A baby’s room should stay between 61°F and 68°F (16–20°C), according to the Lullaby Trust, one of the leading safe-sleep organizations. Below 61°F (16°C) is generally too cold, even with appropriate sleepwear. Overheating actually poses a greater risk than a slightly cool room, but letting temperatures drop well below this range forces your baby’s body to burn extra energy and oxygen just to stay warm.
Why Babies Lose Heat So Quickly
Babies are far less capable of regulating their own temperature than adults. They have a higher surface-area-to-body-weight ratio, which means heat escapes faster through their skin. They also lose a significant amount of heat through their heads. A baby’s wet skin can drop 2° to 3°F through evaporation alone, and premature or low-birthweight babies often lack enough body fat to insulate themselves even in a warm room.
When a baby gets cold-stressed, their body diverts energy and oxygen toward generating warmth. Research from Children’s Hospital of Philadelphia shows that if a baby’s skin temperature drops just one degree below the ideal of 97.7°F, their oxygen consumption can increase by 10 percent. That’s a meaningful metabolic burden, especially for newborns or preemies who are already working hard just to grow.
The Risks of a Room That’s Too Cold
A room that dips below 61°F puts your baby in a position where layering alone may not compensate. Sustained cold exposure can lead to mild hypothermia, where the baby’s core temperature falls below 97°F. Signs include cool-to-the-touch skin (check the chest or back of the neck, not hands or feet, which are often cool normally), lethargy, weak crying, and poor feeding. In severe cases, the skin can appear mottled or blueish.
Cold air also affects the respiratory system. Research published in 2022 found that breathing air below about 40°F impairs the nose’s ability to fight off viruses like RSV, influenza, and the common cold. While indoor air rarely gets that cold, an unheated room in winter can easily reach the low 50s overnight, especially near drafty windows. Babies who breathe consistently cool air may be more vulnerable to respiratory infections during cold and flu season.
Overheating, on the other hand, is linked to a higher risk of sudden infant death syndrome (SIDS). The CDC advises watching for signs like sweating or a hot chest. This is why the safe range has both a floor and a ceiling. The goal is a comfortably cool room, not a warm one, paired with the right amount of sleepwear.
How to Dress Your Baby for the Room Temperature
Sleep sacks and wearable blankets use a rating system called TOG (Thermal Overall Grade) that tells you how much insulation the fabric provides. Matching the TOG to your room temperature is the simplest way to keep your baby comfortable without loose blankets, which are a suffocation risk in the crib.
- 75°F to 81°F: A lightweight 0.2 TOG sleep sack, or just a onesie.
- 68°F to 75°F: A 1.0 TOG sleep sack over a short-sleeve bodysuit.
- 64°F to 72°F: A 1.5 TOG sleep sack. Add a long-sleeve bodysuit underneath if the room is at the lower end.
- 61°F to 68°F: A 2.5 TOG sleep sack over a long-sleeve bodysuit or footed pajamas.
- Below 61°F: A 3.5 TOG sleep sack with warm pajamas underneath. At this point, though, consider warming the room rather than adding more layers.
Do not put a hat on your baby indoors. Babies release excess heat through their heads, so a hat can actually cause overheating, even in a cool room. To check whether your baby is too cold or too warm, feel the back of their neck or their chest. If the skin feels clammy or sweaty, remove a layer. If it feels cool, add one.
Warming a Cold Nursery Safely
If your home regularly drops below the safe range overnight, the simplest fix is running your central heating on a low setting with a thermostat. A room thermometer near the crib (but out of reach) gives you a reliable reading, since the temperature in the nursery can differ from the rest of the house.
Space heaters are an option but come with serious safety requirements. Nationwide Children’s Hospital recommends placing any portable heater on a flat surface at least three feet from anything flammable, including curtains, bedding, and crib fabric. Plug it directly into a wall outlet, never into an extension cord or power strip, which can overheat. The most important rule: never leave a space heater running while you sleep or while the baby is alone in the room. Only use heaters with a safety certification label from a recognized testing lab like UL.
A safer alternative for overnight use is a small oil-filled radiator with a built-in thermostat and automatic shutoff. These don’t have exposed heating elements and maintain a steadier temperature than fan-forced heaters. Even so, keep them away from the crib and check that they can’t be knocked over.
Quick Temperature Check Without a Thermometer
If you don’t have a room thermometer, use yourself as a rough guide. Stand in the nursery wearing a single layer of clothing. If you feel comfortably cool but not cold, the room is likely in the right range. If you’re reaching for a sweater or notice your own skin feels chilly, the room is probably below 65°F and your baby needs either a warmer sleep sack or a slightly warmer room. The Lullaby Trust notes that keeping the heating on all night is rarely necessary. In most cases, one extra layer of sleepwear is enough to bridge a small gap between your room temperature and the ideal range.