Pollutants that affect indoor air quality are usually grouped into two categories: particulate matter and gaseous pollutants. Particulate matter includes small particles from such things as dust mites, animal dander, tobacco smoke and pollen. Gaseous pollutants include gas cooking stoves, pesticides, cleaning products and vehicle exhaust.

One goal of indoor air quality monitoring is to ensure that the air inside a structure is safe to breathe. This can be an issue in facilities where people work with toxins or dangerous substances. For example, in a biological research facility, release of a bacterium or virus into the air could be a health threat. Likewise, in a chemical plant, a release of chemicals could be dangerous.

A thermostat timer is part of a programmable thermostat that allows the temperature of a room or home to be regulated according to the time of day. Both analog and digital timers exist, with digital timers generally being more flexible. The unit itself is usually integrated into the standard thermostat of a home, giving it control over the heating and cooling systems that are installed. Many homes use a thermostat timer because of the amount of money that can be saved, and because they work automatically.

The simpler of these devices will essentially activate or deactivate the appliances plugged into them when a room's temperature reaches a preset threshold. Some units have more than one receptacle in order to accommodate the operation of several appliances. These small components allow users to protect against heating system failures by activating a portable heater in the event of cold temperatures, or they might be used with heat lamps, tank heaters, or engine block heaters in garages and marinas. They can even be linked with lights or strobes to create an instantly recognizable, highly visible freeze warning.

Such devices are also useful for preventing a pet's environment from getting uncomfortable. The control possible with a plug-in thermostat, when used in the appropriate environment and dry conditions, affords users more controllable and comfortable environmental conditions with a better-managed energy impact.

A network thermostat, sometimes called an Internet thermostat, allows property owners to control the temperature of their heating and air-conditioning systems from other locations. This is done through an Internet protocol network accessed by computer or mobile phone. 

A furnace thermostat is a control unit for a central heating system such as those found in homes and businesses. The thermostat’s purpose is to maintain a temperature that is near the desired temperature, called a set point. To do this, the thermostat turns a furnace on and off remotely as needed to maintain the set point temperature.

When used in conjunction with heating and cooling systems, a duct fan is intended to propel the hot or cold air into a room or space. This increases the efficiency of the furnace or air conditioner by effectively increasing the number of blowers associated with the unit. Such fans are commonly used in spaces that are difficult to heat or cool using ductwork alone, such as manufacturing spaces with high ceilings. A duct fan may also be used when maintaining temperature is critical, such as in a room housing computer servers that must be prevented from overheating.