Vented vs Unvented Cylinders & Boiling Water Taps

The traditional setup: a hot water cylinder fed from a cold water tank in the loft, relying on gravity for pressure. Cheaper to install and simple to maintain, but you'll notice weaker pressure in showers and taps, particularly on upper floors.

Fed directly from the mains, so no loft tank needed and significantly better pressure throughout the house — the standard choice in most modern installations. They must be installed and serviced by a G3-qualified engineer, since they're a sealed, pressurised system with specific safety requirements.

A separate small tank under the sink heats a small volume of water to near-boiling and keeps it topped up, so you get instant boiling water without a kettle. They run on electricity (not your boiler), so the running cost is about how efficiently the unit holds its heat — better-insulated tanks (like Quooker) cost less to keep running than cheaper alternatives that lose heat faster and have to reheat more often.

For cylinders, it's mostly about insulation quality and cylinder size relative to your household's actual usage — an oversized cylinder wastes energy keeping water hot you don't use; an undersized one runs out and reheats more often. For boiling water taps, it's the tank's standing heat loss. In both cases, the fix is usually correct sizing at installation, not the technology itself.