of pleasure, and while it is understood that he cannot prevent the enjoyment from reaching his senses, he intentionally derives pleasure from the issur. (For example: one passes by a house of avodah zarah and cannot prevent the pleasing scent emanating from within from reaching his nostrils, but he intentionally enjoys the smell.) According to Abaye this would be permitted; Rava, by contrast, holds that it is forbidden.
A parallel can be drawn to the present case as well. A person found in the house cannot help but feel the warmth of the steam, but it can be assumed that he will enjoy the warmth as well. Thus, this case would seemingly fall within the dispute of Abaye and Rava.
In reality, however, even Rava would agree that it would be permissible to stay in the house. While the prohibition against enjoying the scent of avodah zarah is min haTorah, that of deriving pleasure from a melachah on Shabbos is miderabanan (see Ketubos 34a), and according to certain opinions, Rava agrees with Abaye's conclusion in such cases (see Rashi d.h. ein, Pesachim 26a). Even those that maintain that Rava forbids deriving enjoyment prohibited mibrebanan all agree that when a need is present Rava is lenient (see Tosafos d.h. vetisbera, ibid.). The fact that it was cold outdoors created a definite need to remain indoors, and all would agree that he may do so.
Rabbi Feinstein ascertained that there is no need to close the vents either. Although one may not actively derive forbidden pleasure, when found in a situation where the prohibited enjoyment reaches him compulsorily, one has no obligation to separate himself from it by relocating to another location (e.g., to immediately backtrack when confronted with a smell of avodah zarah) or placing a division between himself and the issur (e.g., by closing the vents). (This is true according to Abaye, and in our case, according to Rava as well).
Other authorities assert that although one is not required to leave his house in this case, one would be obligated to close the vents to prevent the steam from entering the room. An exception can perhaps be made in cases of extreme cold, for even healthy individuals are considered ill in the face of severe chill. (This rationale is used to permit-under certain circumstances-asking a non-Jew to heat one's home in the winter [see Shulchan Aruch Orach Chaim 276:5].)
(Igros Moshe, Orach Chaim, 1:123. Az Nidberu 6:76)