I don't see any reference to HEAT WAVE in the play itself, just that the guys were doing a dance they used to do on Fire Island. Perhaps Mart Crowley added the HEAT WAVE detail when he did the screenplay for the film and they used it again for the recent Netflix version.
For the film, you see one of the guys holding the Vandellas' LIVE album. But in the Netflix version and the recent Broadway revival, I think they were holding the HEAT WAVE album.
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