Really depends on the construction and that is where the manual J comes in. You have some real heat gains with a 2 story & lots of glass. It would be beneficial to have a local do a heatload for you. A lot less money than having the wrong size unit and unhappy wife for years to come. With that big sqft split you may consider two systems too. If you don't want to go that route it is usually 400 sqft per ton here in s fla. See if there is a local Johnstone Supply in the area, if you have one that does not lock out non-tradesman you should find what you need. Besides Goodman A/C is made in Tx. Good luck Been more than a few years since I did installs but a cheap ductulator (slide rule for duct sizing)will give you the duct size. Use .08 for the multiplier on the ductulator for quiet ducts. Return air grilles are 144 sqin per ton less they get noisy.

I would find out who the subcontractor is, go to their office and talk with the owner/sales staff about options. If you are building a house that size and installing a builder grade system, I think you will be unhappy. When you build a large home that probably have nice finishing touches in it, people geherally forget the most important item-- the heating/cooling system. They tend to spend the least amount of thought on it and it is the one thing they utilize every day. The contractor will also give you options and pricing. Your electricity/gas prices look ideal for a dual fuel heat pump. I don't know if your quoted electricity/gas rates include taxes, delivery charges, etc. However, it still looks pretty good. I would suggest a couple of things for your building envelope. Make sure you windows are at least lowE2, preferably with argon gas. You have a lot of them and heat loss/heat gain is a major consideration. Not all windows are created equal. Secondly, I would go no less than R-38 in the top floor ceiling and preferably to R-50. Your upstairs will normally get 4-5 degrees warmer than downstairs. You might also look into radiant barrier for the upstairs on the deck sheeting during the install. That will cut down your heat gain in the summer and make a noticeable difference in your home's comfort. AT least R-19 in all exterior walls and R-30 under the main floor crawl space. You los a lot of heat through the floor during the heating season-- more than folk realize. YOu'll need to have these final numbers -- whatever they are-- for the HVAC person to do a proper load calc so he can size the heating and duct system properly. Don't let the contractor snow you. You have rights as you are the homeowner. I am assuming this is a custom home and not a tract plan. If you are pying the bill, you have rights. If it is a custom and there has been an allowance set for the heating system, you will likely need to pay additional money to get a better than builder grade system. My builder was supposed to install energy star rated heating equipment in mine and somehow it got changed. it was inadvertent but I got it changed back. Cost me a little to upgrade my HP to what I wanted but it has paid off, I just wish I had known a little more about heating systems and options before we went into the process. I've since upgraded my insulation to R-57 in the attic and installed radiant barrier. This spring/summer I will upgrade the crawl space insulation to R-43 by adding styrene rigid board to seal my R-30 insulation. I will have a nice tight envelope. You are in the best position to get what you want. It's always easier to do it right the first time than to go back and fix something. And... not all HVAC contractors are equal. Check on the HVAC company reputation with the better business bureau, etc. Remember, cheapest may be better for the contractor, but may not be better for you. Then again, you may find someone with better pricing who will also do it the right way. My three cents worth (inflation).

agreed. while your climate in N. La. is considered mixed humid and I'm in hot humid south La., the heat pump will work well in your area. I'd look into variable speed air handler for the upstairs unit to help handle humidity. where did you find someone to do the calcs? congrats on that! tell us more about your build. best of luck

Sizing can be less of an issue when you have multiple units. Because each unit is controlled independently, provided of course the unit itself is not over sized for the area in which it serves resulting in excessive short cycling. In your case 3 ton plus 2 ton isn't necessarily equal to 5 tons of cooling... unless you drive those thermostats really low. By having two systems with total capacity of 5 tons (which, most of the time this would be oversized for a 1700 - 1800 sq ft structure) has a few advantages. 1. You have the ability to use one system only during low heat days or set the opposing unit higher. The unit set higher only runs if load conditions warrant.... meaning if it's not hot, the thermostat controlling the unit does not call... the unit can not run without a call... 2. Utility bills can be much less... because you rarely use both systems at the same time. You run the bedroom system when you sleep, the other when you're awake. If you have a home office in one the bedrooms you may need to rethink things a bit. 3. Extra capacity for when it's hot out. When it's hot you have the capacity to cool the home. (even while entertaining guests --- additional people add heat) Remember heat waves come, heat waves go... a so call 'properly sized' AC system is essentially properly sized roughly 10% of the time... especially if that system is a single speed AC system. Alot of people I come across like to sleep cool. So for that reason I doubt I would change the configuration of the space. Once you realize what you have, the choices you make are mostly budget type concerns. Essentially a set up like this runs like a 2 stage system. This kind of subject is above the pay grade of many... choose your contractor wisely. I service the Katy, Texas area.