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  1. #1
    Join Date
    May 2009
    Posts
    8

    RH<40%. Still have condensation on windows

    Hello,

    Our home was recently completed and when the cold weather set in I started noticing condensation on the windows. During warmer weather the RH in the home usually hovered around 55%. During the recent cold weather the RH was around 50%.

    I recently installed a Honeywell DH150 to control the humidity level and hopefully eliminate the condensation issue. The DH150 is being controlled by a HW Vision Pro IAQ. The IAQ won't go below 40%. The RH is now always between 38-40%. The condensation has been reduced but it is still present when the outside temperature is <30 or so. It's enough to form beads of water on the lower portion of the windows.

    We have Anderson 400 series low e glass window with wood interior frames. I'm worried that the condensation is going to cause the window frames to rot.

    Our home is in St. Louis, MO. The area being serviced by the DH 150 is approximately 3500 square feet. Foam insulation was used for the entire structure.

    I've been using our ceiling fans to try to circulate the air near the windows but no noticeable change occurred.

    Is my RH still to high? Do I need to get a controller that will allow me to set the DH below 40%?

    We also have wood floors throughout the house so how low can the RH be without negatively effecting the woodwork?

    I'm at a loss.

    Any thoughts are appreciated.

  2. #2
    Join Date
    Mar 2005
    Posts
    997
    Id look at getting it down to about 35% with outside temp at 30

  3. #3
    Join Date
    Apr 2002
    Posts
    11,808
    a lot of water comes out the building materials the first winter after new construction

    Bay windows will be very prone to condensation, drapes increase the risk as well.

    In the cold weather you need more fresh dry air brought into the home, and more so the first winter. I would say something that can change the air at a rate equal to once every 3 hours. Systems like that seem to work hard the first winter, then the following winters they never have to work that hard.

    I think of it as the problem of relying on a dehumidifier to ventilate a home. Try cracking open a window and let a bathroom fan run steady.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  4. #4
    Join Date
    Aug 2006
    Location
    Wisconsin
    Posts
    1,506
    Do you have an outdoor air sensor? If not I would put one in. There is a frost setpoint that you can lower to prevent condensation on the windows. You must have an outdoor sensor to make it appear. It will then control the humidity to the maximum level that prevents condensation at the given outdoor air temperature.
    Buy American! The job you save may be your own.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,581
    This sounds like you have the basics for a perfect home. Just need a few adjustments.
    The objective is to keep moisture on windows down to the point that the moisture does not drip on to the window sills during the coldest weather. Window binds that slow air flow or t-stat set-back both lower the glass temperature which increases the condensate on the glass. Open the blinds on the windows have condensation to avoid the extreme cold glass temperatures. Avoid set-back during the coldest windy weather to avoid the need to over-dry the home.
    How many people are in the space? Is there water in the basement crock? Do you bring in fresh air with your DH150? How much and how long?
    Your most important objective when the windows are closed is to have enough fresh air to purge indoor pollutants. This is an air change every 4-6 hours. During winter, adequate ventilating with cold, fresh, dry air will also remove enough moisture to keep windows dry in most situtations. As the windows warm and the outdoor moisture levels increase, adequate summer fresh air ventilation needs supplemental dehumidification during times when the cooling load is not enough to maintain <50%RH.
    A good method of determining the amount of fresh air ventilation in the home is to monitor the CO2 level in the home. Knowing the number of occupants and square footage of the home, provides the info to determine the amount of fresh air you are getting. For now, increasing the fresh air ventilation with your DH150 enough to minimize the moisture on the windows is a simple fix. Set the %RH to dehumidify at +50%RH.
    Keep us posted on additional questions. 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
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    Yep I wouldn't worry too much as your home is new and the material used to build the home is still wet and alot of moisture is trapped with in the wall and under your basement slab, garage slab so be patient and wait for atleast a year to pass and I bet you'll notice great improvement once the moisture has a chance to escape and yoru home dries out. I'm running a ERV 130 REnewire model and am keeping the RH in my 100+ yr old home right at about 25%-30% in the cold weather and is great.

  7. #7
    Join Date
    Dec 2000
    Location
    Michigan
    Posts
    724

    Smile Yes Virginia there is a Santa Claus

    Quote Originally Posted by Carnak View Post
    . Try cracking open a window and let a bathroom fan run steady.
    The next time you quote me please use the correct name so everyone will understand it: XAVIER”S KISS HRV!

    What is now necessary in all home that are energy efficient is not only must you control your temperature you must also control your Relative Humidity all year round.

    Xavier's simple rule is take the outside temp add the number 20 (up to a maximum of 45%) and that should be your indoor winter Relative Humidity to avoid water on your windows and other "hidden" places.

    I do not recommend an outdoor sensor as they are “reactive” not proactive unless they are connected to the weather channel

    I recommend you listen to the weather forecast and if the forecast is for 10 degrees or less then I adjust my flow through “POWERED” humidifier to 30%. Like Teddy stated, in the morning I have some moisture on my windows but it will disappear. Then when the forecast is for higher temperatures I raise back my humidifier to 40%

    P.S. for an even faster controlled air change, open a larger window and run the dryer on “Air” only for an hour.
    This is XAVIER"S “super duty" KISS HRV!
    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

  8. #8
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by Xavier View Post
    The next time you quote me please use the correct name so everyone will understand it: XAVIER”S KISS HRV!

    What is now necessary in all home that are energy efficient is not only must you control your temperature you must also control your Relative Humidity all year round.

    Xavier's simple rule is take the outside temp add the number 20 (up to a maximum of 45%) and that should be your indoor winter Relative Humidity to avoid water on your windows and other "hidden" places.

    I do not recommend an outdoor sensor as they are “reactive” not proactive unless they are connected to the weather channel

    I recommend you listen to the weather forecast and if the forecast is for 10 degrees or less then I adjust my flow through “POWERED” humidifier to 30%. Like Teddy stated, in the morning I have some moisture on my windows but it will disappear. Then when the forecast is for higher temperatures I raise back my humidifier to 40%

    P.S. for an even faster controlled air change, open a larger window and run the dryer on “Air” only for an hour.
    This is XAVIER"S “super duty" KISS HRV!
    I tell them to crack a window because I do not want them to down draft an atmospheric appliance. It is just a fast test to illustrate when they need more air, not a permanent solution.

    You must then crack a window as a pressure relief for your 'postive pressure vent system', which is the complete opposite of your self described HRV.

    Windows tell you when you need more air. Humidifiers should be dinosaurs on a smartly built home.

    I just tested one of the apartments I built, somewhere between 1.5 and 1.6 ACH at 50 Pa. Fix one leak and it beats R2000 (air tightness), the standard for the most energy efficient and readily buildable homes in the world. Still a light year beyond your frame of reference
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #9
    Join Date
    May 2009
    Posts
    8

    Update

    Thanks for all of the great information.

    There are two adults and six dogs (yes we're crazy animal people) in the home. No window coverings.

    I'm not using the ventilation option on the DH150 because a Trane ERV300 was installed when the home was built. I turned the ERV off about 2 months ago when cooler weather set in because we also have a Hardy Outdoor Wood Boiler located about 50ft from one side of the house. The intake for the ERV is located on the back of the house but would occasionally draw in the smoky smelling air. I thought we would be ok turning it off because we are constantly letting the mutts in and out.

    After reading everyone's suggestions, I turned the ERV back on at 80% and the RH dropped from around 40% to 32% in about 4 hours with the outside temperature was below 20 and thermostat set on 70. There was a drastic improvement in the amount of condensation on the windows. There's still a small amount on the window corners on the main floor and a little more on the upstairs windows that benefit from the ERV due to the open floor plan. The RH upstairs has dropped to 35% from over 40%.

    To remove the remaining condensation, does anyone think I should still get a different controller for the DH150 that will allow me to set it below the 40% setting the HW VP IAQ allows?

    The chimney on the OWB is only 4 foot tall, so my project tomorrow is to triple its height to hopefully eliminate smokey air being pulled in by the ERV.

    Thanks again for all of the help.

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