You are on the right track. You have a classical "lazy a/cs" or significant duct leakage.
By having a tech measure the cooling coil temperature with refrigerant gauge, you and the tech can figure out duct leaks or "lazy a/c". If the cooling coil temp is 30^F below the return air temperature, check for duct air leakage. If the coil is warmer, slow the air flow until you get the 30^F split minimum. Your tech should be able to answer you question about the different speeds for heating.
We are assuming the refrigerant charge and equipment is functioning normally.
If you find the coil is cold enough, check all of the duct connections for leaks. Also building air leaks could contribute to the problem during windy conditions.
During peak cooling loads, you should be able to get to 50%RH. During low/no cooling loads and high outdoor dew point plus the moisture from the occupants, normal properly setup a/cs will not be able to keep the moisture down to 50%Rh. A small whole house dehumidifier is needed with enough capacity to remove the moisture in the infiltration/ventilation and from the occupants is needed. Usually 3-6 lbs. of dehumidification could be needed when the outdoor dew points are +65^F. Units like the Ultra-Aire whole house dehumidifier are designed to supplement the a/c during these conditions.
When you are done, you be able to set the temp and %RH for what you want. Even with a/c "off" you will have the 50%RH for minimal operating cost.
Hope this helps, looking for more questions.
Regards Teddy Bear

 

Thanks for the reply Teddy...

When you say check the ducts, am I checking them at the unit and following them to the boot registers? The plenum and ducts have been sealed with mastic but I don't believe the boots have. The return airs have also been sealed up with mastic (you can see it when you remove the filter) and I don't believe those are leaking.

I did do a differential temp between return air and air coming out of the vent and got about a 16° difference. Reason I say "about" is because I was using a cheap infrared temp gun.

And as far as my other question, if the tech does lower my blower speed, is it safe/possible to have both cold and heat on a blower speed?

Thanks!

 

Ok, I found a few places where air was leaking out of the duct coming off of the unit (looks like the mastic wasn't put on correctly) I will add more mastic to this to seal them. Another question is what's the best way to seal the ducts to the register boots? Mastic? What about the register boot itself, it's sheet metal that's covered in my attic insulation but surely I can do something to improve that. I will also spray foam any gaps from the boot to the sheetrock to ensure to leaks there. Any ideas????

 

We have some top notch duct installers on this site. Air tight and covered with a closed cell foam tape thick enough to avoid condensation. All sweating surfaces need to have enough closed cell foam insulation to avoid condensation during high dew point weather. Some are sealing their attics and dehumidifying the space to stop condensation and mold.
There are other ways but complicated. Most attic in the humid climates of the US have mold in the attics. The modern a/cs make these spaces much colder and colder caused more condensation. Most people accept this.
Keep us posted.
Regards Teddy Bear.

 

Ok guys, I have an update...

Called installer who sent over a tech. Went up into the attic and found some condensation on this duct work. See pic attached. He put some water based mastic on it and said that should stop the condensation (side note, it's been 48 hours and a lot of the mastic has not dried yet! I don't think this is normal)

I then read him word for word of TEDDY BEARS advice. He went on to change my blower speed on both of my units. I have HIGH, MED HI, MED and LOW. Both units had a COOL set on HIGH and HEAT set on MED HI. He placed the HIGH on PARK, changed the MED HI to COOL and put MED on HEAT.

He then received an emergency phone call and said he had to leave but said that should fix my high humidity issue!

Needless to say, it's been 2 days with the system running like this and I have not noticed a humidity change in my house. Still reading 57% - 64%. Do you think we need to lower the blower speed even more? Possibly to MED and put HEAT back to MED HI?

I've been calling them but of course they're swamped w/ emergency jobs right now and I'm loosing it over here... :gah:

Anybody have anything for me???

Thank you all in advance...

 

I give the tech for accepting advice from a bear in the woods, "or web". I would have him measure the low side pressure and estimate the coil temperature. Looking for the coil temp that is -30^F the return air temperature. Read to him word for word. Lower the speed until the coil temperature is 30^F lower than the return air temperature. This should get you to 50%RH after a hour long cooling run. If not you have major outside air getting into your home.
Leave the heating air flow where it is.
Evening or cool damp weather, you will need a whole house dehumidifier to maintain 50%RH. When the outdoor dew points are below 50^F, fresh air infiltration or ventilation will maintain <50%RH.
Where have the sharp techs gone, on to greener pastures, I hope??
Regards Teddy Bear

 

Turn on the heat for a couple hours during the middle of the day.
I will keep you posted on being in Houston. Help hing by passing on the tips we talked about. He needs to train his tech.
Regards Teddy Bear

 

By turning on the heat, is that for the mastic to dry or to drop the humidity in the house?

And couldn't I just switch the blower speed from MED HIGH to MED and see if that makes the humidity drop? Or could I be setting myself up for other issues?

Thanks!

 

Shameless bump...

 

Drying the mastic. Mastic kept wet by condensation will not dry easily.
Turning off the a/c during the day may well do the same thing.
Regards Teddy Bear

 

Thanks Teddy!

And what about lowering the blower speed one more setting and checking if that makes a difference on my humidity? I'm getting the run around by the installer right now...

 

Did you watch as they applied the mastic? Did they remove the shiny vapor barrier and seal the physical duct inside, or just the outer jacket that's visible in the pictures? I could understand how that could lead to more problems, I live in a dry climate, but could see how things could get worse if the duct itself (inner core) wasn't sealed well. I could be way off, so don't think to much of it, Teddy Bear is the resident humidity expert.

 

Yes I watched... He pulled back the shiny part and insulation. He the took off the corrugated flex line exposing the collar. He placedar mastic around the collar, placed the flex line back on (zip tied it). Then he placed the insulation and shiny back over the corrugated line (zip tied that) then put a lot of mastic around all of that. I went up to the attic yesterday and it was still not dry and I felt some condensation at the bottom part of the duct.

 

Slowing blower speed always removes more moisture from the air and causes more condensation on the air handling equipment exposed to high dew point air. A 30^F split is ideal for 50%RH during high cooling loads. 75^F, 50%RH, a 55^F dew point requires a 45^F coil temperature. Then look for condensation and re-insulate the spots that have condensation with a closed cell foam tape like Rubetex.
This will get you 50%RH on a hot day. Get a small whole dehumidifier like the Ultra-Aire for 50%RH during low/no cooling loads and high outdoor dew points.
Regards Teddy Bear

 

Sounds like a plan Teddy... I will do that. I will slow the blower down to MED and monitor the humidity. I will also watch for any extra condensation on the air handling equipment.

I know that my plenum is insulated on the inside and has mastic all on the outside. But where the supply air goes out into the ducts, that part has no insulation, just the sheet metal it's made out of. The ducts off of the supply has tape and mastic. I know you say lowering the blower speed I'd be dealing w/ more condensation so would wrapping the supply air up in some Reflectix work?

Also, I'm having trouble finding some of that closed cell foam tape at the big box stores. I'm just finding thin strips, and I would imagine I need something a little thicker. I'll check some HVAC spots in my area.

 

Ok... Here's an update guys! Might be a lengthy one so I'm sorry.
My blower has 4 speeds HIGH, MED, MED LOW, and LOW. (I was mistaken earlier sorry).
All readings were taken inside Master Bedroom from same supply and return.
When reading temps on supply/return, I used 3 different thermometers to measure temperature and took the average.

Blowers set on MED speed. Thermostat set at 76°
Outdoor Temp/Humidity = 92°/54%
AcuRite Digital Monitor shows = 73°/57%
Return Air = 74.9°
Supply Air = 60.6°
Difference of 14.3°

Changed blower to MED LOW speed. Thermostat got up to 79° before A/C started.
Outdoor Temp/Humidity = 91°/56%
I let the A/C run for 30 minutes straight (set thermostat down to 74°) After 30 minutes thermostat showed 75°
AcuRite Digital Temp/Humidity = 73°/56%
Return Air = 74.3°
Supply Air = 58.5°
Difference of 15.8°

I was REALLY hoping lowering the blower speed, I would see a bigger difference. I already took it down from HIGH, to MED. Then I tried MED LOW and it only dropped it
1°. So I moved it back to MED and I'll await suggestions.

And as far as condensation goes, none was on top but I did notice a little bit at the bottom of the handler (see pics), but again, that was only after 30 minutes of run time at the lower speed.

Thank you all in advance for your patience and advice...

 

Why not stay on Med Low. Let it run for a few days. It takes time to drop the %RH because of moisture in the materials inside the home.
Tape on insulation on any of the sweating ducts.
Keep us posted.
Regards Teddy Bear

 

Ok Teddy.... I will move both blowers to MED LOW and monitor them.

And by tape on insulation on sweating ducts, what does that mean exactly? Should I not concern myself with the condensation seen on the bottom falling into the drain pan?

 

Add insulation to the condensing areas. Try the bubble type with tape on the outer edges to form an air seal to keep damp air from getting into space between the insulation and the duct. Rubitex is a brand of closed cell foam rubber that would be better than the bubble type. Falling into the drain pan? I would insulate any cold area.
Keep us posted.
Regards Teddy Bear.

 

Sorry if I missed if this was mentioned, but has anyone let him know that by lowering the fan speed to help with the latent levels, will also decrease the amount of sensible heat removed?

 

Ok everybody... Here's an update.

I have moved both blowers to the MED speed and have a noticed a slight drop in humidity. I am now around the 55-60% range. (I have never seen 55% before this). As far as condensation on the unit, I don't have much except for the little at the bottom of the unit which drips into the drain pan (which I still plan on insulating). I do have one duct that I can't seem to stop it from condensing. I have some GREAT STUFF Window and Door w/ the Great Stuff gun as well. Can I just put this all around the duct work and see what happens? Thanks for any advice once again, guys!!!!

 

Great Stuff duct insulation will look like a homeowner failed badly at the installation.

Why not use 3" foil tape and 1" foil faced polyiso foam board to insulate the ducts that are sweating?

Make it straight, square, and neat. No one ever regrets creating a masterwork.

PHM
------

 

If I remember correctly, we (as professional HVAC people) can not use that kind of foam as it doesn't meet the flame and smoke spread requirements. You as a homeowner can do what you want in your own home. I would insulate everything into one big ball of insulation, in my own home of course.

 

I'm not sure if you're telling me to go ahead and do it... Or it isn't safe to do it! I'm obviously doing something wrong w/ that duct because I completely took it apart and put mastic on the take off then on the duct, pushed the insulation and foil wrapping and zipped tied it tight. But it's still having condensation. I used that Great Stuff around some others and it seemed to work but now w/ what you're saying maybe I shouldn't have!

 

Haven't read the whole thread, so maybe this has been discussed.

Do you have an attic ventilation fan running? Those fans can pull conditioned air from the house, and the conditioned air gets replaced with humid outside air.

 

Thanks for the response but no, I do not have an attic fan.

 

Just remember during the drier weather, you might want to step up your blower back up to regain the sensible heat removal that you have lost, due to lowering the blower cfm's. Seems like with the condensate issues you are having by lowering the cfm's, a whole house dehumidifier might have been the best route.


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The best meter would be a digital with temp/%RH readings. I would take the reading during hottest part of the day and not the outside conditions. The typical inside temps while noting the space temp/%RH.
Regarding catching the condensate, note all of the conditions and the amount of condensate during a minimum of 15 mins. and steady state.
A tech can measure the coil temperature with a refrigerant gauge connected to the coil refrigerant.
Again best to measure during the heat of the day and noting the actual indoor/outdoor condition, temp/%RH of both.
You may be at a correct setup, just trying to confirm and the amount of air infiltration via duct leaks and wind. Wind increases fresh air infiltration.
Regards Teddy Bear

 

Hey Teddy... Again thanks for all the advice as well as thanks to everyone else who's trying to help me out.

Here are some numbers...
Outdoor Temp/Humidity = 95°/63%
Indoor Temp/Humidity = 74°/54%

I'm also noticing some condensation on the bottom of my drain pan falling on to the wood floor beneath it. It appears cold air is coming out of my secondary drain line hitting the drain pan and causing it to condensate at the bottom of it. I don't have much room to insulate this part as my pan is on a platform. The pan sticks out about an inch from the platform. I shoved some attic insulation under there in the mean time, any suggestions????

 

Ok I'll shut up, since he apparently doesn't care about any sensible heat removal loss. Carry on soldiers.


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It's an oddity of hackery that it is often possible to both lower humidity and trade off sensible while actually forcing the system to perform closer to the required BTU requirements. <g>

PHM
--------

 

Your house is as good as it's going to get with the builder grade equipment installed and complete mess of a all flex duct system it's a typical new construction mess. It's a ac system to get the house cool and sold and then that's all you get. But hey it's got all the pretty stuff our wives like so they are pretty and uncomfortable. 20g in flooring and a 2500 ac system typical builder.

It's time to spend the money hire a qualified contractor and plan on replacing the existing junk builder system's with correct high end HVAC equipment scrap the flex duct spider mess and design a custom duct system using quality materials that will deliver correct airflow to all areas. IE variable speed blowers, multi stage cooling or a vfd driven compressor HVAC equipment is what you need along with a correctly designed duct system will deliver exactly what you are after.

You've done about all the optimizing of your existing stuff you can. What it's doing now is all you are going to get out of it ever and as the house and equipment ages it's going to get a whole lot worse. We are ac guys our job is to deliver bad news to people who don't want to pay to fix problems on a daily basis. They all want it fixed and precious few want to pay the money to get their desired results.

 

Thanks for the response and suggestion.

 

I would be curious to know the tonnage of the unit and how long does the unit run when there is a call for cooling before the thermostat is satisfied? I've seen oversize units that don't run very long cause humidity problems. Humidity is only being removed when the compressor is running. Sometimes people think that a bigger unit is just better but if it's too big there is just not enough run time to get the humidity removed. Might not even be the issue here but just a thought.

 

I have timed the units run anywhere from 10 to 25 minutes.

 

Seems like a reasonable amount of run time to get the humidity out. Are you getting lots of condensate out of the drain line? Not sure if it was discussed yet but what is the configuration of your return air ducting? Could you be pulling in warm humid air from a leaky return duct in the attic ? Just thinking out loud here...

 

I checked all my returns (I have 4 12 x 12s in the bedrooms, a 20 x 25 on one side if the house and a 20 x 30 on the other) and none seemsm to be leaking at the plenum or where they meet the sheetrock. Even then, I out some great stuff on the attic side where they go into the sheetrock and all returns have mastic on the inside.

 

I know you had the humidity down some at one point. What are you currently at? Have you tried lowering your temperature set point and letting the units continue to run and see if the humidity comes down any more? I may have to ponder this a bit more. ..

 

Yes! I currently have my AC at 75. Used to have it at 76/77 and now my wife is dying of coldness at 75! LoL. And the lowest humidity number I've seen was 53% indoors but I'm not 100% what the outdoor temp/humidity was. =/

 

I'm having the same issues. did any of these pointers help?