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Eric Gans
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Residential Comfort & Energy Efficiency

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I invite you to explore my YouTube channel, where you'll see first-hand some of the issues we are out there fixing.

Sunday, November 10 2019



Source U.S. EPA

Your home is a complex system.  Before you do work on any specific part, you need to know a few key building science principles.  There is nothing more frustrating than learning that you should have done this or you should have done that...after you already paid for the wrong solution.  This happens all too often in home remodeling and retrofitting because there are so many different trades involved and unfortunately, incorrect or outdated ways of thinking are guiding contractors and homeowners to the wrong solutions.
As a certified Building Analyst through the Building Performance Institute with over 500 home energy audits conducted and with over fifteen years of home remodeling experience, I understand and specialize in all of the remodeling trades with a focus on building science principles to lead the way and guide us to the source of the problem to find the best possible solution.  Here is an example of how this can work.


I was the second appointment in two days for a homeowner with a condensation problem in Columbia, MD Howard County.  To be clear, condensation was on the pane of glass inside the home and could be wiped away.  This was a summer issue during hot, humid days which are plentiful in Maryland.  Also, this issue is not to be confused with fogging between the glass panes that cannot be wiped away.  That type of issue is a different problem related to the window unit.  This issue had to do with indoor air quality.

The house had brand new HVAC installed in 2018 and the installation service team had been out trying to solve the issue for the homeowner three times.  The HVAC mechanics pointed to the basement windows as the problem but suggested that the homeowner get an energy audit as well.  The homeowner was not sure but started to do some more research.

Inside view of basement windows.

The homeowner knew that the humidity in the basement was higher than any other part of the home.  Condensation was forming on the window glass down there only.  They were becoming more and more convinced as the days went on that the window frames were so leaky that condensation was forming by the air leaking through the windows and interacting with the cool air inside (summer issue) and the windows had to go.  On the tip from the HVAC crew, they had the energy audit scheduled, but they later told me that they almost canceled to just go with the windows.


The dehumidifier could not keep up.

FAMILIARITY solutions (like windows and doors) without considering all possibilities can cost a homeowner a lot of money and heartache.  Emotions are in play and purchasing decisions are made under duress and with the hope that the decision will solve the issue.  Sometimes it does and sometimes it does not.  As a general rule, windows should be purchased for the purpose of renewed functionality (old broken windows), beauty, less maintenance, but should rarely be purchased to solve comfort or efficiency problems and ALWAYS get a blower door test done before you replace your windows.  You will be surprised to see that most windows are NOT leaky!



Here is how I was able to help.  First, if you have a theory about an issue, you have to use every tool available in attempt to prove the theory, or at least parts of the theory.  So, I thought the window idea was decent and I set up my blower door, depressurized the house and inspected the windows in the basement with my odorless smoke maker and I did not observe any leaks.  The best thing about this moment, which happened within the first thirty minutes of my arrival was that the homeowner was able to see for themselves that the windows were not leaky.  I didn't have to try to convince them with a bunch of words.  Through building science testing and principles, we were able to collectively rule the windows out and the burden of purchasing new windows was lifted!

Blower door testing pulls air out of the home through an opening
in the house (front door)& pulls air in from the outside through cracks 
in your home making it easy to see if windows are leaky.

Next, I wanted to take a look at the new heating & cooling (HVAC).  It was "new" according to the homeowner.  I checked the size and age of each unit.  I took a look at the outside and inside units.  The house was zoned with two systems and in my opinion, needlessly.   The house was built in the '80s.  It is a typical four-bedroom house with a basement, first floor, and 2nd floor.

Typical single-family home in Columbia, MD

Bigger is not always better in HVAC.   In summer, a larger machine in a smaller home runs a shorter time and does not effectively pull humidity out of the air.  I found that the house's HVAC combined was 5.5 tons for 3000 sq ft of conditioned space with 8' ceilings.  The number of square feet of floor space that can be cooled by a ton of AC capacity depends on climate, shade, insulation levels, internal heat gains, and air leakage.  This home would rank in the range of a home with average air tightness, R-values, shade, and reasonably well-installed AC systems.  The calculation would be 800 square feet cooled per ton.  Calculation: 3000/800=3.75  Needed for this size home: 3.5 - 4 ton system would suffice.  Again, this home has 5.5 tons, too much.  This conclusion would lend to more humid indoor air quality.


The humidity reading in this house - 66% Humidity - Too High
45-50% is ideal all year in Maryland


Utility closet reveals no pressure boundary (air barrier)

Next, I was curious about the basement.  A small utility closet revealed a 4' portion of the rim joist (at the top of the foundation wall) and it revealed that there was no thermal/pressure boundary (insulation).  Likely that was to be the case around the entire perimeter at the leaky rim and band joist, but accessing that area would be costly because the ceiling drywall would have to be removed.  It might be something that should be done if other possible remedies do not help with the moisture issue.  In any case, any accessible portion of the rim joist should be air sealed and insulated to the recommended levels in your area.  In Maryland it is R-19.  So, another likely source of humidity issues in this home was due to the infiltration of warm, humid air at the leaky portions of the rim joist.


The next step in my search for answers to the problem was to locate any source of interior moisture in the basement.  Showers, washing machines, and sinks, and determining how often they were used and what, if any, exhaust fans were in place and how often were they being used.  As it turns out the bathroom was used on occasion and the clothes washer was in the basement and used regularly.  Testing performed on the bathroom exhaust fan revealed that the fan was not functioning.  Therefore, there was no way of getting any moisture created in the basement to move "outdoors".

Bathroom Exhaust Fan

The living space inside the home is referred to as the envelope.  Other moisture sources in the home can also contribute to humidity levels in the basement.  I moved along to test other exhaust fans in the kitchen and bathrooms.  I discovered that there was not a single working exhaust fan in the home. Showers, cooking, and moisture from the inhabitants of the home were all getting trapped.  It is also summer so windows are closed in MD if you want to be able to breathe.  This finding, along with the others, began to guide my recommendations.


An energy audit is comprehensive and looks at the entire home's insulation and pays particular attention to the boundary between the inside and outside of the home.  When the boundary is compromised, as it typically is in most homes, HVAC machines have to fight against outside air infiltration (summer) and exfiltration (winter).

In this case, here was my diagnosis based on the information that was discovered:

The windows are least likely to be the source of the condensation/humidity problem in the basement because they are tight
  • The HVAC is sized too large 
  • Indoor air quality control is insufficient due to a lack of proper exhaust, primarily in the high moisture areas (kitchen/baths).
  • The home does not have a sufficient thermal/pressure boundary (insulation) and therefore is allowing additional outside moisture to enter the home which is also adding to the issue.
Recommended solutions:
  • It was suggested that during extremely humid days, only run one HVAC air conditioner so it has to work a bit longer to draw moisture from the inside air.
  • Install exhaust fans in each bathroom and the kitchen and vent each exhaust fan to the "outdoors"
  • Air seal the thermal/pressure bypasses in the home to reduce the connection to the outside.
I think this is a helpful article. Thanks for posting. I have one as well that may be helpful to your reader that provides info and quick fixes for window condensation at
Posted by Tamara on 03/06/2021 - 09:22 AM

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