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Specialists in Electric Hot Water Cylinders

Unvented Cylinders vs. Instant Water Heaters: What Homeowners Should Know

14 November 2023

Having hot water available when you open the tap is an incredible thing that most of us take for granted. That is, until your water heater fails. Then it becomes apparent just how much we depend on these devices in our lives.

If you’re replacing an aging appliance, building a new home, or putting an extension on your existing home, it’s important to make the right choice in water heaters. Today, you have new options. One of those is an instant water heater. How do these devices compare to unvented cylinders?

What Are Instant Water Heaters?

Instant water heaters do precisely what it sounds like – they heat water on demand for immediate use. They don’t store heated water in a cylinder. You might be more familiar with them as “tankless” water heaters, instantaneous water heaters, or on-demand water heaters.

They’re usually small units installed on a wall in the home. Water from the mains feeds into the appliance, and a heating element or gas-fired burner warms the water when you open the hot tap at the sink to wash dishes or in the shower for bathing.

How Do They Compare?

Today, unvented cylinders have become the most popular type of “thermal store” water heaters in the UK. They’re reliable, come in a range of capacities to fit your water usage needs, can be installed almost anywhere in the home, and provide mains pressure hot water at every tap, no matter where it might be located in relation to the cylinder. That’s a far cry from what old-style vented cylinders could do. But how do newer instant water heaters compare?

Pressure: You get mains pressure water at all the taps in your home with both unvented cylinders and tankless water heaters.

Quantity of Hot Water: With an unvented cylinder, you’re limited to the amount of hot water in the cylinder at any one time. The cylinder begins refilling as you use water, but it takes time to heat it, so you’ll notice that your water goes from hot to warm and then cold with heavy use.

With a tankless design, you theoretically have as much hot water as you need because it’s heated as you need it. You could continuously draw hot water from the kitchen sink and never run out.

However, it only works that way in some situations. Instant water heaters don’t have the capability of supplying hot water to multiple taps in the home indefinitely. So, you might be having a lovely shower, but when someone decides to run the hot water in the kitchen at the same time, your water temperature will drop in the shower. With a three-phase electrical supply, you could in theory supply water to a shower, a bath, and a basin sink. With a single-phase electrical supply, you could supply hot water to a shower and basin/sink.

Vented or Unvented: You also have a choice of vented or unvented design. Vented units are unpressurised while unvented are pressurised and fall under G3 regulations.

Which is right for your needs? At EasyFlow, we can help you make an informed decision that ensures you have plenty of hot water for all your needs. Contact us today to learn more.


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