The issue is the house isn't being cooled,not what size equipment should have been installed. If I tell you the equipment is undersize,do you believe my word might cause the builder to install different equipment? I don't think what folks on the net think's will mean a thing to your builder. I suggest contacting your utility company to see if they will do a free energy audit and evaluate the ac system. If you have tools and some experience with hvac and planing to work on it yourself,let us know.

you are undersized, especially for Georgia climate.

IMO

New home builds (recent builds) it's not uncommon to reach 1000 sq feet per ton. This would put you within that range.

However, figuring whether a unit is adequately sized by sq. footage alone is rather foolish just as much claiming a system is dramatically undersized because houses of a different era ran at about 500-600 sq foot per ton.

What would happen if there is some sort of capacity related problem with your systems operation and you just chose to believe that the systems were undersized without a professional in person diagnosis to eliminate that as a possibility?

You need to 'pay' for a professional 3rd party diagnosis to challenge the builder with. If the equipment is functioning normally without any capacity related problems, then pay some more to have a 3rd party perform a heat load calculation performed to again challenge the builder.

I service the Katy, Texas area.

Around 4 Ton for the first floor and 3-3 1/2 Ton for the 2nd floor. Have your HVAC guy do the calculations, they have a chart for your climate zone

A total of 7.5 tons for a new build 3,900 is very over sized. The second floor typically has the higher cooling load, so it makes no sense to put the large unit on the first floor.

"It took 3 hours to cool from 75 to 72 last night after we ran the oven for an hour."

The summer design temperature for Georgia is 93-94 degrees F. What was the temperature yesterday? Was the sun down when the AC shut off? How long did you have the oven on?

If you want the house to be 72 degrees during the hottest part of the day, then you are likely to be under sized. You might be able to get by with the 2 tons on the first floor, but I think 2 tons is not going to work for the second floor. Equipment is normally sized with a 75 degree indoor summer temperature. You could try 75 degrees and see if you can get the humidity down to 40%. It is comfortable for most people. A properly sized AC will run several hours before shutting off. What you described is not unusual.

Ask your builder for a copy of the load calculations. This should have been done by the HVAC contractor to determine the sizes. If he can't produce it then ask him to hire a professional to do a new calculation. That is the only way to determine if you are properly sized.

just wait for those July/August Temps...some persons on this forum can't seem to grasp that fact!...I suspect the OP will be very miserable with poor comfort during those months...

IMO

Tiger it's a new home, so any ac problems in that kind of wheelhouse and there's all kinds of misery. Dealing with builder problems, dealing with 3rd party to check the work of the said builder, scheduling, finding a 3rd party smart enough or even willing to get involved in this mess?

Yeah, it's going to be ugly... no way around that.

New homes of today are tightly sealed, well insulated, higher efficiency windows. The common recommendation of this board is to perform a manual J heat load calculation.

So if after you feed everything into the heat load calculation, it spits out a number that seems low in terms of sq. footage per ton... so what do you do?

Over size the equipment?

Then after the larger sized equipment is installed you go to a closet and notice mold growing up the wall.

Certainly the heat load, sizing of this equipment may be wrong from the get go. But the mentality of this forum board is to always assume things on the old method of sq. feet per ton... but then always recommend a Manual J heat load calculation?

So I would like those who constantly recommend a Manual J heat load calculation to come clean and tell us all which method is really appropriate... sq ft per ton OR a manual J heat load calculation.

In my professional opinion you can't have it both ways.

With that said it's not uncommon for new homes to have debilitating capacity problems... not due to sizing of the equipment, but the lack of being installed properly. This is what needs to be determined first.

It's up to the homeowner if they want to trust the skill of only the builder or find a third party contractor willing to investigate this mess and hold the builder accountable.

A forum board post doesn't do anything close to what is needed to get the builder to correct blunders.

My stance on this situation remains the same.

I service the Katy, Texas area.

To determine what size your HVAC units should be you can sit and guess all day long.

Your HVAC contractor needs to make his calculations based on SQ footage, climate zone, account for the loss etc. They usually have charts that they follow.

To give you an example to get basic unit size, you figure about 400 SF per ton so 2000 SF / 400 = 5 Ton unit.

So the contractors who said they're way undersized are right.

GN builders, not necessarily. There will be differences in builds because newer builds are designed to be more efficient.

If you have R38 or higher insulation, triple pane windows and other higher efficiency things... the load calculation of the same sq. footage and R19 insulation and single pane windows will be entirely different loads.

The calculation does entail measuring the space in terms of sq. feet and such, but that is just one small part of the calculation.

You don't build an energy efficient home by building one that requires 400 sq ft. per ton of air conditioning. You really work for the power company... don't you? LOL.

So I would like those who constantly recommend a Manual J heat load calculation to come clean and tell us all which method is really appropriate... sq ft per ton OR a manual J heat load calculation.

I am coming clean. The appropriate method is a Manual J calculation. There is no excuse not to do it for a new build. All the building parameters are known so there should be no guessing on insulation values and the performance of the windows. If the results of the calculation appear to be too high or too low, then most likely there is an error in the input parameters. Entering the wrong data become the classic garbage in, garbage out scenario.

Using 400 SF per ton will result in over sized equipment for a new build even in Phoenix, AZ.

Don't get excited Austin, this was just an example...All this Energy Efficiency, R-38 insulation, triple pane windows, I yet to see a house loaded with all these features around my region, not to mention I have seen a few triple pane windows at the show, and IMO if a house has this windows, it should come with a mandatory gym so a homeowner can build some muscles to lift or crank open triple pane windows.

That said, my house is 4,200 FT, I built it in 2002 before all this "energy efficiency" hit the media and before the ugliness of solar panels on the roofs started to become a common thing around here.

I have R-13 insulation, R-30 in the ceiling, I added foam insulation on the exterior, casement Andersen Windows, pretty much standard construction, and I don't complain about my AC bill as a matter a fact I pay almost as much for Cable LOL go figure.

It would be nice to see a load calc broken out by upstairs and downstairs...while a load calc is the best thing going for sizing, it is not infallible. Sometimes good common sense must prevail...

IMO

"To give you an example to get basic unit size, you figure about 400 SF per ton so 2000 SF / 400 = 5 Ton unit. "

I don't think anyone has used these numbers for a very, very, long time.

OP: Get the builder's load caculation data for your house. If he doesn't have one, there's your problem.

Some localities require this calculation to be done in order to get a construction permit. Since this is a new construction home, it is performed off the architectural plans. Also a Manual D (which determines the ducting requirements).

Here also when going for construction permits, architect usually provides the RES check to show that the dwelling being this a new homes, additions, and alterations meet the requirements of the IECC or meets the requirements of a state energy codes.

HVAC contractor also provides In some jurisdictions the furnace specs, etc.

The state of California requires new residential homes to have a Manual J calculation.

"To give you an example to get basic unit size, you figure about 400 SF per ton so 2000 SF / 400 = 5 Ton unit. "

I don't think anyone has used these numbers for a very, very, long time.

I think these numbers are used today in any place that allows an HVAC contractor to get away with it. I think in the near future you will not be able to get a permit to replace existing equipment without a load calculation.

Applying for a building permit in CA is a plain nightmare for Architects... I talk to a few architects from there and you basically have to provide specifications for each screw that is being used more or less.

I think in the near future you will not be able to get a permit to replace existing equipment without a load calculation.

That's not what I think... I think technology will take over and Inverter systems will dominate and because of the way in which inverter systems operate they won't over cool. The only problem at that point will be under sizing and improperly installed systems. (So I think calculations will still be needed to some degree, but mostly so you don't undersize... the over size risk will be gone.)

So in other words, you have a home that requires 2 tons of cooling, you put in a 5 ton system and because the system you install is an inverter it never reaches the 5ton levels of cooling. The 'inverter' HVAC system is designed to only deliver the amount of cooling the structure needs, nothing more.

You pay extra for the equipment that you don't need, and the capacity of the system you will never use is never realized. The manufacturer is able to reduce sku's because sizes are only 2, 3, 4, 5 ton.

Smarter HVAC manufacturer's reduce sku's further making only 3 ton and 5 ton models. These 3 ton and 5 ton models have a switch that will drop 1 ton of capacity off of them.

If things continue as they have, I think we could begin to see this within 10-15 years from now. Everything is in place for this to happen now. (2019)

Realize the inverter HVAC systems I am talking about here are able to ramp up and down within a few 1000 BTU's of needed capacity for the structure in question.

Because of this, the problems associated with proper dehumidification in high humid climates will also be much less of a problem.

Crystal ball, deactivate!

I service the Katy, Texas area.

" The state of California requires new residential homes to have a Manual J calculation.

Yes. Man J load calcs are required for equipment replacement jobs as well as for new construction. Both new and replacement work also require duct leak testing and remediation when the leakiness exceeds certain prescribed percentages. Remediation rules are different and reasonable for replacement jobs with inaccessible duct sections than with new builds.

I've contracted to have heat/AC replacement jobs done twice in the last 3 years, two different locations, and the better bidding contractors look at work assuming that the existing equipment is oversized. They were right for both homes based on the load calcs.

" Applying for a building permit in CA is a plain nightmare for Architects."

Sorry but I don't think this is very accurate. My experience has been quite different. Each aspect of the building code and other applicable laws have rules and expectations that need to be followed. Follow the ones that apply to the work being done and there are no issues or problems. In my experience. Better done projects follow standards that exceed code requirements and the building inspectors notice these situations and act accordingly. This may vary somewhat from jurisdiction to jurisdiction but in two different ones, I've encountered no problems at all.

"To give you an example to get basic unit size, you figure about 400 SF per ton so 2000 SF / 400 = 5 Ton unit. "

So the contractors who said they're way undersized are right.

My point was primarily that this is way too high a cooling capacity for 99% of homes. In addition, it takes into account nothing about an individual home's needs so is of no value.

"The the contractors who said that they're way undesized are right" couldn't be further from the truth.

Don't get excited Austin, this was just an example...All this Energy Efficiency, R-38 insulation, triple pane windows, I yet to see a house loaded with all these features around my region...

Well GN Builders I did some looking and it appears you are located in Plainsboro, NJ. and utility rates are around 11 cents or so a kwh.

Your AC season is at best 3 months. So naturally efficiency isn't going to be the big holler to you as it is in a warmer climate that runs the AC nearly 10 months of the year and in some cases have higher utility rates than you do. If you were running your equipment upwards of 2200 hours or more a season & higher utility rate your attitude would change. (every market is different)

In addition to that, if the AC is over sized it lacks the ability to dehumidify properly.

So then mold starts growing on various walls even more so if the property in question is located within a high humid climate.

Triple pane windows are offset with counter balance so they aren't any harder to operate than any other window in my experience... and if you're in a hotter, humid climate they will be shut most of the time.

This isn't to say that the OP of this thread doesn't have a system that is sized properly... But I've seen too many occasions in my own newer neighborhoods the problem is more often associated with equipment related capacity problems than the equipment being undersized.

You have to realize, there is more money in replacing equipment than there is in fixing it and so more people come in claiming the system is undersized. Then the new system breaks and no one can fix that either.

That's why you need someone who can fix it.

I service the Katy, Texas area.

There was a theorem that I was taught in college economics called the law of diminishing returns...still applies today with some good ole common sense!...

I don't know why everyone is hung up on my example...As I stated in my post it was just an example. If the contractor who came in and said 2 Ton unit is to small, and if a 4 Ton unit per my example is to big, he will stick a 3 Ton in there.

That said, it don't get any simpler than this.

All someone has to do is call a qualified HVAC contractor who will calculate the loads and suggest the right equipment for that house.

I'm sure if the house is located in Florida or the North Pole, the contractor will not be doing HVAC calculations based on NJ climate. Just saying. :-)

Mainly because it's 'most likely' to be wrong for the problem the OP posted and for the climate in which the OP lives.

Think about it this way... a climate that has 3 months AC season how much chance is there in having serious problems in such a climate as opposed to an AC season that has double or triple your AC season.

You don't know, what you haven't seen. How could you?

Now throw in higher humidity climate and mold growth potential.

This isn't me hung up on your example, this is me explaining why your example is dangerous for some climates.

I live in a high humid climate, and a climate with as much as 10 months of the year is the cooling season. So because of that I see many more problems.

People only call when they have trouble. If the season is over, the phone goes silent. That's the point.

Well GN Builders I did some looking and it appears you are located in Plainsboro, NJ. and utility rates are around 11 cents or so a kwh.

Your AC season is at best 3 months. So naturally efficiency isn't going to be the big holler to you as it is in a warmer climate that runs the AC nearly 10 months

Central NJ is served by PSE&G. The current electricity rate for service and delivery is about 17.3 cents per KWh. Cooling season is May - September. Not a long as Katy, Texas, but costly when you combine the hours with the high rates. The state of NJ encourages using less electricity. It is not to the level of California, but it is headed in that direction.

Just to check back in because I was traveling for several days -- I assume I can request a copy of the Manual J calculation for our house? The punch list guy said that they used it because "that's why I can't tell you a specific square feet per ton".

It's been upper 90's during the day here for the past week. If we keep it turned down all the the time - whether we are home or not - it stays cool. Turn it up 3-4 degrees during the day when no one is here and it takes 4 hours to make up the difference, even at night with the sun down.

The downstairs vents feel fine - strong air blowing through. Big room upstairs are vaulted, but bathrooms and walk-in closets are 8 ft. When I feel these vents, it feels like air is just falling out of them, no force at all.

The downstairs has two 14x25" returns separated across the house. The upstairs has a single 20x20 return for 1950 square feet, probably 75% is 12.5' vaulted ceilings. So, the downstairs has 700 square inches of return vents, and the upstairs has 400 sq. inches.

Thoughts?

need more return upstairs....you size AC cooling for the average high temp, not the extreme highs. Your area (and mine as well) is experiencing a very dry heat wave. Having said that , I still believe you are undersized. How is your home's inside comfort level, specifically inside RH on each floor? What is your cycles per hour for upstairs once thermostat setting is achieved? Not sure where this thread is going or what you are looking for...

IMO

It's been upper 90's during the day here for the past week. If we keep it turned down all the the time - whether we are home or not - it stays cool. Turn it up 3-4 degrees during the day when no one is here and it takes 4 hours to make up the difference, even at night with the sun down.

Given the large square footage per ton for this property I don't think this is overly out of specification. It's not uncommon to have to run equipment longer when dealing with tight sealed, well insulated structure and smaller capacity system... this is really what you want for moisture removal with most likely entry level equipment (single stage equipment).

If the house is tight sealed, moisture problems can be apart of the structure due to normal functions of the household taking showers, doing laundry, cooking etc. If the AC system doesn't run that long it will probably have trouble removing that moisture consistently.

A 2 ton system only needs around 800 CFM of air to function, if you are using a pleated filter check to see with the system blower on if the filter is sucked hard into the filter grill. It should be loose fitting. If it is sucked hard, reduce the restriction by using a less restrictive filter. This can be done by choosing a cheaper filter. Filters are priced by size and material. The more restrictive material the more it will cost. Restrictive cuts air flow. A reduction of air flow will reduce system capacity.

If after putting in a less restrictive air filter it still sucks hard, that could be your problem in terms of capacity. But from what you post, it sounds quite normal to me for the size this structure is and the tonnage or capacity of the equipment.

Another test you could do is take a temp drop of your systems. Take a temperature reading at supply just after the AC coil and take a reading of return temperature (where the filter is located).

Return temperature - supply temperature = temperature drop.

It's also not uncommon for closets to be low air supplied as these are often outliers of the room and not much time is spent in those areas. If too much air is supplied to those areas it may cause whistling noises, which is counter productive.

Occasionally I am in similar homes of this nature in my area and the comments are that of the AC not having as much 'cooling' force, my opinion is that this is by design. I am in more of a humid climate and because humidity has much more challenges than temperature alone a longer run time is beneficial and because system sizing is typically smaller the cost of operation is lower. (Efficiency is another explanation of this).

A return of 400 sq. inches for a 2 ton system is fine. The rule of thumb is 1 sq. inch per 2 CFM of air. The 2 ton should be set to 800 CFM of air flow.

Where is the duct work located for the upstairs system? If it is installed in an unconditioned attic space then I suspect you will have problems. The duct losses are significantly higher in unconditioned space.

In general I agree with using temperature set backs. However if you are sized close to the cooling load then expect long recovery times to make up the 3 -4 degrees. What is your normal AC temperature setting? Have you measured the humidity. It takes a few months for a newly constructed house to dry out. The humidity level may be high causing you to set the thermostat lower in order to feel comfortable. I would think you will not have a humidity control issue with your sizing.

Request a copy of the Manual J calculation. Don't be surprised if they can't find it or the copy they give you has yesterday's date on it.

I agree with Mike...doubt a load calc was ever performed. however, one return for 1900 sq ft that includes a vaulted ceiling simply is not enough. You will improve airflow and comfort level by adding more return.

TD