Ives1122 - The HVAC guys were very honest about the filter system and I am getting a 4-5 inch filter system, which they recommended.
JHZ563 - The guys I am using run a small local shop and have been quite busy servicing others in the hot weather around here. After the initial service call, the guy indicated that he would come out about a week later with the others in the shop and do an estimate. They came Tuesday the 5th, gave me a fair estimate and I put half down so they could order the equipment. They expected the new units to be in late last week and indicated they would install sometime this week. I am satisfied with their services so far and cannot complain about it taking time, as I understand that they have clients who are ahead of me and there was a 3-day holiday weekend.
As for doing the full system, the current system is 20 years old and took a direct hit by lightning 18 years ago. Lightning struck the chimney cap, went down to the furnace, burned out a circuit board on the furnace, burned out a relay on the ac compressor, and did a bunch of damage to other low voltage items throughout the house. The HVAC system got fixed and has worked fine for the past 18 years, but one has to wonder if there was any long-term damage to the furnace that could show up, if I only replaced the ac. I also work in commercial real estate and know that the life expectancy of equipment is generally 20 years at best, so I figure that replacing it all will save me money in the long-run.
NWL
