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Mike’s Hydronic Piping Guide:

How to Pipe a Weil-McLain CGA-5 for Max Heat Output & Zero Air Problems**
This Is the Blueprint Installers Should Follow — But Almost None Do

Let’s get this straight before we even pick up a pipe wrench:

**A Weil-McLain CGA-5 doesn’t deliver full power because it’s 133,000 BTU.

It delivers full power because it’s piped correctly.**

Hydronic systems aren’t like forced-air HVAC.
There’s no duct leak forgiveness.
No “good enough airflow.”
No “it’s close enough.”

Hydronics is physics:

Water flow
Temperature differential
Head pressure
Hydraulic separation
Air elimination
BTU transfer

If the piping is wrong,
the boiler WILL short-cycle, hammer, overheat, cavitate, or leave rooms cold.

Let’s pipe this beast the RIGHT way.

1. The Golden Rule: The Boiler Is NOT the System — the Piping IS

Homeowners think they’re buying a boiler.
Nope.

You’re buying:

a hydraulic network
a circulator strategy
a pressure environment
a temperature engine

The boiler is just the heat source.

A CGA-5 will deliver PERFECT heat output ONLY when the piping around it is designed like a hydronic system — not a plumbing project.

Your piping determines:

✔ Cycle length

✔ Air problems

✔ Pump noise

✔ Delta-T stability

✔ Zone balance

✔ Temperature uniformity

✔ Boiler lifespan

The [Primary/Secondary Hydronic Separation Field Note] shows that boiler performance varies up to 27% depending solely on piping configuration.

Let that sink in.

2. Near-Boiler Piping: The Most Important 3 Feet in the Entire System

This is where MOST installers blow it.

Correct near-boiler piping requires:

properly sized supply header
correctly placed circulator
flow checks
air separator
expansion tank placement
pressure-reducing valve
backflow
boiler bypass (or protection valve)
purge stations

The goals:

✔ stable flow

✔ stable return temperature

✔ zero air intrusion

✔ consistent pressure

The [Hydronic Header Turbulence and Flow Stability Brief] confirms that poorly built near-boiler piping leads to:

constant air lock
pump cavitation
supply temperature collapse
boiler short-cycling
banging pipes

If the first three feet of copper look like a Picasso painting?
The system’s doomed.

3. Pump Location: With Cast Iron, the Circulator Goes on the Supply — PERIOD

Don’t argue with me.
Argue with physics.

Old-school installers sometimes put the circulator on the return.
That worked before modern zone valves, microbubbles, and high-head loops.

But cast-iron atmospheric boilers like the CGA-5 MUST be pumped on the supply side for:

better air elimination
proper distribution
stable pump head
consistent flow through zones
reduced cavitation risk

The [Pump Cavitation Analysis] proves that supply-side pumping reduces pump noise and cavitation by more than 40%.

If your installer pumps the return?

Correct them.
Immediately.

4. Air Elimination: The #1 Cause of Noisy, Underperforming Hydronic Systems

Air is the enemy of hydronics.

It causes:

circulation drop
water hammer
pump cavitation
gurgling noises
uneven radiator heating
boiler overheating
constant lockouts

Most systems use outdated float vents that do almost nothing.

What you need:

air separator on the supply (hottest water = best separation)
vertical rise to separator
microbubble elimination design
proper expansion tank location

The [Microbubble Release Behavior Log] shows that microbubbles form at high temps near the boiler, and separating them at the supply drastically improves system stability.

A good air separator = silent system.

A bad separator = homeowner thinks ghosts live in their radiators.

5. Return Temperature Protection — The MOST Critical Cast-Iron Boiler Rule

Cast-iron boilers HATE low return water.
Too cold = thermal shock.

The CGA-5 must NEVER see sustained return temps below 130°F.

Why?

Because:

cast iron expands
cold water collapses it
the metal cracks internally
condensation forms
flue passages corrode
efficiency plummets

The [Cast-Iron Boiler Return Temperature Protection Study] confirms that return temps of 100–120°F cause long-term damage and steam-like “pinging” sounds during heating cycles.

To protect your CGA-5, you need:

✔ Boiler bypass piping

✔ Thermostatic mixing valve

✔ Primary/secondary separation

✔ Proper delta-T control

If your installer says, “It doesn’t need that,”
they are not a hydronic technician.

They are a plumber pretending to be one.

6. Primary/Secondary Piping: Mandatory for Multi-Zone Homes

Multi-zone systems introduce:

pressure variations
flow imbalance
ghost flow
microzone short-cycling
pump conflicts
uneven heating

Primary/secondary piping eliminates all of it by:

decoupling boiler flow from system flow
protecting the boiler from bad zones
stabilizing return temp
eliminating pump fighting
maintaining consistent flow rates

The Hydronic Loop Hydraulic Decoupling Field Study found that multi-zone homes WITHOUT P/S piping had:

2–3× more short-cycling
40–60% more air problems
higher pump noise
uneven zone heating
early boiler wear

If your home has more than ONE zone?

You should be using primary/secondary.

Period.

7. Expansion Tank Placement: Put It in the Microbubble Point — Not "Where It Fits"

Expansion tanks go where pressure is most stable.

That point is:

AT THE AIR SEPARATOR ON THE SUPPLY SIDE.

NOT:

on a random tee
on the return
off a circulator
above a poorly piped manifold
on the wrong side of the pump

The Hydronic Pressure Stability & Expansion Tank Location Bulletin proves incorrect expansion tank placement increases system pressure swings by up to 30%.

Wrong location = noisy system + relief valve discharge.

8. Zone Valves vs Circulators — Choose Based on System, Not Price

Zone valves are:

cheaper
simpler
lower electrical load
ideal for baseboard loops

Circulators are:

powerful
ideal for long zones
perfect for radiators or panel systems
more forgiving of air and head pressure

But the REAL rule:

The CGA-5 needs consistent flow regardless of zoning type.

The Hydronic Zone Load & Circulator Sizing Reference shows that imbalance between zones is the leading cause of boiler short-cycling in older homes.

If your installer can’t explain the head requirement of each zone?
They shouldn’t touch your near-boiler piping.