Winter condensation on windows in a house that is very well insulated.

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.

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Is there a sump pit in the basement? If so is the sump lid well sealed? Are their ducts in the basement? Are they well sealed? Check basement RH in the winter in relation to RH in the living areas of the house, Check duct tightness. You could be pulling moisture through duct leaks into the living area.

Do they have gas appliances like a stove?  for every pound of gas burned you pump a pound of water vapor into the house.  It can be pretty significant if you are someone who cooks a lot.  I would also check the Manual J that was done for the heating system that was installed.  If the system was oversized then it will not run long enough to remove moisture from the air which is a very common problem with high efficiency houses.  The sizing of the unit is critical.  If it is oversized, it will turn on and off and keep the temperature where the client likes it, but not run long enough to cycle all the air in the house through the unit allowing moisture to build up.

i read a lot of what has been written here. I agree they should not be running a humidifier. One should never have been installed in the first place.
I was asked once to trace down a moisture problem in a rich guy's house and I got him to buy me a great moisture meter, then spent 2days poking around, doing IR, data logging, blower doors, researching every avenue I could think of, it was all fruitless. I was ready to give up, then i saw the gardener walk in with four 5 gallon buckets to water the plants. Hmmm, now how do I get this guy to pay me for that?

Back to your issue,
I had a similar problem with a house years ago that I fixed by phone.
Where is the air intake for the HRV? In the one I fixed, I was not high off the ground and the wind, working with the way the house sat on the lot, buried the intake under leaves every fall. Not good.
I had another where the owners were complaining about odors from the HRV and we found a bird nesting in the intake.
Take a peak at that, and the filters in the HRV.

Did you give back the moisture meter??

Green Building Advisor had a piece recently about a humidity situation where the HRV intake duct had standing water in it.

I had a situation where the intake was low enough the lawn mower filled it with clippings. 

Have you considered the Panasonic Whisper Green continuous run fan? With the motion sensor control the guess work about is the homeowner using the vent fan goes away.

I second that motion - I've used Panasonic Whisper Greens on a couple occasions to solve a thorny IAQ problem at minimal operating expense.

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.


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.


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