Compact Electric Models
A point-of-use, under sink water heater is usually installed for any one of three reasons. Firstly, it may be used to provide hot water to remote fixtures that are not supplied by a larger water heater. Secondly, it may be used to eliminate the long delay in receiving hot water at distant fixtures. And thirdly, it may be installed as an inline water heater to augment the main hot water heating system. By choosing to install an under sink water heater in each remote area of your newly constructed house, you will save on plumbing and material costs.
Whatever your reasons for installing an under sink unit, you will always receive hot water as soon as you turn on the faucet. If you are accustomed to wasting gallons of cold water while waiting for hot water to come out of the spigot, this feature alone will make your purchase worthwhile.
A point-of-use, under sink water heater can be an electric tankless water heater, or a small electric storage tank unit. Unlike tank models, tankless under sink water heaters can provide an endless supply of hot water. These instant hot water heaters are also more efficient than tank models, because they are not subject to standby heat losses. In addition they also have a longer warranty.
On the other hand, an under sink tank unit costs less than its tankless counterpart, and most of the min-tank units can be simply plugged in to a standard electrical outlet. Other than the very low capacity models, the under sink tankless water heaters require a 240V electrical supply, and they will need to be wired into your circuit box with dedicated double-pole breakers.
Most instant, under sink hot water heaters are low capacity units that are used to serve one or two sinks. Some of the higher capacity tankless models can supply sufficient hot water to run a shower, or even a shower and a hand basin at the same time.
A tankless model that is used to serve a low flow hand basin, needs to have a minimum flow rate which is lower than the flow rate of the hand basin it serves, otherwise, the water heater’s flow-detection sensor will not activate the heating process when the faucet is turned on. Typically an under sink tankless water heater has a minimum flow rate of 0.5 to 0.75 gallons per minute.
The Bosch PowerStar models are highly rated point-of-use, water heaters that can be installed under a sink. Only the lowest capacity model in the PowerStar Series, the AE3.4, is small enough to run on a 15 amp circuit. All of the other PowerStar models require 240 Volt wiring. The PowerStar AE12, AE 115 and AE125, require a 200 Amp electrical service.
The Powerstar AE 3.4 can serve one bathroom sink in warm climates only. The AE 7.2, AE9.5,and AE12 can serve one bathroom sink in all climates. The PowerStar AE115 can supply sufficient hot water for 1 shower or 2 bathroom sinks in warm climates only. The AE125 can serve 1 shower or 2 sinks in all climates.
Other high quality tankless under sink models are the Titan SCR2 tankless water heater models,Stiebel Eltron’s Tempra and DHC series, as well as models manufactured by Eemax, Seisco, and Chronomite.
The most popular point-of use, under sink tank water heater models, are compact 2.5, 4 and 6 gallon mini-tank units. These small tank units are well insulated to reduce standby heat losses, and most models have glass-lined corrosion resistant tank linings and a sacrificial magnesium anode rod.
A mini-tank unit is usually mounted on the wall under the sink. The 2.5 and 4 gallon models can be plugged into a standard 110-120V outlet, but the 6 gallon model needs to be hard wired. With only a 10 amp current draw, no special wiring is required.
The most highly recommended mini-tank units are the Bosch Ariston water heater series, and the min-mini-tank models manufactured by Stiebel Eltron, Eemax, Insinkerator and Rheem.