Best Under-Sink Water Heaters
The cheapest fix for the tap that takes ninety seconds to run hot.
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The Bosch Tronic 3000 T ES4 is the one to buy for a single bathroom sink: 4 gallons on a standard 120 V 15 A outlet, 1,440 W, glass-lined, wall or floor mounted. For a kitchen sink where you wash up by hand, the ES8 at 7.1 gallons. The Rheem MiniTank is the pick if a published leak warranty matters.
Every plug-in unit here is 1,440 W on a 120 V 15 A circuit, so they all refill at the same speed. What differs is stored volume, physical size, and warranty — and in practice the deciding factor is almost always whether it fits the cabinet.
Quick picks
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| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Bosch Tronic 3000 T ES4 (4 gal)Four gallons on a standard wall outlet: the simplest fix for the bathroom at the far end of the house where hot water takes 90 seconds to arrive. | A single far-away sink | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  Bosch Tronic 3000 T ES8 (7.1 gal)The larger mini tank: 7.1 gallons delivered per draw cycle on an ordinary 15 A outlet, which stretches the category from one faucet to a small bathroom. | A sink plus a small basin | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 3 |  Rheem Professional Classic MiniTank, 6 galSix gallons on a shared 120 V outlet from a brand with real warranty support: five years on leaks, two on parts, and four capacities in the same family if six is the wrong number. | Wall-mounted point of use | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 4 |  Eemax EMT6 (6 gal mini tank)A 6-gallon plug-in tank with a published 50 to 140°F adjustable range and real dimensions on the spec sheet — the one to specify when the install has to be drawn before it is built. | Commercial-style under-counter installs | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 5 | EcoSmart ECO 11A single-fixture electric unit, not a whole-house one: 13.8 kW at 240 V delivering 1.3 to 3.2 GPM depending entirely on how cold your inlet water is. | One fixture, or a warm-inlet apartment | Check price on Amazon No live price feed on this site, so we show none. #ad |
The picks in full
Pick 1 — A single far-away sink
Bosch Tronic 3000 T ES4 (4 gal)
Four gallons on a standard wall outlet: the simplest fix for the bathroom at the far end of the house where hot water takes 90 seconds to arrive.
| Capacity | 4 gallons |
|---|---|
| Voltage | 120 V |
| Power | 1,440 W |
| Current | 12 A |
| Circuit | Standard 120 V 15 A outlet |
| Tank | Glass-lined with CFC-free foam insulation |
| Mounting | Floor or wall, bracket included |
| Thermal efficiency | 98% |
What is good
- Plugs into an existing outlet — no electrician, no permit, no panel work
- Front-mounted temperature knob rather than a hidden thermostat
- Wall or floor mounting makes it fit a vanity cabinet or a utility corner
- Eliminates the long wait and the water wasted waiting
What is not
- Four gallons is one sink, not one shower
- 1,440 W recovery means you notice the limit if you drain it
- Still a standby load, albeit a small one
Skip it if: Skip it if you want this to feed a shower. Four gallons at 1,440 W will produce a warm rinse and then cold water — the mini-tank category is for hand washing and dishes.
No live price feed on this site, so we show none. #ad
Specifications above from Rural Energy listing, Bosch Tronic 3000T; Walmart listing, Bosch ES4 Tronic 3000 T. We have not tested this unit ourselves.
Pick 2 — A sink plus a small basin
Bosch Tronic 3000 T ES8 (7.1 gal)
The larger mini tank: 7.1 gallons delivered per draw cycle on an ordinary 15 A outlet, which stretches the category from one faucet to a small bathroom.
| Capacity | 7.1 gallons |
|---|---|
| Voltage | 120 V |
| Power | 1,440 W |
| Circuit | Standard 120 V 15 A outlet |
| Delivery | Up to 7.1 gallons per draw cycle before recovery |
| Tank | Glass-lined, foam insulated |
What is good
- Nearly double the ES4's storage on the same 15 A outlet
- 7.1 gallons covers washing up plus a basin without recovering
- No wiring work needed
- Same simple serviceable design as the smaller unit
What is not
- Takes more cabinet space than the 4-gallon version
- Same 1,440 W recovery, so it refills no faster — it just holds more
- Larger standby loss than the ES4
Skip it if: Skip it if the cabinet under the sink is shallow. The ES8 is noticeably bigger than the ES4, and a mini tank that does not fit the cabinet ends up on the floor beside it.
No live price feed on this site, so we show none. #ad
Specifications above from Rural Energy listing, Bosch Tronic 3000T ES8. We have not tested this unit ourselves.
Pick 3 — Wall-mounted point of use
Rheem Professional Classic MiniTank, 6 gal
Six gallons on a shared 120 V outlet from a brand with real warranty support: five years on leaks, two on parts, and four capacities in the same family if six is the wrong number.
| Capacities available | 1.5, 2.5, 4.0 and 6.0 gallons |
|---|---|
| Voltage | 120 V, grounded shared outlet via power cord |
| Mounting | Floor or wall, bracket included |
| Footprint | Up to 93% smaller than a standard electric tank |
| Warranty | 5-year leaks, 2-year parts |
What is good
- A published leak warranty, which most mini tanks do not carry
- Four capacities in one family, so you can size to the fixture
- Shared outlet means it can share a circuit with the disposal
- Wall mounting frees the cabinet floor
What is not
- Rheem does not publish a first-hour rating for the MiniTank line
- Six gallons is still a point-of-use volume
- Cord-and-plug connection limits where it can legally go in some jurisdictions
Skip it if: Skip it if the outlet under your sink is on a GFCI circuit shared with a garbage disposal that trips. A mini tank that loses power silently is a tank of cold water you only discover at the faucet.
No live price feed on this site, so we show none. #ad
Specifications above from Rheem Professional Classic MiniTank product page. We have not tested this unit ourselves.
Pick 4 — Commercial-style under-counter installs
Eemax EMT6 (6 gal mini tank)
A 6-gallon plug-in tank with a published 50 to 140°F adjustable range and real dimensions on the spec sheet — the one to specify when the install has to be drawn before it is built.
| Capacity | 6 gallons |
|---|---|
| Voltage | 120 V |
| Current | 12 A |
| Power | 1,440 W |
| Temperature range | 50 - 140°F, adjustable |
| Dimensions | 18 in H x 15-3/4 in W x 15-1/2 in D |
| Weight | 26 lb |
What is good
- Full dimensions and weight published, which matters for a cabinet or a millwork drawing
- Adjustable down to 50°F for tempered-water-only applications
- Plugs into a 110 to 120 V outlet
- Smaller EMT2.5 and EMT4 share the same mounting approach
What is not
- Wider and deeper than the Bosch ES8 for the same nominal capacity
- Same 1,440 W recovery as every other plug-in mini tank
- Thinner retail availability than Bosch or Rheem
Skip it if: Skip it if cabinet depth is the constraint. At 15-1/2 inches deep it is the bulkiest 6-gallon unit here, and under-sink depth is almost always what rules a mini tank out.
No live price feed on this site, so we show none. #ad
Specifications above from Eemax mini tank specification sheet (PDF). We have not tested this unit ourselves.
Pick 5 — One fixture, or a warm-inlet apartment
EcoSmart ECO 11
A single-fixture electric unit, not a whole-house one: 13.8 kW at 240 V delivering 1.3 to 3.2 GPM depending entirely on how cold your inlet water is.
| Output | 13.8 kW at 240 V; 11 kW at 220 V |
|---|---|
| Flow | 1.3 - 3.2 GPM depending on inlet temperature |
| Breaker | 60 A double-pole |
| Wire | 6 AWG |
| Current draw | 54 A |
| Energy factor | 0.998 |
| Set point | Digital, 1°F increments |
What is good
- One 60 A circuit instead of three, which many existing panels can take
- Honest published flow range tied to inlet temperature
- Small and light enough for a utility closet or under a counter
- Good match for a single shower in a warm-inlet region
What is not
- 3.2 GPM is only reachable with warm inlet water
- Still 54 A — not a plug-in appliance
- No modulation headroom if a second fixture opens
Skip it if: Skip it as a whole-house heater anywhere north of the Sun Belt. At a northern winter inlet temperature it lands at the bottom of its range, which is a hand-wash flow rate, not a shower.
No live price feed on this site, so we show none. #ad
Specifications above from EcoSmart ECO 6 / 8 / 11 specification sheet (PDF). We have not tested this unit ourselves.
Measure the cabinet first
This is the step people skip and then regret. Under-sink cabinet depth is usually 20 to 22 inches to the back wall, and the trap, the stop valves and the waste all compete for the same space.
| Unit | Capacity | Dimensions | Weight |
|---|---|---|---|
| Bosch Tronic 3000 T ES4 | 4 gal | Compact; wall or floor mount with bracket | Not published on the listings we read |
| Bosch Tronic 3000 T ES8 | 7.1 gal | Larger than the ES4 | Not published on the listings we read |
| Rheem MiniTank 6 | 6 gal | Up to 93% smaller than a standard electric tank | Not published |
| Eemax EMT6 | 6 gal | 18 in H x 15-3/4 in W x 15-1/2 in D | 26 lb |
| Eemax EMT4 | 4 gal | 19-1/4 in H x 11-3/4 in W x 10-3/8 in D | 24 lb |
What 1,440 watts actually delivers
At 1,440 W, a mini tank adds roughly 5 to 6 gallons of hot water per hour at a typical rise. So:
- 4 gallons — hand washing and shaving at one basin, all day. Drain it and you wait about 40 minutes for a full refill.
- 6 to 7 gallons — washing up at a kitchen sink by hand, or filling a small basin. Still not a shower.
- Two fixtures on one unit — works if they are not used simultaneously and both are close by. A master bath sink and a toilet-room sink, for example.
The 240 volt alternative
The EcoSmart ECO 11 is in this roundup because it is the honest answer to "what if I do want a shower from a point-of-use unit". At 13.8 kW on 240 V it delivers 1.3 to 3.2 GPM depending on inlet temperature, which is a real shower in a warm-inlet climate.
What it costs you: one 60 A double-pole breaker, 6 AWG wire, and 54 A of draw. That is real electrical work, but it is also the smallest electrical ask of any whole-fixture electric tankless unit, and many existing panels can take it. Electric tankless water heaters.
Installation, briefly
- Shut off the cold supply under the sink and drain the line.
- Tee the cold supply to feed the unit, and run the unit's outlet to the hot side of the faucet.
- Mount the unit — wall bracket if the cabinet floor is needed, floor standing if not.
- Fill the unit completely and purge air through the faucet before powering it up. Energizing a dry element destroys it.
- Plug it in, set the temperature, and check every connection after an hour under pressure.
Two safety notes that matter: the relief valve has to be able to discharge somewhere safe, and a cabinet is exactly where a slow leak goes unnoticed for months. A cheap leak detector in the cabinet is the sensible companion purchase.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Leak detector
A mini tank lives in a cabinet, which is exactly where a slow leak goes unnoticed for months.
- Anode rod
Mini tanks have one too, and in hard water it is what decides how long the unit lasts.
How we chose
Published dimensions first, because fit is what actually rules these units in or out; then capacity; then warranty terms as published; then availability. We have not tested these units. How we pick.