If you use your pool only on weekends, reduce your heater thermostats settings by eight to ten degrees during the week. Furthermore, when leaving for vacation for more than a week, turn off the pool heater, including the pilot light.
The lower the U-value, the better the insulation. In colder climates, a U-value of 0.35 or below is recommended. These windows have at least double glazing and low-e coating.