Air curtains provide a barrier of air to help lower energy costs by eliminating untempered outside air from entering through open doors. Exhaust fans force out stale air and pull in fresh, clean air for a more comfortable environment. Combusion air intake systems control the amounts of outside air for proper combustion of oil and gas heating appliances and for more efficent heating. Duct fans increase capacity to HVAC systems, while ductwork circulates air throughout a building. Energy recovery ventilators regulate the temperature and humidity of the fresh air they pull in and can improve indoor air quality. Kitchen and range hoods maintain proper ventilation in kitchen and cooking areas. Portable blowers and carpet dryers quickly dry wet carpeting, rugs, and other flooring surfaces. Direct-drive and belt-drive tubeaxial fans are used to help exhaust contaminated or hot air created in industrial applications, and supply air to help cool or pressurize interior spaces.