Hurlcon Astralpool HX 120 Gas Heater Heat Exchanger - HX120 also WX series
Hurlcon Astralpool HX 120 Gas Heater Heat Exchanger - HX120 also WX series is backordered and will ship as soon as it is back in stock.
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Astralpool Hurlcon HX 120 heat exchanger (tube bundle) replacement for all Hurlcon and Astralpool HX, WX, and WWDG series heaters. Also known as the tube bundle, or heater coils. Tubes are made of cupro-nickel.
Where replacing a heat exchanger due to a leak, we strongly recommend replacing the Manifold & Seals.
Important Information on Heat Exchangers for Pool & Spa Gas Heaters
The CuproNickel and Copper components used in these heat exchangers have remained consistent for nearly 30 years. This is a time-tested, proven design known for its durability and thermal efficiency in pool and spa heating systems. We regularly see heaters with these heat exchangers last over 20 years when cared for.
How They Work - Pool and spa gas heater heat exchangers transfer heat from the combustion chamber to the water that circulates through the unit. Materials like Copper and CuproNickel are used due to their excellent thermal conductivity, helping the system heat water quickly and efficiently.
Common Cause of Failure: Chemical Corrosion. The most frequent cause of failure in these heat exchangers is chemical corrosion, not mechanical or manufacturing faults.
Signs of Corrosion Damage:
- Tiny pinholes forming in the tubing or fittings (particularly on elbows)
- Blue or green discoloration in the water
- High copper levels detected in water tests
These symptoms mean the heat exchanger has been chemically attacked.
Why Spa and Pool Heaters Are Especially Vulnerable
Pool and spa heaters operate under high temperature conditions, which can amplify the effects of poor water chemistry.
Spa water, in particular, is often treated with high levels of sanitizer and kept at elevated temperatures, increasing corrosive risk.
Low pH (acidic water) and the use of bromine tablets are especially harsh on heat exchangers.
Even a brief imbalance in water chemistry can lead to permanent damage.
Pro Tips: Test and balance your pool or spa water weekly to protect your investment.
Maintain:
- pH between 7.2 – 7.8
- Total alkalinity between 80 – 160 ppm
- Calcium Hardness: 150-400ppm
- Avoid use of Bromine tablets if possible
- Never use Chlorine tablets
Warranty: These heat exchangers include a 1-year limited warranty. However, damage caused by chemical corrosion is not covered under warranty, as it is a result of water chemistry mismanagement rather than a product defect.
Learn More:
For detailed guidance on identifying and preventing chemical corrosion, click: Corrosive Water Damage
Weight When New: 4.5-4.6kg - If heat exchanger weighs less than the above, the copper has been eroded away. If it weighs more, it may be full of calcium.
In plumbing, named sizes are not the actual measurements. A pipe called “50mm” or “2"” does not measure 50 mm across. Instead, it follows nominal sizing, an internationally-standardised naming system.
Use the Outside Diameter (OD) to check your pipe against fittings. Below is a quick reference for common spa & pool pipe sizes:
| Imperial Name | Metric Name | Pipe Diameter (OD) |
|---|---|---|
| 1" | 25 mm | ~33.4–33.7 mm |
| 1.5" | 40 mm | ~48.1–48.4 mm |
| 2" | 50 mm | ~60.2–60.5 mm |
| 2.5" | 65 mm | ~75.2–75.5 mm |
These are nominal sizes and are designed to fit matching fittings — not to measure exactly what their name suggests.
Understanding Plumbing Sizes & Nominal Measurements
Plumbing sizes can be confusing. PVC and many other pipe systems use nominal sizes—the size is a name, not the exact measured dimension. This convention is used across most pool and spa systems so that pipes and fittings remain compatible.
Why pipe sizes don’t match the measurements
The Nominal Pipe Size (NPS) system standardises pipe dimensions so that pipes, fittings, valves, and accessories interoperate. Plumbers work with these nominal names every day, but DIYers can be tripped up if they try to match by a tape-measure alone.
How to Measure Pipe Correctly
-
Pipe size is identified by:
- The pipe’s Outside Diameter (OD).
- The fitting’s Inside Diameter (ID) (socket opening).
- Pipe Class / Schedule (e.g., Class 9, 12, 18 or Sch 40) relates to wall thickness and therefore the Internal Diameter (ID) and pressure rating.
- The outside diameter of a fitting is not useful (wall thickness varies by manufacturer).
PVC Pressure Pipe AS/NZ 1477 Dimensions1:
Common nominal sizes with typical outside diameters and indicative inside diameters by class.
| Imperial Name | Metric Name | Outside Diameter (OD) | Class 9 IDº | Class 12 IDº | Class 18 IDº |
|---|---|---|---|---|---|
| 1/2" | 15 mm | ~21.2–21.5 mm | 18.3 mm | 17.8 mm | |
| 3/4" | 20 mm | ~26.6–26.9 mm | 23.7 mm | 22.4 mm | |
| 1" | 25 mm | ~33.4–33.7 mm | 30.5 mm | 29.8 mm | 28.1 mm |
| 32 mm | ~42.1–42.4 mm | 38.5 mm | 37.5 mm | 35.4 mm | |
| 1.5" | 40 mm | ~48.1–48.4 mm | 45.2 mm | 44.1 mm | 42.8 mm |
| 2" | 50 mm | ~60.2–60.5 mm | 55.2 mm | 53.7 mm | 50.5 mm |
| 65 mm | ~75.2–75.5 mm | 68.9 mm | 67.0 mm | 63.2 mm | |
| 2.5" | ~73 mm |
- º Internal diameters vary slightly by manufacturer and class.
- 1 Not all pool/spa fittings match these dimensions exactly. Some do not follow Australian or international standards. Chinese spas may use proprietary fittings.
Hose & Tube Dimensions
Common flexible hose sizes used in pool/spa systems (approximate IDs).
| Imperial Name | Metric Name | Inside Diameter (ID) |
|---|---|---|
| 3/8" | 9–10 mm | ~9 mm |
| 3/4" | 19 mm | ~19 mm |
BSP – British Standard Pipe Thread Sizes
BSP thread names are also nominal. The thread OD will not equal the nominal name.
| BSP Thread Size Naming | Outside Diameter (mm / inch) | TPI |
|---|---|---|
| 1/16" BSP | 7.7 mm / 0.304" | 28 |
| 1/8" BSP | 9.7 mm / 0.383" | 28 |
| 1/4" BSP | 13.16 mm / 0.518" | 19 |
| 3/8" BSP | 16.66 mm / 0.656" | 19 |
| 1/2" BSP / 15 mm | 20.99 mm / 0.825" | 14 |
| 5/8" BSP | 22.99 mm / 0.902" | 14 |
| 3/4" BSP / 20 mm | 26.44 mm / 1.041" | 14 |
| 7/8" BSP | 30.20 mm / 1.189" | 14 |
| 1" BSP / 25 mm | 33.25 mm / 1.309" | 11 |
| 1-1/4" BSP | 41.91 mm / 1.650" | 11 |
| 1-1/2" BSP / 40 mm | 47.80 mm / 1.882" | 11 |
| 2" BSP / 50 mm | 59.61 mm / 2.347" | 11 |
| 2-1/4" BSP | 65.71 mm / 2.587" | 11 |
| 2-1/2" BSP | 75.18 mm / 2.960" | 11 |
| 3" BSP | 87.88 mm / 3.460" | 11 |
| 4" BSP | 113.03 mm / 4.450" | 11 |
| 5" BSP | 138.43 mm / 5.450" | 11 |
| 6" BSP | 163.83 mm / 6.450" | 11 |
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