The designer did not listen to my instructions. I told the salesman that the floor was highly insulated below the subfloor and that the vinyl covering had a temperature limit of 85 degrees. He specified your hottest possible arrangement for the floor size. (Three inch spacing with 3.7 watt wire and very narrow areas at the edge.) It should have had 4 or 5 inch spacing with your cooler 3.0 watt wire. ) I did not catch it until I had it for a while and was very bothered that it was too hot. Eventually I had to send it back and order a much shorter wire.
I'm sorry, we no longer stock the older-style 3 watt cable in a size that is required for your space. We apologize if there was a mixup in our discussions with you. We have historically had very good results with 3.7 watt cable spaced at 3" for enclosed porches. Enclosed porches are usually subjected to high amounts of heat loss, even if the floor is well insulated. It is better to have plenty of BTUs with some to spare than to not have enough. The thermostat that you purchased comes with a floor sensor. With the floor sensor installed in the floor, the thermostat can be set to limit the actual floor temperature to a specific temperature. This "Floor Limit" can be set to any temperature that you desire, or is required by the flooring manufacturer. The floor temperature will not exceed the value you enter, whether the wire is spaced at 3" or 4". We have found that 4" wire spacing works well in a second floor room with a heated room below, but may not have enough output for an enclosed porch. We rarely, if ever, quote 5" spacing because of "striping" of the heat which can result in cold spots in the floor. In the end, we always design a system that we believe will consistently deliver a great result. Thanks for your feedback, we appreciate it.