Help with replacing AC estimates
We purchased a 2,400 sq ft house that is 20 years old in southwest FL on an island (aka, hot, humid & salty air). The house has the original air handler that still runs in the garage with a compressor outside from 2002. When I went to have the unit serviced, we were told there is way too much damage to even clean the unit outside and the air handler is filled with some kind of black growth and is rusted out.
So,now I'm shopping for a new AC unit. I have received 4 estimates and I'm looking for some guidance on the conflicting information I've been told.
First estimate quoted me a 13 SEER Bryant, a 13 SEER Trane and a 14.5 SEER Carrier. He said I should not go above 14.5 SEER given the age of our duct system. He said we won't know if the duct work can handle higher SEER ratings for 6 months to year after installing.
2nd estimate quoted me a 13, 15 or 16 SEER Carriers. This guy told me there would be no problems with our ductwork going with higher SEERs since it currently can handle a 4 ton unit. The 16 SEER also has a variable speed Air handler and a 2 speed cond. unit. He Recommended this given the high humidity levels in our area.
3rd guy didn't give me anything in writing and 4th quoted an Amana but he didn't spend more than 3 minutes at the house so not an option.
So my questions are:
1) How do I know if our existing ductwork can handle a higher SEER? Since I'm assuming currently were at like a 7-8 SEER, how do I even know it can handle a 13 seer?
2) I was also told that the Carrier unit is better for our area since it has copper instead of aluminum and will not oxidize in the salty air. Is there any truth to this?
3) Everyone has just said to replace our unit with another 4 Ton unit. Is there anything else I should be asking?
4) The first estimate guy crawled around in our attic and found areas where our ducts need to be mastic sealed and showed me pictures. The second estimate guy only poked his head into our attic and looked around and said our ducts all looked fine. But he didn't crawl around. Is that appropriate? What should these guys be doing when they provide me with an estimate?
Thanks in advance for your help!