Double pane windows are very effective here in Florida just like up North. I recommend you talk with a contractor who builds high efficiency homes in Florida and 140 mph hurricane rated homes.
Single pane windows are one of the biggest reasons so many home owners have high energy bills here in Florida besides low insulation in the attic and leaky duct work. In most case we cool our homes in Florida 8 months out of the year and if we like it cooler this could be costly.
I would consider upgrading the windows if it's in the budget. I recommend these window specs:
- Low-E type (SHGC.30) or better (Energy Star Certified)
- Argon gas filled, helps with heat gain and noise reduction
- Double pane, reduces heat gain
- Vinyl frame type, reduces convection and never needs painting
You mentioned you live in Orlando, so you probably have OUC as your power company. I would recommend you call them and ask for Kevin, Dean, or Shawn. They are very knowledgeable about windows in general and if requested they also offer FREE home energy audits and rebates. Go to OUC.com to find out more if you are interested.
For more information:
Read "Should I choose vinyl or non-vinyl replacement windows?" a Q&A answered by Susan Davis.