Because we have such amazing weather in Arizona, many homeowners are interested in heating their pool during the cooler months. You have options.
Solar Blanket
Your cheapest option, for a couple hundred bucks, you can put a plastic solar cover on your pool and raise the temperature up to 10 degrees. This makes the water tolerable a month earlier and a month later than your normal swim season, essentially extending your swim season from Spring Break to Fall Break. The downside is handling and storing the bulky blanket.
Solar Panels
An energy efficient means of heating your pool, Solar panels can be added to a new or existing swimming pool. The number of panels and thus the cost will be determined by the surface area of your pool. Plan on spending $5000 for a solar heating system.
Natural Gas/Propane
Gas heaters are great options for those who have pool/spa combos. A typical gas heater can heat up your hot tub in the dead of winter in less than an hour, and the cost is a few bucks. Plan on spending $2000 for a gas heater and $11/ft to run a gas line from your gas meter to your pool equipment. Gas heaters are efficient, but an expensive option to heat your pool. Heating your pool will cost a couple hundred bucks to get it heated, but once heated, can be maintained for a relatively low cost using a solar blanket when not in use, especially at night.
Electric Heat Pump
When the cost of natural gas and propane skyrocketed, electric heat pumps became more attractive. A new heat pump will cost a little less than $4000. Similar to a central air conditioning unit, but in reverse, a heat pump will extract existing heat from the outside air (rather than generating heat), and transfer it to the pool water. A heat pump has the ability to heat water 20 degrees above the ambient air temperature. So if it is 65 degrees outside, your heat pump will create 85 degree water. Not enough for a hot tub, but sufficient to swim. Be sure to install your heat pump in a warm sunny location to get the most out of it.
Another amazing feature of the heat pump is its dual ability to cool your water. Ever dove into your 90+ degree pool water in the middle of July and felt suffocated and unrefreshed? Some have even gone to the store to buy a couple bags of ice in a futile attempt to make a refreshing splash. Your heat pump can do that for you, cooling your water to a refreshing temperature.