Put in tonight’s low and what the coop is like, and get the honest answer from four extension services and a fire marshal — which, most nights, is that a dry, draught-free flock is fine and the heater is the bigger danger. In summer, put in today’s high instead.
Tonight: 20 °F (−7 °C)
Most likely fine — if they are dry and out of the wind
Nothing here diagnoses a bird. A chicken sitting fluffed up and off her food, or with a comb or toes gone grey or black, is a question for a vet — and so is any bird you are worried about.
Every line checked 2026-09-25 against the source named beside it.
Quick answer: there is no single temperature that is too cold for a healthy, feathered adult chicken. Ohio State Extension: “most chicken breeds can tolerate cold, even sub-freezing temperatures, complications can arise when wind and moisture are accompanied with cold temperatures.” The real risks are a draught at roost height, a damp coop and — once it reaches the single digits °F — frostbite on big combs. Whether to heat the coop is where the official sources split: the University of Minnesota adds heat below 35 °F in the coop, Maryland and Ohio State say acclimated adults in a dry, draught-free coop need none. And every one of them warns that heat lamps start fires.
Why the draught matters more than the number
A chicken is wearing a down coat and sleeping in a huddle. What beats that is wind getting under the feathers and water in the air. Maryland Extension puts it plainly: “Holes that allow fresh air to blow directly on the birds can chill them and lead to problems.” Moisture is the other half, and it is the one that causes frostbite. Minnesota: “High moisture in a coop, combined with cold temperatures can lead to condensation, which can cause frostbite.” Ohio State adds that “humid air creates more frostbite risk than drier air.”
So the two questions the checker asks before anything else are the two I check first on a cold evening: can the wind reach them where they sleep, and was there condensation on the windows this morning? If either is yes, that is tonight’s job, and it matters more than the forecast.
The fix for damp is more air, not less, which feels wrong in January. Kentucky: “If there is condensation on windows or uninsulated walls of the coop in the morning, ventilation must be increased to keep the coop dry.” The trick is to let air in high up, above the roost, and stop it blowing across the birds.
Frostbite: which birds, and when
Frostbite is a big-comb problem. The University of Kentucky: “Frostbite is most common in roosters because they typically have larger combs and wattles, but any hen with a large comb, such as a leghorn, can be vulnerable as well. The incidence of frostbite in chickens with the smaller comb types, such as pea and strawberry, is much less.” It also says when to start watching: well-kept coops should prevent it, “but with extremely low temperatures (single digits and below), frostbite can become a problem.” That is the one temperature line the checker draws for frostbite, because it is the only one a source has published.
Minnesota’s suggestion for big combs is petroleum jelly, with an honest limit: it helps insulate the comb and prevent damage, and “Petroleum jelly does not treat frostbite.” A comb or toes that have gone grey or black is a question for a vet, not for a web page.
Should I heat the coop? The sources disagree
This is the question everyone actually asks, and four extension services give four answers:
- University of Minnesota Extension — “When temperatures fall below 35 degrees F, provide supplemental heat at the height of the nest boxes or lower rung of the roost.” Note that this is the temperature in the coop, where the birds are, not the forecast.
- University of Maryland Extension — “As long as adult birds are protected from the wind and wet weather, they should not need any additional heat even during the coldest time of year.” It adds that heat can help older hens keep laying, and that bantams and molting hens may need some when full-size birds do not.
- Ohio State University Extension — “Cold tolerant chicken breeds acclimated to the weather living in an insulated, dry coop with adequate ventilation do not usually need supplemental heat.”
- University of Kentucky — a heat lamp can take the edge off “sub-zero for a few days”, but “Flocks can do well at sub-zero temperatures if you use a deep litter system and an in-bucket water warmer, with no external heat required.”
I do not heat mine. But I am not going to pretend Minnesota’s extension service does not say what it says — so the checker prints all four and lets you decide.
If you do heat it: heat lamps burn coops down
This is the part I would put in capitals if I could. Kentucky: “Each year, chicken coops (and some attached houses) have been lost to fires caused by heat lamps.” Maine: “many barns (and livestock) have been lost to fire due to heat lamps.” A coop is a wooden box full of bedding, dust and feathers — Maryland lists all three as what makes a heater a fire hazard — and a bulb that drops into it is a fire.
If there is a lamp in your coop, the fire authorities’ rules are short:
- Secure it properly. “Relying on the spring clamp alone is not adequate to prevent the lamp from dislodging” (the National Fire Protection Association, via the Clark County Fire Marshal).
- Hang it from a safety chain, never by the cord, with a cage over the bulb (UMaine and Minnesota).
- Keep it away from anything that can burn — bedding, the roost, the walls.
- No extension cords in the coop. Use equipment made for agricultural use.
Radiant panels and brooder plates “heat the birds but not the surrounding air space”, and Minnesota lists them before heat lamps. Buy one that is approved for use around livestock, and read its fire warnings anyway. One more thing a heat lamp does that people do not expect: left on all night, the birds read it as daylight, and when you switch it off in spring they read that as the days shortening (UMaine).
Water, feed and roosts in a cold snap
Water freezes at 32 °F, and “Water that is frozen over is not available to the birds and they cannot break through the ice” (Maryland). Check it morning and evening, or use a heated base — which is also a heater, so the same rules about cords and bedding apply.
Feed is another place the sources point in different directions. Minnesota: feed intake “may increase up to 25% during cold weather.” Ohio State: “Chickens will eat less in the winter than the summer.” Both agree that feed should always be there. A handful of scratch grains before they go to roost helps; Minnesota’s reason is that “digestion of scratch grains also produces heat.”
Roosts should be wood, wide enough that a hen can sit down over her feet — a 2×4 laid flat is what Minnesota and Maryland both describe. Metal and plastic hold the cold.
And in summer: how hot is too hot?
Heat, unlike cold, comes with published numbers. The University of Minnesota puts the comfort zone for most poultry at 60 to 75 °F. “As temperatures increase towards 85 F, the birds will adjust their behavior and decrease feed intake and production,” and “When air temperature increases towards 100 F, the birds’ core body temperatures will increase to lethal temperatures unless relief is provided.” Humid air makes it worse. The first signs, from Mississippi State, are panting and drooping wings; later, combs and wattles lose colour and the birds go quiet. Shade, moving air and cool water — they drink two to four times as much in the heat — are the answer.