An energy recovery ventilator is a device similar to a heat recovery ventilator (HRV) but that also includes a humidity regulator to remove excess humidity (or add humidity) to the air that is being brought into a house. Energy recovery ventilators (ERVs) are especially suited for use in climates where cooling loads place strong demands on HVAC systems. However, ERVs are not the same as dehumidifiers. What they do is transfer moisture from the humid air stream – the incoming outdoor air in summertime – to the exhaust air stream. The desiccant wheels used in many ERVs become saturated quite quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. In some cases, ERVs may also be effective in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream is transferred to incoming outdoor air.