“ Our second floor is boiling in the summer and the basement is FREEZING! ”

Energy Efficient Homes Oakville

“ Our second floor is boiling in the summer and the basement is FREEZING!”

In the dog days of July, this often-heard lament from sleep deprived, disappointed homeowners resonates with some of our childhood experiences. Back in the day, the only solution in high summer was to go into the basement for a restful sleep, unless you were among the privileged who had AC in the 60’s and 70’s; a luxury we now take for granted. So, what can you do about it? There are a many potential sources of heat loss and heat gain affecting the comfort of your home:

  • Is there insulation missing in the walls?
  • Are the ducts installed correctly and properly sealed?
  • To what degree is your home sheltered from direct sunlight?
  • Is the window shading used as per the HVAC design?
  • Where do prevailing winds come from?
  • Is the A/C evaporator and condenser free, clean and clear?
  • Is the air filter clean?
  • Is the building envelope detail correctly?
  • Are the windows good quality and what about their installation?
  • Is the air barrier continuous giving a tight building?
  • Is one furnace enough or should the one furnace be zoned?
  • Is the furnace and AC properly sized? And are they working correctly?

All good questions, but the list is dizzying!

After being dismissed with what seems like excuses in “builder speak”, despondent homeowners often start scouring the internet for advice and many are left in a quandary bemoaning their recent build, and at a loss for a solution. While, as listed above, there could be myriad contributing factors. What’s the next step? While no HVAC system or house construction is perfect, there is a simple checklist to go through to review the HVAC system starting with simple measurements and non-destructive tests, before you start ripping your new walls apart!

Any, and all, of the above items could be discussed at a much greater length, however, in this article, we are going to concentrate on the duct-work and its air tightness.

We spoke to Dara Bowser, of Bowser Technical, a seasoned expert in HVAC design, for some advice. Dara referred to duct leakage as the “elephant in the room”, commenting that, prior to recent code changes the HVAC industry, was well aware that unsealed residential duct systems lost between 20 and 50% of their designed airflow from leakage.

The Ontario building code has recognized the need for tighter duct systems, and in the recent past (since 2014) has required all transverse joints in the duct-work to be sealed to a class C. Bowser, a valued part of the Chatsworth team of partners, brings his knowledge and experience to many of our custom builds to ensure the system is functioning as designed maximizing comfort and system efficiency.

He catalogs the options for sealing ducts ranging from simple foil tape to progressively better options of mastic brush on sealant, then to an aerosol type sealant applied to the inside of the ducts. Unfortunately, the good old duct tape just doesn’t cut it!

Dara recommends that a duct system be sealed and performance tested with resulting benefits of greater efficiency and even comfortable air distribution. Frequently home owners tend to compensate by adjusting the thermostat to try to achieve comfort in a particular area of the home, effectively wasting the additional cooling or heating that is over supplied to other areas. He points out this increases the cooling loads with an unbalanced, unnecessarily increasing electrical loads on our local utilities.

Bowser recommends Aeroseal, an aerosol based product as either part of the build or as part of a great solution to addressing post construction duct leakage. This provides a solution to duct leakage without the destructive mess of tearing down drywall to access the ducts and apply an external sealant. Chatsworth has used Aeroseal with significant results recapturing a large percent of air leakage. Even the best system of duct-work, without sealing, will leak due to inherent characteristics of installation.

Tibo Phung of Aeroseal GTA explains the process here:


“In a nutshell, we block off all entry and exit points of the duct system in order to isolate the leaks. At this point, we pressurize the system to determine our baseline measurement for duct leakage. If the leakage is enough that it justifies sealing, we will then inject our specialized aerosol sealant. Since the entry and exit points are still blocked, the sealant has nowhere to go except out the leaks and it seals them as it does so.

We watch on the computer as the pressure builds and the leakage is eliminated. The end result is a sealed duct system that maximizes HVAC throughput, performance, and efficiency. The sealant remains permanently flexible to accommodate for the expansion and contraction of the sheet metal ducts, which is why the procedure is meant to be a one-time application and last the lifetime of the building.”

On a particularly complex and large recent Chatsworth build, Tibo Phung from Aeroseal GTA commented further:

“The final tally after sealing the 4 systems was a combined recovery of 1430 CFM of duct leakage. This means the amount of air conditioning that would have been enough to cool one and a half 2,000 sq-ft homes!!!!


Although appreciable, this loss falls within the expected 20-50% loss for unsealed ducts and the final testing and measurements taken, after sealing, confirmed that the duct system was performing up to the design criteria and the resulting comfort and system control was readily apparent.

Tibo and his team have successfully sealed duct systems for Chatsworth, yielding great results and much more comfortable home for our clients Thanks to Aeroseal!


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