This 20-40-60 Min Push Button Timer by Fantech allows you to control your HRV/ERV system with multiple settings. The green light will show when the button is pressed one time, energizing your HRV/ERV system to high speed for 20 minutes. To run your system for 40 minutes on high speed, press the button twice and the yellow light will come on. For a full hour of high speed, press the button on this control three times, and the light will turn red. Ideal for areas with excess moisture, steam and/or odors, this timer will be a great addition to your home.