Most chickens do not need extra heat at that temperature.
Make sure wind does not blow directly on the chickens while they are sleeping on the roost.
But do not close things up entirely, because they still need fresh air. People seem to report more frostbitten combs in closed up chicken coops (higher humidity, from the chicken poop and chicken breath) than in open coops that actually get colder but stay less humid. So the idea is to have some air movement, but in places other than where the chickens sleep. Some people find it works well to have ventilation above the heads of the chickens while they are on the roost. Some other people have the air movement at one side or end of the chicken coop, while the chickens sleep at the other side or end.
A good check for how much air movement is too much: if the chickens' feathers are staying nicely in place, it is fine. If the feathers are blowing around, there is too much wind. This applies when they are on the roost at night, not to all parts of the coop & run. It is fine for the chickens to have access to windy areas when they are awake, when they can choose to be in the wind or not.
A specific detail: pay attention to water. It can freeze quickly at those temperatures. Thirsty chickens will not eat dry food, so soon they are both thirsty and hungry, which is not good when they are needing to eat extra food to keep warm! So either provide a heated water source (so it does not freeze), or be prepared to carry fresh water several times each day (first thing in the morning, about an hour before dark, and however often is needed in between.)