All new construction needs to have a proper and accurate load calculation. Some municipalities require it but many do not.

You are doing the right thing by asking for the report and trying to understand it. You are already finding issues with the report and you are not an HVAC expert. I encourage you to learn as much as you can. If the equipment is not properly sized it will unlikely to perform well, waste energy, and possibly have a shortened life.

If you have two independent systems, then there needs to independent calculations for each area. The calculated values are then used to size the equipment. A ton is equal to 12,000 BTUs. AC sizes come in 1/2 ton increments unless it has a 2-stage condenser. The increments a one ton for 2-stage AC systems. Furnaces usually are sized in 20,000 BTU increments (60K, 80K,).

The input data to the calculation is critical. If you put in garbage, then garbage will come out. An HVAC contractor to pick the sizes he wants to use and then rigged the report to make his size look correct. You goal to to review the report, ask questions and see if the input make sense to you.

The outdoor design temperatures for the St. Louis airport according the document I use are 8F and 93F degrees for winter and summer. The report states 0F and 100F. These numbers are supposed to be the average high in the season, not the all time record ever recorded. There is some extra margin in the calculation.

The indoor temperatures for winter and summer are usually 72F and 75F degrees. They used 70F degrees for heating. If you like a very warm house in the winter than you may want to change the temperature.

All the insulation values of the walls and ceilings, the sizes of windows and there R values, and the orientation of the house has to be accurately entered. Ask the contractor to show this to you for each level. There is no excuse not to enter this correctly.

What may have happened here is that a simple report was put together because you started asking questions. Keep asking the questions until you are satisfied.

Finally do you know what equipment you are getting? You should be given a list of equipment which includes the model numbers.

Mike - thanks for the info, you are helping to build my confidence as I didn't want to say it, but "What may have happened here is that a simple report was put together because you started asking questions".

AC: Lennox 13ACX N024 (or N030 for the other unit) Merit Series

Furnance: Lennox ML193DF
SERIES. Don't have the specifics on BTUs for each model will snag photos this evening when we visit the house.

low end Lennox...not for my nice new home...

You also might want to post your information and questions on the HVAC Talk Forum. It's a forum for HVAC contractors and they are another good resource. Here's a good thread where they discuss Manual J load calculation. I agree with tigerdunes, no Lennox.

I would not rule out Lennox completely, but I would recommend not buying their lowest end models.

Are you working with a builder and an HVAC subcontractor? Builders try to spend the least amount of money on HVAC equipment. They will hire the lowest subcontractor they can find who will install equipment with a name brand.

I feared i might be going down the rabbit hole on this one really really should have done my diligence on this up front. Hate to hear i have an inferior product:(

I am working with my builder (custom home) and his HVAC sub. I did ask why only 1 load calc for 2 separate systems and was told the load is combined between the 2 as one effects the other. Am i getting smoke blown at me with this response?

For the noticeable errors they stated it was for the more conservative measurement (ie used 11' ceilings for second floor, when they are 10'), used the 0F and 100F degree temps instead of the normal 8F and 93F respectively. Also sounds like a line...this could easily add up to measurements that are significantly off, right?

When i asked for the inputs, they are saying this is the best report they can provide.

Lastly, was told: Your house only requires 3 tons of cooling and you have 4. You will not have cooling issues as evidenced by the house maintaining temp today and it is 95 degrees.

So i am not feeling confident in these responses. I am going to keep pushing on how it was determined to be accurately sized, as i am assuming oversized could be an issue as well. But outside of that I don't think there is much i can do for the brand of equipment i already have.

1. They are oversizing the equipment. This is common. You'll have problems dehumidifying in the summer because of this.
2. They are blowing smoke. Sure sign of incompetence. The load calc needs to be done for EACH floor. Let your builder know you're not satisfied with their "explanations" and to resolve the issue to your satisfaction before anything progresses with the HVAC work.
3. The golden rule....... those with the gold make the rules! If you don't want Lennox, just tell your builder that!

Am I understanding that the home has already been completed?

The "load calculation" shows 30K BTU or 2.5 tons. Ask the builder why was 4 tons installed, or the 4.5 tons you have verified.

What are the sizes of the first and second floors? Is there a basement and is it mostly underground?

Is there anything in the contract about the AC systems?

Jackie - don't stress too much. HVAC load calculations are one of the most embarrassing parts of a new home build. The frequently show ridiculous errors and I have never seen one that was truly correct. The entire thing is pretty much a sham.

What the HVAC companies want is to build a system that will keep your house 70 when it is 100 out so that you won't call back to complain. The unit will short cycle, not clear humidity as well as it should, it will waste energy and it will have a somewhat shortened life. It is how 99% of homes are built so don't feel like you missed something. Even with due diligence, it is hard to find contractors how will size a unit appropriately. Last time I pushed back (pre construction) on a load calc, the contractor threatened to walk away. His price was several thousand dollars less than the competitor and he has the best service in a somewhat rural market. The system is 6 years in and works great. Service has been outstanding. And it is a vacation rental and service is most important.

As far as your Man J - you have great walls but most impressive is your magical doors. Either way, they are all crap. Even when inspectors actually look at them, they are crap. My jurisdiction is 100% clear that they must be done, but there is apparently no requirement that they are accurate. The largest mistake is probably that they judged your house as "average" when it comes to air tightness. These things are used for new and old construction - I certainly hope you aren't building an "average" house....

For others, best practice is an independent load calculation done (ie not by HVAC contractor). Best done by an energy rater.

A direct vent fireplace is a closed system with a double walled vent (combustion air enters through outer part and combustion gasses exhaust through the inner part).

I'm curious why the house would have two gas furnaces instead of a hydro-air system with a boiler and two air-handlers.

Jackie,

I agree with Sophie on this one. There is no such thing as a 'truly' accurate heating or cooling load for that matter.

Your air conditioner 'if properly sized according to heat load manual J' will be oversized 90% of the time it runs.

Heat of the day is 3-6pm in almost every location in the USA. This amounts to 1/8th of a day. You could whittle and nit pick, of which is not going to do you any good at this point.

St. Louis cooling season is probably at best 3 months. While this area can get humid, it is nothing like my location in Katy, Texas.

RELAX. Enjoy your new home. If you worry about every feasible, possible thing that could be wrong with your new home it will drive you insane. It is not worth all this aggravation.

How many homes has this home builder built? Do home builders get things wrong? Yes. My job sometimes depends on them getting it wrong. But at the end of the day a 'properly executed' heat load calculation is wrong 90% of the time.

So the 'true' accuracy you are looking for is a big fat MYTH.

Watch the weather report and pay attention to temperature rise and fall information. The high of the day and what time of day this is expected. It is not worth getting yourself all worked up over this.

A hydro- air system system with a boiler and two air handlers would be more expensive. I am not sure you would achieve the same 93% efficiency as the installed Lennox furnaces.

I agree with Sophie. Your only recourse is if the contract was breached or a building code was not met.

A hydro-air system would have a higher initial cost but would be more cost effective to operate. I don't think it would take long to break even in St. Louis. The efficiency of a gas-fired condensing boiler can be as high as 98% but is commonly 95 to 96% and can be wall-hung in a basement and be direct-vented through a side wall.

Small air handlers would be placed where a furnace would have been but with no gas connection or open flame.

"There is no such thing as a 'truly' accurate heating or cooling load for that matter."

Maybe not but there is such a thing as grossly oversized....... like 4.5 tons instead of 2.5 tons!

"There is no such thing as a 'truly' accurate heating or cooling load for that matter."

Austin, I thought you've said you rarely do load calculations? If so, what's this comment based on?

Another excuse not to do a load calculation. One of these day I will post a top 10 list.

Here's another load calculation thread on the HVAC Talk AOP Residential Forum that you might find educational and interesting.

http://hvac-talk.com/vbb/showthread.php?2195159-Going-LoadCalc-Loco

The reality is 99% of contractors don't do a load calculation (or a proper one) either because they are too lazy or don't know how. Don't ask where the numbers come from in those municipalities where a load calc is required by code!

sktn, here's a good back pocket thought to keep in mind.

In a house with existing equipment (not a new build), if the load calc comes up with a spec for equipment of the same or larger sizes as are currently installed, it's probably been jimmied and you should dismiss its results. And even if so, there are many not too expensive retro fix-up tasks that can often be done (adding attic insulation if accessible and sealing air intrusion points, sealing or replacing ducts, adding additional return air ducts) that can add greatly to comfort and efficiency and reduce operating costs.

If the bidding contractor says a load calc isn't necessary, thank them for their time and call a few more.

St Louis with a 3 month cooling season? Has the climate gotten colder since I moved in 1981? I rather doubt that.

I live in Louisville and I usually have to start running my 2nd floor air conditioning in early-mid April, and it runs until late Oct at least. I have a 1 1/2 story house - very little attic. Yes, it IS well-insulated and when we put a new roof on 3-4 years ago, I added a vent cap to get some of the heat out of the attic. It has helped. But I like to sleep in a cold room, and if the outside temp is 70° or above, it will be far warmer than that upstairs and I'll be hot at night.

The good news is that I only run heat up there (usually set at 62° for about 3-4 months a year. No point in heating it if I'm not up there and if I want it cold at night!

Load calculation mantra:

Let's run load calculations to properly size the air conditioner for the 10% highest loads during the summer time. (Location Dependent)

This is how load calculations are calculated are they not?

Do they make a thermostat that has only temperature set point?

Is everyone the same when it comes to temperature and comfort?

Certainly vastly oversized is not ever a good idea, especially for a climate like St. Louis. But you could argue oversized until you are blue in the face with no value to the conversation at all for the simple reason an air conditioner is as I have said repeatedly 'oversized 90% of the time it runs'.

How does the St. Louis Area differ?

The other common arguments on this board: lets put duct work inside the structure because there is so much heat gain sticking them in the attic. But then you say oh gotta run those heat loads every time you replace equipment... you know to make sure the heat load was done correctly the last time.

If the heat load comes up errant and you determine it was undersized or oversized guess what the duct work is too? Yeah, lets get people to spend more money over and over because we never got the heat load right to begin with? Don't worry I got the heat load police on speed dial. LOL.

The heat load calculation is a tool for those who know how to use it. It is not an accurate tool by any stretch of the imagination as to how it is commonly displayed on this board and others.

Temperatures change all the time. The heat load calculation is sized for a 'specific' moment in time under the 'most common' worst conditions the structure may be put under.

There is more to a heat load than just sizing the equipment. Proper sized equipment and improper sized duct work amount to what?

The real estate market is comprised of roughly 60% home owners and 40% rentals. Yeah this is another excuse called economics 101.

The thing is this house is already done. There is nothing short of a lawsuit that is going to change anything. Is that really how you want this experience to be?

3 months of the year you're going to run the air conditioner and most of that time it will be running in the afternoon and early evening probably be cycled off by the time the new to be home owner gets home from work.

With that said If you want a heat load calculation and you live in my area (Katy, Texas) I will perform one for you, but I will charge you for it. The price varies depending on the size of the home and the number of HVAC units. I don't do partial load calculations. It's either the whole structure or nothing.

Austin - your arguments get lost in your non sequiturs.

What everyone wants from their a/c is a reasonably long run time. The smaller the unit, the longer the run time. Go too far and you won't be cold enough. Very simple. Every expert (Building Scientist) agrees that the vast majority of houses have oversized a/c units.

Even if a unit is oversized for 90% of the day, it is still the smallest it can be while stilll maintaining a cold enough house. Yes - it will cycle those 90% of the times. But right sized will perhaps have 20 minute runs instead of 10 min runs. That is a rather large advantage.

Parts of Austin's argument are funny because of the conclusions he reaches. He makes the exact argument for why a Manual J load calculation and Manual D duct calculation should be done, to avoid having to spend even more money at a later date to fix wrong sized equipment and wrong sized duct work that cause an uncomfortable house. Then Austin reaches the illogical conclusion that the load calculation shouldn't be done because not enough HVAC contractors are properly trained to perform the calculations. Therefore Austin concludes that no calculation can be trusted because there isn't a "heat load police."

Then Austin says that only a lawsuit can fix the current problem created by a contractor who didn't perform a proper Manual J load calculation. Once again, that would be another logical argument for why it is so important to have a proper Manual J load calculation and Manual D duct calculation performed in the first place. Then Austin reaches another illogical conclusion, that no one should want a lawsuit, so the buyer should just sweat it out in their home during the hottest times of the summer, for year after year in their lovely, new home (or sauna depending upon the season.)

I'm telling you, there's a lot of comedy value in Austin's posts. The HVAC contractor "doth protest too much, methinks."

To the OP, I see that your contractor is a serious contractor based on the software he’s using. This is the best and most expensive software in the industry. Used properly it will yield the most accurate results. Your contractor should be able to import your architectural drawings into the software, plug in all the data from the drawings, do the detailed calcs and create the Manual J and Manual D duct designs right from the software.

The reason you might not be getting the detail you’re expecting is because you may not be paying him for all the time it takes to plug in the minutiae of details to get this right.

As a consultant that owns all this same software and took the time to learn how to use it, I stopped - years ago - offering this service for free so that it can be shopped around to find the lowest bidder. The money, time, training and effort just to acquire the tools and knowledge involved with this software was enormous !

… And then people expect it for free. That never happens anymore; I have to be paid for professional services or I’m out.

I would recommend that since the OP appears to be working with a serious professional, speak with them about your concerns and offer to pay for their time to enter all the details correctly into their software. That also would include the time spent on-site measuring and acquiring dimensions and details.

I would also recommend installing completely variable speed systems, such as Carrier Infinity Greenspeed, making sure that the ductwork can handle the cfm required and then just relax. The Greenspeed system with operate at the capacity required, self adjust to the ductwork static pressure (within reason) and delivery the conditioned airflow required.

I basically agree with the advice given here by Sophie Wheeler & Austin Air.

IMPO

SR

David,

Sure, heat loads are more complicated so I could argue the same thing to you. Which is ultimately the point I am trying to make. The points I make rarely stick first go around because I don't know how people will glisten the knowledge as how I type it out.

There's this nugget from the OP:

For the noticeable errors they stated it was for the more conservative measurement (ie used 11' ceilings for second floor, when they are 10'), used the 0F and 100F degree temps instead of the normal 8F and 93F respectively.

Why pad the structure numbers? If the heat load is so accurate you might say?

A heat load calculation is a rule of thumb. Or a ball park if you will... but if you pad your numbers it shows you lack confidence does it not?

At the end of the day it's still off 90% of the time. Who in their right mind strives to be 100% right only to wind up being ultimately 10% right? Remember a heat load calculation is a rule of thumb. Rules of thumbs are guides. There are a myriad of ways to get things wrong outside that of a Heat Load calculation. Even if you get the heat load calculation right it still does not mean the installation was done right. Duct system etc. They all play a part. But for a climate like St. Louis it's small potatoes compared to my climate.

Seasonal consequences: If this home was in a high humid climate like Florida or my neighborhood of Katy, Texas I would be more concerned. I could heat and cool the St. Louis market from a stretcher, blind folded and one arm tied behind my back for the simple reason this market does not have near the trouble I am faced with 10 months of the year.

So sometimes you must put certain markets into context of what really is important and what is not. In other words, don't take an ant hill and make a mole hill out of it.

If someone is taking and ant hill and making a mole hill out of it you must at some point question their judgment as well as their motive. Who do you trust?

Everyone has an opinion. Who is right. Or better yet who is it that is going to come to your home to fix it?

"Everyone has an opinion."

As I understand it, the principles and practices established in the last 30 years (and still under development) by Building Science experts are facts and not opinions. These findings concerning using load calcs, changed building techniques and practices, equipment types and locations, are all well studied and accepted.

It seems that your approach, Austin, is to discount the validity of practices you don't follow. That's fine and apparently is adequate for your market and customers. It's not fine elsewhere and your view doesn't change all the various puzzle pieces that are widely accepted as being part of how to do these tasks "the right way".

"Remember a heat load calculation is a rule of thumb."

Another one for my top 10 list.

I think the authors of the manual who work at the Air Conditioning Contractors of American (ACCA) would not share this opinion.

Here is 2016 version of the Manual J book. Is written by the ACCA and it is also accredited by ANSI (American National Standards Institute). It is a real standard which is updated periodically to keep up with changes in building science.

It seems that your approach, Austin, is to discount the validity of practices you don't follow.

Not at all. But in an imperfect world in which one learns faults of the so called experts turns me into an expert in my own right. Does it not? Do I not make valid points in this thread and others? Does the sun not rise in the east and build temperature throughout the day until a certain point in the evening until the sun sets in the west. Do temperatures not change? Do they remain fixated at the highest temperature of a climate that is used to calculate a heat load using a manual J?

If a manual J is not a rule of thumb or an elaborate guess please consider a home that was built 20 years ago.

If you put 10 contractors up to the challenge of producing a heat load for the structure how many would come back with the same conclusion?

10 ACCA members: could they come up with the same conclusion?

AKA Rule of thumb: If the heat load estimate of a structure varies among 'so called' professionals who designed the calculation (or anyone performing the calculation) how could it be nothing more than a rule of thumb? Please answer that Mike.

Systems are often coined as being grossly oversized on this forum board and others going merely by square footage of the structure. When in fact anyone that truly knows the aspects of a manual J heat load calculation realizes that windows are one of the biggest heat load factors of a structure.

So you want me to believe that a heat load calculation is not a rule of thumb when many of you participate in merely a square footage rule as a means to justify the size of the equipment. Sure, it's a forum board where only I am held to accountability of what I say and do. How convenient for the two of you. No skin in the game, you're merely a home owner. Congratulations.

The practices of building homes 20 years ago are not the same as they are today.

Are they?

If any of my questioning is inadequate in any way please tell me where I am wrong.

23 years hands on experience. I come to your home. I service the Katy, Texas area.

Running my own company 10 years as of 2018 in one of the hottest, most humid climates on the planet. I believe my resume speaks for itself. Thank you very much.

The manual is based on the laws of thermodynamics. I would not describe that as a rule of thumb. It also describes to professionals as yourself as to how the data should be taken and calculated to come up with a heat gain and heat loss. If multiple professionals put in the same data and do the same calculation the results will be the same.

However we know if several people do a calculation on the same house the results will be different. The reason is the same data has not been entered. But that is not a good reason to discredit all load calculations. There are some places where the contractor may use a "rule of thumb" for rates of whole house air exchanges. But there is no excuse not to measure all windows, sizes of rooms, orientation of the structure, and enter reasonable estimates for insulation values. Contractors who do calculations for all new installations know many of the values based on calculations done on similar houses in the neighborhood. It is not as hard or imprecise as you think it is.

The goal of the calculation is to select the proper sized AC and furnace, or heat pump. There are not many choices for sizes so even if the results are not precise in most cases the same equipment would be selected. In the cases where the numbers fall between two sizes, the contractor can explain the results to the homeowner and make a recommendation about rounding up or down.

If doing load calculations in Katy, Texas does not fit your business model, then continue to do what you are doing. I am sure you will be successful for another 23 years doing no load calculations. But as a professional, please don't tell homeowners who are asking questions on this forum the correct way to buy a new HVAC system that a load calculation is a waste of time and money.

Austin, a load calc isn't a rule of thumb, it's a proven science/engineering-based calculation developed by the real experts.

Yes, estimates are used, there's no choice. Whether the structure being assessed is new or 20-100 years old or more, it has heat gain and loss that can be calculated with reasonable accuracy. That determines what size equipment is needed to do the job properly. You know that already. Those calculations are usually required by building codes in most places for new construction and, increasingly, for equipment replacement in existing structures too. Fact is, it's not just the building code driving the need for load calcs - if building a new structure, there's no way to guess what the heating and cooling requirements are.

I'm not sure why you challenge the validity of something so well accepted and proven in the industry. To suggest you know or understand more than the experts and to defend your seat of the pants approach is silly and, frankly, demonstrates either misunderstandings on your part or your decision that it's okay to be sloppy with this aspect of your work. As before, if you don't do load calculations and your customers accept that, great.

So over the weekend we have went to the house observe the system and it is short cycling: runs for ~10 min, its off then kicks on again after about 10 min. We have not been able to get the upstairs to run on its own when we were there...the thermostat was set higher than the main level...need to observe this one some more.

We only had 1 humidifier included in our contract. Is there a preference to which unit we put it on? Originally was planning for the main floor since its all hardwood, there is some hardwood upstairs but just hall way and a office nook, rest is carpet.

We are going to share our concerns with the builder about the oversized units. Not sure what I expect to happen, but feel its important to talk through the hack job of sizing the units.

What thermostats were installed? What are the sizes of the filters? These are additional items that should be reviewed.

Low humidity in the winter is caused by outside air infiltration. New construction should be be tight and not need a humidifier. I would avoid using it if you can. Humidifiers that are not regularly cleaned and maintained become a maintenance headache.

The main floor furnace is probably the best option for the humidifier.

Running 50% of the time is not altogether bad. It depends on other factors, like how hot was it outside? What was the thermostat setting? How many cycles per hour was the thermostat set to produce? And so on.

If multiple professionals put in the same data and do the same calculation the results will be the same.

Provided their math is correct. Who are you hiring? Are you paying for it? What's in it for the person doing it? They're trying to sell you are they not?

It's one thing to do it in the comfort of your home and have the measurements provided for you and you're doing it because you want to with 'NO MOTIVE', If we're being serious we both know this is not what happens in the 'real' world.

This house on this thread as an example: they have all the measurements, the R values, yet they still add fluff to pad the numbers. Why? So you think arguing how thermodynamics play into this and how everyone will come up with the same calculations. It's a joke Mike. A bad one at that.

It's one thing if you are building a new home, quite another if you are on a home that is 20 years old. I am not a home builder. If you don't know what the R-values are what do you do? Guess. Oh you mean use a 'RULE OF THUMB'? Ironic isn't it?

But clearly Mike you don't think like that do you?

But as a professional, please don't tell homeowners who are asking questions on this forum the correct way to buy a new HVAC system that a load calculation is a waste of time and money.

Never said that Mike. What I did say: Are you paying for it?

If you're not paying for it, you may be getting duped. Professional salesmen know what sells. Slight of hand is very easy via heat load calculation. Intentional or other wise it's unlikely you will know.

Heat waves that come and go, make people believe they need a larger unit than what they have. Then the guys in the white lab coats pat each other on the back and proclaim that most AC systems are oversized. Congratulations Mike, they love you because you keep the cycle going.

So over the weekend we have went to the house observe the system and it is short cycling: runs for ~10 min, its off then kicks on again after about 10 min.

This may mean many different things. It doesn't necessarily mean due to oversizing of equipment in every situation.

Due to differences in market and climate the contractor may have installed accessories to the system that limit it from running under certain scenarios or there may be a low refrigerant charge condition due to improper charging and or refrigerant leaks. (Just because the system is new means nothing.)

You will have to keep pressing on your home builder to make sure these issues are corrected. But realize AC equipment is complicated there can be more than one reason an AC system is short cycling.

If the temp is being satisfied in the structure and you can verify this via the setting on the thermostat then it could be short cycling or it could be due merely the ambient conditions on the structure. If the thermostat is not satisfied and the system shuts off, it is likely a control typically there to protect the system from damage.

If the load is light (mild OAT temps), a properly sized AC will short cycle. It's the nature of the beast when dealing with single speed AC systems.

Ray,

Here are the answers to your questions:

Who are you hiring?

A licensed HVAC professional.

Are you paying for it?

Of course. It is added to the total price just like all the other materials and service required to do a proper installation. It is part of the costs of doing a new installation.

What's in it for the person doing it?

It is a way to increase the confidence level that the correct size is being installed. It demonstrates to the buyer that HVAC installer is serious about doing a proper installation. In some states and counties a load calculation is required in order to receive an energy rebate. It may be required for a permit application. It could justify a higher selling price and profit because an additional service is provided.

They're trying to sell you are they not?

Yes they are. The HVAC business is very competitive. Doing a little extra work up front may make the sale over the other guy. This is especially true if a calculation shows smaller equipment can be used and save the buyer money.

This house on this thread as an example: they have all the measurements, the R values, yet they still add fluff to pad the numbers

Go back to the second post and read the load calculation carefully. The cooling load was calculated to be 2.5 tons for the whole house. The calculation was done after the HVAC installer installed two systems of 2 and 2.5 tons. Yes some of the values entered were incorrect. But the contractor didn't how to jury rig the calculation to make it match what was installed. Then when the home buyer questions the calculation he responds by saying why are you complaining, your house only needs 2.5 tons but we did you a favor and installed 4.5 tons!

Now the AC appears to be short cycling. Hopefully it is due to a bad installation with a possibility of being fixed and not due to over sizing. Let's see if we can guide the new homeowner get her HVAC systems working properly.

Jackie, you might want to reach out to a business that specializes in designing AC systems. Then have them check the Manual J calculations that the HVAC sub-contractor made so you have a professional, second opinion. I did a quick internet search and found this AC design business as an example. Good luck!

Mike, it doesn't work that way. I've said enough about this topic if you don't get it by now you never will.

Actually I fully understand what is going on. My hope is homeowners asking questions about load calculations understand.

Happy to see this subject brought up although I'm sure most building new, didn't make it this far. I think the OP got "shorted" but no worse than most building new in this current building climate. With such a hot market one has to be careful they don't spook the best or only opportunities. I think it's important to get a 2 stage system as a minimum.

Getting a properly sized system is much like getting a building envelope to perform at current levels of international energy code. For most people, the best chance is to hire a design and building team who already understand the details from past projects. At this stage of the game it's often too late. Ductwork in a vented attic or low levels of roof deck insulation can effect cooling loads as much as western windows depending on the details.

Martin Holladay has the best articles on this topic. Calculating cooling loads and When do I need to perform a load calculation? are free while Who can perform my load calculation? is behind the paywall but relevant here.

When builders get experienced with a particular plan, the need for load calcs diminish. For custom designs costing hundreds of thousands, using a third party to help with design, sizing and commissioning can be a wise investment. Some architects and builders include this with their services.

Energy Star is the most common way to achieve a better level of verified performance. This goes beyond energy use to include comfort, indoor air quality and durability. The program ensures bath vent fans, outdoor air ventilation systems and kitchen vent hoods are installed properly. With a reported energy savings of $300 a year, simple paybacks are reasonable. Not all HERS raters do load calcs but most can point you in the right direction.

If you only care about HVAC system design, hiring the right 3rd party can help. If building in the south, try Allison Bailes with Energy Vangaurd. He has influenced the need for better rules of thumb, like 1 ton per 1000 sqft for homes that meet international levels of energy code. This can be useful when comparing results to what the HVAC contractor wants which is typically closer to 1 ton per 500 sqft. I find HVAC contractors more willing to install smaller systems when they have stamped letters from a mechanical engineer, which in our case is the HERS rater.