Got an electric-only home and wondering how to keep your hot water bills under control? Without a gas supply, the choice between an instant electric water heater (like an electric shower) and a hot water tank with immersion heaters becomes crucial. Let’s break it down and tackle the burning questions, such as:
- What’s cheaper: an instant water heater (example: electric shower) or a hot water storage tank?
- Does better efficiency always mean lower costs? Maybe NOT
- Is an electric shower really as expensive to run as people say?
- Are overnight economy tariffs worth it for hot water?
- How can you make immersion heaters cheaper to use?
- What’s the most cost-effective way to heat water in an all-electric home?
- I have no gas supply, what is the cheapest hot water system?
- Electric showers I know but what about the kitchen sink hot water or bathroom basin hot water?
Grab your favorite drink (heated however you like!) and let’s explore the pros, cons, and clever tips to make your water heating efficient and affordable.
Introduction
Heating water is one of the most energy-intensive activities in any household. For homes without a gas supply, electric water heating becomes the default choice. This article compares two popular methods: instant electric water heaters, which heat water on demand, and hot water cylinders with immersion heaters, which store heated water for later use. We’ll consider energy efficiency, installation costs, and lifestyle factors to provide a balanced perspective.
The Basics, instant water heaters and hot water storage tanks
Instant Water Heaters
An instant electric water heater warms water on demand, eliminating the need for storage. It heats water directly as it flows through the unit.
- Advantages: Space-saving, energy-efficient, no heat loss.
- Disadvantages: Limited flow rates, higher upfront cost, dependent on electricity tariffs.
Hot Water Tanks with Immersion Heaters
Hot water cylinders store a large volume of preheated water, usually heated overnight using immersion heaters.
- Advantages: High capacity for simultaneous use, economical with off-peak tariffs.
- Disadvantages: Heat loss, bulky size, potential energy waste when not in use.
Current Standard in Most Homes
Hot water tanks remain the default in UK homes due to historical reliance on immersion heating and their compatibility with central heating systems. According to the Energy Saving Trust, most homes still use some form of a storage system for hot water works well for larger households with predictable schedules but can lead to inefficiencies for smaller homes or single occupants.
How Efficient Are These Systems?
100% Heating Efficiency
Both instant water heaters (like an electric shower or kettle) and hot water storage tanks (also called a water cylinder) convert nearly 100% of the electricity into heat at the precise moment of heating. There is an important difference in overall efficiency (not exactly related to costs), please read the following 3 times:
- Instant electric water heating is 100% efficient at the moment of heating, with all electricity converted into heat.
- Hot water storage tanks lose heat over time, making them less efficient. It’s like boiling a kettle for tea; if you leave it for an hour, the water cools down.
This means that for every unit of electricity you use, all of it goes into heating the water. Sounds perfect, right? Well, there’s more to it.
What’s the Difference?
Instant Water Heaters (for example: Electric Shower, Kettle)
An instant water heater heats water as it flows through the unit. Think of it as similar to how a kettle boils water, but on a continuous flow basis. For example:
- When you turn on an electric shower, water is instantly heated as it passes through the heater.
- Efficiency: No heat is wasted because the water is only heated when you need it. Also the exact amount of water is heated, no less, no more!!
Hot Water Storage Tanks (Water Cylinders)
A hot water storage tank works differently. Water is heated in the tank (usually by an immersion heater) and stored until you need it. This is great if you have a big household, as the tank can supply hot water to multiple taps and showers at once.
However:
- The tank stores hot water all the time, so some heat escapes into the surrounding air, even with good insulation. This is called standby loss.
- The longer you store the water, the more energy is lost, especially if the water isn’t used right away.
- Water hot water. If the entire volume of water is not used, then energy has been wasted. Similar to heating 5 cups of water but only using 2!!
Why Does Practical Efficiency Matter?
Although both systems are 100% efficient in converting electricity to heat, the practical efficiency—how much of that heat is actually used—differs:
- Instant Water Heaters: Only heat water when needed. There’s no waste from stored hot water, making them more practical and efficient for low or irregular water usage.
- Hot Water Storage Tanks: Can waste energy through standby losses, especially if the hot water isn’t used often or if it sits unused for long periods.
Key Takeaways
- Instant Water Heaters: Best for smaller households or people with unpredictable schedules, as they waste no energy.
- Hot Water Storage Tanks: Better for larger households with consistent hot water needs, but they come with standby losses.
Understanding these differences can help you choose the system that saves you money and suits your lifestyle best!
Savings with Overnight Tariffs
One of the primary advantages of hot water cylinders is their compatibility with Economy 7 tariffs, which offer cheaper electricity rates during off-peak hours. By heating water overnight, households can significantly reduce energy costs.
- Example: Heating a 150L tank from 15°C to 60°C requires 8.71 kWh of electricity. At an Economy 7 rate of £0.15/kWh, the cost is £1.31 per tank .
- However, savings can be reduced by higher daytime rates, making it essential to evaluate your total energy usage.
Challenges of Wasted Energy
For households with irregular schedules or single occupants, the traditional storage system can lead to wasted energy. Heating a full tank of water when no one is home results in unnecessary energy use and higher bills . In contrast, instant wat produce hot water only as needed, ensuring no energy is wasted.
Balancing Water Demand and Usage
The choice between systems often depends on your household’s water demand:
- High Demand: Storage tanks can supply multiple outlets simultaneously, ideal for large families.
- Low Demand: Instant heaters work best for households with lower usage or where water demand is spread throughout the day.
Flow rates are a key consideration for instant heaters. For instance, an 8kW instant water heater can supply around 4 liters per minute, sufficient for a shower but not for multiple simultaneous uses
Impact of EPC Ratings, Energy Performance Certificates (EPC)
The UK domestic home EPC (energy performance certificate) favor homes with hot water cylinders, that have dual immersion heaters (2 heating elements) and an electricity meter supporting dual tariffs. Government guidelines assume storage tanks are paired with off-peak tariffs, enhancing efficiency ratings . Removing a cylinder can lower your home’s potentially affecting its resale value. A hybrid approach—retaining the tank but bypassing it for daily use—offers the best of both worlds.
Best of Both Worlds: Hybrid Approach
For households looking for flexibility, combining an instant water heater with a retained hot water cylinder provides a versatile solution:
- Daily Use: Use an instant heater for small, on-demand needs.
- Large Demands: Reactivate the storage tank during peak use periods or for scheduled overnight heating.
By bypassing but not removing the cylinder, you maintain future flexibility and benefit from better EPC ratings.
Tariff Comparisons: Overnight vs. Standard Rates
While Economy 7 tariffs offer cheaper overnight rates, they may not suit all households:
- High Daytime Usage: Households with significant daytime electricity use (e.g., electric cars, work-from-home setups) may find standard tariffs more economical .
- Regular Tariffs: Standard rates provide a const throughout the day, reducing the need for precise scheduling.
Installation Costs and Practicality
Instant Water Heater Installation
Installing an instant water heater is often straightforward, especially in homes with modern electrical systems. Costs typically range from £300 to £800, depending on the unit and wiring requirements . Compact and wall-mounted, these units save space and can be in under a day by a qualified electrician.
Retaining Existing Cylinders
Keeping the existing hot water cylinder avoids unnecessary removal costs and preserves future options. Bypassing the tank requires minimal plumbing work and can be quickly reversed if needed.
Conclusion
Choosing between an instant electric water heater and a hot water cylinder depends on your household’s size, water usage patterns, and energy tariffs. For small or irregularly occupied homes, instant heaters provide unmatched efficiency and convenience. Larger families may benefit from the capacity and off-peak savings of a hot water cylinder. For maximum flexibility and efficiency, a hybrid approach offers the best of both worlds.
References
- Energy Saving Trust – Hot Water Systems
- Which? – Instant Water Heater Efficiency
- Economy 7 Tariff Details
- EPC Guidelines on Hot Water Cylinders
- Instant Water Heater Flow Rates
- Hot Water Storage Tanks and Energy Ratings
- Tariff Comparisons for Electric-Only Homes
- Installation Costs for Electric Water Heaters