First, I live in Florida near the coast, so one can definitely expect humidity during the summer.

But other homes I visit don’t struggle like ours does. During the warm months, our house is rarely below 70% humidity, and we even set the AC at 68 degrees to help. (During the day, it usually runs about 72.) The AC system is only 4 years old, and we have it inspected each year. Filters are all clean.

All windows are fairly new, and I re-caulked them last summer. We added new insulation to the attic 3 years ago as well. The roof is 4 years old and has Energy Star-rated shingles.

We have a 2-ton system for 980 square feet of living space, but it just isn’t doing the job. I’ve tried running a dehumidifier, but that made the house heat up even more.

I know that a variety of factors affect the cooling of a home, but can anyone offer other ideas?

How tall are the ceilings?

Has it ever worked properly with that 2 ton unit?

Maybe set your fan to a lower speed?

quote:

Originally posted by stoic-one:
How tall are the ceilings?

Has it ever worked properly with that 2 ton unit?

Ceilings are very low…7 feet, I think.

It worked well at first, but the last two years it seems to be struggling, so it might be the unit.

They previous system had the same issues with humidity.

quote:

Originally posted by Skins2881:
Maybe set your fan to a lower speed?

That’s definitely worth a try- hadn’t thought of that.

If this started with the new AC unit, the unit might be oversized and runs long enough to cool but not long enough to dehumidify. Have seen this several times over the years.

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Originally posted by thomjb:
If this started with the new AC unit, the unit might be oversized and runs long enough to cool but not long enough to dehumidify. Have seen this several times over the years.

I forgot to mention that it is a 2-stage unit and is set to continue to dehumidify if it reaches the set point. The problem there is that if I leave it on, it will run non-stop through the night to try to get the humidity down.

I know there are a few HVAC experts here but in my building experience where the HVAC system can’t pull enough humidity out of the air it’s a result of the unit being too large and not running enough to pull the water out of the air.

If you can find a qualified firm to run a “Manual J” calculation on your home you may find that your home should have a smaller unit that will run longer and be able to pull the humidity out of the air. Interestingly enough adding insulation to your ceiling may have contributed to your situation.

Indoor humidity around 70% is not good. Should be closer to 50%.

Slower speed fan.

My house is 4000 sq ft in SW Florida and my house has too much humidity for a few months during the summer. I’ll turn the temp down a few degrees to get the AC running longer and I also have a backup dehumidifier that I use in the summer months.

quote:

Originally posted by Maestro:
We have a 2-ton system for 980 square feet of living space, ...

I'm no HVAC expert, but that sounds like too big a unit for that space. We have a 2-1/2 ton unit for 1300 sqft + basement and that is slightly over-sized. (We were right on the cusp. Next smaller would've been slightly under-sized.)

It seems counter-intuitive, but too much tonnage is as bad as too little.

There are variables, of course, but the rule-of-thumb is 1 ton per 600 sqft.

quote:

Originally posted by Maestro:

quote:

Originally posted by thomjb:
If this started with the new AC unit, the unit might be oversized and runs long enough to cool but not long enough to dehumidify. Have seen this several times over the years.

I forgot to mention that it is a 2-stage unit and is set to continue to dehumidify if it reaches the set point. The problem there is that if I leave it on, it will run non-stop through the night to try to get the humidity down.

If you don't intervene, does the humidity get down to an acceptable level?

I'd call my AC guy. Do we have an AC guy here?

quote:

Originally posted by tatortodd:

quote:

Originally posted by Maestro:

quote:

Originally posted by thomjb:
If this started with the new AC unit, the unit might be oversized and runs long enough to cool but not long enough to dehumidify. Have seen this several times over the years.

I forgot to mention that it is a 2-stage unit and is set to continue to dehumidify if it reaches the set point. The problem there is that if I leave it on, it will run non-stop through the night to try to get the humidity down.

If you don't intervene, does the humidity get down to an acceptable level?

It gets lower, but the temp of the house gets down to 62-65.

Google fu says! El Linka thingy

High Humidity In House With Air Conditioning–What Gives?

We mentioned above that running your air conditioner is usually the primary way to combat high humidity in your home. However, if you feel humid, hot, and clammy even with your AC on full blast, there could be a problem with your unit.

Common causes of high humidity in a house with air conditioning include:

Oversized unit. Contrary to what you might think, an air conditioning system is less effective at controlling temperature and humidity if it is too large. This is largely due to the power of the compressor, which allows it to run for short periods of time—too short to remove all the humidity from the air.

Frozen coils. Your AC coils won’t be able to perform their job effectively if they’re covered in frost. As a result, your air conditioner won’t cool or dehumidify the air as well as it should.

Dirt and dust. Even if you regularly replace the air filter of your AC unit, dust, dirt and other debris will still collect in the system over time. If you don’t have the expertise nor time to perform the tasks on the manufacturer-recommended air conditioner maintenance checklist, enlist the help of a licensed professional.

quote:

Originally posted by ensigmatic:

quote:

Originally posted by Maestro:
We have a 2-ton system for 980 square feet of living space, ...

I'm no HVAC expert, but that sounds like too big a unit for that space. We have a 2-1/2 ton unit for 1300 sqft + basement and that is slightly over-sized. (We were right on the cusp. Next smaller would've been slightly under-sized.)

It seems counter-intuitive, but too much tonnage is as bad as too little.

There are variables, of course, but the rule-of-thumb is 1 ton per 600 sqft.

It's based on climate. In Florida given the exact same size houses you'd end up with a 1/2 ton or so larger unit then you would in Michigan..

Are you basing the humidity on how it feels? Or do you have reading from a hygrometer? If you’re using a hygrometer, have you tried a second to verify?

I’m guessing you’d know the difference, 70% is significant. But figured I’d ask.

quote:

Originally posted by Maestro:

quote:

Originally posted by tatortodd:

quote:

Originally posted by Maestro:

quote:

Originally posted by thomjb:
If this started with the new AC unit, the unit might be oversized and runs long enough to cool but not long enough to dehumidify. Have seen this several times over the years.

I forgot to mention that it is a 2-stage unit and is set to continue to dehumidify if it reaches the set point. The problem there is that if I leave it on, it will run non-stop through the night to try to get the humidity down.

If you don't intervene, does the humidity get down to an acceptable level?

It gets lower, but the temp of the house gets down to 62-65.

This tells me the unit is too large for your needs. I assume the evaporator is in the attic? Also, which gas are you using?

quote:

Originally posted by Maestro:


We have a 2-ton system for 980 square feet of living space

I think that is your problem right there, or at least part of it.

IMO your system is oversized to your square footage.

I’m no HVAC expert but you probably should be running a 1 or 1.5 ton system for that size home. Your AC doesn’t probably run long enough to remove the humidity from the air before it hits your target temp.

Anyone else want to weigh in here?

They went through a through evaluation and decided that a 2-ton was the best size. Fitting the last week, it is running 24/7, so it’s not going on and off. As someone mentioned, unit size also depends on geographical location.

I tried lowering the fan speed- we will see if that helps.

Thank you all!

quote:

It worked well at first, but the last two years it seems to be struggling, so it might be the unit.

This right here tells me something has changed. It may be in need of service, and by that I mean cleaning the evap coil and condensing coil(I get leaves piled up around my compressor over time), and a charge verification. If it's not short cycling, is cooling, but not dropping out moisture, I lean toward the evap side. Be it dirty or the blower speed too high. MAKE SURE THE FAN IS IN AUTO, leaving the fan on all the time can actually just put humidity still in the evaporator right back into the air. Regardless, call a respected local service tech.

This isn't really a remote troubleshooting exercise if it was working initially.

Also a 2 stage system is inherently more difficult to talk someone through without knowing what mode it's operating in. It's not an on off thing. I also don't think 2 tons is necessarily over-sized for that SQ footage in FL depending on a LOT of factors.

Are you sure about the 7' ceilings? The only reason I asked about ceiling height was because normal ceilings are 8', but I went up a half a ton on my house because it has 9' ceilings.