You'd need a pretty powerful blower to damage a duct system, nothing you would ever find in a residential system. More likely your furnace would not get the correct temperature difference and may not operate correctly, which isn't that big of a problem if you have a 90+ furnace. It would probably be easiest to operate your blower on a slower speed, as long as you still get the required airflow. A rule of thumb is 400 CFM/ton, so about 1,000 CFM should do you just fine, you certianly don't need 2500 CFM. You may want to consider a high-quality pleated filter or an electrostatic air cleaner for your allergy problems.

Thanks, TigerDunes. We're about 7 miles inland with nearby rivers. 1st floor is about 2800 sq ft with 800 upstairs. The coils and/or tray is leaking so water is affecting the ceiling even after changing the ceiling drywall and wrapping the lines, not enough to cave in (yet), but I really think the air handlers need to be replaced to avoid mold, etc. I do not want to keep a leaking system. Although we could just pull the upstairs air handler (the likely culprit), repairing doesn't make sense to me if by replacing I can also increase efficiency since the system is more than 13 yrs old. One could reasonably expect it to fail in a couple of years. Might as well bite the bullet, but I could wait if new and theoretically better technology is about to emerge. Currently, the system cools well and we haven't been in this house for a winter, but it should keep the house comfortable enough for us since I don't like excessive heat (I know, FL is hot!). We have gas fireplaces which DH likes to use. Again, since I wanted to cure the handler problem, it seemed prudent -- if not mandatory - to replace the condensors, reduce electric consumption and get the tax credit, at least from the fed if FL doesn't move forward with their rebate . He will flush the lineset and said the new system requires a smaller, not larger, size than the existing. If you don't think it a problem to have a slightly larger copper run, then I could happily forego opening up the walls and resultant drywall repairs. But if I need to, I will buy the new linesets. I don't know the heat strip info right now, but I recall it will have emergency back-ups and will be sized to what we have now. Is there anything specific I should request regarding the heat strips? I have new programmable commercial Honeywell thermostats which will work with the new system. Don't have the model #s here, but you can program heat and cool times and temps on one screen. I agree FAD, and he is. Since anyone can have a bias and get used to their tried and true, I just wanted to learn more from you guys. Thanks for your help!

By the way, my decision to replace the entire a/c system is due in part to these factors: 1. Outside condenser broke down and it's 24 years old and uses R22 freon which is now being phased out in favor of R410A refrigerant. I didn't want to get a replacement R22 unit and I prefer to switch to R410A. 2. Evap coils are 24-years old and full of R22. Can't be cleaned because they have too many curves in the copper tubes, so they have to be replaced. 3. Existing lineset is full of R22 freon and the oils that go into the liquid. Many installers prefer to flush the existing lineset, but I got a lot of advise on this board to replace the lineset with a new one. This way you don't have to worry about the flush being done right. At minimum, I wanted to replace the evap coils, lineset, and outside condenser. Unfortunately, my existing gas furnace was installed upright in the attic and the evap coils are about 5 feet from the gas furnace. Even though the gas furnace works fine, I decided to get a variable speed high efficiency motor gas furnace to get the best possible SEER-15 with the new matched evap coils and new outside a/c unit. So, I'm getting a complete new system with new ducts, new lineset, new gas furnace, new coils, and new a/c condenser. If parts of my existing ductwork weren't original from the early 1950s and I wasn't using R22, I would have only replaced the broken outside condenser. It would only have cost me about $2000 to do this. I would have been happy with SEER-13.

tigerdunes, I have seen your great responses on many posts. Getting my neighbor to spend for a new system is tough as he is cheap..LOL. As he has a wife and two small kids, he need to do what is best for them. I also believe his blower motor is not working as expected as mine blows much harder then his. Furnace is Lennox G40UH(x) series. I am looking at the manual and wonder does this blower have a manual 2 speed on the circuit board and maybe wired at the slow speed. (I read this somewhere) http://0190acd.netsolhost.com/manuals/G40UH_Series.pdf I am not thrilled to go in his attic when it is this hot but I worry for his family. How do I tell if the blower is okay?