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Expansion Tanks for Antifreeze Systems

Unheated areas are typically covered by dry systems or with antifreeze systems. These areas may experience a wide range of temperatures over a period of time. Higher temperatures will cause the antifreeze to expand and thereby increase the pressure of the system. When a backflow prevention device is installed between the antifreeze system and the wet pipe system, this pressure may increase to the point of system failure resulting in leaks or burst fittings & pipe. NFPA 13, (2010 edition), section addresses this potential problem by requiring the use of an expansion chamber/tank.

The expansion tank is essential for successful system operation when a backflow prevention device is installed between the antifreeze system and the wet pipe system, (or if the entire system is antifreeze). The expansion tanks are required by to be listed for fire sprinkler system use.

At this time, our office is aware of only two manufacturers that have UL approval on expansion tanks for NFPA 13 systems. One is Young Engineering Manufacturing, Inc. out of California at 909-394-3225. They have an East Coast distributor at Atlantic American Fire Equipment, 508-839-7400. The other is Amtrol out of Rhode Island at 401-884-6300. Also be aware that these tanks come with a minimum pre-charge, and this pre-charge has to be increased as per the manufacturer's specification for the specific application. Then this charge needs to be inspected periodically as per standard inspection requirements. The proper size tank must also be purchased for a particular antifreeze system.

The 2010 edition of NFPA 13 requires a test and drain connection at the remote portion of the system for systems with more than 40 gallons of antifreeze solution. This requirement can be found in section, and comes from NFPA 25, which requires the concentration levels to be checked at both ends of the system.

NFPA 13R, (2010 edition), section 5.4.3 requires antifreeze systems to be installed according to NFPA 13, which means that the expansion tanks must also be listed when used in NFPA 13R antifreeze systems.

Hydro-Pro, Maine Life Safety, and NFPA 13D standards do not require tanks to be listed for fire sprinkler system use. Our office however will only accept standard non-listed, lower-quality expansion tanks for these standards when the total antifreeze solution does not exceed 40 gallons. When antifreeze solutions exceed 40 gallons in those systems, then only expansion tanks listed for fire sprinkler system use will be accepted for these standards. NFPA 13 and 13R systems, however, always require the tanks to be listed for fire sprinkler system use, regardless of antifreeze solution volume.

When an antifreeze loop comes off a wet pipe system, and the check valve has a 1/32" hole in it, according to Figure in NFPA 13, then an expansion tank is not required, however the assumption is that the wet pipe system is large enough in volume to absorb the pressurized antifreeze. NFPA does not mention this, but in Maine an expansion tank on the antifreeze system is also required to be installed whenever the volume of the antifreeze system exceeds the volume of the wet pipe system that it flows back into. The exception to this would be if engineering data can be supplied to otherwise justify the omission of the expansion tank.

Fire Sprinkler Industry, please take careful note of this handout before bidding. Expansion tanks listed for fire sprinkler systems are very expensive. I will see to it that the bidding field is level in this area, with no exceptions, so please do not overlook this very important part of your system design. Pressure-relief valves are not allowed in place of expansion tanks because they lead to dilution of the antifreeze solution.

Antifreeze systems installed without expansion tanks where they are required, are very susceptible to leaks and burst fittings, jeapordizing fire safety, and causing great inconvenience and cost to clients, not to mention generating negative publicity for fire sprinkler systems. Enforcement action will be taken against fire sprinkler contractors who omit the expansion tank where required, or who install a non-listed expansion tank where one is required to be listed for fire service. Where required, the listed expansion tank is an important design feature, critical to the reliability of the fire sprinkler system operation.


[Updated 1-11-12 to reflect currently adopted standards with their references.]