Condensation drops on HVAC vents

[Donald]

Daughter in NC has drops of water on the metal HVAC vents. I assume vent metal is cold and water condensing. RH inside is 55%.

I am thinking the only solution is to add a dehumidifier to the HVAC and dehumidify more than just when the AC is actually running.

Will the vent metal or screws rust over time?

 

[hemitom]

Yes they will rust over time .
dehumidifier will definitely help.
in a hot humid climate I would insulate all duct work if possible.
Ideal humidity is 30 to 50 percent I suspect at certain point of the house the humidity is higher than 55%

 

[Mechanician]

Recirc setting should help. Make sure the door is working.

 

[Nukeman7]

Recirc setting should help. Make sure the door is working.

I believe the OP is referring to the HVAC system in the home, not a vehicle.

 

[Lubener]

I am surprised the a/c isn't lowering the RH unless its oversized for the house..A dehumidifier shouldn't be needed.

Make sure she isn't running the blower fan in the furnace all the time as that will raise the RH. when the a/c is being used.. When running the a/c the blower setting on the thermostat should be "auto".

 

[Mechanician]

I am surprised the a/c isn't lowering the RH unless its oversized for the house..A dehumidifier shouldn't be needed.

Make sure she isn't running the blower fan in the furnace all the time as that will raise the RH. when the a/c is being used.. When running the a/c the blower setting on the thermostat should be "auto".

From what I've read about matching the size of unit to the house - this sounds right.
The unit needs to run longer to achieve the set temperature, that way it can remove more of the humidity.

 

[E150GT]

I read that most systems are not properly sized especially in hot climates. I also read that newer systems are way less efficient at removing humidity vs the older units.

 

[alarmguy]

We came from a 3000 sq ft home with two HVAC systems, bought new, 16 years we lived there. Central and more dry SC area.

Downsized to a 1800 sq ft "retirement" home three years ago. Coastal area of North Carolina. First year, I complained A/C system not working correctly and after investigating found out it was only a 2 ton unit. Very disappointed, there is even a thread in here with another guy from BITOG had an issue in the coastal area of SC (different builder) Anyway I called AC company that installed the system... Owner OR someone big in the company, it was a big company, installs for production builders and local builders.

After getting off the phone with him, I was mostly convinced, now two years later I am certain he was right. He was very confident in the way he described sizing a unit. After all this unit was 1/3 smaller (3 ton vs 2 ton) than a family member home of the same size nearby... but that home was 20 + years old and a cathedral ceiling. He said, it's all a formula to make sure the air is properly dehumidified and if it is oversized it could/will create mold issues. I checked the units of a high end builder in my area and noticed they are sized the same as ours. Actually our unit of the same brand was one step up of the ones used by a so called "higher end builder"

Taken into account in the formula is New construction, better insulation, low e window glass, better tight construction, exposure, maybe roof? , he spoke 100% confidently. I am now convinced. Our house, nice and dry in an area where the nearby ocean blows humid air all summer long. I think what built more credibility because I do not see it everywhere in use, even by some "custom" home builders. Being the house is tight, I guess it shows they were sticking to a "program"? in the sizing. Inside one of two air intake boxes for the system, under the main air filter, is a 6 inch small air filter, under that small air filter is a 6 inch or so duct with solenoid controlled flap that when the unit turns on, the flap opens and draws in outside air from a vent in the roof. Part of an air exchange. I guess if this was some cut throat cheap company that extra step would not have been done. (or maybe its new building code?) I dont know but I dont see it in all new home builders in different areas and companies.

I can testify our electric bill is stupid cheap. I mean, stupid cheap and even this year, "exceptional drought" nothing but sun, heat and humidity has convinced me even more how much I like the system and my way of programming (another thread)
Anyway, no complaints, ... system works great, winter time heat pump takes a long time IF I set it back 8 or more degrees when sleeping and temps in the low 20's ... I learned I should not be doing that for winter heat. Last home main level had NG with a gas pack in the system and spoiled me.

 

[Touring5]

Maybe get a HVAC Guy to check pressure drop and air velocity. One of the factors in A/C is getting the air velocity through the evaporator right. Too slow and the air is super cooled which can cause freezing or perhaps too cold for the ducts to avoid condensation (?). Too fast and humidity removal is affected.

 

[alarmguy]

Daughter in NC has drops of water on the metal HVAC vents. I assume vent metal is cold and water condensing. RH inside is 55%.

I am thinking the only solution is to add a dehumidifier to the HVAC and dehumidify more than just when the AC is actually running.

Will the vent metal or screws rust over time?

Is this a new home? I suspect older home? Sounds like your solution is the only one, unless doors are being left open, or big air leak someplace? Maybe the ductwork is drawing in outside air from the attic or crawlspace. Meaning a badly sealed duct or a open duct someplace in there.

 

[Hohn]

I read that most systems are not properly sized especially in hot climates. I also read that newer systems are way less efficient at removing humidity vs the older units.

Quite the opposite, actually. Newer systems can actually crush old systems for dehumidification. I say this because I had a new system installed 3 days ago and it's night/day difference in effectiveness. Stunning actually.

The enabling technology is the inverters and variable controls in the system. My system has a variable speed and a variable expansion valve. This allows the coil to say a constant cold temp even at very low air flows.

So when not much cooling is needed, the air flow slows drastically, but still constantly flows over a cold coil. SO you get nearly continuous running and dehumidification separate from actual cooling output.

 

[Hohn]

Delete

 

[Hohn]

Daughter in NC has drops of water on the metal HVAC vents. I assume vent metal is cold and water condensing. RH inside is 55%.

I am thinking the only solution is to add a dehumidifier to the HVAC and dehumidify more than just when the AC is actually running.

Will the vent metal or screws rust over time?

If the RH is 55% inside at a temp of, say 74F, that means the dew point in the house is 57F. That's dry enough you shouldn't be having major condensation issue in a properly setup system.

Which means the coil temp is probably very cold due to low refrigerant. This would cause the air to be supercooled and cause the ducts to be much colder than they should be also.

And with the coil running really cold, it means it doesn't take as long for the system to achieve the set temperature, causing a short cycling of the system. This means higher average humidity.

It's replicating some of the same failure modes associated with having too much a/c capacity for a given space.

 

[opus1]

I am surprised the a/c isn't lowering the RH unless its oversized for the house..A dehumidifier shouldn't be needed.

Make sure she isn't running the blower fan in the furnace all the time as that will raise the RH. when the a/c is being used.. When running the a/c the blower setting on the thermostat should be "auto".

^This.

I was told by my HVAC guy that the fan should run constantly during heating season to circulate the air and run it past the UV-light I had installed in the ductwork. For cooling, the fan should be on auto so that it's not running when the AC itself is off. Constant circulation hinders the coil's drying off and, as already said, will raise the humidity in the house.