Hunson Model RT Direct Mains Pressure Cylinders — What You Need to Know
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Hot‑water cylinders have changed a lot over the decades — and among the pioneers was the Hunson Model RT. Once celebrated for delivering a better shower experience, it now belongs to a bygone era. In this guide we explain what made the Hunson RT special, why it was discontinued, what challenges came with it, and what homeowners should consider today when replacing an old RT cylinder.
What Was the Hunson Model RT?
Back in the 1970s, when most hot water cylinders in New Zealand were copper low‑pressure units, the Hunson Model RT stood out. Traditional cylinders relied on gravity or header tanks — and pressure was limited by the copper brazing seams, making them ill-suited for high-pressure mains supply.
The Hunson RT introduced an innovative approach: it combined the familiar storage capacity of a “low‑pressure style” tank with a heat‑exchanger coil that supplied mains‑pressure hot water — at least to the shower. Essentially, it aimed to give homeowners a stronger shower pressure while still using a copper-based cylinder.
At the time, this was seen as a leap forward — offering a semi‑instant hot water experience for showers, while the rest of the house still operated on conventional low‑pressure plumbing.
Why Was the Hunson RT Discontinued?
Although the Hunson RT was a clever workaround for its time, advances in hot‑water cylinder technology eventually made it obsolete. There are a few key reasons:
- Pressure limitations of copper construction: Copper and brazed seams simply weren’t designed to handle sustained mains pressure — whereas modern cylinders use welded steel construction which is far stronger and more reliable under mains pressure.
- Evolving hot‑water demands: Since the 1970s, household expectations have changed. Modern families are likely to run multiple hot water outlets simultaneously — showers, dishwashers, washing machines. The Hunson RT, designed to deliver mains pressure to only one outlet (usually the shower), no longer meets these demands.
- End of lifespan: Many Hunson RT cylinders are now decades old — beyond their expected service life — making replacement inevitable.
Because of these factors, the Hunson RT line was phased out, and is no longer produced or recommended as a mains‑pressure cylinder today.
What Were the Trade‑offs and Challenges with Hunson RT
Even though the Hunson RT was advanced for its time, it came with compromises. Homeowners replacing an RT cylinder should be aware of these:
- Semi‑hybrid pressure behaviour: The RT was neither a traditional low‑pressure cylinder nor a full modern mains‑pressure cylinder. Its design delivered mains pressure to the shower via a heat exchanger — but taps, baths, and laundry stayed on low‑pressure supply. That meant inconsistency in water flow throughout the house.
- Incompatibility with modern plumbing standards and tapware: As modern homes shifted to mains‑pressure systems, tapware and mixers were designed for equal pressure. The RT’s hybrid pressure output made it harder to justify or retrofit modern tapware without risk of mismatched flow.
- Risk of inadequate output under demand: Since only one outlet would get mains pressure, running multiple outlets or high-demand appliances simultaneously often resulted in poor performance — an unacceptable limitation by today’s standards.
- Maintenance and reliability concerns: The complexity of the dual‑mode design (storage plus coil) increased maintenance demands; and over time, copper and weld seams age — making the system less dependable compared to modern welded‑steel, fully mains‑pressure cylinders.
In short: while the Hunson RT was a clever stop‑gap solution for a time, its compromises make it a poor fit for modern hot‑water expectations.
What to Consider When Replacing a Hunson RT Cylinder
If your home currently has a Hunson RT cylinder — or if you suspect it does — here are important considerations when replacing it:
- Upgrade to a full mains‑pressure cylinder: Modern mains‑pressure cylinders (welded steel, enamel‑lined or stainless steel) are the standard for new installations. They deliver equal, robust pressure to all outlets — showers, taps, appliances — and suit modern tapware and plumbing.
- Check cylinder size and household demand: Ensure the new cylinder capacity matches your household’s hot water usage (e.g. number of people, simultaneous showers, appliances). For typical Kiwi households, cylinders starting around 180 L are common; larger households may need more.
- Verify compliance with safety and water‑use regulations: Modern cylinders must have proper safety valves (e.g. temperature–pressure relief, cold‑water expansion valves if required), and meet current building code requirements.
- Upgrade tapware if needed: Because older tapware may not be designed for mains pressure, it’s usually best to upgrade taps, mixers, shower roses etc. when installing a new cylinder — to ensure correct flow and avoid leaks or damage.
- Budget for proper installation: Switching from a hybrid RT to a modern mains‑pressure cylinder often involves more than just swapping tanks — you may need new valves, waste‑pipes, updated plumbing, and adequate drainage.
Exploring alternative options:
While Hunson hot water cylinders may no longer be available, there are numerous alternative options to consider when replacing your hot water cylinder. Here are a few popular choices:
Rheem VE MP Range:
- 180L – 488x1720mm with 2kW or 3kW element; 580x1166mm in 3kW only
- 250L – 580x1555mm in 3kW only
- 300L – 580x1815mm in 3kW only
Rheem SS MP Solar Ready In/Outdoor Range:
- 180L – 488x1770mm in 2kW or 3kW
- 250L – 580x1620mm in 3kW only
- 300L – 580x1910mm in 3kW only – pair with Reclaim CO2 Heat Pump Water Heater for industry-leading efficiency
Rinnai SS MP Range:
- 180L – 550x1300mm in 2kW or 3kW
- 250L – 550x1730mm in 2kW or 3kW
- 300L – 550x2045mm in 2kW or 3kW
- LPG – Rheem 26L/min continuous flow water heater
Why The Cylinder Guys Recommends Upgrading to a Modern Mains‑Pressure Cylinder
If you’re still using an old Hunson RT cylinder — or unsure what kind of system you have — contact us today. We’ll assess your home’s hot water needs, recommend the right modern cylinder, and handle installation or upgrade properly. With The Cylinder Guys, you get a hot water setup that’s safe, efficient, and built for today’s New Zealand home.