What are the pros and cons of having my backflow preventer inside vs. outside?

Indoor: pros

• Freeze protection. This is the biggest advantage in cold climates. A frozen device can crack, leak, or take out your water service.
• Less vandalism and theft. Brass assemblies are a known theft target, and indoors there’s no damage from vehicles or landscaping.
• Cleaner look. Nothing sits in front of the building.

Indoor: cons

• Discharge and flood risk. An RPZ-type device can dump a large volume of water from its relief valve. Without a drain or pump hole, there is real water-damage liability.
• Clearance and access. The device needs working room around it and height off the floor. The annual test also needs access, which may mean disrupting tenants or occupants.
• Shutdown during testing or repair. Water to the building is interrupted, which is harder to schedule around when the device is inside an occupied space.
• Leak damage. Any leak or failure happens over finished floors and finishes rather than outside.

Outdoor: pros

• Discharge goes outside. There’s no interior flood risk.
• Easy access. Testers and the water utility can reach the device without entering the building, with no disruption to tenants or occupants.
• Fewer clearance problems. It’s easier to meet code clearances, and it often satisfies utilities that want the device near the meter or property line.
• Simpler retrofits. There’s less interior piping and construction.
• Frees up interior space. No mechanical room footprint is needed.

Outdoor: cons

• Freeze risk. In cold climates, the device needs an insulated, heated enclosure (often with heat trace), which adds installation and ongoing electrical costs. Without one, freeze damage is a real possibility.
• Theft and vandalism. The device is exposed, so theft is possible.
• Weather and impact damage. Snow, ice, plows, mowers, and vehicles are all hazards.
• Flooding and submersion. The device can’t sit in a pit or low spot that can fill with water, since that creates a cross-connection risk. It must be mounted above grade.
• Appearance. Enclosures can be unsightly, and landscaping may be needed to hide them.
• Winter testing and repair. Work is less pleasant, and sometimes harder, in cold or wet weather.

The bottom line: In the Northeast, location depends on use. Seasonal devices, such as those on irrigation or summer water systems, are typically installed outdoors and removed or drained before freezing weather. Year-round devices, such as those on fire systems, are generally installed indoors or in heated enclosures to prevent freeze damage.