I know you may not know the answer to this question, but I'll ask it anyway. Why the increase in size from 3.5 ton to 4 ton? Sometimes air conditioners are undersized, but more often it is an issue of poor ductwork and air distribution causing comfort issues. Increasing tonnage in this case would then be bad unless deemed necessary by a proper heat load calculation. If you heat with propane, and it's expensive, you will not be too happy with the price to heat with straight electric heat. Heat pumps heat more efficiently but do carry a higher price tag. If you heat for at least 2 months out of the year, I would strongly look into it. By my statement about comfort and efficiency, I mean that there are higher efficiency options, which you were quoted (14.5 SEER) despite what I feel is an unreasonable upcharge compared to actual equipment cost difference. However again I do not know whether your indoor model is changing with that 14.5 SEER upgrade. Which brings me to my next point, variable speed indoor units can raise efficiency while also increasing comfort because they can provide a more precise airflow by adjusting RPM to overcome duct static issues, can be set up to control humidity, and are generally quieter, especially if you run the fan during the day. I would recommend a variable speed air handler with any system. For York, model would be the MV16C/MV20D and that would require a coil as well, FC48C/FC60D, for instance (2-piece set up). The AHP is a bare bones air handler. Nothing wrong with that, if you are looking at upfront cost versus added comfort and efficiency. 2-stage equipment is another option at your disposal and can help with humidity control by running at a lower capacity most of the time for longer periods of time. Doesn't seem like all your options were explained to you by this dealer. I like York equipment, and I have no immediate problems with what you were quoted, but York offers better options in terms of comfort and efficiency. Cooling season is big for you, so higher efficiency and 2-stage units might be worth looking into. Don't be afraid to get 2 or 3 more estimates until you feel comfortable. Carrier is also a good brand to look into with their "Infinity" system.

Update: Before the install, I did wind up modifying the track in the air handler for the 1-inch air filter. I used 2 pieces of steel banding, 2 inches wide, cut to length, and placed them over the manufacturer's track using a few dabs of automobile body putty (Bondo) to keep it secure. It is now a smooth track for the filter to slide on. Goodman used the track as part of the frame of the air handler so it had some crimpings in it and the filter would not easily slide in. I also trimmed away some foil faced insulation that prevented the filter from seating properly. A 20"x24" filter now fits perfectly. I am glad that I did these minor mods as I would have been fighting this monthly when I change filters. The unit was installed Friday, 6/22, after I had it for about 5 weeks waiting on the installers. It took two guys 8 hours. I fed them both breakfast and lunch (I treat my installers well). The old supply air plenum and the plenum after the air handler had to be replaced to match the new unit. The old 5/16" liquid line had to be replaced with a new 3/8" line. 3 holes were cut into the finished ceiling and 1 in the wall so that the new line could be run. I'll repair the holes when I get a chance - no big deal. The TXV sticks out about 8 inches from the air handler. Looks funky and I have to be careful not to hit it while moving things around in that area. The old outside unit had sunk about 4 inches into the ground. I filled the hole with soil that I was saving, packed it down, put a plastic condensor mounting pad on the dirt, and used 3" thick brick to elevate the outside unit (which is huge in size compared to the old 7 SEER unit; 14 SEER = more coils = larger unit). The outside unit is much more quiet as expected but the new mult-speed air handler is also a little more quiet than the old one. The fan is set on low speed and I'm not sure of the setting of the old unit as the lables on the motor had worn away after 21 years. The sheet metal in the new air handler is flimsy and the track for the air filter can be improved by Mr Goodman. The outside unit looks decent. These comments were also noted by the installers. I plan on taking the outside and inside coils to a local scrap facility and sell the copper. Maybe I can get a few $$ for a couple cases cases of my favorite beer. I can now start saving 40% on the cooling and heating part of my energy bill and use this to combat the 65% increase in electric rates in the State of Maryland. All in all, I thought that I got a good value for the money spent (only time will tell if I made the right choice with Goodman). I got a 14 SEER system with Copeland scroll compressor, thermo-expansion valve on the air handler, hard start capacitor, 15 kw heat strip kit, bypass humidifier, and 10 year parts warranty for $2477 from a local HVAC supply shop. I paid $1200 for a pro install (needed the pro install for the warranty). Total cost was $2k less than...

I have a luxaire 3 ton 14.5 seer heat pump. that is the same as York. I just purchased in october 2009. Mine has worked like clockwork so far and I used it alot here in NE ohio this winter. I have been very happy with it. Your 4-ton sizing sounds just perfect for your size house. 5 tons is oversized expecially considering how well built yours is. You will find the new York system is very quiet and efficient. That sounds like alot of money though to be honest. Maybe York costs more than Luxaire.

I live in the Seattle area as well, and I was considering the same thing last year. I went with Heat Pump and 80% for a variety of reasons, but the main one is that relatively speaking, our electricity is cheap and you have more redundancy with Heat Pump and 80% furnace. 95% of the year, the heat pump gives me enough heat to keep my house at 71 degrees 24/7. When it gets below 32 degrees or so outside (which isn't very often), the furnace kicks in to supply heat. If the heat pump ever fails, you can use the furnace for heat at any temp. And since 95% of the time, you are running on Heat pump anyways, the gas usage of the 80% eff furnace isn't going to matter much. Remember that because a heat pump gives you MORE heat energy than you put into it (by moving heat from the outside to inside), it is over 100% efficient! No gas furnace can make the same claim. I went with a Bryant Evolution system though and not any of the brands you mentioned. Their evolution control is the best in my opinion and I have been totally happy with it. Whichever way you go though, you do definitely need to make sure you have enough air return. No matter how good the system, an insufficient return will cause all sorts of problems.