The tank under the sink
The tank is a small insulated vessel in the cabinet. It is connected to the cold water supply, so it refills as you draw water out. Insulation keeps the heat in, which is why the unit can hold the water hot without heating all day at full power. Tank size differs by model, from 2 to 7 litres in our library, and the size decides how much cabinet space you need. Our installation guide lists the tank size of every model and the cabinet measurements we have.
How the water is heated and kept hot
An electric element heats the water in the tank and a thermostat holds it at the set temperature. When you draw water, fresh cold water enters the tank and the element heats it again. Between uses the unit only tops up the heat that escapes through the insulation. Idle power is listed for 24 of the 31 models and runs from 9 W to 35 W. The running cost calculator turns the figure for your model into a yearly cost based on how often you use the tap.
Pressure and getting the water out
The water is pushed out by the pressure of your mains supply, so the tap needs a connection to the cold water pipe and a supply with enough pressure. The minimum pressure differs by model and is in the manufacturer's specification. If your water pressure is low, check that figure before you choose a model.
Safety
Boiling water scalds, so these taps are designed to make accidental use harder than a standard mixer tap. 12 of the 31 models in our library list a child safety feature on their model page. The way it works differs by brand, so read the manual for your model. If young children use the kitchen, compare the safety features of the models you are considering.
What to read next
To see whether the cost makes sense for your household, read are boiling water taps worth it. To compare models, start with the best boiling water taps or the instant hot water tap overview. If you have already picked one, the installation guide covers who fits it and what to check in your cabinet.