80% Humidity in brand new home, is my unit undersized?

[ddyraw]

Hi there! I have a brand new two level 2960 sq ft home with a split system and a conditioned crawl space. I live in the Raleigh, NC area. Each day around 3 PM, my home begins heating up pretty badly. I understand that this can be normal, and temperature wise we are maxing out at around 75 degrees according to the thermostat, but I have taken the temp of my kids rooms and they were at 80 degrees. I understand some of that can be normal, but our humidity in this home is really high. In the morning, our temperature can hit 69 degrees, but the humidity is at 60%. Yesterday in my upstairs area, at 8PM, the thermostat said 74 degrees and the humidity was 80%. This made the upstairs extremely humid and unbearable. The weather yesterday outside was around 95 degrees with around 50-55% humidity.

I am concerned because the humidity is causing some extra nail pops and drywall issues, plus it is terrible for sleep! I understand this level of air quality is also really bad for health, and great for mold and fungus.

As I said, we have a 2960 sq ft home with a conditioned crawl space. We have a Lennox 3-ton 14 SEER system, model 14ACXS036-230A**. This whole system seems like it just cannot keep up with this house. The temperature difference between the returns and the vents is 8-10 degrees. We have the wrightsoft load calculation summary, but many of the numbers are 0, or set to N/A. It also is incorrect about there being a fireplace, and there is no calculations for the ducts or the crawlspace.

What I would really like to know is, does any of this sound normal? Can this much humidity in the home be a normal function of a properly sized or functioning system? Can a 3-ton system actually cool a 2960 sq ft home properly?

Should I get another load calculation done for the home?

I really appreciate an help you all can provide, I am just not sure what is normal or not!

[ksefan]

Wow, that sounds pretty bad for new construction. I would call the installers back out for a check up. Maybe they installed it during the winter and never came back to setup the system properly for summer.

[dan sw fl]

Hi there! I have a brand new two level 2960 sq ft home with a split system and a conditioned crawl space.

I live in the Raleigh, NC area.

Each day around 3 PM, my home begins heating up pretty badly. I understand that this can be normal, and temperature wise we are maxing out at around 75 degrees according to the thermostat, but I have taken the temp of my kids rooms and they were at 80 degrees. I understand some of that can be normal, but our humidity in this home is really high.

In the morning, our temperature can hit 69 degrees, but the humidity is at 60%.
Yesterday in my upstairs area,
at 8PM, the thermostat said 74 degrees and the humidity was 80%.

This made the upstairs extremely humid and unbearable. The weather yesterday outside was around 95 degrees with around 50-55% humidity.

I am concerned because the humidity is causing some extra nail pops and drywall issues, plus it is terrible for sleep! I understand this level of air quality is also really bad for health, and great for mold and fungus.

As I said, we have a 2960 sq ft home with a conditioned crawl space. We have a Lennox 3-ton 14 SEER system, model 14ACXS036-230A**. This whole system seems like it just cannot keep up with this house.

The temperature difference between the
returns and the vents is 8-10 degrees.

We have the Wrightsoft load calculation summary, but many of the numbers are 0, or set to N/A.
It also is incorrect about there being a fireplace, and there is no calculations for the ducts or the crawlspace.

What I would really like to know is, does any of this sound normal?
Can this much humidity in the home be a normal function of a properly sized or functioning system?
Can a 3-ton system actually cool a 2960 sq ft home properly?

Should I get another load calculation done for the home?

I really appreciate an help you all can provide, I am just not sure what is normal or not!

Differential temperature (DT) 8'F to 10'F from the Air Handler outlet to the first diffuser [ vent ]
indicates a Failed A/C system.
_____________ DT should be ~ 21'F !!

Crawl space being conditioned is Rather ODD.
_____ Sounds like you may be conditioning the OutDoors.

[ddyraw]

Thanks for the quick responses Dan and ksefan! This definitely seems concerning!

I was told that the crawl space received conditioned air to reduce humidity in the crawl space. Kind of ironic considering there is massive humidity upstairs, LOL.

So if I put a temperature gauge at a Air return, then measure at the first vent, that is a valid test? I was told it was not by the company, even though during my inspection, the inspector noted that the DT was 10'F. Hopefully I can post pictures soon, so I can share the load calcs!

Is there anytime a functioning a/c system should allow 80% humidity?

[dan sw fl]

Thanks for the quick responses Dan and ksefan! This definitely seems concerning!

I was told that the crawl space received conditioned air to reduce humidity in the crawl space. Kind of ironic considering there is massive humidity upstairs, LOL.

So if I put a temperature gauge at a Air return, then measure at the first vent, that is a valid test?

I was told it was not by the company, even though during my inspection, the inspector noted that the DT was 10'F. Hopefully I can post pictures soon, so I can share the load calcs!

Is there anytime a functioning a/c system should allow 80% humidity?
NO. I presume you don't have five windows open.

Send me your Manual J calculation [ PDF ].

MY Gmail address: racingdan11

Assistance: Https://www.mysimplifiedhvac.com

You are in need of a different HVAC/ Mechanical contractor.!
I will let you know.

[pecmsg]

Thanks for the quick responses Dan and ksefan! This definitely seems concerning!

I was told that the crawl space received conditioned air to reduce humidity in the crawl space. Kind of ironic considering there is massive humidity upstairs, LOL.

So if I put a temperature gauge at a Air return, then measure at the first vent, that is a valid test? I was told it was not by the company, even though during my inspection, the inspector noted that the DT was 10'F. Hopefully I can post pictures soon, so I can share the load calcs!

Is there anytime a functioning a/c system should allow 80% humidity?

What inspection?

[STEVEusaPA]

3 tons seems light for 3000sq ft in NC

[Mr Bill]

3 tons seems light for 3000sq ft in NC

You think? It certainly would be in Houston.


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[BNME8EZ]

You have several problems some related others not. Let's start with the home, you say it was new, how new? When a house is built it soaks up moisture. Any rain that comes falls on open wood, that wood gets wet and sometimes does not have a chance to dry before the sheet rock goes on. Then you have the sheet rock, the mud that is used to finish the seams puts off a lot of moisture. One other part of the construction to consider is the insulation. If the insulation gets wet or is wet it takes a long time for that to dry as it is covered by the sheeting on the outside and sheet rock on the inside. You say the crawl space is conditioned but is it sealed? To seal a crawl space the dirt floor has to be covered with a heavy plastic sheet with all the seams sealed as well as where it meets the walls, posts, etc. or it has to be concrete with all openings sealed. The walls must be insulated as well as the rim joist and there should be no openings to the outside.

If you just started up the A/C for the first summer it is fitting all the moisture in the house from being built as well as all the moisture that you are putting in the house by living there. With the humidity you are talking your system may be overwhelmed right now and will just take a while to get the moisture out.

Then there is ventilation. Most codes require so much fresh air into a structure. Your may be bringing in fresh air directly from outside with no control. 2900 Sq Ft of space will need quite a bit of fresh air to achieve the required air exchanges. Add to this the air required as make up for exhaust fans, clothes drier, water heater venting, range exhaust, etc and if there is no control you may be over ventilating the house.

The 10 degree delta T is not accurate if measured at the registers. A better test is at the inlet and outlet of the equipment. We will see what Dan comes up with but I would doubt that 3 T is over sized at just under 1000 Sq FT/T but it would depend on how tight/well insulated it is.

[jbhenergy]

You think? It certainly would be in Houston.


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Would be just right new construction my area.


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[Mr Bill]

Would be just right new construction my area.


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I understand, the temperature and humidity levels in different towns all across the country are a little different, and some have a huge contrast in these differences. This is why some like me here in the Deep South, freak out when we hear 2-tons on 2500 sq.ft. Heck we would have a 5- ton on 3000 sq.ft. here.


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[dan sw fl]

3 tons seems light for 3000 sq ft in NC

Raleigh NC is a predominantly heating climate.
HDD: 3,208 Design Temp. 24.2'F 99%
Heating Degree Days

CDD: 1,685 Design Temp. 92.5'F / 75.0'F 1%
--- --- ---
1,000 SQ ft / ton is a possibility for some NEW Construction
> R-20 Walls
R-48 Ceiling
SHGC < 0.23. U-factor < 0.3
A.C.H. Natural < 0.2


What construction quality that is actually pertinent to this residence remains a mystery.

[teddy bear]

Get the a/c contractor back in. If sized right, the a/c will cool the space to the desired temp and %rH.
The a/c is adjusted to the correct air flow which will remove enough moisture that at 75^F, 50%RH will be the result. If unable to get to down to 75^F, you need a bigger a/c. You fix the a/c or make it bigger. Now it is big enough to get down to 75^F, but the %RH is +50%RH. You slow the a/c air to increase the latent cooling or moisture removal. You a/c contractor know how to do this. If not, lawyer knows how to sue the a/c contractor.
You will need some dehumidification to maintain <50%RH during evenings and during rainy days.
Sound easy enough.
Keep us posted.
Regards Teddy Bear

[stumpdigger]

3 tons seems light for 3000sq ft in NC

I have a two ton in my house, 866 sq'. My neighbor has a 3000 sq' house with 2 condensing units, at least 7 tons in Chicago land.

[BNME8EZ]

First we need to know how is the 3000 Sq Ft figured. I have just under 2000 Sg Ft in my house on the main floor but then I have a full basement which gives a total of nearly 4000 Sq Ft but it is considered a 2000 Sq Ft house. I have a 2 T 2 Stg Hp in my house and it will keep the house at set point 10 degrees over design. Design is 75/93 and the load came out just over 18k. So a well built house in NC should be fairly close at 1000 ft/T