This is my first post and I hope I have the formate correct, I live and build in central Pennsylvania. I built a house in 2004 using what I thought were the best practices at the time to insure it was tight and very well insulated. Took great pains to properly vent all bathrooms, dryer and range. I used Tyvek house wrap and a 6 mill vapor barrier on walls and ceiling. Used a pre-fab basement wall system that creates a very dry basement. Customer works for a propane gas co. and had a high efficiency gas hot air system installed.  They are having a very hard time with condensation on their windows in the winter. They are very unhappy with me because they feel the house is to tight and I should remove the plastic vapor barrier.  The only thing I changed was using Crestline windows instead of Anderson.                              As a side note I built 6 new homes using all of the same building techniques in my area and had none of these problems. We have discussed the use of exhaust fans allot and they assure me they use them. It is just Mom, Dad and a teenage girl so not an excessive amount water usage.     What should the RH be in the winter and should I just buy them a de-humidifier.  Oh, Yea they do have a heat recovery system they use when the temp reaches 50 degrees. Any help would be welcome.

You need to be a member of Building Performance Community to add comments!

Join Building Performance Community

Email me when people reply –


  • Eric,

    I discovered your post while doing my own research on Crestline Windows and condensation.  I live in the mountains of western NC; we have a similar climate to central PA (garden zone 6a).  My home was built in 2002 with a complete Crestline door and window package.  We have significant moisture -- and ice -- forming on the inside of the windows and doors in cold weather.  I have one door that I had replaced with a Kolbe & Kolbe door because of leaking.  We we get NO moisture or ice on this new door.  So I have to say, I think the problem is the manufacturer.  Our previous home in the same neighborhood had Anderson windows and we never had this problem.

    I have begun monitoring my inside relative humidity closely.  I have installed a de-humidifier in the crawl space and am in the process of investigating a whole-house dehumidifier.  Also we have reduced utilization of our gas logs.  I have been able to lower the inside humidity to 42% and this has ameliorated the moisture problem.

    Good luck to you.


      we have reduced utilization of our gas logs.

      Ventless logs?  There's the moisture source.  

      Eric, if you spend $1000 sealing windows and nothing changes, how will you feel?  

      Would you go on a diet without first stepping on a scale?  

      The first step is a comprehensive assessment of your home.  This needs to include at the very least a blower door leakage measurement, which should be done BEFORE ANY work is done.   You need to know where you started to understand how well your diet went.  And the blower door will help you understand if it's your windows, baseboards, rim joist, or attic penetrations that should have first, second... priority.  

      Understand what illnesses you have before running off half cocked fixing things that may not be broken and missing things that are.   Good luck!

      • You're responding to Robert Hamilton's recent query, not the OP Eric Fletcher.

        Robert knows what his problem is - too much indoor humidity and condensation and icing on his windows. He has already substantially corrected the humidity problem and wants a solution to the window problem.

        For that, he doesn't need a full energy audit and blower door test and since it's a focused problem with a focused solution.

    • If reducing indoor RH has "ameliorated the moisture problem", then the problem is far more likely to have been excess indoor humidity than the window units. Poor installation, without air-sealing the perimeter, is more likely to cause condensation and icing problems than the actual window unit, since it's next to impossible to reach freezing indoor conditions unless there is outside air leakage.

      • Robert.  I suspect you are correct.  Is there anything I can do to remedy "air sealing the perimeter," in a completed home?

        • Assuming that the windows were installed square so that the sash close tightly and the weatherstripping is intact, you can remove inside window trim (casing and sill apron) on all four sides and inject low-expansion window/door foam.

          If you're sealing a lot of windows, it's worth buying a foam gun and canisters, which offer far more control and don't have to be completely emptied after each use.

  • in general a home should ventilate approx, 8 air changes per day. As the home is tighter it will not have that amount naturally, so less than 8 air changes and any moisture produced through living in, cooking, bathing etc. is trapped inside and will raise the humidity level in the home. Dont underestimate how much moisture a family living in a home will produce. The coolest surface temp in a home is the windows. Any window at a certain dewpoint in the home will deposit its moisture on the surface. Think about a cold glass of water on your table at suppertime. The glass will have water running down the side of the glass but do you feel humid?
    Back to the house any level below 8 air dhanges per day needs the air exchanger to help dehumidify the home. To properly set up, the home needs to be infiltrometer tested and that will tell you how many air changes it has and how many cfm it needs to move, to total 8 air changes per day. Just because the air exchanger is installed doesnt mean it is working properly or calibrated to the correct cfm. Also dont know how many air exchangers I have found the intake screen for the air exchanger outside plugged therefore doing no good. I am a heating contractor in minnesota so yes it gets cold here.
    Get the home tested and I bet the homeowner will be ticked how well you built there house, not tear it apart to make it leaky to solve the problem. Hope that helps.
    • No house needs 8 air changes per day, unless it's a very toxic environment. To meet the latest ASHRAE 62.2 ventilation standards (referenced in the IRC and state codes), a house needs in the range of 4-5 AC/day (0.16-0.24 ACH), depending on square footage and number of bedrooms).

      An infiltrometer is a device used to measure the rate of water infiltration into soil or other porous media. I think you mean blower door and manometer.

      Rather than "air exchanger", I think you're referring to a heat-recovery ventilator (HRV) or other balanced ventilation system. An exhaust-only (for cold climates) or supply-only (for warm, humid climates) whole house ventilation system meets code as well.

      • I am referring to the terminology of the products used in the hvac trade by the vendors and tradespeople in the trade at least in the north central us climate. I am sure there are many products in the market that share the same common name. I own and use in my business a retrotec infiltrometer which is also referred to as a blower door tester to measure air leakage rate for a building. Google their website, Not sure how to go about measuring water infiltration into soil with that.
        I am aware of Ashrae 62.1 and the many changes that code and many other codes at the state and federl level constantly changes over time. I know that you can install a ERV or HRV style air to air exchangers in a home to exchange the indoor air with outdoor air for the purposes of energy savings and pressure balance control. In an environment like minnesota with a design temperature of -15 deg. f. Range for winters, I have measured many homes and found negative pressure and found mold behind the exterior walls and gravity vented heating appliances not drafting properly. Also have measured with our blower door tester many homes at 25 pascals in the 3-5 ach per day with water running down the windows and frost forming on the glazing at sub zero temperatures.
        Although I would agree with you that your sizing may be adequate to control indoor air quality from a toxic standpoint, that level of ventilation does not control the humidity level of the homes in the area where we live. I have also done my testing with most of the major window brands and with few exceptions of a defective window seal, the results are consistant showing anything much above 40% humidity in the winter, and finding anything less than 4-5 airchanges and homes have winter humidity problems. We then have moisture on the windows and glaze, and window sill mold problems. With for sure over 200 homes tested over the last 10 years, sizing and balancing with a Alnor flowhood to get to a total of 8 air changes from both mechanical and supplemental means has never proven me wrong, I have also have never had a customer complaint of his air exhanger raising their fuel costs. We also only install the Renewaire ERV style units as we have a fair high humidity in summer months here.
        Your thoughts, as it is nice to converse with someone on issues that have a lot of wide spread problems across the country. Different areas seem to try different approaches to the problems and mine are related to the fairly northern climate we have.
        • I build homes in northern New England with 8500 HDDs and winter minimum design temperatures of -10°. I agree that indoor humidity needs to be no more than 40%, but that much air exchange is not required to get there, as long as there are no uncontrolled moisture sources and spot ventilation is used in bathrooms and kitchens.

          Excess ventilation comes with a significant energy cost - even meeting the ASHRAE minimum standard increases heating costs, but makes up for it in good IAQ and moisture control.

          Building scientist and moisture expert John Straube, having worked for years in Canada's cold climate, says that a blower door result of between 2 and 3 ACH50 is ideal for moisture control when coupled with proper mechanical ventilation.

          As for Retrotec, Infiltrometer™ is the trade name for their blower door, but the industry uses the same language everywhere.

This reply was deleted.