Condensation drops on HVAC vents

[Hohn]

The system in my daughter's new home is probably "builder grade". Unfortunately. Like most, she would focus on the aesthetics of the house, not the mechanicals.

Yes, hence the word "can" in my post doing a lot of work there.

It's the sad reality that spec homes have many mechanicals and such installed that are the absolute cheapest and minimum viable version of the part.

I've lived in two subdivisions. OUr first home was a brand new build. Our current home was built barely 18 months before we bought it.

Both cases proved to me that spec home subdivisions get the very bottom end of materials in general and often workmanship too.

 

[Lubener]

If you shut the fan off while the coil is still wet, the moisture has nowhere to go except into the ductwork. As the coil warms, the water evaporates into the stagnant air inside the ducts and is then pushed into the house the next time the fan starts.

Disagree. If that were the case, the system would never be able to dehumidify the air in the house. During operation and after shutdown, most of the condensation on the coils should drip into the drip pan below the evaporator coil and settles in the condensate pump to be discharged or down into a drain directly. Most of the moisture has already dripped off the coil before the next cooling cycle. Only a small amount is still present on the coils.

 

[Hohn]

Disagree. If that were the case, the system would never be able to dehumidify the air in the house. During operation and after shutdown, most of the condensation on the coils should drip into the drip pan below the evaporator coil and settles in the condensate pump to be discharged or down into a drain directly. Most of the moisture has already dripped off the coil before the next cooling cycle. Only a small amount is still present on the coils.

Not at all. OF COURSE the system can dehumidify the air in the house-- while it's running, it removing much more moisture than the small residue left on the coil. This is why we have to have drains and such.

The residual coil amount of moisture on the coil is small. But not zero. Yes, "most" of the moisture goes to drain. But not all. That residue goes into the ductwork whether the fan is on or not.

Condensation starts with droplets too small to drip. It takes time and accumulation to coalesce into droplets that will actually enter the condensate recovery or drain system.

When you shut off the fan (and the compressor in fixed-speed systems), you freeze in time the water on the coil--the local atmosphere has the same dew point as the coil temp. But the coil temp is rising now, and so is the dew point locally. Rising dew point is rising humidity. The re-evaporation of that residual moisture occurs 100% of the time. The coil "drying" is the air getting wetter. Obviously.

This is one of the many reasons I selected an inverter system with variable fan speed and such. The coil is almost never warm and shut off, nor is the fan. That means you never have re-evaporation and the effective dehumidification is better. It's quite notably better for dehumidification because the fan slows way down and the air barely crawls over the coil, dropping all of its moisture to that coil dew point temp.

It's quite effective. I was expecting it to be better than my old system but I'm gobsmacked at just how much better it is.

 

[opus1]

Did your HVAC guy install the UV light? I am told that the UV light might kill mold on the coils. But nothing short of the type of UV light in operating rooms will kill germs or viruses.

It's in the ductwork leaving the furnace and there is a shield on it.

 

[alarmguy]

We have had nothing but luck with our production builders. Two new homes in 16 years, two different national builders. I wouldnt do it any other way.
HVAC units are made by a handful of companies.
Our last home had two. Heil - still running strong when we sold the house at 16 years old. This was in central SC where the unit was active 24 hours a day for 16 years, either for heat or AC.

Our new Lennox System in the new home, works perfectly. Nice and dry, right down near the coast of NC and yes again, active 24 hours a day heat or AC

Actually there is a more high end production builder not far from us, uses a cheaper version of our Lennox system.

Most people do not know what or how big a builder is, except for the wealthy who actually higher someone who builds a couple homes at a time. Good luck with that. Its a roll of the dice.

 

[opus1]

As for "where does the moisture on the coil go when the system is off?" question, it drains into a catch pan and then goes into the PVC piping leading from the furnace to the floor drain.