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Indoor EV Charging and the Truth About Ventilation Requirements
Most inspectors and installers still get tripped up when it comes to understanding NEC 625.52, especially regarding ventilation for electric vehicle charging in enclosed spaces. The short answer is that mechanical ventilation is not always required. In fact, it usually isn’t, but that hasn’t stopped confusion in the field or unnecessary installations that waste time and money.
Section 625.52 of the NEC addresses ventilation requirements for EV charging equipment installed indoors. If the charging equipment is listed for use without the need for ventilation, or if the battery system used in the electric vehicle does not emit hazardous levels of hydrogen gas during charging, then no mechanical ventilation system is required. Most EVs on the road today use sealed lithium-ion battery systems, which do not produce hydrogen gas in dangerous concentrations. As a result, most residential and commercial EVSE installations do not require any additional ventilation. This is backed up by SAE J1718, which provides testing procedures to measure hydrogen emissions during both normal and fault-mode charging conditions. If the system passes, there’s no ventilation requirement.
However, some older or specialized EV charging systems may still require ventilation. If the EVSE is listed as requiring it, mechanical ventilation must be permanently installed and electrically interlocked with the charging equipment. That means the ventilation system must activate and remain in operation for the entire duration of the charging cycle. If the fan fails, the charging system must shut down or never energize in the first place. The NEC requires that both supply and exhaust air be managed, and the air must be vented directly to the outside. The interlock requirement is especially important for equipment rated 15 or 20 amps at 125 volts, or any system under 50 volts DC, because it ensures that the ventilation fan is always running whenever the charging receptacle is powered.
The code provides two main methods for determining how much ventilation is needed. Tables 625.52(B)(1)(1) and 625.52(B)(1)(2) list the required cubic meters per minute or cubic feet per minute, based on voltage and circuit ampacity. For setups not covered by the tables, formulas in 625.52(B)(2) must be used to calculate minimum air movement. There is also an allowance for engineered systems under 625.52(B)(3), where a qualified individual can determine the required ventilation rate as part of the building’s overall system. Regardless of the method used, the required airflow must be supplied continuously during charging unless the system is listed as not requiring it.
For outdoor installations, ventilation is not an issue. Hydrogen gas is lighter than air and disperses quickly. As long as the charging location is not enclosed, such as in a carport, open parking garage, or driveway, no mechanical ventilation is required. NFPA 88A helps define what qualifies as an open parking structure, and those areas are exempt from the ventilation rules under NEC 625.52.
It is important not to confuse this section with grounding electrode requirements. I have seen contractors drive a ground rod next to a pool pump or EV charger, thinking it helps safety. It doesn’t, and in some cases, it makes things worse. This article is strictly about ventilation related to hydrogen gas buildup, not grounding electrodes or equipotential bonding. Those are entirely different code issues that get mixed up far too often.
The key takeaway is simple. If the EVSE listing says ventilation is not required, then it is not required. If the listing says ventilation is required, then you follow the code exactly and make sure the fan is permanently installed, interlocked, and properly sized. There is no gray area here. Installers and inspectors alike need to stop overthinking it and follow the listing and code requirements.
Most inspectors and installers still get tripped up when it comes to understanding NEC 625.52, especially regarding ventilation for electric vehicle charging in enclosed spaces. The short answer is that mechanical ventilation is not always required. In fact, it usually isn’t, but that hasn’t stopped confusion in the field or unnecessary installations that waste time and money.
Section 625.52 of the NEC addresses ventilation requirements for EV charging equipment installed indoors. If the charging equipment is listed for use without the need for ventilation, or if the battery system used in the electric vehicle does not emit hazardous levels of hydrogen gas during charging, then no mechanical ventilation system is required. Most EVs on the road today use sealed lithium-ion battery systems, which do not produce hydrogen gas in dangerous concentrations. As a result, most residential and commercial EVSE installations do not require any additional ventilation. This is backed up by SAE J1718, which provides testing procedures to measure hydrogen emissions during both normal and fault-mode charging conditions. If the system passes, there’s no ventilation requirement.
However, some older or specialized EV charging systems may still require ventilation. If the EVSE is listed as requiring it, mechanical ventilation must be permanently installed and electrically interlocked with the charging equipment. That means the ventilation system must activate and remain in operation for the entire duration of the charging cycle. If the fan fails, the charging system must shut down or never energize in the first place. The NEC requires that both supply and exhaust air be managed, and the air must be vented directly to the outside. The interlock requirement is especially important for equipment rated 15 or 20 amps at 125 volts, or any system under 50 volts DC, because it ensures that the ventilation fan is always running whenever the charging receptacle is powered.
The code provides two main methods for determining how much ventilation is needed. Tables 625.52(B)(1)(1) and 625.52(B)(1)(2) list the required cubic meters per minute or cubic feet per minute, based on voltage and circuit ampacity. For setups not covered by the tables, formulas in 625.52(B)(2) must be used to calculate minimum air movement. There is also an allowance for engineered systems under 625.52(B)(3), where a qualified individual can determine the required ventilation rate as part of the building’s overall system. Regardless of the method used, the required airflow must be supplied continuously during charging unless the system is listed as not requiring it.
For outdoor installations, ventilation is not an issue. Hydrogen gas is lighter than air and disperses quickly. As long as the charging location is not enclosed, such as in a carport, open parking garage, or driveway, no mechanical ventilation is required. NFPA 88A helps define what qualifies as an open parking structure, and those areas are exempt from the ventilation rules under NEC 625.52.
It is important not to confuse this section with grounding electrode requirements. I have seen contractors drive a ground rod next to a pool pump or EV charger, thinking it helps safety. It doesn’t, and in some cases, it makes things worse. This article is strictly about ventilation related to hydrogen gas buildup, not grounding electrodes or equipotential bonding. Those are entirely different code issues that get mixed up far too often.
The key takeaway is simple. If the EVSE listing says ventilation is not required, then it is not required. If the listing says ventilation is required, then you follow the code exactly and make sure the fan is permanently installed, interlocked, and properly sized. There is no gray area here. Installers and inspectors alike need to stop overthinking it and follow the listing and code requirements.