Point-of-Use Water Heater

A Point-of-Use Water Heater serves one fixture from within a few feet of it, instead of sending hot water down 40 or 60 feet of pipe from a central tank. Two forms exist. A mini tank holds 2.5 to 7 gallons, mounts under a sink or on a wall, and runs on a standard 120 volt outlet at around 1,440 watts, giving about 8 gallons an hour of recovery. A small tankless unit stores nothing and delivers roughly 0.5 to 1.4 gallons per minute at a 40 degree rise from 3.5 to 8 kW, usually on a 240 volt circuit.

Its purpose is the wait, not the volume. A 50 foot run of half inch copper holds about half a gallon, so a distant bathroom faucet wastes that much water and 30 to 60 seconds every time somebody washes their hands. A mini tank kills the wait and the waste. The alternative is a recirculation pump on the main system, which solves every fixture at once but keeps a loop of pipe warm and adds standby loss. The local heater solves one fixture and adds none.

Set beside the whole house options, it is a companion rather than a competitor. An Electric Storage Tank Water Heater or a Heat Pump Water Heater still covers showers and laundry. A Gas Tankless Water Heater already answers distant fixtures if flow is enough. Point-of-use fills the gaps those miss: a garage sink, a wet bar, a workshop basin, a guest suite over a garage, an office kitchenette. Mini tanks also work as a buffer ahead of a tankless unit, holding a few gallons so short draws never trigger the cold water sandwich.

Sizing is simple arithmetic, which makes over buying the usual error. Handwashing needs half a gallon per minute, a kitchen faucet takes 1.5, a shower takes 2. No under sink mini tank will run one for long. Check three things before ordering: outlet or circuit capacity, the cabinet space under the sink including the height of the unit, and whether it needs its own temperature and pressure relief valve with a drain path. Set it to 120 F like everything else, and if it holds a tank, flush a quart from it once a year.