Gas-phase chemical transfer through heat and energy recovery ventilators

Heat and Energy Recovery Ventilators (HRVs and ERVs) improve the energy efficiency of mechanical ventilation, but concerns exist that ERVs may also transfer water-soluble chemical contaminants, impacting indoor air quality. In this study, we tested ventilator units with two different stationary cores; a HRV core, which transfers sensible heat across supply and exhaust air streams, and an ERV core, which transfers both latent and sensible heat. We measured formaldehyde (HCHO) and formic acid (HCOOH) in the supply, return, exhaust, and outside ducts of a residential test facility from December 2024 through April 2025 at various duct flow rates to quantify possible transfer across the stationary cores. Additionally, we measured ammonia (NH 3 ) for several days in December 2024. Our results show that these chemicals do not transfer across the HRV core but may transfer across the ERV core. Moisture and chemical transfer across the ERV core were affected by the climate regime and ventilation air flow rate. The contaminant’s solubility in water (i.e. Henry’s law constant) additionally influenced chemical transfer across the ERV core. Modeling shows that switching from an HRV to an ERV can contribute to a 5.5% to 15% and 19% to 37% increase in indoor HCHO and HCOOH concentrations, respectively but also contribute to a total yearly, whole house energy savings of 2.0% to 4.7% (depending on flow rate). • Water soluble gas-phase chemicals may transfer across the ERV core but not the HRV core. • The transfer of water-soluble gas-phase chemicals in the ERV is influenced by flow rate, the chemical’s solubility in water, and the climate regime. • Indoor chemical concentration may be lower indoors when using an HRV compared to an ERV, but the HRV can be slightly more expensive to operate.