ASHRAE 62.2 Alternative Compliance Path

How the Alternative Compliance Path Works

The basic idea of the alternative compliance path is to increase the dwelling-unit ventilation rate to compensate for the lack (deficit) of local exhaust ventilation in the kitchen and bathrooms. The deficit for the bathroom(s) and kitchen are added together and then divided by four. This result is the CFM that must be added to the dwelling-unit ventilation rate required for the existing dwelling. 

Notice in the example screenshot above that the kitchen and Bath #2 have openable windows. An openable window, whether one or more, counts as a 20 CFM credit toward the local fan deficit. Thus the kitchen deficit of 100 CFM is reduced by 20 CFM to a total of 80 CFM. The Bath #2 deficit of 28 CFM is reduced by 20 CFM to a total of 8 CFM.

In the example, in the section labeled “Use Local Ventilation Alternative Compliance” of the RED Calc Free ASHRAE 62.2-2016 tool, the “Total deficit” is 88. When 88 CFM is divided by four, the resulting “Alternative Compliance Supplement” is 22 CFM. This is added to the initial dwelling-unit ventilation rate of 32 CFM (“Total required ventilation rate, Q_tot” of 90 CFM minus the “Infiltration credit, Q_inf” of 58 CFM), for a required dwelling-unit ventilation rate of 54 CFM.

It is worth noting that if a compliant kitchen range hood and a new exhaust fan were added in bathroom #2, eliminating all deficits, the dwelling-unit ventilation requirement for this example would drop by 22 CFM, to 32 CFM.

Alternative Compliance Path Guidelines

Leaving existing fans in place or not installing a local exhaust fan where there isn’t one seems like a good option because it saves money. However, the best practice is to replace existing fans and install fans where there are none. The guidelines below are intended to ensure that you use the RED Calc ASHRAE 62.2 tools correctly and that you appraise existing fans with care.

1. We recommend that each time you use the RED Calc 62.2 tool that you include entries from the kitchen and each bathroom, whether they include exhaust fans or not. This will help keep things straight.
   
   1. The RED Calc Free 62.2 tools allow only one kitchen (you must check the “Kitchen included” box) and from zero to five bathrooms, the number is selected from a dropdown menu.
   2. The RED Calc Pro 62.2-2019 tool allows from zero to three kitchens and from zero to six kitchens.
   3. If a kitchen or bathroom has no local exhaust fan and you will not be installing one, make sure you enter zero in the “Fan Flow” input box for that room.
2. The “Fan Flow” values entered into the RED 62.2 tools should be the measured airflows of the local exhaust fans in the bathrooms and the kitchen WHEN THE JOB IS COMPLETE. This will result in properly sized dwelling-unit ventilation. Some of you have told us that you enter the “as-found” airflow rates first and print the image of the tool so that you have a record of what was installed when you arrived at the dwelling; this is fine to do. However, your final sizing of the dwelling-unit ventilation with the RED tool should include the local fan airflow rates upon job completion.
3. If you install a new bathroom or kitchen exhaust fan, it MUST meet the requirements of normal compliance, including the minimum airflow and maximum sound ratings. If you do install a new bathroom or kitchen exhaust fan meeting the normal compliance requirements, there will be NO deficit for that bathroom or kitchen.²
   
   1. The ASHRAE 62.2 standard allows the use of double-duty exhaust fans. This means the fan may satisfy the requirements of local AND dwelling-unit ventilation. For the example in this article, if you install a new bathroom fan and set it to run with an airflow of at least 54 CFM, it will satisfy the bathroom local ventilation AND the house dwelling-unit ventilation requirements. For another example, if the dwelling-unit ventilation requirement is 18 CFM, you can install a double-duty fan to run at 18 CFM continuously with an occupancy sensor or wall switch to boost the fan to 50 CFM or more to satisfy the local demand-controlled ventilation requirement.
   2. If you install a new exhaust fan in a bathroom or kitchen that is providing dwelling-unit ventilation, then the control for this fan must be “. . . labeled as to [the fan’s] function. . .” (ASHRAE 62.2-2016, Section 6.2)
4. If you leave the EXISTING exhaust fans in place, they are not required to meet normal local minimum airflow or maximum sound requirements.
   
   1. If the bathroom or kitchen has one or more openable windows, check the “Openable Window” box in the appropriate row of the RED Calc 62.2 tool. This will automatically reduce the deficit for that fan by 20 CFM.
5. If you intend to leave an existing bathroom or kitchen exhaust fan in place, take the time to do a safety inspection (this is not required by the ASHRAE 62.2 standard).
   
   1. Do your best to determine the remaining service life of an existing exhaust fan. Good data for exhaust fan service life doesn’t exist, but for older fans, six to ten years is probably a fair estimate. There is evidence of old fans causing house fires. Until the early 1990s fans were usually not thermally protected; fans older than this should be replaced.

      

   2. Cleaning the fan can extend its useful life and make it safer to operate.
   3. Develop an inspection checklist for exhaust fans you intend to leave in place. If the fan is not satisfactory, replace it.
   4. Educate the occupants about inspecting and cleaning the fan; every six months is recommended.
6. Based on optimum indoor air quality and safety, it is considered best practice to install a new exhaust fan in each bathroom and in the kitchen.