There are occasions when a ventilation scheme must include some form of heating for the replacement air to prevent the temperature of the air in the room from being lowered to an uncomfortable level.

Unless the air replacement openings can be located behind existing radiators, or the incoming air can enter from a room already warmed, the most convenient method is to use an intake fan in conjunction with a heater battery, either electric, hot water or steam, the required heat output being calculated by a similar formula as given for Heat Removal, using the known factors of air volume supplied and the temperature rise required.

e.g.	A ventilating unit supplying 1530m³/h of air at 0°C which is to be warmed to 19°C before being discharged into the room. What will be the required output of the heater battery?
	The formula is now transposed to read:
	kW  =	m³ × °C
		3000
	=	1530 × 19
		3000
	=	9.7

Electrical heater batteries are made with the elements built into a sheet steel flanged short duct complete with safety thermal cut-out, ready to fix to a duct or wall, the elements being of the 'black heat' type. Hot water and steam heater batteries are not so flexible in application as the electrical type, particularly for the smaller outputs such as used in the above example, and the selection of a battery for a particular duty should be left to the manufacturers. The additional resistance to air flow of the heater battery must also be taken into account; this will depend on its type, size and design.