State Water Heater Water Heater Brochure

Secondary HX-Stainless Steel 316L
Primary HX
Commerical-Grade
Copper
Drum
Coil
Hot Water Outlet
Bypass Valve
Cold Water
Inlet
Flow
Sensor
Flow Adjustment
Valve
SECONDARY HEAT EXCHANGER 316L STAINLESS STEEL
(CONDENSING MODELS ONLY)
The secondary condensing heat exchanger is made of high-quality 316L stainless steel. This is where the rest of the
heat transfer occurs. Due to the lower temperature acidic condensation occurs, and stainless steel is required in order
to avoid corrosion.
For condensing heat exchangers, it is more suitable to use 316L stainless steel because of the extreme environment
(heat, acidic condensation, chloride) that the material is subjected to.
PRIMARY HEAT EXCHANGER:
COPPER VS.
STAINLESS STEEL
• Heat transfers 25 times more readily
through copper than stainless steel.
Consequently, for the same amount
of heat transfer, stainless steel heat
exchangers need to be larger than
copper heat exchangers, leading to a
larger pressure loss.
• At higher temperatures, it is the nature
of stainless steel to become prone
to a number of problems not usually
experienced at room temperature. It
is vulnerable to pitting corrosion and
stress corrosion cracking (SCC).
• Stainless steel is NOT better for
durability because it is harder.
Hardness causes the material to
become brittle. Stainless steel
will crack after numerous cycles
of thermal expansion/contraction,
especially with chloride in the
water. Copper heat exchangers
are less brittle and better suited
for expansion/contraction without
cracking.
• In a dual heat exchanger design,
corrosion is not a big concern
in the non-condensing primary
heat exchanger because no
condensation forms on the exterior
of the pipes. Stainless steel is
unnecessary for this stage.
Note: 140, 240, and 340 condensing line units use
C1220 copper and do not have a bypass valve
* Diagram represents 540
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