A Heat Budget for the Sleeping Infant: Room Temperature, Wrapping, and the Overheating Boundary

A sleeping infant produces heat continuously and can lose it only through the wrapping around it and the air of the room. This paper computes, from stated assumptions, the boundary in room-temperature and total-insulation space at which dry heat loss can no longer balance heat production, and turns that boundary into a tog-budget rule with an explicit safety margin. Four reference infants are modelled, from 3.5 kg to 10.0 kg. For the 5 kg reference infant, who produces 9.5 W while asleep, the no-margin balance boundary at a room temperature of 24 °C is 2.15 tog of total wrapping insulation; applying a 25 percent margin gives a working budget of 1.56 tog at 24 °C, 2.42 tog at 20 °C, 2.85 tog at 18 °C, and only 1.13 tog at 26 °C. Combinations in common use fall on both sides of the budget: a vest, a sleepsuit, and a 1.0 tog sleeping bag total 1.7 tog and sit outside the budget at 24 °C and above, while the same clothing with a light sheet totals 1.1 tog and stays inside it up to 26 °C. A 2.5 tog sleeping bag worn over a vest and sleepsuit totals 3.2 tog and is outside the budget at every room temperature from 18 °C upward. Fever and high humidity shrink the budget substantially: at 24 °C a fever of 38.5 °C lowers the 5 kg budget to 1.18 tog, and air at 80 percent relative humidity lowers it to 1.31 tog. The rule must not be applied to a febrile, unwell, or premature infant as a substitute for care; its failure cases are stated at full size in Sections 4 and 5.