We have a 450 square foot lanai, and did not add a duct to the lanai and it cools just fine when we had it enclosed. We keep the original sliders open all the time and keep the lanai sliders closed most of the time, but open them when the temperature is in the low 70's or lower. It was done in May so we have been through a summer with it. We thought we might have to add a split unit, but were happy to find out we didn't. The bill went up $40 to $50 per month in the hottest months, and maybe $20 in the cooler fall months.
As far as code, all the contractor had to do was make sure there was a vapor barrier. That was satisfied when we put Chattahoochee River Rock down as the flooring, but other surfaces would have been fine as well.
My advice is make sure you get high rated doors and windows when you do your enclosure, and make sure plenty of insulation is added above the lanai. If that is done properly, you may not need a new unit at all, especially if you lanai faces north or east.
|