You're on the right track, but it's crucial to consider several factors before connecting an emergency HVAC system to a UPS already powering emergency lighting. While both might be considered emergency loads, simply being an "emergency load" isn't enough to guarantee compliance. Here's a breakdown of the considerations

Key Considerations and Code References (NFPA 70, NFPA 110):

1. Capacity of the UPS

This is the

primary concern. Can the existing UPS handle the additional load of the emergency HVAC system in addition to the existing emergency lighting? You need to perform a load calculation to determine the total required kVA/kW. Consider inrush current of the HVAC system (especially compressors and large motors). UPS systems can have limitations on surge capacity. Exceeding this can damage the UPS or cause it to shut down. NFPA 70 Article 700.4(B)

This addresses the capacity requirements for emergency systems. It's critical that the UPS is sized to handle the entire connected load without dropping below acceptable voltage or frequency.

NFPA 110

This standard provides more specific requirements for emergency power supply systems, including load testing and performance criteria. Look at the UPS's nameplate rating and performance specifications.2.

Type and Classification of Emergency HVAC System



What type of HVAC is it? Is it for smoke control, maintaining a safe temperature, or something else? The specific function will determine its criticalness and the allowed transfer time. NFPA 70 Article 700.1

Define what makes this HVAC system an "emergency system." Is it legally required, or does it serve a critical function related to life safety?

NFPA 110 Class & Type

This classification determines the minimum required runtime and transfer time of the emergency power supply. Ensure the existing UPS meets the requirements for both the lighting and the HVAC system. A smoke control system, for example, will likely have very stringent transfer time requirements.3.

Transfer Time



NFPA 70 Article 700.12(E)

If using a UPS, the maximum transfer time to the emergency power source (the UPS in this case) is generally 10 seconds, and sometimes even shorter. Ensure the HVAC system can tolerate this transfer time.

NFPA 110

Different types of emergency systems have different transfer time requirements. Review NFPA 110 for specifics. Some HVAC systems (e.g., smoke control) might require instantaneous transfer, which a typical UPS might not provide unless it's already online and powering the load.4.

Maintenance and Testing

Adding the HVAC system will increase the load on the UPS, potentially shortening its lifespan and impacting its reliability.

NFPA 110 requires regular testing and maintenance of emergency power systems. You'll need to update your testing procedures to include the HVAC system and ensure the UPS continues to perform adequately under the increased load. NFPA 70 Article 700.3(D)

Addresses testing and maintenance requirements.5.

Coordination with Fire Alarm System

If the emergency HVAC is part of a smoke control system, it must be properly coordinated with the fire alarm system. This includes shutdown and startup sequences during various fire scenarios. Ensure the UPS can handle the load profile during these sequences.6.

Segregation of Circuits (May be Required)

While general emergency systems can be connected to the same source, some jurisdictions or specific applications might require separation of circuits for critical components like smoke control systems. Check with your local Authority Having Jurisdiction (AHJ).

NFPA 70 Article 700.9(D)

Some emergency circuits, such as those powering fire pumps, must be kept entirely independent of all other wiring.7.

Authority Having Jurisdiction (AHJ)



The most important step is to consult with your local AHJ (e.g., building inspector, fire marshal). They have the final say on what is acceptable and might have specific requirements beyond the NEC and NFPA 110. They can interpret the code and determine if the proposed connection is safe and compliant.

In Summary



Perform a comprehensive load calculation

This is non-negotiable. Determine the exact power requirements (including inrush) of the HVAC system and the existing emergency lighting.

Verify UPS Capacity

Ensure the UPS can handle the total load with adequate margin.

Check Transfer Time

Confirm the transfer time of the UPS is acceptable for the HVAC system.

Review NFPA 110

This standard contains detailed requirements for emergency power systems.

Consult the AHJ

Discuss your plans with the local building inspector or fire marshal.

Therefore, while technically possible and sometimes permissible to connect an emergency HVAC system to a UPS already powering emergency lighting, it's FAR from a simple "yes" or "no" answer. It requires a thorough engineering analysis, code review, and approval from the AHJ. Failure to do so could result in a system that doesn't perform as expected during an emergency, jeopardizing life safety. Flag for review