If your using a sulfur burner, that humidity is fine "usually". I know people that prefer high humidity during budding and dont even use burners or mold protection. And then I know people that freakout when it goes above 40%. I think its entirely environment/situation/strain dependent. Dehumidifiers will definitely heat up the room depending on the size. Im suprised your 2 1000 watts only heat up the room not even 10 degrees. Must be a fairly large area. Is it completely sealed or are you trying to heat/cool a very large area aside from the grow area? How long does it take to reach 79 F? And have you considered a burner? Thats really the only way to save electricity.