Since high performance windows will reduce the cooling load on the home, it may be possible to install a smaller air conditioner than would be needed with standard windows.

The chart above shows that the same 2000 ft² house that would need about 4.5 tons of cooling to maintain comfort with single pane windows may only need a 3 ton unit with high performance windows.

Or for an existing house where the air conditioner can't quite keep up with the cooling load, high performance replacement windows may reduce the load enough to maintain comfort.

The left vertical axis of the graph shows that the peak electrical load is reduced significantly with high performance windows too. This helps the electric utility company, since reduced peak demand will allow them to provide reliable power to more homes without needing to build costly new power plants.