Typically 35% of the heated air in commercial buildings is lost through ventilation and air infiltration. In large, open, highceilinged buildings with high ventilation rates, the proportion can be even higher, particularly where there is local exhaust ventilation for fume control. Radiant heating reduces these energy losses by heating the occupants directly, not the air. Units typically contain a gas or oil-fired burner that is used to heat a tube, cone or plaque that emits infrared radiation when hot. The infrared radiation is focused and directed by reflectors within the units. This means that the air temperature, and hence the energy lost through ventilation, and the amount of fuel used is significantly lower than in a building heated by fan convectors or low temperature radiators. Radiant heating reduces losses and can improve comfort as there is more control over when the heat is on and where it is directed – the whole space need not be heated. Correct positioning of the heater is important and should be placed directly in line with the person/object requiring the heat. Typical applications for radiant heating include retail units (particularly DIY outlets), sports centres, warehouses, factories, workshops and animal houses.
Indirect-fired packaged warm air heaters consist of a gas or oil burner, heat exchanger and hot air fan. Air from the room is recirculated through the heat exchanger and back into the room at high velocity. The hot air may be discharged directly from the unit or ducted into the room. Flue gases are discharged to the atmosphere outside the building. Both floor standing and suspended units are available. Indirect-fired packaged warm air heater modules use a similar set of burners and heat exchangers, but are designed to fit within air handling units to heat the fresh air being introduced to the building. Only the module is eligible for the ETL and not the air handling unit in which it is mounted, or the associated ductwork. Installation or replacement of indirect-fired warm air heating should always be considered in conjunction with possible building fabric improvements and minimising uncontrolled air leakage. There may also be benefits from the installation of ventilation heat recovery in some circumstances. Condensing models (units that recover additional heat from the water vapour within the exhaust gases) are available that offer far superior energy efficiency over typical non-condensing models. These may be more expensive but are still very cost effective over their lifetime.More information (PDF)