Residences FAQ

A: In general, you should follow the guidance of local public health officials when wildfire smoke threatens your location. It is anticipated that persons who are either susceptible to or affected by COVID-19 may have health conditions that also make them vulnerable to wildfire smoke exposure and while social distancing guidelines are in place, finding cleaner air shelters might be challenging. If you need to reduce your exposure at home, you should stay indoors and set up a clean room. While increasing ventilation rates is good for reducing COVID19 risk, this is not recommended during wildfire smoke events. However, the same filtration options, such as portable air cleaners or MERV 13 filters in HVAC systems, that will reduce risk of COVID19 will also reduce indoor particle concentrations from wildfires. Information on clean rooms can be found from the US EPA and the Indoor Environment Group of Lawrence Berkley National Lab. The US CDC has provided additional advice on protecting yourself from wildfire smoke during the COVID-19 pandemic.

A: There is neither evidence of, nor any reason to believe that portable space heaters directly create any increased risk of COVID19. ASHRAE recommends that you continue to keep occupied spaces heated to normal levels, because spending time under thermal stress such as excessively cold spaces can lower resistance to infection.

There are, however, other issues to consider when selecting and operating a space heater. Be aware that unvented combustion space heaters (e.g. using kerosene, propane, natural gas, etc.) release products of combustion into the indoor air. Without adequate ventilation, these contaminants can build up to unacceptable or even hazardous levels. Unvented combustion emits NO2 which is a reactive oxygen species (i.e. a known breathing irritant,) and could increase susceptibility to respiratory infections, such as COVID-19. Unvented combustion-based heaters are banned in some jurisdictions. Electric space heaters do not pose those risks, but the placement of any portable heater requires some thought and care, to avoid overheating any nearby materials.

A: ASHRAE recommends following guidance from the CDC which includes minimizing contact, having a household plan which includes basic information on how to protect yourself and how to keep your home sanitary.

Additionally, follow the guidance in the Task Force’s Technical Guidance for Residences presentation which is intended to supplement CDC recommendations with options related to controlling virus transmission through the air using the home’s heating, ventilating and air-conditioning (HVAC) equipment and related factors.

This Technical Guidance for Residences includes guidance for all homes, homes with forced-air systems, multi-family homes and guidance for homes with COVID-19 positive or high-risk individuals.

A: Yes, guidance on how to run your residential Heating Ventilating and Air-conditioning (HVAC) system can be found in the Task Force’s Technical Guidance for Residences. This document includes guidance for all homes, homes with forced-air systems, multi-family homes and guidance for homes with COVID-19 positive or high-risk individuals.

A: In general, a well-designed, maintained and operated heating, ventilating and air-conditioning (HVAC) system that meets applicable standards for ventilation and filtration will reduce the risk of transmission in your home. If, however, there is an infected individual, care should be taken to isolate them from the rest of the household which may include isolating parts of the HVAC system. See guidance for creating an isolation space.

Note also that it is ASHRAE’s position that:
Ventilation and filtration provided by heating, ventilating and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.

Guidance on how to run your residential heating, ventilating and air conditioning system can be found in the Task Force’s Technical Guidance for Residences. 

A: When a household member is known to be infected, additional precautions are required in order to reduce the risk to other household members. The CDC has provided general guidance for this situation. A key aspect is to use a separate room essentially as an isolation space. The following additional actions should be considered when creating such an isolation space:

• Select isolation space
• Separate HVAC systems
• Install air barriers
• Operate exhaust ventilation

Please see the Technical Guidance for Residences for more details.

A: The CDC recognizes various categories of high-risk individuals and has general guidance for high-risk individuals. If there is not a known infected individual but there is a high-risk household member, additional protection can be afforded by creating a protected space for the high-risk individual. The following actions should be considered:

• Select protected space
• Separate HVAC systems
• Install air barriers
• Operate supply ventilation
• Operate stand-alone air cleaner

Please see the Technical Guidance for Residences for more details.

A: Generally, this is safe and some minor adjustments are in order.

The typical 1-inch (thick) filter in most systems can be replaced with a filter up to MERV 13. Above this MERV rating the additional airflow resistance of high-performance filters may impact the performance of the HVAC system. If you have a 2-inch or greater filter then you can upgrade it safely with filters up to MERV 16. A 4-inch or greater filter will need to be changed far less frequently.  If installing a new filter grille or holder, consider one that can take a 4-inch filter.

You will need to adjust the fan setting to make the fan run even if there is no heating or cooling. Many thermostats have a “fan only” setting that can be used or you may have a smart thermostat or fan controller that can be used to provide a minimum operating time of at least 15 minutes per hour.  In hot humid climates, be aware that continuous fan operation may reduce the ability of your system to control humidity. Please refer to the user’s manual of your system or consult an HVAC contractor for more information, and consider asking your contractor to upgrade your filters. Care must be taken when replacing filters because of exposure from surface contaminants.

A: Yes, but it is important to avoid ozone production because it is a contaminant of concern. Look for equipment meeting UL Standard 2998 Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners.

This kind of germicidal equipment uses mercury vapor lamps that produce ultraviolet light at 254nm, which is effective at inactivating many pathogens including SARS-CoV-2. Light at this wavelength does not produce ozone, but the mercury vapor lamps also produce ultraviolet light at shorter wavelengths that do produce ozone. Manufacturers have overcome this problem by using titanium-doped quartz in the lamps, which block the ozone-producing wavelengths. These products require careful design, installation and maintenance to be most effective.

A: Perhaps. Direct sunlight has disinfectant properties in addition to having other benefits for people. Research has not yet determined exactly how strong that effect is for the SARS-CoV-2 virus. Window glass absorbs a lot of the ultraviolet frequencies where the disinfectant benefit comes from so, it is best to let sunlight in through open windows. However, this practice should only be used in addition to and not as a substitute for following all the recommendations from the CDC and the ventilation and air cleaning guidance found here. One must also take care to balance open windows with other concerns including thermal stress and pressure balancing.

A: Generally, yes. While there can be a potential to recirculate a small amount of contaminated air if someone is infected, the ERV/HRV will still be an overall benefit in single-family homes.

A: In general, it is not necessary to upgrade the filter treating the supply of outdoor air. According to current knowledge, there is a very low probability that the virus will enter from outdoors into the house through the mechanical ventilation system. In addition, a higher effectiveness filter may be more prone to clogging and will reduce air flow. One factor that might change this recommendation is if the outdoor air intake is near another building’s exhaust vent or near a location where people congregate.

A: Generally, yes. If your work involves typical use of a computer and normal accessories and other routine office work, the ventilation requirements in ASHRAE Standard 62.2 should be enough. However, if your office work is more intense (e.g., heavy duty use of laser printers, use of a 3d printer, soldering or other activities not typically performed at home), you may wish to look to ASHRAE Standard 62.1 for guidance on adequate ventilation.

A: Yes. Care should always be taken when disposing of condensate water as it can contain virus and other harmful contaminants. If possible, the condensate should be emptied outdoors or into a toilet. To avoid aerosolizing any potential virus, care should be taken not to splash when emptying the container and wearing a face mask is recommended. The container should be washed as should your hands after the operation is complete. If extra care is needed, such as if the dehumidifier is in an isolation space, consider using full PPE.

A: You should go ahead and fix or replace your system. As noted in Task Force’s Technical Guidance for Residences, it is important to maintain normal thermal comfort conditions. When replacing your system, consider including upgrades such as providing better filtration as discussed in the Residential Guidance.

Some precautions you can take are to ask the contractor to use facemasks when they are working in your home. You might also ask the contractor to only enter as few rooms in your home as possible, that you can clean after the work is done (or the contractor themselves may do this). Other additional precautions to consider if you are in a higher risk group are possibly to leave the home or use portable filtration in occupied rooms during the day while the work is being done. You should definitely discuss these options with your contractor to make a plan that you are both comfortable with. Contractors may also have their own plans to protect you and their workers that should be part of any conversation before work starts in your home. The U.S. Occupational Safety and Health Administration provides guidance for “In-Home Repair” at the following links:

• COVID-19 Guidance for In-Home Repair Services
• In-home repair services

A: Generally, not. The outdoor part of your AC unit is typically only connected to the indoors through refrigerant lines—not air ducts—and there is no transmission path for air.

However, there are a few types of systems that do have outdoor air connections. Some window and portable air conditioners may pull in air from outside. In some large multifamily units, heating and cooling may be supplied by Packaged Terminal Air Conditioning (PTAC) units with similar outdoor air intakes. There may also be specific ventilation intakes unrelated to any heating or cooling system. In all these cases, social distancing rules are recommended between those intakes and people outdoors.

A: High efficiency particle filtration is rarely an option in such equipment. Instead, consider operating a portable air cleaner that has a high clean air delivery rate (CADR) in North America, a high clean air efficiency (CAE) in Europe (see additional info here), or is equipped with a HEPA filter and does not emit ozone. For more information, the EPA’s guidance to air cleaners and air filters in the home is here.

A: High efficiency particle filtration is rarely an option in such equipment. Instead, consider operating a portable air cleaner that has a high clean air delivery rate (CADR) in North America, a high clean air efficiency (CAE) in Europe (see additional info here), or is equipped with a HEPA filter and does not emit ozone. For more information, the EPA’s guidance to air cleaners and air filters in the home is here.

A: High efficiency particle filtration is rarely an option in such equipment. Instead, consider operating a portable air cleaner that has a high clean air delivery rate (CADR) in North America, a high clean air efficiency (CAE) in Europe (see additional info here), or is equipped with a HEPA filter and does not emit ozone. For more information, the EPA’s guidance to air cleaners and air filters in the home is here.

A: No. Ozone at high enough concentrations can inactivate the SARS-CoV-2 virus, but these levels of ozone are generally well above levels considered safe for occupant exposure. 

For air cleaning devices, ASHRAE holds the position that

Devices that use the reactivity of ozone for the purpose of cleaning the air should not be used in occupied spaces because of negative health effects that arise from exposure to ozone and its reaction products. Extreme caution is warranted when using devices that emit a significant amount of ozone as by-product of their operation, rather than as a method of air cleaning. These devices pose a potential risk to health

Electronic air cleaning products have been known to emit ozone incidentally.  ASHRAE recommends products that have been certified as certified air cleaning devices by the California Air Resources Board  or as zero ozone emitting devices using UL 2998.

For more information: the full text of ASHRAE’s position on filtration and air cleaning is here and the EPA guidance on residential air cleaners is here.

A: If there is an infected or vulnerable person in your single-family home it is advisable to delay testing. Otherwise, it is generally okay to go ahead with the blower door test. However, blower door tests of occupied multifamily dwellings are not recommended.

A blower door moves a large amount of air, which in general should reduce the concentration of any virus-containing particles, but it can also re-suspend dust which might contain viral particles. For this reason, it would be best to stay out of the home and away from the blower door during the tests and at least an hour from the time the blower door is shut off, or if that is not possible to wear N95 masks. You should discuss safety with the contractor in advance to ensure they will be following company or manufacturer safety protocols that consider factors such as technician health, appropriate PPE, social distancing and surface disinfection. If both pressurization and depressurization tests are being done, it is recommended to do the pressurization test first.

A: Yes, provided your unit ventilates the house with outdoor air. Direct evaporative cooling takes air from outside and cools it with evaporation and sends it indoors. This type of evaporative cooler will increase ventilation rate like an economizer or summer whole-house cooling fan and would similarly reduce risk. Some evaporative coolers do not take their air from outside and do not increase ventilation. Be sure to find out which type you have.

Portable evaporative coolers may be helpful for comfort, they probably won’t reduce risks of airborne infection unless, like direct evaporative coolers, they supply outdoor air to the house.

A: When there are periods of very low ventilation, a portable air cleaner can reduce the risk of COVID-19 infection. The best options include HEPA filtration and some sort of disinfection such as from UV-C. When buying electronic air cleaners, it is important to have them certified to be low ozone emitting. The Environmental Protection Agency has more information available on air cleaners for the home.

A: Central exhaust systems in all parts of the world are designed to ensure that air only goes out—never into—the apartment from a central exhaust duct. In the US and Canada, most codes require a continuously operating exhaust fan at the top of the duct, and/or a back-draft damper at every local exhaust connection. These measures prevent air from one apartment entering another via the central exhaust duct. Other international codes and construction practices provide different means of ensuring that air always moves into—never out of the exhaust ducts.

• If there is a switch that activates a local exhaust fan, turn it on and repeat the test to make sure air is now leaving your apartment.
• If there is no local fan, or if air is still entering the apartment from the exhaust duct, seal off that opening with cardboard or plastic sheeting and tape.
• Notify the building manager of the potential risk and ask for their plan and their schedule for correction of this problem.

(Note that your bathroom or kitchen may also have a supply air grille as part of your heating, cooling or ventilation system, which blows conditioned air into the apartment by design. Don’t accidentally seal off these supply grilles)

For videos of how to check your exhaust vent go to https://vimeo.com/460681697 and https://vimeo.com/511387096.

A: For most systems, upgrading your filtration by replacing your current filter with one rated at MERV 13 has little or no effect on cooling and heating performance. However, some residential systems were not intended for MERV 13 filters or might be poorly designed or installed. In such cases, the extra air flow resistance of a better filter may result in poor system performance; in some cases, the additional resistance can lead to freezing the cooling coil (where the coil gets covered in a layer of ice)—a problem that can result in compressor failure.  If you have any doubts about the state of your system before upgrading the filter or think that cooling or heating performance has been significantly reduced after installing a better filter, have your system’s air flow checked and adjusted by a licensed HVAC professional. 

A: ASHRAE does not recommend humidification for COVID-19 risk reduction. There is not sufficient evidence that raising humidity has a significant effect on the risks of COVID-19 transmission. If you usually humidify during the winter for comfort or other reasons, however, COVID-19 is not a reason to stop. For risk reduction, ASHRAE recommends more ventilation and better air filtration as described in ASHRAE’s residential guidance.

A: Congratulations - Moving to a new residence is an exciting time! The features that reduce risks from COVID-19 are the same features that provide good indoor air quality: ample outdoor air ventilation and excellent air filtration. The ASHRAE Residential IAQ Guide has helpful information on building, buying or renting a dwelling with good indoor air quality. If you’ve already selected a residence, consult with an HVAC contractor to help you consider improving ventilation to the standards outlined in ASHRAE Standard 62.2, and improving the central heating/cooling system filtration to MERV-13 or higher. Then at move-in time, if others have been in the dwelling during the previous 48 hours, wear a mask, and open all the windows long enough to change the air completely. An hour or so is usually sufficient.

A: If a member of the household is a high-risk individual it may be useful to create a protected space for that individual to reduce the risk of the individual being exposed to potentially infectious air. Additional Guidance for Creating a Protected Space.

To keep potentially infectious air from leaking in from other parts of the house, that protected space must remain at a higher pressure than the rest of the house. This is usually accomplished by mounting a fan in a partly-open window, and running that fan so it forces outdoor air into the room.

You can check with a short length of toilet tissue that your protected space is staying at a higher pressure than the rest of the house. From a position inside the protected space, hold that short length of tissue along the gap at the base of the door between the protected space and the rest of the house. Then take your hands away from the tissue. If the tissue remains against the door gap for at least three minutes, then protection is probably effective. This means that air is moving from the protected space to the rest of the house, so that any potentially infectious air outside the protected space remains in the rest of the house.

However, when that length of tissue falls away from the base of the door instead of being held against the gap, it means the protected space is no longer effective. In that case, check to make sure that any central system HVAC inlet and outlets are sealed off with cardboard and masking tape. Also make sure the window fan is operating in a way that forces outdoor air into the protected space, and that any other windows in the space are either closed tightly or only barely cracked open (less than 1/4” (6 mm).

A: Not necessarily. There are circumstances where opening windows is not a good idea or where there are better options. In general, it is preferable to use a mechanical ventilation system if available. If no mechanical ventilation is available, consider the following situations before opening windows.