Secondary Author(s)

Withers Jr., Charles; Bonilla, Nicholas; Martin, Eric

Report Number




HVAC; Buildings; Air Quality; Ventilation; Air Flow; Residential; Air Conditioning


Existing evidence strongly suggests that viral infectious diseases can be transmitted via an airborne route across distances in indoor environments. Accordingly, the risk of airborne transmission within homes should be managed. The public health emergency associated with SARS-CoV-2 makes controlling airborne transmission of respired viruses in indoor environments critical, especially in poorly ventilated indoor environments. The effectiveness of engineering interventions requiring minor efforts that create a negative-pressure isolation zone (IZ) for a contagious person has yet to be tested for existing residential homes.

To mitigate the risk of airborne virus transmission and maximize health protection for the population in existing single-family homes, this report investigates the relative effectiveness of several control strategies. Although very high-efficiency MERV filtration, high ventilation rates, and other controls can help be effective, most occupants are not likely to have the time or means for advanced measures found in hospitals. This project focuses on relatively simple efforts that utilize existing or easy to acquire materials and straightforward processes.

The risk of transmission of a contagious airborne virus can be reduced by isolating a sick person in a depressurized IZ of a single-family home. Within this report, the remaining occupied part of the house outside the IZ is referred to as the main zone (MZ). Further protection can come from bringing outside air into the MZ using an existing mechanical ventilation system or even a lowcost window fan. This increases ventilation and dilution of pollutants and helps maintain positive pressure with reference to the IZ.

In our test facility, which is a single-family manufactured home, various controls were implemented under various operating conditions. A total of 17 cases were tested, with test conditions summarized in Table ES-1. These strategies were designed based on various heating, ventilating, and air-conditioning (HVAC) operating scenarios, intervention measures, and utilization of exhaust or window fans for pressure control. Interventions involved efforts like closing the IZ door and/or sealing IZ supply air grilles. The primary metric used in this project to evaluate potential containment effectiveness is the "IZ with reference to (w.r.t.) MZ" pressure difference. ASHRAE 170 standard requires a hospital isolation room pressure differential of at least -2.5 Pa w.r.t. adjacent zones. This pressure differential requirement was the primary basis of comparison. The use of generated particulate matter was a supplementary means of observing containment. To test the potential effectiveness of IZ containment, fine particulate matter (PM2.5) was generated from an essential-oil-based diffuser, and tracer gas was injected in the IZ followed by real-time monitoring of the particulate matter and tracer gas transfer from IZ to MZ. Combining the data from pressure differential monitoring and observed concentrations of PM2.5 and tracer gas across the zones, the potential effectiveness and weakness of several cases were demonstrated.


Date Published


Local Subjects

Buildings - Air Conditioning; Buildings - Air Flow; Buildings - Air Quality; Buildings - HVAC; Buildings - Residential; Buildings - Ventilation


FSEC Energy Research Center® Collection



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