Economy Seven Water Heater Range – 100 to 500 Litres
Economy Seven Water Heater Range
Economy 7 water heaters are domestic hot water storage heaters that use off-peak electricity at cheaper rates to heat water, normally overnight, via an immersion heater or heaters; they are also known as Economy 7 direct cylinders or economy seven hot water cylinders.
They are sometimes incorrectly referred to as economy 7 boilers, boilers do central heating, the correct technical term is domestic water heaters i.e. they produce sanitary quality warm water for baths, showers,wet room or taps.
Economy seven hot water cylinders in stainless steel from Flexiheat UK
Economy 7 Electricity Tariff Explanation
Economy 7 is a type of dual-rate electricity tariff. It gives you two different electricity prices:
- A cheaper electricity rate “off peak” for 7 hours overnight
- A more expensive “daytime” rate for the rest of the day
The 7 cheap hours vary by supplier and region of the UK. This is commonly 11pm–6am or midnight–7am, but some areas use different hours in winter vs. summer.
Your meter determines the exact timing of the different economic times.
The night rates for Economy 7 electricity are significantly cheaper, often around one-third of the standard rate.
Economy 7 can be integrated with renewable energy sources like solar panels i.e. Photovoltaic (PV) technology.
Economy 10 ?
Did you know? – There is also an “Economy 10” tariff available in some parts of the UK. Check with your energy provider to see if you qualify. Economy 10 is an even better but less common direct equivalent to Economy 7, because:
It offers 10 hours of cheaper electricity (not all overnight), which is:
- Usually split into three time blocks: some at night, mid-afternoon and late evening
- This is great for water heating because your Economy 7 hot water cylinder can “top up” in the afternoon by using the boost element.
Economy seven hot water cylinders product range
The 100 litre to 500 Litre economy 7 hot water tanks are a dual immersion cylinder fitted with 2 x 3 kW immersion heaters as standard.
We also have the option of 3 x 3 kW immersion heaters that can be fitted to our 215 Litre to 500 litre economy 7 hot water cylinders models, or the option of 3 x 6kW immersion heaters if so required.
Dual element immersion heater economy 7 approvals – BBA, CE, WRAS (Water Regulations Approval Scheme is an independent UK certification body for plumbing products and materials, helping business and consumers choose compliant products that keep water safe), KIWA, ISO, WRC.
Dimensions detail of our economy 7 hot water cylinders
Unvented direct economy 7 hot water heaters – Dimensions drawing for 80 Litre to 500 Litre models
Economy 7 hot water tank dimensions from Flexiheat UK
Economy 7 Cylinder Sizing Guide
| Household Size | Recommended Cylinder Size | Hot water use |
|---|---|---|
| 1 person | 100–130 litres | Enough for 1 shower + general use |
| 2 people | 130–180 litres | Good for 2 showers, washing up |
| 3 people | 180–210 litres | Most common small-family size |
| 4 people | 210–300 litres | Good for multiple showers + baths |
| 5+ people | 300–500 litres | Needed if you take baths or have high usage |
or another method of water cylinders heater sizing
Hot water demand calculation guide
A rough guide to daily hot water usage per person:
| Usage Type | Litres per person per day of hot water at 60°C |
|---|---|
| Bath | ~80 litres |
| Shower (8Ltrs a minute power shower) | ~60 litres |
| Shower (8Ltrs a minute standard shower head) | ~35 litres |
| Washing up (by hand) | ~10 litres |
| Dishwasher | ~15 litres |
Rule of thumb: Allow 45 to 60 litres per person per day for average mixed use.
If you already have a water tank using Economy 7 tariffs and you frequently run out of hot water or have to use the “boost” immersion heating element during the day-
- You may need a larger capacity tank.
- Your timing switch/thermostat may be set incorrectly.
Choosing a slightly larger Economy 7 cylinder can maximise the amount of hot water stored during the cheaper, low-tariff period.
Domestic hot water heat up times
| Cylinder Capacity (Litres) | Time to heat from 10C to 60C with 2 x 3kW immersion heaters working (Minutes) |
| 100 | 58.33 |
| 200 | 116.67 |
| 300 | 175 |
| 400 | 233.33 |
| 500 | 291.67 |
Please double these times if using only one of the 3kW immersion heaters, i.e., using off-peak electricity to heat overnight, or halve these times if using the upgraded 6kW immersion heaters (6kW top and bottom immersion heaters).
Unvented cylinder
Most modern economy 7 cylinders are unvented products, providing consistent, high-pressure hot water from the mains supply.
Unvented cylinders are sealed and filled directly from the mains water supply, designed to provide hot water at high pressure and manufactured in stainless steel, with the advantage of high insulation levels (i.e., injected polyurethane foam lagging to the ErP standards) to reduce heat loss for our economy 7 cylinders.
Power Requirement for immersion heaters
Our immersion heaters can be powered by single- or three-phase power supplies.
For the 3 kW heating elements – these are 240 volt / 1 phase powered and require 13 amps of power per element.
If you upgrade to the 6 kW heating elements, they can be wired for either 1-phase / 240 V or 3-phase / 415 V; when using a single phase, each element requires a supply of 26 amps, while on three-phase, each element requires 9 amps per phase.
How can I determine if I have access to Economy 7 rates?
If you have Economy 7, your meter will either:
A. Show two readings, usually labelled something like:
“Rate 1 / Rate 2” or “Day / Night”
One number will increase during the day, the other during the night.
B. Have two physical meters feeding one consumer unit – some older installations have two separate meter units on the wall — one for day electricity and one for night electricity.
C. Smart meter showing multiple registers – like “R1 and R2” Or “IMP R01 / IMP R02”
You can also check your energy bill
Your bill will clearly show:
- Two metered unit rates (e.g. “Day Rate” and “Night Rate”)
- A note saying Economy 7, E7, or Two-rate tariff
If you only pay one unit rate, you don’t have Economy 7.
Economy 7 hot water cylinders explained
Economy 7 water heaters are electric hot-water systems designed to heat water overnight during the cheap-rate hours of an Economy 7 tariff. They store the hot water in a tank fitted with insulation so you can use it during the day without paying peak electricity prices.
Here’s how they work:
They use an immersion heater element inside a hot-water cylinder
This is like a big electric kettle element inside a hot water tank.
A timer or circuit powers it only at night to save money
During your 7 off-peak hours (e.g., midnight–7am), the immersion heater switches on automatically and heats water inside the economy 7 water heater.
The tank stores the hot water
Because the economy 7 water heater cylinder is insulated, the water stays hot for many hours, so you can:
- Shower in the morning & evening
- Wash up
- Use hot water throughout the day
all while having paid the cheaper night-time rate.
Types of Economy 7 water heating
Off-peak only cylinder (storage heaters)
This type will only heat at night and can save money if sized correctly, however you might run out of hot water later in the day if undersized.
Cylinder with “boost” (dual immersion cylinder via two switches)
Many feature two immersion heaters powered by seperate switches:
- Bottom switch → heats overnight (Using the bottom immersion on the cylinder)
- Top switch → “boost” heater you can switch on during the day (Using the top immersion on the cylinder)
This allows you to top up the domestic hot water during peak hours if you run out, or the temperature becomes colder, by using two switches.
Unvented cylinder
Most modern economy 7 cylinders are unvented products, providing consistent, high-pressure hot water from the mains supply with a economy 7 unvented cylinder.
Unvented cylinders are sealed and filled directly from the mains water supply, designed to provide hot water at high pressure and manufactured in stainless steel, with the advantage of high insulation levels (i.e., injected polyurethane foam lagging to the ErP standards) to reduce heat loss for our economy 7 cylinders.
Power requirement for immersion heaters
These immersion heaters can be powered by single- or three-phase power supplies.
For the 3 kW heating elements – these are 240 volt / 1 phase powered and require 13 amps of power per element.
If you upgrade to the 6 kW heating elements, they can be wired for either 1-phase / 240 V or 3-phase / 415 V; when using a single phase, each element requires a supply of 26 amps, while on three-phase, each element requires 9 amps per phase.
Contact Flexiheat UK to find out further information
Should you require further assistance,information,questions on the product or to purchase / order one of our Economy 7 Cylinders range,which are guaranteed for 25 year domestic use against faulty materials of the stainless steel tank ( 5 years guaranteed for commercial use) then please contact our customer sales team on 01202 822221 or click here for our email contact form to send an email.
Flexiheat UK
Flexiheat UK