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  1. #1
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    Lowering humidity in Houston, Tx

    First off, amazing forum I so happened to stumble upon when searching how to lower humidity in my home!

    I live near Houston, Tx and as many of you know it is hot and humid. I have read many threads regarding this topic and have learned a lot (thank you).

    I have not yet to seem to have seen a question I have so here it goes a long w/ some background...

    Brand new home built 2 years ago. 3700 sq ft 1 1/2 story home. 2 units. One controls all the bedrooms with thermostat in master bedroom. The other controls the rest of the house and the upstairs
    (both have their own thermostat and the unit has a Honeywell TruZone control in the attic.

    Indoor humidity in my home ranges from 57% - 64% (depending on ac demand) while keeping our Carrier Edge thermostat at 75 - 76 degrees.
    I did change the thermostats run cycle from a default of 4, down to a 2. Now, my question is lowering my blower speed. I have a Goodman furnace (was not successful when looking
    for a model number) but after looking at the electrical diagram it appears to have 4 speeds: HIGH, MED HIGH, MED and LOW. Cooling is on high. And heat is on MED HIGH AND LOW (why does
    heat have 2 blower speeds?) Anyway, my question is would I need to get someone to move my cooling setting to MED HIGH or MED? Can cooling and heat share the same blower speed? I'm trying
    to lower my humidity down and I'm trying to get an answer to be able to tell a HVAC TECH exactly what I'm trying to do.

    Thank you in advance!

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  3. #2
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    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
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #3
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    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!

  5. #4
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    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????

  6. #5
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    Quote Originally Posted by MSanchez214 View Post
    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.
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #6
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    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...

    Anybody have anything for me???

    Thank you all in advance...
    Attached Images Attached Images  
    Last edited by MSanchez214; 08-29-2016 at 06:57 AM. Reason: wrong info...

  8. #7
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    Quote Originally Posted by MSanchez214 View Post
    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...

    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
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #8
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    Quote Originally Posted by teddy bear View Post
    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
    I will do that Teddy! Thank you...
    Will you by chance be in the Houston area any time soon? I know a guy who has humidity issues in his home and he could really use your help!

    Also, is it odd for the mastic the tech put (from the picture attached in a previous post) to not have dried yet. It's still wet and gooey to the touch?

    Thank you in advance!!!

  10. #9
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    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
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #10
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    Quote Originally Posted by teddy bear View Post
    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!

  12. #11
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    Shameless bump...

  13. #12
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    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
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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  15. #13
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    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...

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