Final answer:
Direct-vent appliances draw air for combustion from the outside atmosphere and discharge all flue gases outdoors, maintaining indoor air quality by preventing the accumulation of combustion pollutants.
Step-by-step explanation:
Appliances that are constructed and installed to ensure that all air for combustion comes directly from the outside atmosphere and all flue gases are discharged outdoors are known as direct-vent appliances. These include various types of fuel-burning appliances such as space heaters, wood stoves, gas stoves, water heaters, dryers, and fireplaces. The purpose of these appliances is to prevent combustion pollutants, which come from the burning of materials, from accumulating inside the home. Using such appliances helps to maintain indoor air quality by ensuring there is a constant supply of fresh air for combustion and an efficient path for exhaust gases to leave the house. It’s important to always follow manufacturers' instructions and provide adequate ventilation when using fuel-burning appliances.