Humid basement causing mold problems

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Old 07-19-18, 06:03 AM
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Humid basement causing mold problems

Hello, I live in St. Louis where it is hot and humid all summer long. I have a 2 story 2600 square foot house with a full walk out basement. The back basement wall is framed, not concrete. The basement is mostly finished with several rooms. I had no humidity or mold problems (that I knew of) until about 5 years ago. I noticed the basement room doors were sticking. I have a large collection of vintage clothing and wood furniture in the basement. I noticed that it was starting to mold. I have no leaks in the basement and it does have a working sump with drain tile that does run quite a bit when it rains.

I installed a dehumidifier about 3 years ago. It runs non-stop and shows 70-75 percent humidity most of the time. Last year I installed a 2nd dehumidifier in another room. It shows 60 percent most of the time.

This summer, in another room I have found mold on several of my items. I am now leaving that door open but the humidity stays close to 70 in there.


My AC unit is about 3 years old. I believe it is sized correctly for the house. Main floor humidity is around 55%. I have no cold air returns in the basement, but do have 3 air ducts blowing AC into the basement.


What to do??? Do you think installing one or two cold air returns will help? Just install another dehumidifier? Any idea why my basement stays so humid as soon as the humidity outside rises?
 
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Old 07-19-18, 09:21 AM
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I would read up on water problems in basements. Easiest are things outside like making sure the ground is graded and sloped to direct all water away from the home. Make sure you have gutters and all downspouts have pipes to carry the water at least 10 feet away from the home. If you have a foundation perimeter drain make sure it is clear and functioning. After that it gets into more extensive things that can require excavating around the basement to install a perimeter drain and a damp proof coating to the outside of the foundation/basement walls.
 
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Old 07-19-18, 09:32 AM
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What size and brand are the dehumidifiers? What is the temp of the basement? How many square feet is the basement?
 
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Old 07-19-18, 01:44 PM
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Thanks for the replies so far.

I have read up on water problems but still somewhat at a loss. 2 years ago I added some soil to an area that was not sloping away from the home, now it is. At that time I also found a drain that had collapsed from tree roots. I re-routed that and it now drains away from the home. They are not all 10 feet, but with the current grade that would be hard to do without running a pipe a long distance under ground through tree roots.

My basement is about 1300 square feet. It is sectioned into 1 main room and 4 smaller rooms. In the main room I have a GE 50 pint dehumidifier. In one of the smaller rooms where most of my vintage clothing is located, I have a GE 30 pint dehumidifier. The basement temperature is between 68 and 70 degrees during the summer.
 
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Old 07-19-18, 02:48 PM
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Hi hc, You are dealing with 2 sources of moisture beyond what you and others living there generate.
1. All homes lose air to the outside which gets replaced by that hot humid air you mentioned. Just checked St Louis and it is 86 at 61% RH. Using a temp and humidity calculator when that outside air cools down to 71 its moisture capacity goes up to 100% RH.
2. The other source is, as discussed, moisture passing through your concrete floor and foundation and you mentioned the sump does run quite a bit when it rains so we know the soil outside is on the wet side.

First step should be to pick up one or a few humidity meters. You will also want to measure the temperature at the same time in each location. The calculator I linked to will help you compare readings. Be sure to check the outside temp and RH at the same time.

Supply and return air flow should be matched as closely as possible to avoid pressurizing or depressurizing any space. Those pressures will increase the amount of outside air coming into your home.

That will get you started.

Bud
 
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Old 07-19-18, 05:22 PM
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My home is on a lot with a very high water table. Adding fill for a significant slope had little effect. I hope using a brand name isn't against any rules but I installed an "AprilAire 1850" dehumidifier in my basement. This thing is rated for a 3000sq ft home. Since doing so there has been a very noticeable decrease in the basement/home humidity as measured with a meter. You may wish to check if there is any warranty issues if you install yourself.
I would also suggest cutting some vents into your basement return ducts. If you use closeable ones you could shut them in the winter.
 
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Old 07-20-18, 06:41 AM
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More good comments and input, thanks everyone. I do have a meter to measure humidity in the basement and I check it regularly. I'll be working soon to install at least one cold air return in the basement. However, it begs the question: Should I have my supply vents open in the basement during the summer? I do not need them open for comfort as it stays cool enough with them closed. However I thought opening them would help move the humid air through the HVAC system and remove some of the humidity. But perhaps the vents being open is causing more humid air to be pulled into that space??
 
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Old 07-20-18, 08:17 AM
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Just to note, outside, inside house, and inside basement humidity readings cannot be compared as each is "relative" to the immediate temperature. Use the calculator (post #5) to calculate a dew point from RH and temp. Use that dew point and a reference temp ( I use 70) to determine what the RH would be at all locations if they were at the reference temp. Then you can compare humidity at different locations and outside.

Bud
 
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Old 07-20-18, 09:16 AM
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My basement is about 1300 square feet...I have a GE 50 pint dehumidifier...I have a GE 30 pint dehumidifier.
I'll be honest, something doesn't add up.

A basement with no apparent water(leak) issues and 2 humidifiers running in a relatively small area should generate a bone dry environment.

Supply and Return should be open to allow air flow!

What type of basement, are walls insulated?

Are humidifiers running all the time, do they ever achieve the desired dryness?
 
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Old 07-20-18, 12:42 PM
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I agree something doesn't add up! I cannot figure it out. I have no leak issues. My basement floor is mostly tiled with 2 smaller rooms having concrete floors. Most of the walls are finished and are insulated. The 2 smaller rooms have concrete walls on 2 or 3 walls, finished/insulated on the others.

Once summer hits, the dehumidifiers never shut off, or reach the desired humidity level. I have one dehumidifier running into the basement drain, and the other thru a wall to the outside so that I don't have to constantly empty them!

EDIT: The dehumidifier in the small room does shut off occasionally. The one in the large room never does.
 
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Old 07-20-18, 01:47 PM
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If you use a few RH and temp meters as I described you can start ti identify where the moisture is coming from. You can't compare a yesterdays reading to a today one that is why I suggest several and they aren't expensive.

I didn't see a date as to when the house was built, maybe I missed it. That date gives us an idea as to how the foundation was built. I suspect it has the typical damp proof coating on the outside below grade and that does no do well at stopping moisture vapor.

But, take a bunch of RH and temp readings and normalize them to one reference temp as I described. Wherever you get the higher new RH reading is likely to be a source of your problem.

Bud

PS, your floor drain may be putting that moisture right back into your basement if it isn't draining to somewhere well away.
 
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Old 07-21-18, 04:14 AM
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Bud's comment about the floor drain may be the answer. My basement dehumidifier drains into 5 gal buckets that I empty daily. You could try that for a while and see if it makes a difference. Steve
 
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Old 07-21-18, 09:02 AM
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I live in high humidity coastal area. Find that key to avoiding basement mold is keeping basement is keeping humidity below 60%. Above that there are problems.

Humidity indicators are often not accurate so have several of them.

Have ordinary floor model dehumidifier set at 55% and no mold. Unit has clean filter light which has to be taken care of occasionally. The basement is well sealed so infiltration is no an issue.
 
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Old 07-21-18, 10:18 AM
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The better large dehumidifiers come WITH a bilge pump that can pump that water outside.
 
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Old 07-22-18, 12:40 PM
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The floor drain is part of my sewer system. It doesn't drain into my yard. Not sure how that could be a problem?

On Friday I cut an opening into my cold air return duct in the basement, roughly the size of 2 input ducts. Today is Sunday and the humidity is still very high in the basement (67-68%). Should the cold air return in the basement be near the ceiling or the floor? If near the ceiling I would think it would pull more of the warm air out. But at the floor would promote better circulation?

One room that seems to have higher humidity could be the culprit. It has 1 wall mostly exposed concrete on the outside. Should I try to paint that wall? Another wall is solid dirt under my garage. A 3rd wall is exterior consisting of drywall, plastic, insulation, whatever the builder put on the outside of the studs, then vinyl siding on the outside. The 4th wall is an interior wall. I leave that door open. This room also houses my furnace/AC and hot water heater.
 
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Old 07-22-18, 01:32 PM
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Doubtful your floor drain is part of your sewer system as it would need a trap and refilling to protect against sewer gas. I could be wrong. Many floor drains simply drain into the perimeter drain system which when working drains to some place away from the house or into a sump pit. That perimeter system can become filled with silt and stop working. You mentioned that conditions seemed to change 5 years ago.

I do professional troubleshooting and I realize that juggling humidity, dew point, and temp is not an everyday activity for many. But troubleshooting without those numbers as previously explained brings our advice down to guessing.

When you measured the RH in the basement, what was the temp and what was the outside temp and RH.

Here's a detail that is important. All homes exchange all or the inside air with outside air at a very high rate. I would guess every 4 hours in your case so your ac system, which is actually a giant moisture removing machine, is actually trying to dehumidify a lot of the outdoors.

Now, when an ac system fails to remove enough moisture the problem is either air leaks or the system is too big, thus cools quickly without drying the air. The ac pros may have to review what you have.

How long does your ac unit run when it cycles on?

Bud
 
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Old 07-22-18, 02:45 PM
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Just did a reading. In one area of the basement, it was 71 degrees with 67% humidity and the outside temp was 81 with 57% humidity. Other part of the basement was 71 degree with 63% humidity, but that is the smaller room where there is a dehumidifier set at 60.

I thought home AC units (not a heat pump) were closed loop systems which do not draw air from the outside.

I'll have to time how long the AC unit runs and get back to you on that.

Here are a few more questions:
1. We have a 2 story home without zone cooling (do not have 2 units). To try and keep it cool upstairs, we run the AC unit fan all the time. Does that matter?

2. We have a spare bedroom on the 2nd floor which is not used. The bedroom does have a cold air return. We keep the vent in that room closed and the door closed. Is that a bad idea?

3. We do keep some of the vents on the main floor of the house closed as well, to try and force more cold air to the 2nd floor? Will that have an impact?
 
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Old 07-22-18, 03:18 PM
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Running the ac fan all the time returns any moisture left on the coil back into the air. It also increases the air exchange with the outside.

Any fan based system typically does not intend to exchange air with the outside but in the process of blowing and sucking air to and from rooms it creates either positive or negative pressures. Those unintended pressures push or pull air from the outside through all of those leaks I have been suggestion. I specifically measure this leakage as part of my energy auditing business.

Closing off the spare bedroom upstairs reduces the load on the air conditioner further shortening its run cycles. Open the door and open the return. After the humidity problem is identified you can address the size of the ac unit.

I adjusted those readings to all be at 70 so we can compare.
Basement RH = 69.3
Basement small room = 66.2
Outside RH = 82.25

This indicates the outside air is contributing to your inside moisture.

Switch the fan back to normal operation, not continuous.
Open up the spare bedroom door and the return vent.

Then let's see if the numbers change.

Bud
 
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Old 07-22-18, 04:50 PM
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Will do Bud, thanks for being so responsive and for all your input!

What about the vents on the main floor, should I open all of those as well?
 
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Old 07-22-18, 05:02 PM
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For now open them all up so the ac unit will run more and remove more moisture. Bottom line is your ac should be controlling the humidity. Any idea as to what size that unit is?

Bud
 
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Old 07-23-18, 04:58 AM
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Your dehumidifiers are small. Dehumidifiers are sized at 80 degrees, at 68 your 50 pint is probable more like a 40 pint. Have you tried taping plastic to the floor for a day to see if moisture is coming from the floor? You can do the wall this way as well.
 
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Old 07-23-18, 07:03 AM
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Hmm, interesting about the sizes of the dehumidifiers and the plastic. Might need to try that! Thought I was buying a good sized dehumidifier, but looks like there is a GE 70 pint. Still, where is the humidity coming from....

Checked today in the basement, the temp was 71 and RH is 61. Outsize temp is 74 and outside RH is 71.

Bud, can you do the math for me and give me your thoughts?

My AC unit ran this morning for 11 minutes and 40 seconds.
 

Last edited by hcliffe; 07-23-18 at 07:35 AM.
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Old 07-23-18, 07:18 AM
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Adjusted to 70 as before:
Basement RH would be = 63%
Outside RH would be = 81%
Compared to yesterdays numbers the outside RH is down 1.5% while the basement is down 6%.

Numbers are headed in the right direction, which options have you changed?

Bud
 
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Old 07-23-18, 11:22 AM
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Have made the following changes:

1. Created a cold air return in the basement. This is still at the ceiling level. Should it be moved down by the floor? I can use the void of the existing wall to make this change.

2. Opened the vent in 2nd floor spare bedroom and leaving that door open.

3. Opened all vents on the main floor.

4. Changed AC fan from "On" to "Auto" so it no longer runs continuously.

Noticed this morning that the large dehumidifier said "40" and was not running!! Getting optimistic, but still concerned about when outside humidity goes way up again.
 
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Old 07-23-18, 12:58 PM
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Quote: "Noticed this morning that the large dehumidifier said "40" and was not running!! Getting optimistic, but still concerned about when outside humidity goes way up again."

From post #10 you said "EDIT: The dehumidifier in the small room does shut off occasionally. The one in the large room never does."

That is definitely good.

As for the return being high or low, I've seen them both ways and not being a hvac guy I can't say which is better. Big plus is having a return down there to compliment the supplies.

When it gets hotter out the ac will run longer and probably reduce the humidity even further.

The house also acts as a sponge and you are now drying everything out. I would suspect conditions to continue to improve. Keep taking readings and chart them with notes as to what is going on outside, temp, RH, and rain. You should also include the small room and maybe upstairs.

Watch for the run time on your ac and note the outside temperature and look to see if the size is noted on that ac unit. I suspect it is oversized as many are. Ideally it would run almost continuously on the hottest day at a reasonable set temp, say 75.

Use your RH meter and measure right next to that large dehumidifier to see if they agree. It would be nice if the numbers were close. Maybe another brand meter.

Bud
 
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Old 07-24-18, 07:43 AM
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With the meter next to the large DH, it reads 71 degrees and 56% RH. The DH says 60, but it only changes in 5 degree increments, so I'd say they are pretty close. At the same time, the outside readings are 82 and 58% RH.


I will be gone for several days, so all measurements will be postponed. Thanks again for your help.


My wife does think it is warmer on the 2nd floor now which is not good. That's why we had the main floor vents closed.
 
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Old 07-24-18, 08:46 AM
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The air flow for heating and cooling systems cannot be adjusted by simply closing off either intake or supply registers. In some homes they have excess registers designed in so the amount of return and supply and their location can be shifted between summer and winter. Nice idea but they never come with instructions and people randomly at their whim open and close them. In reality there are careful calculations that should be used to ensure a balance between supply and return while maintaining sufficient air flow over the heat/cool exchangers. Too much or too little is not good.

I don't remember if you mentioned the date built on your home but rarely do they provide ducting and registers that meet those calculations. That would drive their bid up and they will do anything to provide a low bid, even install a poor system. Grrr!

Keep mama happy and close what you need but when you get back we will check the readings to see how they are affected.

I ran those inside and outside numbers and the inside RH is down 5.2 while the outside is up 5.5.

58% RH at 70 in the basement is looking good. (56% at 71).

Bud
 
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Old 07-30-18, 10:11 AM
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Back from my trip.

Current status of vents:
1. Basement cold air return is still open and at the ceiling.
2. Basement supply vents are open
3. Spare bedroom on 2nd floor vent is open, and door to room is open.
4. Vents on main floor are mostly closed.
5. AC fan is set to "on" to provide better circulation.
6. Temperature on 2nd floor is tolerable.....

Basement meter reads 70 degrees and 61 RH
Outside measures 68 degrees and 87 RH

Thoughts?
 
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Old 07-30-18, 12:09 PM
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Welcome back. Compared to your readings on 7-24 the humidity at 70 is up to 61% from 57.9% while the outside humidity has dropped from86.5% to 81.25%. So the house is not performing quite as well now as it was.

You switched the fan to "on" again and that can increase the RH. If you could turn that off for a couple of days to see how low it can go.

Bud
 
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Old 07-30-18, 01:58 PM
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Thanks again for the quick reply Bud. Fan has been set to Auto now for a few hours.

Basement reads 69 degrees and 63 RH, while outside is 77 and 67 RH.
 
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Old 07-30-18, 02:02 PM
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BTW: Found these 2 articles which support what you suggest about the Auto setting.

https://www.energyvanguard.com/blog/...stat-Like-This

https://www.coolray.com/help-guides/...iserably-humid
 
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Old 07-30-18, 03:35 PM
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Energy Vanguard is always a good reference, Dr Bailes.
Your numbers haven't changed a lot, 60.9 in basement and 84.5 outside, a bit higher. Humidity levels are slower to change than temps.

The issue with leaving the fan on gets complicated by larger cooling systems. The coil just gets loaded up with moisture and the thermostat is satisfied so cycles down. That means all of the water still collected on the coil is coming right back inside. A smaller ac unit has to run longer, more moisture gets removed and not cycled back. Still need to know how big your ac is, not that you are changing it now, but to help understand why the RH is so high.

Bud
 
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Old 07-30-18, 04:13 PM
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OK, let's see if we can summarize what we have learned.
With fan off we saw the best RH, but that was with the help of both dehumidifiers. One may have been cycling.

Leaving the fan off also reduces pressure differences that may be contributing by increasing the air exchange with the outside and all sets of readings show the outside RH as being higher, thus a possible source for the high humidity. Balancing supply and return air flow along with tracking down any leaks in the ducts or plenum are on the list.

The floor drain should not be part of your sewer system, codes have not allowed that for a long time (I'm not a pro on this). But sewer gas always needs a trap and only work when supplied with a regular flow of water, like a sink. Capture that water and dump it outside or down a real drain.

At some point your ac system should be able to cool and dehumidify the entire house. The dehumidifiers might need to help due to limited air circulation but they should not be the primary moisture removing appliances.

Bud
 
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Old 07-30-18, 05:38 PM
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I checked on a few things:

1. I spoke to my friend who is a licensed plumbing contractor in St. Louis and used to live in my subdivision. He says my floor drain is definitely connected to the county sewer system. There is a P trap. It does not run dry because in the summer my AC unit drains into it, and in the winter my furnace attached humidifier drains into it.

2. My AC is a Goodman model GSC130601DD which is a 5 ton unit. My house is 2650 square feet not counting the basement. It was built in 1993.
 
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Old 07-30-18, 06:50 PM
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Ok, I did more reading and you are correct it can be connected to the sewer system, not my first choice as the trap has to be maintained and dehumidifiers a and ac units aren't always in use in their season. So we'll put that to the bottom of the list and as last resort collect and dump that condensation.

Again, I'm not a hvac pro, but 5 tons is on the large size. The detail that ties size to the house performance is the cycle time. Check run times and then off times while noting the outside temp and RH.

When they evaluate a house for cooling requirements the size is calculated at or near a worst case cold temperature. At the design temp it is assumed that the ac unit will be running continuously. I found a listing for St Louis for a summer design temp of 94. At temps near that the ac unit should not be cycling, runs continuous. MOST ac installers will not want their install to fall short so they add a ton or so.

I'll let the ac pros advise on size but for your list, that 5 ton unit is a contributor.

Bud

PS, still thinking as I realize replacing the ac unit is not an option until it totally dies.
 
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Old 07-31-18, 04:47 AM
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I don't want to become a pest so let me know if you are done or want to continue.

I see three sources of moisture but we have only been discussing basically one. Through the floor and foundation is another but difficult to quantify.

The third is from the people living there, cooking, showers, perspiration, fish tanks, plants, drying cloths inside, dryer vented to inside (make sure it hasn't become disconnected), storing firewood inside, and I'm sure you have considered all of these just need to review.

My point is, there is a lot of moisture (water) coming from somewhere. If you were to collect all of the condensation from both dehumidifiers plus the ac unit it should be several gallons per day, just look at the ratings on those dehumidifier units.

No solutions to offer, just thinking.

Bud
 
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Old 07-31-18, 12:33 PM
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You are certainly not being a pest Bud, I appreciate all of your input and insight.

I have tile on about 85% of the floor in the basement, not sure if moisture makes it thru that or not. The walls are about 75% finished with insulation etc.

As for moisture from people, there are only 3 people living here. When we shower use exhaust fans, same when we cook. No fish tanks, no inside house plants. Our dryer vent has become disconnected in the past but that is obvious when it happens so I reconnect. I can't think of any other significant form of moisture in the house.

The main DH is still running almost nonstop. Inside temp is 71, RH is 62, forgot to check outside readings, will need to do that.

What is a feasible/acceptable/target inside RH with temp of 71?
 
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Old 07-31-18, 03:11 PM
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Thanks, I do get pushy at times, comes with age and declining patience as well as declining memory.

Your inside moisture levels are running below the outside air, but that is with both ac and DH running. IMO, the ac should be able to handle the humidity and cooling all by itself, with the exception of any rooms closed off from the air flow.

Here is another link for related reading. It mentions lowering blower speed and that might help if it doesn't ice up the coil. Basically, cooling every inch of your house as much as possible increases the load on the ac unit and increases the run time thus removes more moisture. Do some more testing with the fan in auto so we get a better picture of what the "on" selection is contributing.
http://www.greenbuildingadvisor.com/...ized-ac-system

Bud
 
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Old 08-01-18, 08:10 AM
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I've had the fan in "auto" since I got back on Monday.

This morning's readings:
Basement 70 and 61
Outside 71 and 77


Main DH still running.
Is it feasible to get the basement RH below 61?
 
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Old 08-01-18, 08:41 AM
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Is your basement ceiling a drop-in or fixed in place with no access. I've examined the top of the foundation on dozens of homes while depressurized so I can locate leaky areas and virtually everyone had some major leaks. The top of the foundation was never a priority when built and they assumed the thing layer of whatever they put down before the deck was constructed would be adequate. They were wrong so we are stuck with a significant leak area that once hidden by a finished basement cannot be addressed. In some cases the rim is visible from outside and a little caulking can be applied, but rarely can the entire rim be accessed. Just a thought.

With fan in auto vs "on" it looks like you gained about 8% from the first readings. But another 10% or so would be nice.

I assume you still have excess air still flowing down under the basement door. Can you add more supply to the basement? And possibly less return but I need to think on that. Looking to neutralize the airflow coming from upstairs.


As for getting below 61% that should definitely be possible with the added DH. At some point we can turn those off to see where the RH goes to better understand their contribution.


Bud
 
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