Generally, no, heat not needed. It really needs to be extremely cold to really consider anything.
however, every living animal has its limits, so heating/heat lamp isn’t something everyone should ignore. And even if you lived in the extremes, you could just not provide heat and the healthiest/heartiest survive. birds are pretty hearty, overall.
All that, and I do have a heat lamp in my coop. But it is connected to a thermostat to not allow it to turn on unless very cold (It is a red light, so should not disturb the birds), and it generally has only ever turned on at night. We noticed last year, during the polar vortex (High winds for a sustained period, along with very cold temps) that some of our chickens were not doing much at all. The heat lamp was on, keeping the coop close to 0F, so pretty cold inside still. We added feed in the coop to encourage them to eat, since some were not moving to go outside to the normal feed stations. It was a severe drop in temp, along with high winds. Their coop and run is protected from the prevailing winds as it sits fully behind the barn, which fully blocks the west winter winds. It is well ventilated with the entire slanted roof raised up off the walls to provide ventilation that easily moves air through the coop up and out (and above their heads). I think the heat lamp helped temper the worst of the sustained temp drop, but didn’t really provide heat as the temp stayed near zero F. Since we have a kid involved in the chicken keeping activities, we opted for a heating lamp to help lessen the worst of the temp drops, and hopefully avoid any sudden deaths. Kid understands the whole circle of life, and helps butcher birds, but gets upset when one dies suddenly/unexpectedly.
My neighbor uses a heat lamp inside his coop for his small flock of leghorns, and one male. They are all fine and lay right through the winters for him. And his coop isn’t well ventilated according to standards usually cited in here. But, he provides heat, which is likely “hotter” than my heat bc his coop is smaller with less ventilation. But his birds continue to do well.
No, heat isn’t required. It’s really a personal choice.
