I did the same when I bred budgies only to stop huge temperature fluctuations, mine was set at 8 degrees and it made a huge difference. I dont have any heating now with the pigeons but if used correctly it is not a bad thing. If you get a really hard spell like we have now or if you get a really mild winter you cant predict. Heating will only turn a really hard winter into potentially a mild one so you are not really wrapping them in cotton wool. It makes sense for the guys that work not to have drinkers frozen up all day if possible.
Paul.