If your home uses a boiler and a hot water cylinder rather than a combi boiler, the cylinder is as important as the boiler itself. An inefficient, aging or incorrectly sized cylinder wastes energy, affects your hot water pressure and can leave you without adequate hot water. Kelly Heating NI installs all three main cylinder types across Belfast, Lisburn and the wider Greater Belfast area.
Open Vented Cylinders
Open vented hot water cylinders are the oldest type of domestic hot water storage and are now increasingly uncommon. They rely on a cold water storage tank — typically in the loft — to feed the cylinder by gravity, and require an overflow pipe to vent safely. Many have been replaced over the past two decades as homeowners have upgraded to combi boilers or more efficient unvented systems.
If you still have an open vented cylinder and are experiencing problems, or would like to upgrade to a more modern system, we can assess your options and advise on the best course. In many cases, upgrading to an unvented cylinder or converting to a combi boiler is the right long-term decision — but Kieran will give you an honest view based on your property and circumstances.
Ask About Open Vented CylindersUnvented Cylinders
Unvented hot water cylinders are now the most common type installed in domestic properties across Belfast and Northern Ireland. They are fed directly from the mains water supply, which means they deliver hot water at mains pressure — better flow rates, better shower performance, and no need for a header tank in the loft.
Key advantages of unvented cylinders include:
- Mains-pressure hot water — better flow to showers and taps throughout the home
- No cold water storage tank required in the loft
- High efficiency and large hot water capacity
- Compatible with multiple fuel sources — gas boiler, oil boiler, solar thermal
- Built-in safety features as standard — thermostat, pressure relief valve, tundish
- Suitable for modern homes and properties with multiple bathrooms
Combinations such as oil boiler with solar thermal, gas boiler with solar thermal, and even PV solar integration are all possible with the right unvented cylinder. Kieran will advise on the correct cylinder size and specification for your home's hot water demand.
Get an Unvented Cylinder QuoteThermal Store Cylinders
A thermal store cylinder is the right choice for larger properties or homes with multiple heat sources — for example, an oil boiler combined with solar thermal panels, a wood-burning back boiler, or a heat pump.
Unlike conventional unvented and open vented cylinders — which store domestic hot water directly — a thermal store stores a volume of central heating water that is heated by multiple fuel sources simultaneously. Domestic hot water is produced on demand by passing cold mains water through a heat exchanger inside the thermal store, heating it instantly.
This design means the system can draw on whichever fuel source is cheapest or most available at any given time — maximising the use of free renewable energy when available, and falling back on oil or gas when needed. Compatible heat sources include:
- Gas boilers and oil boilers
- Solar thermal panels
- PV solar (via an immersion heater diverter)
- Air source or ground source heat pumps
- Back boilers and wood-burning stoves
- LPG boilers
The combination of fuel sources is effectively unlimited, making thermal stores a future-proof option for homeowners looking to gradually move toward renewable energy while keeping a reliable conventional backup. See also our solar thermal page and heat pump page for more on compatible renewable systems.
Ask About Thermal Store CylindersNot Sure Which Cylinder Is Right for Your Home?
The right choice depends on your property size, number of bathrooms, current heating system, and whether you have or are considering renewable energy sources. Kieran will assess your home and give you a clear recommendation — with no pressure toward the more expensive option if a simpler solution is the right answer.
It depends on the cylinder's condition, age and compatibility with the new boiler. Kieran will assess this during your site visit. If the cylinder is in good condition and compatible, keeping it is often the sensible choice. If it's aging or mismatched, replacing it alongside the boiler is usually more cost-effective in the long run.
Yes — both unvented and thermal store cylinders can be specified with a solar coil to accept heat from solar thermal panels. If you're considering adding solar thermal now or in the future, it's worth ensuring your new cylinder is solar-compatible from the outset.
Yes — unvented cylinders should be inspected annually as part of your boiler service. The pressure relief valve, thermostat and expansion vessel all require checking. Kieran covers this as part of the annual boiler service where a cylinder is present.
Yes — we cover Belfast, Lisburn, Holywood, Dunmurry, Carryduff and the wider Greater Belfast area for cylinder installation and replacement.