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What to Do to Reduce Humidity

On this page you can find a solution to your problem!

Read the question, but do not skip the answers and feedbacks if it seems that your issue is a slightly different. The most of the solutions are the same and you just have to analyze information on the page and adapt it to your particular case.

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All the secondary pages, just like this one, are free of charge and represent clear solutions to high/low humidity problems!


Question
The current humidity levels in my home are between 52%-56%. I have just replaced my entire HVAC system with a Trane xr 15 (2.5) ton Heat Pump, (3.0-3.5) ton Electric Air handler, (for the tax credit). Anyway at first I had the cfm set for (3.5) ton on the air handler but dropped back to (3.0) ton due to the noise out of ducts and return. Here is the set up and layout of my home. it is 1605 heated, (6) windows all Double Vinyl, low e. argon, r-38 in attic, the duct system is all metal with a main trunk line 10 inch feeding (2) 8 inch drops furthers from the room, all the rest a 7 inch drops. I have (7) total. Load on my home per manual J and Remrate software was 28,256 Btu's. So that is why I sized with a (2.5) ton system with an avg. temperature of 92 in summer and 40 in the winter. Ok with all that said my question is about the humidity levels and the cfm settings. What do you all think about this? The system is running 15 min and cycling off then is off about 20 min or so before come back on this is on a 94 degree day. My system model #'s & t-stat are listed below as follows:

Trane XR 15 model # 4TWR5030A1000A
Trane air handler model # 4TEE3F039A1000A
T-Stat is a 802 model made by Honeywell.
Trane Clean Effects whole house filter

What if anything else can I do to help get the humidity a little lower in my home do say around 45-50%.
Thanks.

Answer
Just installed similar new Trane split system here in North Carolina, 1700 total Sq FT, including 300 Sq FT den in basement.

Trane XL15I 4TWX5030A1 2.5 ton HP
Trane 4TEE3F39A1 3-ton AHU (variable speed)
Trane BAYHTR1410 10kw single stage aux heat strip
Trane TCONT602 thermostat
Per AHRI 15.75 SEER, 13 EER, 9 HSPF

I have set-up as follows:

Dip switch positions 1-4, set for 39A, 2.5 ton, 400 cfm/ton (default-normal)
Dip switch positions 5-6, set for "enhanced"
Dip switch positions 7-8, set for 1100 cfm (default-med. high), aux. heat fan setting.

I had a problem with humidity also, was pulling moisture from basement into return. i added a dehumidifier in basement and now run 40-45% RH at t-stat setting of 72 F. Quite comfortable now.

Answer
With outdoor temperatures at 90*F, you should be able to get to <50%RH. But, fan "auto" is important. You are evaporating the moisture on the cooling coil back into the home. Also, check your a/c supply temperature for minimum 25*F temperature difference to max moisture removal. If the supply is higher, slow the fan more yet.
You biggest problem is ahead. Maintaining 50%RH during wet cooler weather will be much more difficult. Your cooling time will decrease to the point where your coil will get wet enough to get moisture down the drain before the house is cooled. The moisture on your coil evaporates back to the home before the a/c recycles. That is when you really will need a dehumidifier. Also, if you had a dehumidifier, you could run your fan more. When you heat or occasionally cooling, fan "on" with a dehumidifier works great.
One more issue is the lack of fresh air ventilation when the home is occupied. Windy cold weather gets you plenty of fresh air. Calm warm weather gets you no appreciable natural fresh air. At a minimum, you need a fresh air change every 5-6 hours. If you had fresh air, your moisture problem is greater. With a whole house ventilating dehumidifier, you could have the best of both worlds, fresh air when the home is occupied and <50%RH.
Answer
Just installed similar new Trane split system here in North Carolina, 1700 total Sq FT, including 300 Sq FT den in basement.

Trane XL15I 4TWX5030A1 2.5 ton HP
Trane 4TEE3F39A1 3-ton AHU (variable speed)
Trane BAYHTR1410 10kw single stage aux heat strip
Trane TCONT602 thermostat
Per AHRI 15.75 SEER, 13 EER, 9 HSPF

I have set-up as follows:

Dip switch positions 1-4, set for 39A, 2.5 ton, 400 cfm/ton (default-normal)
Dip switch positions 5-6, set for "enhanced"
Dip switch positions 7-8, set for 1100 cfm (default-med. high), aux. heat fan setting.

I had a problem with humidity also, was pulling moisture from basement into return. i added a dehumidifier in basement and now run 40-45% RH at t-stat setting of 72 F. Quite comfortable now.

Answer
With outdoor temperatures at 90*F, you should be able to get to <50%RH. But, fan "auto" is important. You are evaporating the moisture on the cooling coil back into the home. Also, check your a/c supply temperature for minimum 25*F temperature difference to max moisture removal. If the supply is higher, slow the fan more yet.
You biggest problem is ahead. Maintaining 50%RH during wet cooler weather will be much more difficult. Your cooling time will decrease to the point where your coil will get wet enough to get moisture down the drain before the house is cooled. The moisture on your coil evaporates back to the home before the a/c recycles. That is when you really will need a dehumidifier. Also, if you had a dehumidifier, you could run your fan more. When you heat or occasionally cooling, fan "on" with a dehumidifier works great.
One more issue is the lack of fresh air ventilation when the home is occupied. Windy cold weather gets you plenty of fresh air. Calm warm weather gets you no appreciable natural fresh air. At a minimum, you need a fresh air change every 5-6 hours. If you had fresh air, your moisture problem is greater. With a whole house ventilating dehumidifier, you could have the best of both worlds, fresh air when the home is occupied and <50%RH.
Answer
My Trane manual with VS furnace documents a 350 cfm/ton setting and says it is recommended in humid climates, does this conflict with your info?

At one time I blithely changed the settings myself (am a homeowner in hot-humid S. Texas) but since then have learned it possibly might require an adjustment in charge. Therefore, at present I decided the CFM first, and then had the pro adjust the charge, to be sure I did not cause something out of whack. At present, I am being very aggressive with the choices, using Comfort-R plus the 350 cfm base flow rate, so the airflow should be 80% of that (280 cfm) for the major part of each cycle. The system is working better this year than it ever has before for humidity removal.

An aside: There were a couple other changes this year too, so I cannot suggest airflow is the sole reason. The new AC pro identified a TXV which was not working right (affixed to the line with tape (!)) and changed that to a proper metal bracket. A modest fresh air inlet was added too, it seems to offset as much infiltration as it creates; the result is improved humidity control with no visible energy penalty.

Long ago, I read on this forum, professionals who observed that very low airflows were appropriate for humidity control as long as the other important rules were not violated.

One last thing: I would not trust the results of any one humidity meter unless it was recently calibrated. What you may think 55% could actually be 50-52% in reality, or the error may skew the other way. This applies to cheapo Wal-Mart meters, the Totaline 1400 thermostat, even a very professional looking device I borrowed from an engineer, which apparently had not been calibrated recently.

P.S. In the process of getting things right, I believe the technician did add some refrigerant.
Answer
My Trane manual with VS furnace documents a 350 cfm/ton setting and says it is recommended in humid climates, does this conflict with your info?

At one time I blithely changed the settings myself (am a homeowner in hot-humid S. Texas) but since then have learned it possibly might require an adjustment in charge. Therefore, at present I decided the CFM first, and then had the pro adjust the charge, to be sure I did not cause something out of whack. At present, I am being very aggressive with the choices, using Comfort-R plus the 350 cfm base flow rate, so the airflow should be 80% of that (280 cfm) for the major part of each cycle. The system is working better this year than it ever has before for humidity removal.

An aside: There were a couple other changes this year too, so I cannot suggest airflow is the sole reason. The new AC pro identified a TXV which was not working right (affixed to the line with tape (!)) and changed that to a proper metal bracket. A modest fresh air inlet was added too, it seems to offset as much infiltration as it creates; the result is improved humidity control with no visible energy penalty.

Long ago, I read on this forum, professionals who observed that very low airflows were appropriate for humidity control as long as the other important rules were not violated.

One last thing: I would not trust the results of any one humidity meter unless it was recently calibrated. What you may think 55% could actually be 50-52% in reality, or the error may skew the other way. This applies to cheapo Wal-Mart meters, the Totaline 1400 thermostat, even a very professional looking device I borrowed from an engineer, which apparently had not been calibrated recently.

P.S. In the process of getting things right, I believe the technician did add some refrigerant.
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