At 22 years old, your system is ancient. It is 8 SEER. You can easily get 13-16 SEER today, which will result in a significant improvement in efficiency and comfort. We just replaced our 22+ year old 10 SEER Lennox heat pump with a 19 SEER Carrier Infinity system (pretty high end in the Carrier line). Our old system was still running reasonably well, but we had had a few (minor) service calls recently, and I figured that we were probably on borrowed time. Better to replace it at a time and place of our choosing rather than HAVING to replace it when it fails in the middle of a summer heat wave or a a winter cold snap.
We love our new system. When it runs, it usually runs on low. We can barely hear it. It maintains are desired temp very well and, by running longer, removes more humidity, increasing our comfort.
Here are some features of our system (that I would recommend to anyone getting a new system):
1. Two stage condenser (outside unit). Runs at low most of the time (that it runs). Cranks up to high when a significant cooling demand is requested (drop thermostat down a few degrees) or if it is so hot that low cannot maintain the desired temp.
2. Variable speed air handler (required in order to get the most out of two stage condenser). Again, runs on low most of the time. Running for longer periods at low speed maintains desired temp better and removes more humidity from air. Controlling humidity better ctually allows one to run at a higher than expected temp and still maintain comfort.
3. Dehumidify on demand. Even if the current temp is at or below the desired temp, the system may still run at low speed for dehumidification. Again, less humidity, more comfort.
What would I recommend for you?
1. Require a Manual J calculation to ensure correct system size. Some might call it a load calculation. Your current system may or may not be correctly sized for your home. Manual J takes into account square footage, home orientation, windows, insulation, heat gain/loss, and more parameters. Do not rely on "rule of thumb" estimates like 1 ton per 500 sq feet. Do not assume that your original system was correctly sized.
2. Consider two stage condenser/variable speed air handler. This may up the price, but it will also increase efficiency and increase comfort. I suspect that there is not much point in getting either a two stage condenser or a variable speed handler but not both, but I'm not an expert.
3. When comparing estimates, make sure that the dealers are quoting comparable systems. If one dealer quotes a Carrier Infinity System, and another quotes a Goodman builder grade system, you can bet that the Goodman will be cheaper. It would be like comparing a Cadillac (or your favorite luxury car) to a Chevy Impala. The Impala might be a fine car that will get you where you want to go, but, feature for feature, it is probably not comparable. Generally, a brand will have "good, better, best" models. At the least, when comparing between brands, it is probably a good idea to compare similar tiers.
4. Someone upthread mentioned that quality install is as important as quality equipment. I agree. However, I do think that not all HVAC equipment is created equal, just like all cars are not created equal.
5. Do you have any accessible ductwork (like in an unfinished basement or garage) If so, consider having it checked to ensure that it is well sealed and insulated. About 40% of our ductwork was accessible (in garage). We had trunkline resealed (mastic and tape) and branch lines replaced with R8 insulated flex duct. The idea is to create air tight (to the extent possible) duct system to preserve your cooled air and to prevent air infiltration. I can tell a difference, if for no other reason than our garage seems to be hotter than it has been in the past.
6. Ensure that refrigerant lines are sized correctly for new system. What you currently have is probably sufficient, but you want to be sure. Your current system probably uses R22 (freon). Your new system will probably use R410A (puron). If the lines can be reused, ensure that they are flushed (I think they use nitrogen). You want to get all of the remnants of the old refrigerant/lubricant out of the lines so that it does not contaminate your new equipment (the two refrigerants and lubricants are not compatible).
7. Try to have some idea of a "good" installation. When our system was installed, we had a few punch list items that to be addressed afterwards: some ductwork not adequately sealed (could feel cold air coming out of a seam), condensate trap not installed correctly (easily determined simply by looking at installation instructions and comparing to our installation).
8. Consider getting a system with a "communicating" controller (thermostat). The controller will,optimize the operation of the condenser and air handler for efficiency and comfort. This is a higher end feature, but I think it is worth the cost.
I strongly recommend these two forums. You will find several helpful pros that will help assess your equipment needs and will help evaluate your quote (e.g. do competing quotes specify comparable equipment and work to be done).http://ths.gardenweb.com/forums/hvac/
(I especially like "tigerdunes" here).http://hvac-talk.com/vbb/forumdisplay.p ... ntial-HVAC
Spend some time reading these forums. Pay special attention to posts from people getting new systems. Take note of the responses of the pros. You will find that people are often quoted systems that are too large or are not based on a rigorous calculation (Manual J). People often post competing quotes that are not really comparable (two stage condenser/variable speed air handler vs single stage condenser/single speed air handler).
Do not be duped into buying more tonnage than you really need.
Be aware that a new, modern system might run longer than your current system. That is ok. It is supposed to work that way, especially if you go the two stage/variable speed route.
Good luck! I hope you like your new system (when it is installed) as much as we do.