An air-conditioning system works with help from a condenser, left, which is the part of the system outdoors. The ductwork system is also a critical part of keeping the house cool.

Every year, thousands of Arizona residents email Rosie Romero's website or call his radio show with questions about everything from how to prevent fires in their chimneys to what to do about the tree roots in their sewers. One of his goals is to provide answers that suit the specific lifestyle wherever someone lives in Arizona.

QUESTION: I'm having a 2,300-square-foot home built for me, but I don't know how "efficient" an air conditioner I should have installed. The builder will put in a 13 SEER-rated AC as part of the package, but will upgrade to a 14.5 SEER for $550 more or a 16 SEER for $3,000 more. What's your advice?

ANSWER: The efficiency of air conditioners is rated by what is called the Seasonal Energy Efficiency Ratio or SEER, and of course, the higher the rating the more energy efficient an air conditioner will be. Many older HVAC systems have SEER ratings of 6 or less; the minimum allowed today is 13.

If you pay a $3,000 upcharge for a 16 SEER model, you might not recoup your investment with the resulting lower monthly payments for energy unless you live in the house for a very long time. In addition, remember that when those SEER ratings are done, they are measured by technicians in perfect "laboratory" conditions. In the real world, you may not have those conditions.

If you choose to buy a more costly AC, make sure the builder puts in rigid ductwork rather than flexible ductwork. Rigid ducts will be more durable and provide fewer air-flow restrictions. You also want them to install oversized air returns in the house in multiple locations. You might want to consult with an outside air-conditioning firm about the quality of the equipment that the builder will install.

Over the long run, you will be more comfortable in your home if it has a well-designed and -constructed ductwork system than you will be with a more costly piece of equipment.

Q: Does misting the air outside around the condenser of an air conditioner while it is running make it any more efficient?

A: We generally don't recommend doing this because of the likelihood that the coils might freeze is high, even in times of extreme summer heat. Of course, once a year - or after a major dust storm - you should clean your coils to keep them working efficiently. When dust coats the outdoor parts of the condenser, the refrigerant in your system will not remove as much heat.

First, be sure to turn off the power source; then thoroughly hose down the condenser. But remember constant water or misting will do more damage than good.

Q: Should I replace my big-tank water heater for a tankless model?

A: Tankless water heaters - whether gas or electric - can be costly. Besides installing the appliance itself, you may have to run special equipment into each bathroom as well as into your kitchen. You also need to install a water softener if you don't already have one. Hard water with lots of calcium in it can take a toll on a tankless heating system.

But if the investment is feasible for you at this time, you can save up to 50 percent on your water-heating bill. They also save space; so you might feel as if you have added an entirely new closet to your home because you gain a lot of square footage in your garage or a closet.

Remember as well, that when you are ready to bathe or shower, the warm water will not just be sitting there waiting for you. That might mean a change in routine for you and your family. Consult a plumber to find out if an option like this is the best one for you. You might even find some other option for home water heating that is energy efficient and more reliable for you.

For more do-it-yourself tips, go to An Arizona home building and remodeling industry expert for 25 years, Rosie Romero is the host of the syndicated Saturday morning Rosie on the House radio program, heard locally from 8-11 a.m. on KNST-AM (790) and-FM (97.1) in Tucson and KGVY-AM (1080) and -FM (100.7) in Green Valley. Call 1-888-767-4348.