Control Valve Connection Types

This blog is designed to help contractors, engineers, and facility professionals better understand the different control valve pipe connection types commonly found in hydronic HVAC systems—from threaded and sweat connections to flanged, grooved, union, and press-fit options.

Readers will learn what each connection type is, where it is most commonly used, the pros and cons of each approach, and how factors like installation speed, serviceability, leak prevention, labor requirements, and pipe size can influence the right selection. Whether you are working on fan coils, AHUs, central plants, retrofit projects, or new construction, this guide provides practical, field-driven insight to help you specify the right valve connection for the application with greater confidence.

In HVAC hydronic systems, control valve pipe connections determine how the valve physically ties into the piping system.

The choice impacts install time, serviceability, pressure rating, and application fit.

Here’s a clean breakdown of the main types you’ll see in the field

connection types

Threaded (NPT) Connections

What it is: National Pipe Thread (NPT thread) male or female threaded ends. .

Where used: Small valves (typically ½” to 2”)
Fan coils, reheat coils, small AHUs

Pros: Low cost

Easy to install (no special tools beyond pipe wrenches)
Widely available

Cons: Can leak if not sealed properly
Not ideal for frequent removal
Limited to smaller sizes

connection types

Sweat (Soldered) Connections

What it is: Designed to be soldered directly to copper pipe.

Where used: Copper piping systems
Common in light commercial and residential

Pros: Clean, compact install

Good for tight spaces
No threads to leak

Cons: Requires torch/soldering skill

Harder to replace/remove

Heat can damage valve internals if not handled correctly

connection types

Flanged Connections

What it is: Flat faces bolted together with a gasket between flanges.

Where used: Larger pipe sizes (2” and up, especially 2.5”+)
Chilled water mains, boiler plants, central plants

Pros: Very robust and leak-resistant

Easy to remove/replace
Handles high pressure/temperature

Cons: Higher cost

Requires space for bolts and clearance
Heavier

connection types

Grooved (Victaulic-Style) Connections

What it is: Uses grooved pipe ends with a mechanical coupling (often associated with Victaulic systems).

Where used: Medium to large commercial systems
Fast-track construction projects
Retrofit jobs

Pros: Fast installation (no welding or threading)

Flexible (allows some movement)
Easy maintenance/removal

Cons: Slightly higher material cost

Requires grooving tools
Not as rigid as flanged in some cases

connection types

Union Connections

What it is: A threaded connection with a built-in union for easy removal.

Where used: Smaller valves where serviceability matters
Often paired with threaded valves

Pros: Easy to disconnect/remove valve

Great for maintenance

Cons: Still limited by threaded connection constraints

Slightly higher cost than standard threaded

connection types

Press-Fit Connections (ProPress, etc.)

What it is:Mechanical press connection using specialized tools (e.g., Viega).

Where used: Increasingly common in commercial installs
Retrofit and fast installs

Pros: Very fast install

No flame (safer than soldering)
Consistent connection quality

Cons: Requires expensive press tool

Fitting cost is higher
Still gaining adoption in some markets

connection types

What’s the Most Common?

Most common overall: Threaded (NPT) — dominates smaller HVAC control valves (=2”)

Most common in larger commercial systems: Flanged and Grooved

Fastest-growing trend: Press-fit (ProPress-style) due to labor savings and safety

Selection Insight (from a controls standpoint)

FCUs / VAV reheat coils: Threaded or sweat

AHUs (mid-size): Threaded ? flanged transition around 2”

Central plants / mains: Flanged or grooved

Retrofit / labor-sensitive jobs: Press-fit or grooved