Single-stage: Lower equipment cost, less likely to break, low repair cost, low to average efficiency and high electricity cost

Two-stage: Moderate equipment cost, less likely to break, low to moderate repair cost, good to excellent efficiency and average electricity cost

Variable capacity: Higher equipment cost, more likely to break, moderate-to-high repair cost, excellent efficiency and low electricity cost

Variable-capacity heat pumps and ACs are also called “modulating.”

In general, as performance goes up, cost and efficiency go up. The cost to run the AC or heat pump go down.

Two stage is better as it will be more energy efficient and low maintenance with higher performance.

A 2.5 ton AC for a 2100 sq, foot house in NJ seems marginal. Are you able to maintain a 75 degree indoor temperature when the outdoor temperature is in the upper 90's like it is today? If so then the 2.5 ton is the correct size.

The 3 ton 2-stage may give you better humidity control. If you have trouble maintaining a 50% humidity level in the summer, then consider getting the 2-stage AC. Most 2-stage AC operate at about 70% capacity in the low stage. This means the 3 ton would be at about 2.1 tons in the low stage. This is not much mess than your current system. I would not be concerned about not being able to push enough air. The contractor also needs to verify the duct work can handle the extra air flow required for 3 tons of cooling.

If you live in are near Mercer county I can recommend the Carrier dealer who installed my equipment. He will do a load calculation to verify the sizing and offer several options of equipment.

Able to maintain 70 or 72 downstairs with a 5 - 7 higher temp upstairs. Humidity mid 50s to 60s. Can maintain 68 in the winter but system runs much more in cold temp. I'm in Burlington county. I've had one contractor perform manual J and confirmed 2 1/2 ton. I've had three other contractors come in without calc (to my knowledge) and state 3 ton would be better for my home.

Based on your experience and the Manual J calculation the 2 1/2 ton is the correct size. I am surprised the humidity level is as high as you state. What are you using for a humidity gauge?

It is difficult for a single system to maintain even temperatures on both floors for a house of your size. You are not getting enough air flow to the second floor. Have you tried closing any of the vents on the first floor? How much insultation is in the attic? You should have at least R-30.

Current status upstairs (see attached)

Current status downstairs (see attached)

Yes, closed vents in room where downstairs thermostat is located. Have insulation in the attic (blown in) but don't know what the R value is.

Closing off the vents downstairs should help but may produce whistling noises as the air leaks past the vanes. Do you have dampers on the ducts where they come off the main trunk? closing them off would be more effective by producing additional resistance to airflow to the downstairs rooms (and conversely pushing more air upstairs). You would need to reverse this in the fall/winter.

Do you have a basement? If so what is the temperature and humidity level in the basement? You may need a dehumidifier in the basement to help lower the humidity level.

Don't believe I have dampers. Let me ask you this. If I decided on single stage (forget two stage) , could a 3 ton really cause any issues? I realize bigger isn't always better but I'm thinking (layman here) that the increase would be more positive than negative and this is the one opportunity I have to "enhance" what I have now. Wondering since I'm not looking to increase size dramatically it would probably be fine?????

No basement, on a slab

You first have to determine if the duct work can handle the additional air flow. If it can't it will be hear more air noise. The run times will be shorter which could cause a higher level of humidity.

Thanks, I just measured the duct work that the air handler goes into and it's 20 x 8 rectangular. From what I can find that's 750 cfm (I think). Would those dimensions stand for the entire house? Anything we can take away from this?

Also, Return downstairs 30 x 6 (a lot of air moving)

Return Upstairs (23 x 9) won't hold a piece of paper but there is some air moving - not sure if this is normal.

There is a 2nd return downstairs approx 14 x 11. Rather odd, I feel some air moving but don't see that there is any ductwork it's connected to. This ls located as follows: Air handler | Wall | Open cavity | Return Vent.

The problem isn't the size of your heat pump, it's the ductwork. If a 2.5 ton otherwise works fine, I wouldn't get a 3 ton (single stage) - dehumidification will suffer and it will be noisy 100% of the time (as opposed to, maybe, 10%of the time with a 2 stage).