Slimline Direct Unvented Cylinders.

Cylinders with a reduced diameter — commonly around 475mm to 550mm against a standard 545mm to 600mm — designed to fit narrow cupboards, alcoves and apartment plant spaces.

The capacity is preserved by making the cylinder taller, so check available height as carefully as width before ordering.

Not necessarily, but you lose flexibility. A slimline cylinder of the same volume is noticeably taller, so the constraint moves from floor area to ceiling height and the clearance needed to manoeuvre it into position.

Measure the access route as well as the final location — getting a tall cylinder up a stairwell with a turn is often the practical limit.

Yes. Slimline refers only to the physical dimensions. An unvented slimline cylinder works exactly as a standard one — fed from the mains, delivering hot water at mains pressure to every outlet.

The same requirement for adequate incoming flow and pressure applies, typically at least 1.5 bar and around 20 litres per minute.

Yes. All unvented hot water systems are notifiable under Building Regulations Part G and must be installed by a G3 qualified person, regardless of size or shape.

The full complement of safety devices is required too — pressure reducing valve, expansion provision, temperature and pressure relief, and a correctly routed discharge.

Direct means electric immersion heating with no boiler coil. It suits all-electric properties, flats without a boiler, and installations pairing with solar PV or an off-peak tariff.

If there is a boiler and you want it to heat the water, an indirect slimline is the correct choice instead.

Slightly, in some cases. A taller narrower vessel stratifies well, which helps, but heat-up depends mainly on element rating rather than shape.

Twin-element models let you heat only the upper portion for a quick partial recovery, which is useful where full reheat would take too long.