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  1. #1
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    Humidity problem in 7 yr old NC home

    HVAC newbie posting ahead. While I am a technology consultant, I know very little about HVAC. I am seeking advice from professionals – much like I would provide advice in my field of expertise. I have read Inkward’s “High humidity in my 4 year old house in NJ” and other postings. I also realize I do not know a lot of the HVAC terms. So I will try to follow the responses. If other information is required, I will do my best to provide it. Thank you to everyone in advance for your advice.

    We have a humidity problem in our Raleigh North Carolina home that we want to solve. Built in 2007, the 4400 s.f. home includes two floors including a 400 s.f. finished area on third floor/attic. This was a custom builder’s personal home. He and his family lived in the home for about one year before we purchased it. The finished third floor area is roughed-in for a separate unit but it was never installed.

    Currently (and originally) installed:
    Maytag PSA1BC018KA (1.5T) – services first floor
    Maytag PSA1BC030KA (2.5T) – services second and third floors (two zones with separate thermostats)
    Seven air returns; two on first floor, three on second floor and two on third floor
    All downspouts are routed away from the building. There are no noticeable moisture problems in the area near the home.

    In 2012 we noticed surface mildew around electrical plates on exterior walls. Mildew was also present inside a cabinet door in the kitchen island. There was a minor amount of condensation in the crawl space but it was apparent a moisture problem existed. The course of action taken was to seal the crawl space. (August 2012)

    Due to a single unit feeding both the second and third floor, it has been my contention the overall size of the unit is too small for the serviced area. The third floor area (a theatre) is very difficult to cool in the summer. Instead of replacing the unit or installing a specific one for the third floor, we opted to install spray foam insulation.

    The third floor area has a roof top fan directly above the finished area. Another attic fan was originally installed at the other end of the house but was removed when the spray foam was installed in August 2012.

    In the summer of 2013 we learned there was a condensation pipe leaking into an exterior wall. This pipe drains the condensation from the upstairs air handler. The vertical pipe going into the elbow came loose. This had apparently been happening for months and explained the musty smell we could not identify. It seems likely the spray foam installation caused the condensation pipe to dislodge, but we are not absolutely certain.

    Each time the units are serviced (same company – a national firm who purchased the local company who originally installed the units), the service person recommends a dehumidifier. The recommendation is for a whole house unit to be installed in the crawl space. Specifically, they are recommending a Lennox HCWH-90.

    The only humidity meter we have is a basic temperature/humidity device we move around the house. The readings we have seen (both our basic device and expert’s devices) are as low as 10% in January and 70% in summer. Experts have measured as high as 83% - this was directly from a first floor vent.

    We want to solve the humidity problem once and for all – both the low and high humidity levels. We think it will be best to do it before the humidity rises, so we want to do this project in the spring. Another reason we have waited is to determine if the leak might have been the major contributory factor the excess humidity. However, our suspicions are the high humidity will still need to be addressed. An independent assessor described the problem this way: Because the building envelope is sealed, the humidity has no escape path. There is no humidity control in the HVAC. Thus, the humidity problem will continue until a specific control is installed. An additional benefit will be that once the humidity is reduced, the thermostat will not need to be set as low in the summer to be comfortable. We understand this principle – and because I prefer to set the thermostat lower in the summer, am interested in reducing the humidity and increasing our comfort.

    The house is occupied by my wife and me. We are both consultants who work from home, so the house is generally occupied during the day and night. Sometimes I travel – being away for a several days at a time.

    Since installing the spray foam, the attic area (both the finished area and the storage area) is much more tolerable – especially in the extreme winter and summer. We have not turned on the heat in the third floor area during the winter. Occasionally during winter months, conditions are such that cooling is needed on the third floor. To avoid conflict, I manually turn off the thermostat on the second floor (main thermostat I believe) and turn on cooling on the third floor. Lately this does not produce desired results. Cool air flows from the vents, but the temperature does not drop.

    An energy assessment (including blower door test and HVAC tune up) was performed in July 2010 by an independent firm. The results were not significant to me other than the $530 rebate from the power company. The technician did not indicate the results were abnormal. Some ducts were sealed and the description on the invoice says “Duct Testing 1st Floor: 50 cfm @ 25 Pa” and “Duct Testing 2nd Floor: 200 cfm @ 25 Pa”.

    A possibly relevant issue is the absence of a fresh air vent to the air handlers. At the time we sealed the envelope (crawl space and spray foamed the attic) a conscience decision was made *not* to provide a fresh air vent to the crawl space. We were made aware this was not to code, and anticipate rectifying the situation when either replacing the HVAC or selling the home (not in the foreseeable future).

    Questions:
    1. Are our units properly sized?
    2. Do we need both humidification and dehumidification? (We think the answer is yes – because while high humidity is typically given more attention, lower humidity also has negative issues for the occupants and the home itself.)
    3. Is a single unit (either humidifier or dehumidifier) in the crawl space enough? (Will a single unit in the ground floor cause inefficiencies with the absence of one on the second floor unit? Other posts seem to confirm this is an acceptable solution. Suggestions for brand/model are welcomed.)
    4. Can thermostats automatically switch between heat and A/C - and is this a good idea?
    5. What is the general consensus on adjustable thermostats? Considering we are typically home, should we leave the settings the same 24x7? My survey results of local HVAC experts indicates leaving the settings the same 24x7 versus changing while away (usually day) and changing back for arrival (usually night).
    6. Is a fresh air vent needed (either with or without humidification control)?
    7. What other factors need to investigated before proceeding?
    8. Are there any other considerations not mentioned?

  2. #2
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    Arnold mo
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    10% RH in winter, and 70% in summer? Basic building science dictates that you have excessive air leakage in the building. Any ducts in un-conditioned areas could also be a culprit.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  3. #3
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
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    I have to agree. it appears your home has correctly sized equipment, for the insulation level, but with duct leakage, and moisture removal problems.
    you have ductwork leakage most likely. without sealing the supply ducts that are in unconditioned space, or in the walls that are open to the crawl/attic, your humidity issues will continue.
    if the crawl is correctly sealed, and the attic is as well, there shouldn't be any unconditioned space to leak to... your house should be in the 50% or higher humidity in the winter with occupants, and no fresh air provisions...
    large bath fans? big kitchen hoods? lots of cooking?
    The TRUE highest cost system is the system not installed properly...

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  4. #4
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by tagb0000 View Post
    HVAC newbie posting ahead.

    Questions:
    1. Are our units properly sized?
    2. Do we need both humidification and dehumidification? (We think the answer is yes – because while high humidity is typically given more attention, lower humidity also has negative issues for the occupants and the home itself.)
    3. Is a single unit (either humidifier or dehumidifier) in the crawl space enough? (Will a single unit in the ground floor cause inefficiencies with the absence of one on the second floor unit? Other posts seem to confirm this is an acceptable solution. Suggestions for brand/model are welcomed.)
    4. Can thermostats automatically switch between heat and A/C - and is this a good idea?
    5. What is the general consensus on adjustable thermostats? Considering we are typically home, should we leave the settings the same 24x7? My survey results of local HVAC experts indicates leaving the settings the same 24x7 versus changing while away (usually day) and changing back for arrival (usually night).
    6. Is a fresh air vent needed (either with or without humidification control)?
    7. What other factors need to investigated before proceeding?
    8. Are there any other considerations not mentioned?

    During low heating/cooling load conditions, your equipment is oversized. You will need supplemental humidification and dehumidification. Two occupants in 4,400 sqft. will need some humidification to maintain 30-35%RH during with adequate fresh air change to purge indoor pollutants. During cold windy weather, most homes enough fresh air naturally. During calm, moderate temps, you need mechanical fresh air ventilation. 4,400 sqft feet needs 150cfm of fresh air. With several occupants and fresh air ventilation, you need 4-6 lbs. of dehumidification per hour. No problem when the a/c is operating +60% of the time. During low/no cooling loads and high outdoor dew points, a whole house dehumidifier would keep the home <50%RH while being occupied and ventilated.
    Check out the Ultra-Aire XT105H or next size larger. The ventilating option would also provide fresh air when occupied and winds are calm.
    http://ultra-aire.com/products/dehum...ra-aire-xt105h

    Assuming that the crawlspace is covered by plastic and the vents are closed, removing 4-5 lbs. of moisture per hour with a dehumidifier should assist the properly setup a/cs in maintaining a dry comfortable, healthy home.
    Homes are complex. Monitoring the CO2 levels would give us a clue about the amount of fresh air entering the home during normal weather and occupancy.
    CO2 meters.com have simple meters for $100.
    http://www.co2meter.com/collections/...uality-monitor
    Regards TB
    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"

  5. #5
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    Quote Originally Posted by teddy bear View Post
    During low

    Homes are complex. Monitoring the CO2 levels would give us a clue about the amount of fresh air entering the home during normal weather and occupancy.
    CO2 meters.com have simple meters for $100.
    http://www.co2meter.com/collections/...uality-monitor
    Regards TB
    This deserves more explanation. Outdoor CO2 levels are normally 375-450 PPM. Measuring inside the home, no occupancy of course the CO2 levels would be the same. With the CO2 from one occupant mixed into the air in the home, the resulting CO2 levels indicate the cfm of fresh air infiltrating the home.
    Starting with 450 ppm of CO2 outside the following table shows the cfm of fresh air infiltrating the home.

    CO2 ppm Cfm of fresh air per occupant

    450 open door
    650 53 cfm
    800 30 cfm
    1000 19 cfm
    1250 14 cfm
    1500 10 cfm
    2000 7 cfm

    The interior door must be open and the air handler mixing the air in the home.
    During routine heating/cooling cycles and the occupants in the open part of the home provides the most accurate results.
    Regards TB
    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"

  6. #6
    Join Date
    Aug 2004
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    North Richland Hills, Texas
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    Quote Originally Posted by tagb0000 View Post
    An energy assessment (including blower door test and HVAC tune up) was performed in July 2010 by an independent firm. The results were not significant to me other than the $530 rebate from the power company. The technician did not indicate the results were abnormal. Some ducts were sealed and the description on the invoice says “Duct Testing 1st Floor: 50 cfm @ 25 Pa” and “Duct Testing 2nd Floor: 200 cfm @ 25 Pa”.
    Are those numbers what they got before or after the sealing work?
    If it is after, the "2nd Floor" system still has way to much leakage.

    Your low winter and high summer humidity may be caused by mechanically driven infiltration in the home, due to excessively leaking ducts, and the attic exhaust fan/fans you described.

  7. #7
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    Jan 2014
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    Thread Starter
    Mark,
    - Thanks for the input. I am not sure, but I will contact the assessor and find out. I do recall him mentioning a "door" was open on the second floor unit, but he did close it and make some sort of repair. I think there were screws missing/stripped which required a little extra effort. The second floor unit is difficult to access, therefore I cannot easily/quickly tell if something is obviously wrong.

    - All the duct work is now "inside the envelope". Attic area is inside the sealed/spray foamed area. Crawl space is sealed with a liner and all foundation vents are blocked. Of course, this does not mean the ducts are fully sealed (not leaking). If they are leaking, every HVAC person who has been in the home has overlooked it - or has not reported it to me. I do recall the assessor testing some (possibly all) vents by closing some and testing outflow from the open ones. Maybe it is time to repeat this test. (???)

    - One attic fan was removed/sealed. The other is in place with a thermostatically controlled switch. It typically only switches on during the extreme heat of the summer.

    Stay tuned.

    P.S. Amen to your auto-sig.

  8. #8
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    Jan 2014
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    Thread Starter
    TB,
    - Thanks for both responses. Is one CO2 meter sufficient or should I get two (or more)? How long will they need to run to collect enough data to make a decision? I will order them when you give an indication of quantity. The one "+Wall Adapter" looks like it simply includes a USB/AC adapter. I have plenty of those, so unless you think that model is required, I will stick to the one without.

  9. #9
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    Quote Originally Posted by tagb0000 View Post
    TB,
    - Thanks for both responses. Is one CO2 meter sufficient or should I get two (or more)? How long will they need to run to collect enough data to make a decision? I will order them when you give an indication of quantity. The one "+Wall Adapter" looks like it simply includes a USB/AC adapter. I have plenty of those, so unless you think that model is required, I will stick to the one without.
    One meter is enough. You can move it around, but locate centrally. Also the model I showed will data log CO2 to a computer with the available software. You will know after a 3-4 hours of steady conditions. I overnight as good indicator. You see the variation caused by wind and low temperatures. Also operation of kitchen hoods and clothes drier.
    Regards TB
    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"

  10. #10
    Join Date
    Sep 2009
    Location
    Arnold mo
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    I'm not understanding why the need to go taking co2 readings, when we know we have 10% RH in winter and 70% in summer? Those numbers already tell us we have WAY too much air leakage, or am I just being stupid?
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  11. #11
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    Jan 2014
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    Thread Starter
    Quote Originally Posted by teddy bear View Post
    One meter is enough. You can move it around, but locate centrally. Also the model I showed will data log CO2 to a computer with the available software. You will know after a 3-4 hours of steady conditions. I overnight as good indicator. You see the variation caused by wind and low temperatures. Also operation of kitchen hoods and clothes drier.
    Regards TB
    No kitchen hoods exist in the home. There is a downdraft vent in a kitchen island but it is not used.

    What is the recommended location for the meter? Will it store the data without being connected to a PC? (I read the manual, but did not see a clear indicator of the connectivity requirements for storage.) I can connect it to a laptop and set it up virtually anywhere if necessary, but will need the laptop for work during the day. If my office (first floor) is sufficient, I can connect it there easily.

    P.S. As I was getting ready to order the recommended unit, I saw a unit that also reads humidity. Should I splurge for that one?
    Reference: http://www.co2meter.com/products/tim...midity-monitor

  12. #12
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    Quote Originally Posted by tagb0000 View Post
    - All the duct work is now "inside the envelope". Attic area is inside the sealed/spray foamed area. Crawl space is sealed with a liner and all foundation vents are blocked. Of course, this does not mean the ducts are fully sealed (not leaking). If they are leaking, every HVAC person who has been in the home has overlooked it - or has not reported it to me. I do recall the assessor testing some (possibly all) vents by closing some and testing outflow from the open ones. Maybe it is time to repeat this test. (???)
    If the ductwork is within the conditioned space, duct leakage won't cause infiltration issues, but room to room pressure imbalances can.

    - One attic fan was removed/sealed. The other is in place with a thermostatically controlled switch. It typically only switches on during the extreme heat of the summer.
    Why is there still an attic fan if the attic area is within the thermal envelope of the house?
    The the under side of the roof is foamed, the attic needs to be as completely sealed to the outside as is possible, no ventilation at all, and all combustion appliances must have fresh air ducted to them from outside, ideally they should all be sealed combustion type.

    With a tight foamed house, you should not have low humidity in the winter, if anything, you should need a fresh air intake system to keep the humidity down in the winter.

  13. #13
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    Thread Starter
    Quote Originally Posted by mark beiser View Post
    Why is there still an attic fan if the attic area is within the thermal envelope of the house?
    The the under side of the roof is foamed, the attic needs to be as completely sealed to the outside as is possible, no ventilation at all, and all combustion appliances must have fresh air ducted to them from outside, ideally they should all be sealed combustion type.
    This fan is in a very hard to reach place - the very top/crest of the roof. The only access is through a small panel just below the fan. How seriously should I reconsider removing that fan?

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