120 Litre Direct Unvented Cylinder
120 Litre direct unvented cylinder
Our 120 litre direct unvented cylinder is engineered in corrosion-resistant duplex stainless steel and is a competitively priced cylinder. We designed it to achieve high flow rates and a long product life using proven technology and a quality manufacturing process for this unvented hot water cylinder for mains pressure hot water.
We’re so sure of the quality of our 120 litre unvented direct cylinder that they come with a 25-year warranty for use in residential locations like homes, apartments, and so on. The warranty covers the stainless steel hot water cylinder for 25 years, while the other parts, like the immersion heaters, control thermostats, and so on, are covered for one year from the date of purchase, subject to conditions.
What is a 120L direct unvented cylinder suitable for?
A rough guide is that 120 litre direct unvented hot water cylinders suit flats or smaller homes with one or two bedrooms and a bathroom with one bath and/or shower.
However, people’s hot water usage patterns can vary from household to household. We prefer to give you the hot water usage data, and you, our customer, decide if it suits your hot water needs.
In the United Kingdom, we are required to keep DHW at 60°C since it eliminates the possibility of Legionella disease and is the minimum recommended water temperature.
If the stored water temperature is 60°C, the amount of required water is in red, to be blended down to 43°C (the maximum bathing temperature before scalding can occur).
Please use 10°C for England and Wales as the lowest cold-water wintertime temperature and use 5°C for Scotland and Northern Ireland.
If the incoming cold-water temperature is 10°C is 5°C
A bath uses around 135 litres of water at 43°C 89 litres 94 litres
A standard 8-litre shower head x 5 minutes 30 litres 31 litres
And yes, 5 minutes is the average showering time—say all the time and motion studies report.
A kitchen sink holds up to 20 litres of water 16 litres 16.5 litres
To ensure the removal of grease from dishes and cooking utensils, the standard temperature for washing up water is 50°C.
Toilet sink taps—standard type—are around 4 litres per minute; “spray” type taps are 2 litres per minute and tend to be on for a brief period.
Please see the recovery time data below for our 120L direct cylinder to establish if this is the right 120L electric water heater for your circumstances and demands.
This 120 Litre volume direct unvented cylinder is the second most popular seller in this range, however, should you wish a larger volume cylinder, which is our most popular direct unvented cylinder that we sell, then please see the following webpage – 150 Litre direct unvented cylinder
Hot water heat-up time and recovery rates for our direct unvented cylinder, 120 litres in capacity
As standard, our 120 litre direct-pressurised hot water cylinders in high grade stainless steel are fitted with 2 x 3 kW immersion heaters with proven technology and quality.
Our 120 Litre unvented indirect cylinder has the following hot water heat-up time and recovery rates with standard 2 x 3 kW immersions fitted:
Upgraded immersion heater options
We have the option of upgrading the immersion heaters to larger outputs for rapid heat recovery.
We can supply this 120 Ltr capacity direct unvented cylinder with 2 x 6kW immersion heaters, which can be wired in either 1 phase/240 volts (32 amps per immersion is required) or 3 phases (10.66 amps per phase is required); this will halve the recovery times stated above in the chart. We also must upgrade the standard temperature and pressure relief valve to a larger output model.
Or alternatively, you can have 1 x 6kW and 1 x 3kW immersion heater fitted, for a total kW input of 9kW; the standard 10kW T & P valve will remain if this configuration is used.
All of our unvented cylinders have a pressure test, and all are tested to 10 bar pressure and have a max working pressure of 5.5 bar.
Unvented hot water expansion system
The patented internal hot water expansion system, which uses a venturi valve to maintain an air pocket within the stainless steel cylinder, eliminates the need for an external expansion vessel. This unvented system has a long product life because it has no moving parts, which reduces running and lifetime costs.

Our internal air gap and venturi valve system used on our direct unvented hot water cylinders- no external expansion vessel is required and little to no maintenance is required for the unvented hot water system.
As a result, our direct unvented cylinders need less space, pipework and plumbing fittings, making the installation process simpler and lowering both costs and time required for installation.
Unvented Direct Cylinder 120 Litres: Features and Benefits
- Enhanced Venturi valve technology, which automatically replenishes the internal air gap within the unvented cylinder.
- Dual immersion cylinder: 2 x 3kW immersion heaters as standard.
- 3 bars of water pressure at the outlet (subject to incoming pressure).
- Mains pressure hot water directly delivered—enabling high flow rates.
- No expansion vessel or moving parts, ensuring low maintenance.
- ErP “B” heat loss rating for reduce energy consumption
- Benefits from an evolved design and quality manufacturing for improved performance at low flow rates.
120 litre unvented direct cylinder dimension
Our 120 litre stainless steel direct unvented cylinder has the following dimensions:
The highly corrosion-resistant duplex stainless steel 120 Ltr capacity direct unvented cylinder has the following engineered dimensions in mm:

130L Direct pressurised hot water cylinder details highlighted in red – yes, we give you 10 more litres of capacity for free, as they can hold / have 130 Litres of capacity.
Our duplex stainless steel cylinders are available in both direct and indirect configurations as you can see in the following manual
Download the installation & technical manual for our direct and indirect hot water cylinders
Unvented direct cylinder 120 ltr approvals
Our 120 ltr direct unvented cylinder we sell has been approved by the CE, BBA, and WRAS independent approvals (Water Regulations Approval Scheme—a certification body for domestic hot water heating products that assists businesses and customers choose safe products that comply with hot water regulations) and benefits from ISO, KIWA, and WRC approvals as well, proving the quality manufacturing process of our stainless steel cylinders.
Components supplied with our stainless steel unvented cylinder: 120L direct unvented cylinder
2 x 3kW immersion heaters manufactured in incoloy (a super austenitic stainless steel—with high resistance to oxidation), with a control thermostat and high-temperature thermal/energy cut-out thermostat.
Front access to the controls on our electric pressurised hot water cylinder.
A temperature and pressure relief valve to comply with the hot water unvented cylinder regulations.
A complete pressure-reducing valve combination valve/6-bar expansion relief valve (the maximum inlet pressure to the mains pressure hot water cylinder) for the cold water mains inlet
A Tundish: A Tundish has a clear window that allows you to see if water is flowing from the pressure relief valve (PRV). This helps you identify potential issues with the unvented hot water system.
Heat loss ErP rating for this direct unvented cylinder
This direct unvented cylinder has an ErP level of “B” for the thermal insulation to reduce heat loss and ensure running costs are kept to a minimum, which is an excellent rating for an unvented direct cylinder.
The injected polyurethane foam thermal insulation, with an ODP=0 and a GWP=1 rating, is free of CFC/HCFC and provides 60mm of fire-retardant protection. Similar competitor products only have 40 mm insulation to reduce heat loss, and thus the ErP insulation ratings are lower than our direct unvented cylinder.
Delivery of the unvented cylinder
We deliver these direct unvented cylinders on a small pallet delivery service that comes on a lorry directly, with your responsibility to offload. We can upgrade the delivery service to have a tail lift at request to get the stainless steel 120L direct unvented cylinder to floor level.
Contact Flexiheat UK
Please contact us at 01202 822221 to answer any questions or use the company site contact email form to get more information or details, the current stock situation, delivery options, or a cost on the best 120 litre direct unvented cylinder/120Ltr unvented direct cylinder models on the UK market. These are manufactured from high-grade duplex stainless steel (a high-grade stainless steel), with a 25-year warranty, with WRAS independent approvals, have a built-in expansion system, and are a competitively priced cylinder.