The “House with 80% Relative Humidity Inside”
“A lot can change in a house in 15 years.”
— Home Energy Solutions
Why Replacing the HVAC System Wouldn’t Solve the Humidity Problem
The HVAC company initially based the proposed replacement system on the size of the existing equipment without first assessing how the home had changed during the 15 years since that equipment was installed.
Over those 15 years, the home had undergone several changes that affected its HVAC requirements:
new attic insulation had been added
additional air sealing had been completed
a 350-square-foot patio had been remodeled and brought within the conditioned building envelope
a new bathroom had been installed within the conditioned space
The assessment also revealed significant air leakage between the crawlspace and the conditioned living area. Openings in the combustion closet, where the furnace was located, created a pathway for crawlspace air to enter the home. The final report identified the necessary corrective actions and gave the homeowner the information needed to evaluate the available remediation options.
How Open Windows Contributed to High Indoor Humidity
After speaking with the homeowner, we learned that he regularly opened the windows during summer to enjoy the outdoor air and create a cross breeze through the house.
Unfortunately, a lot of moisture vapor was coming inside along with the ambient air. The AC equipment and its dehumidifier (coil) would be off in the evenings until the next day when the ambient (outside) temperatures caused the AC equipment to come on. By that time, a lot of excess moisture had built up in the home and many cooling cycles were required to bring the humidity back down to comfortable levels.
Home Energy Solutions was able to:
educate the homeowner about the source of the excess indoor humidity
help the HVAC contractor avoid replacing equipment that did not need to be replaced
confirm the correct equipment sizing for the home
The HVAC contractor was relieved to learn that the system was properly sized, the equipment was not causing the humidity problem, and replacement was unnecessary.
The evaluation saved the HVAC contractor from spending additional time and labor on an equipment change that would not have corrected the problem. Replacing the AC coil to increase dehumidification would still have left the underlying sources of moisture—the homeowner’s open-window habits and air leakage between the crawlspace and conditioned space—unresolved.
