Help! High Humidity indoors!!

[Peace]

Any HVAC guys have suggestions?
We have been fighting high humidity all summer long in our house (it's our 1st summer in this house).

It routinely runs 58-64% rel humidity inside when it is humid outside (after a rain).

If I blast the AC or the heat, it reduces the humidity down in the lower 50s.
I have been running a dehumidifier in the house all summer... 24/7.

This morning, it seemed particularly bad, so I set our hygrometer on a register.
1) It registered 74% with the fan on.
2) I turned on the heat, then the air, and pointed the dehumidifier into the return, and brought it down to 65%.
3) When I kicked off the AC, and just left the fan on (with the dehumidifier pointed into the return), the hygrometer soared to 83% at the register.

What gives!? I have got to solve this.

Thanks in advance.

[peejman]

Do you have a crawl space?  If so, put a vapor barrier down over the dirt (6 mil plastic sheet).  While you're down there, check the duct work for holes/leaks. 

 

If you're on a slab, the vapor barrier that should be in the floor could be missing or damaged.

 

If you've got an unfinished basement, are the walls damp to the touch?  They may need sealing.

 

Do you have drainage issues around the house?  When it rains, do you get standing water or really soggy spots anywhere near the house?

 

By "running the fan", do you mean ceiling fan or HVAC air handler?  Running the air handler when the A/C isn't running in the summer will increase the humidity in the house.  If humidity is a problem, leave the switch on the thermostat set to "auto" rather than "on". 

 

It's possible your house wasn't constructed with the tyvex house wrap vapor barrier stuff on the outside walls.  That could allow moisture into the house. 

 

It's possible you have very old, or low quality, or simply leaky windows that are allowing a lot of moisture in. 

 

If you have a chimney and the damper doesn't seal very well, that could be allowing moisture in. 

 

It's possible you have some other large air leak in the house, there's ways to check for that. 

[Peace]

Ha!

-Crawl space: Vapor barrier is new and taped/glued 16" up walls
-need to direct water away from front of house. :(
-yes, HVAC blower, not ceiling fan... didn't know that about the HVAC fan!
-1958 wood windows w/ metal storm windows outside
-fireplace. Probably need to make a damper-seal for the summer

All told, it is just dang wet in this house this morning!


So, what is the best way to check for HVAC leaks?

[jhc77]

Preface this by the "I'm not an expert" thing, but I am okay at figuring out issues with HVAC. Symptoms sound like there is an air gap in the unit on the inside of the house. Could be drawing outside air into the system. HVAC should be closed loop system. Seems like your bringing in outside air from some place.
I had a skunk fog something outside one night which recycled into the house. Next day I went to the attic a found a small leak in my unit, patched that real quick.
3M makes a good HVAC tape.

[partypilot1]

If the humidity in your house is higher than normal I would look for water migration (roof, foundation, supply lines and waste). 

[peejman]

Ha!

-Crawl space: Vapor barrier is new and taped/glued 16" up walls
-need to direct water away from front of house. :(
-yes, HVAC blower, not ceiling fan... didn't know that about the HVAC fan!
-1958 wood windows w/ metal storm windows outside
-fireplace. Probably need to make a damper-seal for the summer

All told, it is just dang wet in this house this morning!


So, what is the best way to check for HVAC leaks?

 

 

Turn the air handler on, get down there and crawl over every inch of it that's accessible.  You can just listen/feel for leaks or get a smoke/incense stick and watch for it to blow the smoke around. 

 

You can do the same thing with the windows and doors (though it typically works better when it's cold).  Run the smoke stick around every window and door. 

 

And remember, "duct" tape is a misnomer.... don't use it on duct work.   It dries out and falls apart much too quickly.  Use a good quality foil tape. 

[Dennis1209]

Peejman is absolutely correct, you have excessive humidity entering the space you're trying to condition. After you complete his suggestions and fix it your problem is most likely solved.

 

Another thing to check that can cause and/or add to your problem is your A/C unit. Is it sized properly for your home and set up properly? Forty percent of the function of A/C is to remove latent heat (humidity). If your fan is running to fast and cooling down your home too quickly it doesn't have enough time to condense humidity on your evaporator coil and doesn't let the coil reach maximum condensation temperature. Check your suction line (bigger copper line) at your outdoor condensing unit. There should be an area or two where it is not insulated and it should be dripping wet. That will give you and idea if your unit is under charged.

 

If you are slightly low on refrigerant most of your evaporator coil may not get cold enough to condense moisture in the air, same with too much refrigerant in the system. I don't know what temperature you're trying to maintain in your home but, the psychometrics and physics are the higher the air temperature the more grains of moisture it can hold. Translation: The lower the temperature the higher the humidity. After a rain and/or soggy ground under / around the house, etc., the conditioned space could be at 60-75% RH at 68-72% Fahrenheit. Raise the temperature to 73-76 degrees in the same conditioned space and the RH% drops to around 50-55%. Don't have my psychometric chart in front of me but I'm close from memory.

 

If you find moisture coming from around the doors consider some of that 3M door insulation. If coming from old wooden windows, consider 3m plastic window coverings until you decide to replace windows. All other areas, like Peejman said, moisture barriers. And do your gutters drain the water away from your foundation properly?

 

Good luck!

[Peace]

Thanks!

 

I have been wondering if our AC unit is not oversized for our space.  ie. It cools, but it doesn't run long enough to keep the air conditioned.  If I set the unit on 75 or 76 during the day, it never runs and humidity soars.  If I set it down to 71 or 70, it runs enough to dry the house out a bit -- but that never works on rainy days which makes me look at humidity migrating from crawl space/fireplace, etc.

 

I will check crawl space, gutters, and fireplace first.

 

I can also check evaporator coils, though if the unit is running, it seems to do fine.

 

I had a company out last September that was supposed to clean the duct system (new purchase of an old, nasty house) and check for leaks.  I am calling them back today - I'm not sure that they actually checked for leaks.  I am registering 88%rh at one of my registers right now.  I am alternating between heat/cool today to try to dry the house out a bit.  ugh.

[peejman]

Dennis reminds me of another thing.... check the condensate drain on your A/C unit.  When it's running, there should be a small trickle of water coming out (more than just a drip).  If it drains onto the ground, there should be a sizable wet spot.  It's possible the condensate drain is clogged and the condensation is building up in the heat exchanger. 

 

If it's clogged, you can flush it out with compressed air, pipe snake, water hose, etc.  That can get messy so if your unit is inside, just be aware of that.  Once the drain line is clear, it might be a good idea to pull some panels off to expose the coils and make sure they're not molded.  If so, spray a light bleach solution on them.  The mold should fade pretty quickly, then rinse with water.  The bleach will eat the aluminum if not rinsed off. 

 

You can also scrub it with some soap & water or simple green and a soft bristle brush.  The last resort is the "coil cleaner" stuff you find at Lowes, which is just concentrated sodium hydroxide (soap).  It also must be rinsed off thoroughly.  If it's outside, you can use a pressure washer but be careful, the big gas powered washers have enough pressure to damage the coils. 

[Guest RevScottie]

Thanks!

 

I have been wondering if our AC unit is not oversized for our space.  ie. It cools, but it doesn't run long enough to keep the air conditioned.  If I set the unit on 75 or 76 during the day, it never runs and humidity soars.  If I set it down to 71 or 70, it runs enough to dry the house out a bit -- but that never works on rainy days which makes me look at humidity migrating from crawl space/fireplace, etc.

 

I will check crawl space, gutters, and fireplace first.

 

I can also check evaporator coils, though if the unit is running, it seems to do fine.

 

I had a company out last September that was supposed to clean the duct system (new purchase of an old, nasty house) and check for leaks.  I am calling them back today - I'm not sure that they actually checked for leaks.  I am registering 88%rh at one of my registers right now.  I am alternating between heat/cool today to try to dry the house out a bit.  ugh.

 

You nailed it...your unit is likely over-sized. The unit isn't moving air across the coils long enough to remove the moisture from the air. It is "short-cycling". One reason you notice it on rainy days is with a cooler outdoor temp the unit will run even less. One solution is "load" is introduced to the system to make it run longer. Sometimes on a heat pump system this is done by firing the electric heater coils that are designed for your emergency heat. 

 

In the case of AC units bigger definitely isn't always better. You need to consult a good HVAC company and explain the problem...

[Guest RevScottie]

Here's a link that explains it:

 

http://www.energystar.gov/ia/home_improvement/home_sealing/RightSized_AirCondFS_2005.pdf

[Peace]

Thanks guys.

 

Drain line was a little clogged, and coils were dirty.

 

I'll report back when it's all settled out.

[Peace]

All better now.  Thank you, sirs.

[Dennis1209]

Thanks!

 

I have been wondering if our AC unit is not oversized for our space.  ie. It cools, but it doesn't run long enough to keep the air conditioned.  If I set the unit on 75 or 76 during the day, it never runs and humidity soars.  If I set it down to 71 or 70, it runs enough to dry the house out a bit -- but that never works on rainy days which makes me look at humidity migrating from crawl space/fireplace, etc.

 

I will check crawl space, gutters, and fireplace first.

 

I can also check evaporator coils, though if the unit is running, it seems to do fine.

 

I had a company out last September that was supposed to clean the duct system (new purchase of an old, nasty house) and check for leaks.  I am calling them back today - I'm not sure that they actually checked for leaks.  I am registering 88%rh at one of my registers right now.  I am alternating between heat/cool today to try to dry the house out a bit.  ugh.

 

I won't get into specifics but... The air coming out of your register should be super saturated, meaning it is going to be a very high humidity at that cold temperature and it's normal. Remember what I said above, the colder the air the less grains of moisture it can hold, therefore higher relative humidity. You need to measure the humidity / temperature at your furnace / air-handler / A/C return for an accurate reading.

 

Usually a reputable A/C company will come out and diagnose your problem and measure and size what you need and give you a free estimate. That's an alternative... 

 

Oops... Just read your above post.

 

Nothing better than trying to diagnose a problem via computer :squint:

 

I use to get phone calls at all hours from friends and family that their furnace / air conditioner quit working and ask over the phone, "what do you think the problem is and what do you think it will cost to fix it"? When I retired I moved to Tennessee and sold some of my equipment so I wouldn't have to put up with that stuff. With the exception of ME, I'm out of the BIDNESS :up:

Edited August 7, 2013 by Dennis1209

[peejman]

A programmable thermostat may help with the short cycling issues.  Some t-stats have a setting for how many cycles per hour are allowed or a min number of minutes between cycles.  I think mine has a setting of 10, 20, or 30 minutes min between cycles.

 

Or it may have an adjustment for the amount of temp change before it turns on...   say the setting is 72 deg.  It may be turning the A/C on when it hits 73 deg.  Perhaps you can increase that to 75 deg so it'll have to run longer to reach the set temp. 

 

Either of those may help reduce the cycle frequency.