First of all, it is considered poor forum etiquette to start a new thread when you already have an active thread. Questions that you have not answered in earlier thread. What is the brand, model, size, and efficiency of existing propane furnace? What is its blower size rating? This is important if you are considering just adding on a heat pump with matching coil to existing furnace. If you really require a 5 ton, then this would most likely require significant ductwork modifications to handle the additional CFMs. Has any of the dealers mentioned this? Mighty important. What is your cost/gallon for propane? What is cost/KWR for electric? Tell us about existing problems with current system and location of problems? Basements at or partially below grade have low heating and cooling loads. Tell us about your average temp for both summer and winter? And extremes? What are your inside design thermostat setting for heating and cooling? How did existing 4 ton AC perform when it was working correctly as far as meeting your comfort requirements? The finished basement should have its own separate system preferred or at very least a zoning control. Any opportunity for insulation improvement/upgrade to basement area? I would want to see a separate load calculation for basement zone. Have you seen the load calcs in writing so that you can review? On the software letterhead? Post back. IMO

Bill, If your home rates(Manual J) at 4.3 tons and you have quite a few days over 100F Then my opinion would be to go with the 5 ton system. The 4 ton system would continuously run and may not reach a comfort temperature of 76-78F on those hot days.

IâÂÂm surprised that an Infinity HP was mated with an 80% efficiency gas furnace and not an Infinity 96.6% efficiency MVB or a modulating MVC -3-stage furnace. Either of these furnaces would have the Infinity thermostat and variable speed blower, âÂÂIdeal Humidityâ etc. and probably have been able to better interface with your existing duct system by having the HP & furnace just run at lower speeds/capacities. I have not heard of an 80%AFUE Infinity gas furnace in our region (Canada). Largest capacity here is 113Mbtu @ 2000cfm for an Infinity gas furnace. Higher efficiency (96% Vs 80%) also means a smaller furnace may be installed as well as less fuel burned, lower emissions etc. In our region, Infinity HPs come in 1-ton increments and there is a substantial price differential between models. SR

Let's review what you stated: The original load calculation for the house was 3 tons, but the builder allowed you to pay to oversize it. Builders are happy to take money for upgrades whether it makes sense or not. That extra room you were going to add would not have made a significant impact on the load calculation. All the neighbors with the same model have a 3 ton unit. Do you ever hear them complain their AC can't keep the house at 75 degrees on the hot summer days? You other estimates have specified a 3 ton. They can easily sell you a bigger condenser and make more money, but they are choosing not to do this. You live in Florida which suffers from high humidity. This is the primary reason you should not be over sizing the condenser. You want the indoor humidity to be 40-45%. If you over size you will never achieve this level. The statement that really bothers me is that he is telling you that if you buy a single stage then you should get a 3 ton size. His logic about the 2-stage sizing is wrong in my opinion. The primary reason for spending money on a 2-stage AC is for improved comfort. If you get the 4 ton you are wasting your money. You might as well buy a 3 ton single stage. If you really want this questioned answered then have a load calculation done. A reputable contractor should do this as part of his quote.