New Research Busts HVAC Myth about Duct Leakage in Conditioned Spaces

Comfort Institute (CI) partnered with the Greater Cincinnati Energy Alliance (GCEA) in an attempt to bust the long-held myth that leaky ducts in conditioned spaces do not contribute to energy savings and only leaky ducts in unconditioned spaces should be sealed. Long story short, the myth was indeed BUSTED!


For the study, eleven Cincinnati, OH area homes with “basement duct systems inside the thermal boundary” had their duct systems sealed using the Aeroseal process.


As a by-product, the Aeroseal duct sealing simultaneously made the overall house thermal envelopes tighter. Blower door tests before & after the duct sealing measured whole house CFM50 leakage reductions, averaging 11.4% or 348 CFM50. All 11 homes showed increased tightness, with CFM50 reductions ranging from -1.1% to -28.8%.


If expressed at the lower 25 pa reference pressure for duct testing, 347 CFM50 is equivalent to 221 CFM25 (flow exponent n=0.65). Since only duct sealing was done to the homes, it is inferred that an average of 221 CFM25 of Duct Leakage to Outside was eliminated.


This data refutes the common misconception that duct systems in “basement-style” houses don’t “leak to outside”.


Although measured energy savings data from these homes is limited, this finding also contradicts the common opinion that duct sealing only saves energy if the leaky ducts are located in unconditioned spaces. Energy modelling performed by the Greater Cincinnati Energy Alliance estimates an average of 9.8% reduction in heating and cooling consumption. In the one house where two years before/two years after of utility consumption data was available, degree day and baseload adjusted heating and cooling savings were 16%.


Additional research is planned in order to see if the findings can be replicated, to better understand the variables involved, and to better document energy savings potential.


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