Energy Technology List home
Department for Business, Energy and Industrial Strategy

Tell us what you think about the new ETL website. Take the survey now.

Radiant and Warm Air Heaters

Warm Air Heating

Warm air heating equipment covers products that are specifically designed to provide space heating using the heat generated by a burner to raise the air temperature in the space(s) being heated; and optimising controllers that ensure warm air heating systems operate in an efficient manner.

Indirect-Fired Warm Air Heaters

Warm air heaters are widely used to provide space heating for warehouses, retail sheds, sports centres, factories, and other buildings containing similarly large spaces. Warm air heaters contain a gas or oil-fired burner that is used to heat the air in the space directly, or indirectly by means of a heat exchanger. A fan is used to distribute the warm air throughout the space(s) being heated. Warm air heating is often used as a replacement for traditional water based heating systems within commercial spaces.

The ETL encourages the purchase of higher efficiency indirect warm air heaters. Product types including on/off, high/low and fully modulating are covered; all must have the same efficiencies (when tested) to be listed, but fully modulating products are typically more efficient in use.

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.

Advantages of indirect-fired warm air heating equipment:

  • Low or high-level mounting possible
  • Relatively inexpensive
  • High thermal outputs available
  • More efficient than using a boiler and convector

Direct fire heaters (whether gas, oil or biomass-fired) are not eligible for the ETL.

radiant warm air heaters image 1.jpg

© Dravo Division – Johnson & Stanley Ltd.

Example: Installing an ETL listed indirect warm air heater at a total cost of £9,000 rather than a typical non-condensing product at a cost of £5,500 the potential annual savings are:

  • £1,070
  • 41,400kWh
  • 7.6 tonnes CO2

Radiant Heating

Radiant heating equipment covers fuel-fired products that are specifically designed to heat people or objects in the space below them by infrared radiation without heating the surrounding air directly, and optimising controllers that ensure radiant heating systems operate in an efficient manner.

Typically 35% of the heated air in commercial buildings is lost through ventilation and air infiltration. In large, open, high-ceilinged 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. Correct positioning of the heater is important and should be placed directly in line with the person/object requiring the heat.

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 directly by reflectors within the units, reducing energy lost through ventilation. The amount of fuel used is significantly lower than in a building heated by fan convectors or low temperature radiators.

Typical applications for radiant heating include retail units (particularly DIY outlets), sports centres, warehouses, factories and workshops.

As a rule of thumb, every 1°C reduction in air temperature through the use of radiant heating will produce a 5% to 10% reduction in annual energy consumption.

Electric radiant heaters are not eligible for the ETL.

Radiant Tube Heaters

A radiant tube heater consists of a steel tube with a gas or oil burner at one end of the tube and a flue gas fan at the other. The tube is surmounted by a metal reflector to produce a cone of radiant heat. As gas is burned, the temperature of the tube increases (up to 500°C) and it radiates heat. This heat radiation is directed downwards to heat the occupants of the space, much in the same way as light from a fluorescent tube. If your building is subject to high ventilation rates then installing an ETL listed radiant heating system could help reduce your heating costs by up to 20% compared with conventional air heating systems.

Within the radiant tube heater category, there are three basic types of radiant tube heating included on the ETL:

  • Unitary Radiant Tube Heaters
  • Multi-Burner Radiant Tube Heaters
  • Continuous Radiant Tube Heaters

Radiant Plaque and Cone Heaters

Radiant plaque and cone heaters are mainly used for local or spot heating due to the intense radiant source of heat. This is generated by an exposed flame passing over a catalytic matrix, the ‘radiant matrix’, which becomes extremely hot (up to 950°C).

radiant warm air heaters image 2.png

Optimising Controllers

Optimising controllers for radiant heating systems are also covered by the ETL. These include both standalone units and add-on module type products (for warm air and radiant heaters) and ensure heating systems operate in an efficient manner. These are pre-programmed to control the temperature in zones based on occupancy schedules and to switch the units off when there are zones unoccupied. The controllers also need to incorporate an optimum start mechanism that prevents overheating and a ‘self-learning’ program that monitors and updates the heating curve by taking into account changes in the climate and building usage. In addition, some heaters themselves may incorporate optimising controllers already.

Optimising controllers:

  • Automatically control the temperature in one or more zones within a building in an energy efficient manner that reflects predefined zone occupation schedules.
  • Automatically switch heating equipment on and off in accordance with the predefined occupation schedule for each of the zones being controlled.
  • Should also incorporate frost protection, condensation protection, and anti-tampering mechanism.

Building managers can define the temperature for different zones of a building as well as for different times and days of the week.