Backflow Enclosures

Backflow enclosures protect backflow preventers, pumps, and valves from vandalism and freezing temperatures. Often referred to as "hot boxes," they can be built as a cage, a fake rock, or a box-like structure made of aluminum or fiberglass. Protection from freezing requires a fully enclosed unit with a heater.

• Heated & non-heated enclosures
• Small & very large sizes
• Many different pipe-opening configurations
• Aluminum & fiberglass options
• Hard-to-find configurations

In 1996, the American Society of Sanitary Engineering released a new standard to regulate the growing backflow-enclosure industry. Enclosures built before then were often too small, overly insulated, or fitted with heaters that weren't safe — in some cases little more than a fiberglass box placed over the valves. Drainage was a major problem then, just as it remains today for indoor RPZ backflow preventers. The standard outlined those problems and how to solve them.

In 2006, the standard was updated with more testing detail and clarified that equipment enclosures designed for fluid-conveying components — not just backflow-preventer enclosures — must pass it. In 2017, it was updated again, changing some heater requirements and adding further testing.

The ASSE recommends these enclosures be installed consistent with local codes, which mostly require ASSE certification. A product can only be ASSE-approved once the manufacturer applies and their product is tested in the ASSE lab — a process that can take up to 60 days. Once a product passes, it receives a seal of approval.

Owners increasingly pressure architects, engineers, and contractors to design and build projects fast — and under that pressure, RPZ backflow-preventer placement often gets little thought, with everyone defaulting to what they've always done. That status quo deserves a second look: RPZ devices generally should not be installed indoors.

RPZ in a bottling plant: A bottling plant decided to move its RPZ valve from inside the building to outside. Indoors, the device sat next to transformers and electrical panels. An RPZ's job is to dump water during normal operation — so picture that happening next to switchgear. Of more than 1,000 design engineers we spoke with over the past year, nearly all were surprised by what an indoor RPZ failure can do.

Can the risk be managed indoors? Engineers can add a floor drain or floor sink; manufacturer flow rates help size them. Enlarging the drains is the most reliable fix, though not always practical. With all the evidence available, the safer path on the next project is simply to move the device outside into a proper enclosure.

An RP — the Reduced-Pressure-Principle Backflow Prevention Assembly — required for a project must be installed above ground and inside an enclosure, with the exception of irrigation assemblies that are winterized. Officials found that installing assemblies in utility vaults is a poor idea: vaults flood, rainwater can rise above the test cocks and create a cross-connection risk, and there's no safe entry for testers. By 2008, assemblies were being installed outside and above ground in heated enclosures.

Hefner noted that one large building owner felt above-ground assemblies created a real eyesore — but good landscaping can keep an enclosure hidden even in a front yard, and it starts with early conversation. A design engineer who reviews the water purveyor's requirements and the site's features (parking lots, traffic islands, city streets) has a great starting point, and should talk with a landscape architect about ways to disguise the enclosure.

Early discussion also makes it easier to meet the clearances tied to backflow-prevention assemblies, their enclosures, and surrounding landscaping. To leave room for testing, Lynchburg's Manual of Specifications calls for the following clearances around each assembly:

• Two feet in front of the outermost edge of the RP, and two feet behind
• One foot on both ends of the RPZ

Bushes, flowers, and trees need enough space from the enclosure to maintain those allowances. The clearances were settled with help from the International Plumbing Code (confirming the space needed for testing, maintenance, and replacement) and from discussions with master plumbers and state-certified backflow technicians — many of whom had been getting cut by branches or simply couldn't get inside overgrown enclosures.

Hefner stresses that owners should think about landscape design up front: bushes that start small will grow, and must be kept trimmed. Lynchburg now adds language to site plans stating that landscaping and other site features must not impact the required allowances for any RP or RPGA — now or in the future. Working with the design engineer (and ideally a landscape architect) early tends to save money over the long haul.