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Selecting the Right Unvented Hot Water Cylinder
Selecting the Right Unvented Hot Water Cylinder
If you are not sure what kind of unvented hot water cylinder to choose for a home, extension, or refurbishment, the main things to look at are the type of cylinder, the hot water demand, and the space available. Pick too small and the property can run short of hot water. Go too large and you spend more than you need to on both the cylinder and the energy needed to heat it.
At APM Plumbing & Electrical, we help customers compare practical options for domestic hot water systems every day. This guide gives a clear starting point before you buy.
Direct or indirect?
Direct cylinder
In a direct cylinder, the water is heated by the cylinder itself using an immersion heater. This can be useful where a property does not have a suitable boiler connection or where electric water heating is the preferred setup.
Indirect cylinder
An indirect cylinder uses an external heat source such as a boiler, heat pump, or solar thermal system. A coil inside the cylinder transfers heat into the stored water without mixing the system water with the domestic hot water. Many indirect cylinders also include an immersion heater as a backup.
For many homes, indirect cylinders are the better long-term option because they work well with modern heating systems and can be more efficient.
What size cylinder do I need?
The right size depends on how much hot water the property needs at busy times. The number of bathrooms, en-suites, bedrooms, and the number of people using hot water all matter.
As a simple rule, size the cylinder around the way the property is actually used, not just the floor area.
| Property setup | Typical hot water demand | Selection guide |
|---|---|---|
| 1 bathroom | Lower to moderate | A smaller cylinder may be enough, depending on occupancy and bath use. |
| 1 bathroom + 1 en-suite | Moderate | Often worth choosing a larger size so showers and taps can run without the hot water dropping off too quickly. |
| 2 bathrooms | Moderate to high | Choose more carefully, especially if more than one shower may run close together. |
| 3+ bathrooms / larger family home | High | Avoid undersizing and select with simultaneous use in mind. |
What else should you check?
- Available space: if cupboard space is tight, a horizontal or compact model may help.
- Heat source compatibility: make sure the cylinder matches the boiler, immersion, or renewable system being used.
- Recovery time: the cylinder should reheat well after showers, baths, and general daily use.
- Supplied fittings: check for items such as the immersion heater, expansion vessel, safety controls, valve kit, and tundish.
- Future demand: if the property may be extended or upgraded, it can make sense to size with that in mind.
Step-by-step selection
- Check how many bathrooms and en-suites the property has.
- Think about when hot water is used most heavily.
- Decide whether a direct or indirect cylinder is the better match.
- Confirm the available installation space.
- Choose a cylinder that fits both current and expected future demand.
Why unvented cylinders are popular
Unvented cylinders are popular because they can deliver strong stored hot water performance without needing a separate cold water tank in the loft. When sized correctly and installed properly, they are a reliable choice for many modern homes.
Need help choosing the right cylinder?
If you want help choosing the right unvented hot water cylinder, APM Plumbing & Electrical can help you compare suitable options for domestic hot water systems.
APM may not always stock the cylinder itself online, but you can check related cylinder accessories such as immersion heaters and expansion vessels, or ask APM for assistance choosing the right material.
Visit us at 24 Western Avenue, Acton, London W3 7TZ, call 020 8702 8080, or contact us through our contact page.
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