Hot Water Cylinders vs Heat Pump Hot Water Systems

Two main types of electric water heaters are commonly found in New Zealand homes. These are the good old conventional hot water cylinder and the heat pump hot water system. Both reliably provide us with much-appreciated warm water, but what is the difference and which one suits your home best?

Hot water heat pumps are generally considered the most efficient option, however, they require a much greater initial investment, while traditional hot water cylinders are cheap to install and maintain but can require more electricity to run. Looking at upgrading your hot water heating system and wondering what you should choose? Let’s delve into what they are, how they differ and why they might be the best choice for your home!

What Is A Hot Water Heat Pump?

Hot water heat pumps are a modern water heating system that utilises a similar technology to regular air-heating heat pumps. Heat from the air is transferred into water (like a refrigerator but in reverse) which is then stored in a storage tank/cylinder ready for use. This heat pump technology is used to efficiently heat water for the whole house and can be installed inside or outside the home. 

As heat pump hot water systems only use electricity for the compressor and the fan instead of using it to heat the water directly with an electric element, they are considered a more energy-efficient hot water heating option.

How Do Heat Pump Hot Water Systems Work? 

Heat pump hot water systems extract heat from the air and transfer it to water, which is then stored in an insulated storage tank/cylinder. The heat transfer is carried out using a compressor, evaporator, condenser and refrigerant (like R32 or CO2).

Using the surrounding air to build heat the evaporator transforms the refrigerant from a liquid to a gas, and after passing this gas through the compressor (to raise the pressure and its temperature), the hot pressurised refrigerant releases its heat into the water via a heat exchange system. The refrigerant then passes through a condenser coil which causes it to transform back into a liquid and is then recycled back through the system to repeat the process.

After the water is heated, it is pumped into the top of the hot water storage tank/cylinder, filling the cylinder from the top down. Once the temperature in the cylinder has reached the desired minimum temperature of approximately 60℃, it will turn itself off (The hot water needs to be heated to 60℃ at all times to prevent Legionnaire’s disease). 

Benefits Of A Hot Water Heat Pump

· Greater Energy Efficiency. Hot water heat pumps are widely considered to be more energy-efficient largely due to lower energy use and more efficient operating costs (depending on local electricity rates and outdoor temperatures). This is because they only require electricity to drive the compressor and fan instead of generating heat from scratch with an electric element. This results in a 60 to 75% reduction in energy use while still being able to store the same volume of water making the system more efficient overall than traditional electric hot water cylinders. 

· Good Life Expectancy. Hot water heat pumps are considered safer, cleaner, and greener electric or gas cylinder systems. Typically life expectancy is around 8 – 15 years.

· Lower Emissions. Because they use much less electricity than standard electric resistance hot water cylinders, they have much lower associated emissions. 

· Cost Efficient. Hot water heat pumps use less energy on a daily basis than other hot water heating systems, which will save you money on your monthly electricity bill.

Disadvantages Of A Hot Water Heat Pump

· High Purchase And Installation Costs. The technology involved in heat pump water heaters is far more complex than traditional water heaters, which understandably results in a higher initial price tag both for installation and the product purchase. However, while the upfront cost can be higher than traditional water heaters, the energy savings over time can help balance out this initial investment.

· Air Temperatures Matter. The average air temperatures in your location can have an effect of the efficiency of your hot water heat pump. Heat pump technology performs better in warmer climates, this is because it takes more energy (effort) to draw heat from colder air. 

· Can Be Noisy. Because the heat pump operates using a fan to circulate air and a compressor, there is the associated noise that goes with these things, however these components tend to be located outside of the home in locations that minimise the impact of the noise.

· Extra Space Required. Hot water heat pump units need an adequate amount of space for installation. Whether indoors or outdoors, you will need room for the heat pump and the cylinder and a well-ventilated space with enough room around the unit for adequate airflow for optimal performance and efficiency.

· Regular Maintenance. In order for the heat pump to continue working at optimal performance levels and to prolong its life span, regular maintenance is required, including cleaning and/or replacing air filters regularly, inspecting and maintaining the integrity of the drain line, periodically draining the tank to eliminate residue and professional tune-ups.

What Is A Conventional Electric Hot Water Cylinder

Most New Zealand homes have a traditional electric hot water cylinder, these are considered the standard hot water heating option here and have been for many many many years. The conventional hot water cylinder consists of an insulated and reinforced storage tank, heating elements, and a thermostat to regulate the temperature of the water.

There are two main types of conventional hot water cylinders - low-pressure cylinders, which are generally older and smaller and have poor water pressure, sometimes a header tank in the roof space is also present – and mains pressure cylinders, which are a little more expensive, but they provide a much faster flow rate and larger capacity.

How Do Conventional Electric Hot Water Cylinders Work?

Traditional electric hot water cylinders operate on very simple principles - cold water automatically enters the storage tank when hot water is used, which results in a lowering of the overall water temperature, this triggers the thermostat, and the element turns on to heat up the water again. This continual process ensures a constant supply of perfectly heated hot water.

Benefits Of Conventional Hot Water Cylinders

· Affordability. The number one benefit of traditional hot water cylinders is that they are affordable. The cylinders are cheap to buy and install and do not generally incur any ongoing costs (until they need replacing).

· Long Life Span. Conventional hot water cylinders have a life expectancy of 10 to 15 years. 

· Reliable/Low Maintenance. Due to their simple yet hardwearing design, conventional hot water cylinders require very little maintenance and are very reliable, offering extended life expectancy.

· Easy To Shut Down. Turning the hot water cylinder off while away on holiday is easy, just flip the wall switch.

· Large Storage Capacity. Hot water cylinders come in a range of sizes to suit various requirements, so there is something to suit every situation.

Disadvantages Of Conventional Hot Water Cylinders

· Higher Electricity Costs. Conventional water cylinders are generally more costly to run than heat pump hot water cylinders on a daily basis. High electricity costs in New Zealand motivate many people to look for alternative water heating or electricity generation options.

· Slow Recovery Rate. High demand for hot water in your household may impact efficiency, as they might struggle to keep up with demand (the water gets colder the more rapidly you use it and may eventually run cold).

So, Which Hot Water System Should You Buy?

Hot water heat pumps are approximately 3-4 times more efficient than conventional electric hot water options under the right climate conditions, which means that less energy is needed to produce the same amount of hot water in optimal temperatures. A hot water heat pump is the best solution for households with adequate space for installation and living in relatively warm areas (not below 5 degrees). Hot water heat pumps are a great investment if you’re looking to save money over the longer term and don’t mind the initial upfront costs.

Traditional hot water cylinders are much more affordable and require very little, if any maintenance. They offer a tried and tested hot water heating method that reliably provides hot water for the whole family. Conventional hot water cylinders are the best choice when replacing an old cylinder in an existing home and in new homes where cold temperatures are prevalent. They are also the most cost-effective option for those concerned about making a significant upfront investment. Conventional cylinders are also particularly useful where a wetback or solar power systems are fitted.

Here at Plumbfitz, we provide reliable hot water installation and advice on a range of different hot water cylinders and are happy to discuss solutions to suit your specific requirements. If you are looking for a hot water heating solution for your new or existing home, give us a call today!