#453 – Why You Can’t Install Dry Sprinklers with Mechanical Tees, Elbows & More

NFPA 13 and manufacturers prohibit using specific fittings with dry fire sprinklers—here’s why!

Dry fire sprinkler heads minimize heat loss from climate-controlled spaces into cold ones and prevent water from getting trapped and freezing, impairing sprinkler operation. Dry sprinklers are unique pieces of fire protection equipment with unique rules.

Among these rules are those issued by manufacturers prohibiting installing dry heads into specific fittings, including mechanical tees, couplings, elbows, welded outlets, and gasket-sealed outlets.

To learn why and the risks of not following manufacturers’ installation instructions, read on:

NFPA and manufacturer rules for fittings

The National Fire Protection Association’s NFPA 13: Standard for the Installation of Sprinkler Systems largely defers to manufacturers’ instructions for the appropriate fittings for dry heads:

From the 2022 edition of NFPA 13

15.3.4* Dry sprinklers shall only be installed in fittings as specified by the sprinkler manufacturer.

However, the annex provides some context:

A.15.3.4 Generally dry sprinklers are installed in tees. Dry sprinklers should never be installed in 90-degree elbows. Some manufacturers allow installation of dry sprinklers in couplings, CPVC adapters, and so forth.

So, what do the manufacturers say?

Forbidden fittings for dry sprinklers

Reliable’s “Sprinkler Installation Warnings!!” document summarizes the common no-nos (emphasis added):

Dry Sprinklers must not be installed into couplings, elbows, welded outlets, gasket sealed outlets, or mechanical tees.

Viking offers similar rules, such as these on its data sheet for standard response dry sprinklers, along with the reasons (emphasis added):

1. DO NOT install the dry sprinkler into a threaded elbow, coupling, or any other fitting that could interfere with thread penetration. Such installation would damage the brass seal.

2. DO NOT install dry sprinklers into couplings or fittings that would allow condensation to accumulate above the seal when the sprinkler is located in an area subject to freezing.

Allowed fittings

The go-to fittings for installing dry sprinklers in wet and dry systems are malleable or ductile iron tees (ANSI B16.3 Class 150) or cast-iron tees (ANSI B16.4 Class 125) unless the system is CPVC. Manufacturers approve specifically compatible and listed CPVC adapters and tees for installing dry heads in wet CPVC systems.

Reliable threaded tee diagram
This diagram from Reliable’s data sheet for Model F3-56 sprinklers illustrates some proper threaded tee configurations.

In addition, some manufacturers may provide an otherwise prohibited fitting type specifically designed for a dry sprinkler. For example, Tyco allows DS-ECC Dry-Type Sprinklers to be installed “in the 1 in. NPT outlet of a GRINNELL Figure 730 Mechanical Tee” within a wet system.

So, to summarize, the basic approved fittings are:

  1. Iron pipe threaded tees
  2. Appropriately listed CPVC tees and adapters
  3. Anything else a specific manufacturer’s data sheet and instructions allow

Why are mechanical tees, elbows, and other fittings inappropriate for dry sprinklers?

There are two primary reasons certain fittings aren’t suitable for dry sprinklers, as alluded to in Viking’s installation instructions:

  1. Some fittings interfere with and can damage a dry sprinkler’s threads and inlet/brass seal.
  2. Dry heads’ brass seals must penetrate to a specific depth, and improper fittings can leave depressions where water will pool after a system activation or due to condensation. Draining the system doesn’t get rid of this water, which can freeze around the brass inlet and create an ice blockage.

Let’s examine these impacts in action. First, we’ll look at a correct dry sprinkler installation into an iron tee:

Proper dry sprinkler installation

Above, note the elevated position of the inlet/brass seal. When a properly pitched dry system is drained, there is minimal opportunity for water to collect and potentially freeze. Now, let’s look at an incorrect installation into a mechanical tee:

Dry sprinkler installed in mechanical tee

In this case and the photo above, the dry sprinkler’s threads and inlet don’t fully penetrate into the fitting and pipe, leaving a deep divot. Notice how the water has drained from the pipe-interior cutaway, but leftover water—which may freeze—pooled above the sprinkler.

We also created a pipe cutaway showing a welded outlet installation. Below, see how the position of the dry sprinkler’s inlet is low and water again pools:

Dry sprinkler installed in welded outlet

Finally, here’s an example of why dry sprinklers shouldn’t go into elbows:

Dry sprinklers and elbows

In the interior image on the left above, the brass seal may contact the curvature of the elbow, damaging it and impairing sprinkler operation.

Follow the manufacturers’ installation rules!

Again, there are some general rules for installing dry sprinklers: threaded iron tees or specifically designed CPVC tees or adapters are the go-to fittings, and elbows, mechanical tees, welded outlets, couplings, and gasket-sealed outlets are generally off the table.

However, there are exceptions, so the real rule is this: always look at the dry sprinkler’s data sheet or a manufacturer’s separate installation instructions. As NFPA 13 notes, “Some manufacturers allow installation of dry sprinklers in couplings, CPVC adapters, and so forth.” So, a given sprinkler may have specific fittings that provide additional options.

All dry heads are custom-made, so contact QRFS directly to buy them. Be sure to check out our previous blog on how to order dry sprinklers with the right barrel length. Email us at support@qrfs.com or call 888-361-6662 with any questions or to place an order!

This blog was originally posted at blog.qrfs.com. If this article helped you, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.

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