Warm Air Heating Guide


How a Warm Air Heating System Works

A warm air unit works by heating air over a Heat exchanger. It then blows this warm air around the house by way of a fan unit. The air is distributed by way of registers (adjustable grilles). Warm air is fast operating and easily controlled.


What is the difference between a "Basic" unit and a "MAF" or "ET" unit? Does it matter?

  • A "basic" warm air unit is the entry model of heater in any situation. The temperature is controlled via a room thermostat, while the fan is controlled by a mechanical bi-metal strip instead of electronics. The fan runs at a single speed. There is nothing wrong with a basic model unit, and for many customers on a tight budget, the basic model is an adequate replacement. The new basic unit will still be far more efficient than an older unit.
  • The Modairflow (MAF) or system ET units are more advanced in the technology that they use. The heat ouput of the warm air unit is controlled and adjusted automatically by modulating the flow of warm air. This results in very stable room temperatures and quiet running. The main difference from a basic unit, is that the thermistastat controls the fan speed as well as the burner.

What are the key parts of a warm air unit?

  • Fan Unit - The fan blows the warm air that has been created directly around the house via ducting. It is important that the fan is kept clean (by way of an annual service) to ensure that it is running to its optimum. If your warm air unit is noisy it is likely that your fan has become out of balance and may need replacing.
  • Heat Exchanger - The heat exchanger transfers heat from combustion to circulation air. It is important that the heat exchanger is checked on annual basis to ensure that there are no cracks in it. If your heat exchanger is cracked (especially on older units) it is likely that your whole warm air unit will need replacing.
  • Burner - The burner is (as it sounds) a metal bar that the gas runs through via  an injector. The burner flame is produced by small holes in the burner bar. Once again it is important the burner is kept clean of debris on a regular basis. If the burner is dirty it may cause a poor gas/air mixture that can lead to yellow flames, which in turn can cause a soot build up.
  • Flue - The flue is very a important part of the unit as it takes away the products of combustion (bad gases) away from the warm air unit to outside atmosphere. As you can see in other sections of this guide there are different types of flue, conventional (also known as open), balanced and fanned. In older units, conventional flues are still mostly used. These flues often route through the loft and terminate above the roof by way of a metal terminal or a ridge vent tile. It is absolutely vital for the safe use of your unit that the flue is installed correctly and that it is "pulling" products of combustion away from the heater properly.
  • Gas Valve - The gas valve allows gas to pass to the burner at a desired rate and at the times controlled by the time clock and room thermostat. If you the pilot light on your unit constantly goes out, it may be the case that your gas valve has failed.
  • Limit Stat/Switch - This is a safety device that will cut out the burner if the unit goes into a state of overheating.
  • Time Clock - As with any regular central heating system, the time clock controls when the unit will come on and go off.
  • Room Thermostat / Thermistastat - The room stat controls how the unit will come on and go off subject to the temperature that you set it at. It will maintain the temperature in your home at whatever you set it at. The more advanced thermistastat sends a continuous signal to the unit to ensure an even greater level of accuracy.

  Need advice?

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