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Residential Energy Efficiency Blog

Friday, April 03 2020

As a home energy auditor, one of the rewarding aspects of the job is to help homeowners uncover sources to their energy usage concerns.  It is especially gratifying when the energy audit was scheduled specifically to diagnose the issue before any big ticket decisions are made to try to solve the problem such as replacement windows or high efficiency heating and cooling unit (HVAC).  A well done energy audit can help you prioritize projects around the home in a way that guides you to getting the best return on investment.  If nothing else, you can make an informed decision to spend money on an improvement that will not yield an expected result.  Getting an energy audit puts you in the driver's seat.

There is one very good example of a common issue that I come across all of the time that is simply overlooked.  Expressed as a percentage, I would say that 90% of the homeowners I meet do not give this problematic area much thought, if any thought at all.  In order to get why the issue is such a problem there are two concepts that must be understood.

1. Stack Effect - A Building Science Principle

The first is the stack effect.  The stack effect is a building science principle that basically says that your house is kind of like a chimney in winter months.  When a chimney is in use, the fire is at the base pulling in oxygen to keep the fire alive (negative pressure) and as it heats the smoke rises and billows out of the opening at the top (positive pressure). You do not have to have a chimney in your house for the stack effect to be in play where your live.

When the heat is on during cold days, the warmer air that you are paying for rises like the smoke in the chimney.  Of course, the smoke leaves at the opening at the top of the chimney and so does your precious warm air.

How does this work in a house?  Imagine a bunch of smaller holes around the ceiling of you top floor where the warm air can sneak through.  Warm air escapes through the cracks and holes at the ceiling (positive pressure) which creates a pull pressure at the base of the building (negative pressure).  The stack effect essentially creates a conveyor belt where the belt moves the hot air out up top and pulls the cold air in down in low places (basement, crawlspace).
 

Stack Effect/Chimney Effect
Big inside/outside temperature variances (Delta T) increase the pressure dynamics in a building.


2. Bathroom Exhaust Fans - Dampers

Let's shift gears and focus on the exhaust fan in the upstairs bathroom.  Why the exhaust fan?  Let's think about that for a second.  Take a look at this diagram.

In theory, when the fan gets turned on, the air gets pulled in at the base of the fan and through the blower and into the duct that extends away from the fan to the "outdoors".  Unfortunately, this is not happening in most homes that I visit.

What's the big deal?  Besides not properly getting the moisture beyond the insulation in the attic to prevent mold and other health/safety concerns, there is typically another problem that is overlooked.

Notice where the air is flowing out of the fan in the photo above.  There is a little flap there known as a damper.  When the fan is not in use, the damper closes to prevent the communication of air between the two parts of the home (bathroom/attic).  If the damper is missing or not working properly, the fan becomes a gateway to the attic allowing the stack effect to overwork your heating system which leads to a shorter life, high bills and comfort issues.

This older bath fan in the attic does not have a duct running to the "outdoors".  It is also missing a damper which creates a gateway between in the inside of the house and the outside of the house.  Remember, the attic is part of the outside when there is insulation at the attic floor which is the case for most houses in Maryland.


The larger the gaps for air to leave out of the top of your house, the easier it is for cold air to get pulled in down at the base of your home. This pressure flow through the house is responsible for drafts, cold bathrooms, high energy bills and in extreme cases, moldy attics.

Leaky damper.  Large communication point between the attic and the inside of the house.

If you are not sure if your fan vents to the outside, one easy way to see is to take a look at your roof to see if you have any vents that look like the ones below.  If you see these, there is a good chance your exhaust is venting properly.

Another way is to go in the attic and take a look for yourself.  Here are a few more things to look for.

The upstairs bath fans in this attic have ducts connected to the actual fan, however they are not properly vented to the "outdoors".  The builder simply ran the duct to the ridge of the roof. but stopped short of sending them to the "outdoors".

 

Properly insulated and vented bathroom exhaust fans through the roof with exterior damper kit.
There are so many reasons why those that have a home energy audit done are so glad they did.  Most homeowners are aware of the big things that can help with energy efficiency, such as windows and HVAC.  But, there are less obvious things that are costing you money and getting an energy audit will uncover them for you so you can decide what to do.  

This newly installed fan is in the process of getting a duct installed to run to the "outdoors".  Air sealing around the fan is also key to improve the energy efficiency and comfort of a home.

As much as 40% of a home's energy use is related to HVAC so the idea is not to replace HVAC.  Rather, it is to reduce the amount of time you need to use your HVAC.

A home energy auditor can discuss better options like air sealing and insulation.  We can guide you to prioritizing the right projects. If you are going to spend the money to improve your energy bill or comfort or both, wouldn't it be nice to know that your decision is informed and will yield the results you are hoping to achieve?

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Having your home evaluated by Hometrust is a great way to identify your next home improvement project. 
Certifications earned through the Building Performance Institute demonstrate our ability to:

  • Find air leakage points around your home. 
  • Show you steps to improve energy efficiency.
  • Use science to guide improvements to comfort.  
  • Educate you how to tighten your building's shell. 
  • Learn about these opportunties before it is too late. 
  • Provide a unique perspective on your home's overall performance. 
  • Determine the root cause of any problems.
  • Assess current insulation effectiveness.
  • Measure air flow.
  • Evaluate windows, doors, siding and roofing.
  • Put you in complete control of the outcome.
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    Hometrust Remodeling is a licensed contractor specializing in a whole-house approach to home remodeling with an emphasis on educating our customers, providing energy efficient solutions, maintaining a network of high caliber technicians and using building science principles.  As a result, we can effectively guide Maryland homeowners towards projects that satisfy comfort needs, aesthetics and value.

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