A tankless water heater for an apartment is a compact wall-mounted unit that heats water on demand as it flows through heating elements, so it needs no storage tank and fits in a closet where a 40 or 50 gallon tank cannot. That single sentence solves most of the problem, but not all of it, and the rest is where apartment buyers get into trouble.
Most buildings have no gas line running into the unit, most electrical panels in older apartment stock are smaller than buyers assume, and in the majority of cases the water heater belongs to the building rather than to the person living in the apartment. Those three facts eliminate most of what you would read on a retail product page. We compared spec sheets, installation requirements and owner feedback across the full field, and narrowed it down to ten models that actually make sense for a flat, a condo or a rental unit, and we organized them by the constraint they solve rather than by brand.
Before you scroll to the picks, one honest note. If your building already supplies a water heater, the correct move is almost never to install your own. You would be running a second heating source, doubling your electrical or gas draw, and creating a maintenance liability you cannot legally remove at move-out. Ask the building owner first, and if the answer is no, the only purchase that makes sense is a small point-of-use model serving a single sink. If the answer is yes, this guide is for you.
We also wrote a broader tankless water heater roundup that covers the technology in depth, plus a dedicated list of electric tankless water heaters if you want to go deeper on the fuel type that fits apartments best.
Top 3 Picks for Apartment Hot Water in September 2026
CAMPLUX 4.5kW 120V Point…
- 4.5kW 120V point-of-use unit
- 50F rise at 1.0 GPM
- Measures 7.4 x 10.9 x 2.5 inch
ThermoMate 11kW 240V Electric
- 11kW at 240V
- 2.15 GPM at a 35F rise
- Cast aluminum chamber resists scale
Best Tankless Water Heaters for Apartments at a Glance in September 2026
The table below lists all ten models in the order we recommend them, with the fuel type, capacity and the apartment scenario each one fits. Nothing here is rated for whole-home use in a large house, and that is deliberate.
| Product | Specs | Action |
|---|---|---|
| CAMPLUX 4.5kW 120V Point of Use |
|
Check Latest Price |
| ThermoMate 11kW 240V Electric |
|
Check Latest Price |
| EcoSmart ECO 8 |
|
Check Latest Price |
 Rheem RTEX-11 11kW |
|
Check Latest Price |
| Rheem RTEX-08 8kW |
|
Check Latest Price |
 MIZUDO 120,000 BTU Gas |
|
Check Latest Price |
 Rinnai V53DeN Gas |
|
Check Latest Price |
 ThermoMate 75,000 BTU Gas |
|
Check Latest Price |
 APUS 80,000 BTU Gas |
|
Check Latest Price |
 SIVUATEK 14kW Electric |
|
Check Latest Price |
Every model here needs professional installation. None is a plug-and-play appliance except where the manufacturer explicitly documents otherwise, and the gas models all require licensed work on the gas line and vent.
1. CAMPLUX 4.5kW 120V Point of Use Tankless Heater – The Only Realistic Renter Option
CAMPLUX Tankless Water Heater Electric 120V, 4.5kW Point of Use Instant Hot Water Heater, Save Space for Sink Wall Mounted LED Digital Display CSA Certified
120V
4.5kW
1.0 GPM at 50F rise
7.4 x 10.9 x 2.5 inch
4.5 lb
Pros
- Fast 3-second heat-up
- Smallest footprint in the group
- Self-modulating draw
- LED touch display
Cons
- Only 1.0 GPM
- Hard-wired with no plug
- Some owners report breaker trips
This is the model we kept coming back to, and the reason has less to do with specs than with permission. At 4.5 pounds and 7.4 by 10.9 inches, it mounts inside a kitchen cabinet, under a bathroom vanity or in a laundry closet without a wall being cut. It is also the only model in this entire roundup that runs on a standard 120V supply, which is the circuit most apartments already have at a kitchen counter.
In our comparison it pulled the highest review volume of the group by a wide margin, and the pattern in those reviews is consistent. Owners describe hot water in roughly three seconds at a 50 degree rise, a body small enough to disappear above a sink cabinet, and a touch panel with a clear LED temperature readout. The self-modulating design adjusts power input in real time based on flow rate and set temperature, which is why idle draw stays modest.
The specifications matter for planning. Minimum activation flow is 0.26 GPM, so a single low-flow bathroom or kitchen faucet will trigger it, and the listed connection is a 1/2 inch NPT with a 40 amp circuit breaker and 10 AWG wire. That is a modest electrical demand, but note the word hard-wired: there is no plug, so a landlord still has to approve a circuit run even on a 120V supply.
Apartment-specific note: this is genuinely the only unit here a renter could plausibly argue for, and even then only as a personal fixture rather than a unit replacement. It heats one point of use well. It will not run a shower and a sink at the same time, and a 1.0 GPM flow is a kitchen or single-bathroom sink number, not a whole-unit number.
When this CAMPLUX unit is the right call
Choose it when the goal is hot water at one location rather than hot water for the whole apartment. A studio with a kitchen and a powder room, a rental where you want a dedicated hand-wash sink, an accessory dwelling unit kitchen, or an RV or mobile home that has a standard 120V receptacle but no gas. The 1.0 GPM rating and the 50 degree rise mean you set the temperature high and accept a moderate flow, and for hand-washing, dish prep and a quick rinse that is a trade most people happily make.
It is also the least risky install in the group. Twenty volt hard-wiring on an existing 120V branch circuit is a small job, the wall bracket and mounting hardware are in the box, and the unit carries a 2 year limited warranty. If the landlord says yes to a personal point-of-use unit but no to replacing anything, this is the shape of compromise that usually gets approved.
When this CAMPLUX unit disappoints
The failure mode is capacity, not quality. Owners report the unit not heating enough on higher settings, particularly when incoming water is already cool or when a second fixture is opened. The same group of reviews mentions trips when other high-draw appliances run at the same time on that circuit, and the reset button is awkward to reach on some mounting configurations.
Anyone expecting shower-grade output should skip this one. A 1.0 GPM rating is roughly half what a comfortable shower needs, and no setting change fixes that. The unit is also unvented, which is an advantage indoors but does mean it needs genuine clearance around the wiring opening for airflow.
2. ThermoMate 11kW 240V Electric Tankless Heater – Budget Pick for a One-Bedroom
ThermoMate Tankless Water Heater Electric, 11kW 240 Volt On Demand Instant Hot Water Heater for Point of Use, Self-Modulating LED Display Knob Control, ETL Certified, 2.15GPM at 35°F Rise
240V
11kW
2.15 GPM at 35F rise
Up to 131F
11 lb
Pros
- Handles multiple fixtures
- Scale-resistant cast aluminum chamber
- Self-modulating control
- Compact wall mount
Cons
- Needs 50A double-pole breaker
- 240V wiring knowledge required
- Some cold-water error codes
Here is the value pick, and the value is in the jump from sink-only to genuinely covering an apartment. Eleven kilowatts at 240 volts delivers 2.15 GPM at a 35 degree rise, which is enough for a shower and a sink running at the same time in a one-bedroom. Several owners report lower monthly electric bills after moving off a storage tank, which makes sense given there is no standby loss at all.
The build detail that separates it from cheaper electric units is the cast aluminum heating chamber with the element physically separated from the water lines. That separation is the standard answer to scale, and in a hard-water building it is the difference between a two-year headache and a ten-year appliance. The self-modulating control reads temperature and flow continuously, so output holds steady when a second tap opens.
Plan the electrical side carefully. At 11 kW the unit draws up to 46 amps and needs a double-pole 50 amp breaker with 6 AWG wire, on a 240 volt supply. In an apartment building built before the 1990s that may mean a service upgrade rather than a new branch circuit, and that upgrade is a landlord expense, not a tenant expense.
Apartment-specific note: this is the smallest step up from point-of-use that still counts as apartment water heating. It measures 9.72 by 13.78 inches and mounts on a wall, so it fits a utility closet without taking the floor space a tank would. Maximum outlet temperature is 131 degrees, which is fine for showers but worth knowing if anyone in the household needs hotter water for other reasons.
What makes the 11kW ThermoMate work in a flat
Two simultaneous fixtures at a comfortable temperature is the actual apartment requirement, and 2.15 GPM at a 35 degree rise delivers it where a 2 GPM unit cannot. It is ETL certified with overheat protection and automatic no-water shutoff, which matters in a building where a leak means damage to someone else’s unit below. Side water connections keep the plumbing runs short and serviceable.
For a landlord fitting out a rental, this is a defensible middle ground. It is not exotic, it does not need venting, and it does not need a gas line, so it avoids two of the three arguments that stall apartment installations. Reviewers consistently call the temperature stability and the freed floor space the two biggest wins.
What to watch out for with this model
The 240 volt requirement is the real gate. A 50 amp double-pole breaker on a panel that only has 40 amps spare means an upgrade, and an upgrade in a shared building is a conversation with an association, not a weekend project. A minority of owners also report LL error codes and shutdowns when incoming water is cold, which is a capacity symptom rather than a defect.
Clearance matters too. The housing needs airflow around the wiring opening, and in a tight closet that space is not always available. On hard water, some units in this family need a couple of extra seconds to reach set temperature, so allow a few seconds of patience on first draw.
3. EcoSmart ECO 8 – Best Value and the Smallest Full-Size Electric Body
EcoSmart ECO 8 Tankless Water Heater, Electric, 8-kW – Quantity 1, 12 x 8 x 4
240V
8 kW
2 GPM
99.8% efficiency
12 x 8 x 4 inch
4.8 lb
Pros
- Very small wall-mounted body
- Modulating thermostat
- Stainless internals with in-line sensors
- Warranty on electronics and exchanger
Cons
- Cuts off above about 1 GPM
- Professional install required or warranty voids
- Low flow can mean lukewarm water
The EcoSmart ECO 8 is the one we would look at first for a studio or a single-bathroom condo, because it does something the other 8 kW-class units do not. The modulating thermostat and the in-line temperature sensors sit inside the water flow itself, so the unit corrects for pressure and temperature swings faster than a thermostatic dial can. Reviewers describe the output as noticeably steadier than they expected from a unit this small.
At 12 by 8 by 4 inches and 4.8 pounds it is the smallest body in this roundup, and wall-mounting it inside a closet wall frees the corner a 40 gallon tank would have occupied. Efficiency is rated at 99.8 percent because there is no tank to lose standby heat, which is the honest version of the efficiency argument: you save the standby loss, not the water heating itself.
Two installation details catch people out. The manufacturer requires professional plumbing installation, and self-installing voids the advertised lifetime warranty on electronics, exchanger and element. The connections are also 1/2 inch rather than the 3/4 inch size the documentation implies, so a plumber who trusts the manual will order the wrong fittings.
Apartment-specific note: the lifetime warranty is a genuine advantage in a building where the owner controls service access. If the unit fails in year six and the warranty holds, that is a rare outcome in apartment appliances. What you need to confirm first is whether the building will even let a tenant-owned heater sit in a shared utility space, because a warranty is worthless if you cannot reach the unit to make a claim.
Where the ECO 8 earns its spot
It is at its best as a single-fixture heater with room to grow, meaning one sink today and a second fixture later within the flow limit. Owners report it heating well even from cool incoming water in moderate climates, which is more than several competitors manage. The stainless internal plumbing and the sensors also make it a good pick in a building where water quality is uncertain but not extreme.
For a landlord standardizing across a small building, the small footprint and the transferable warranty are the deciding factors. A unit that fits behind a wall cavity, needs no venting and carries real parts protection is easier to specify and easier to service than a gas model with vent requirements.
Where the ECO 8 falls short
Flow rate is the honest limitation. It cuts off above roughly 1 GPM and can deliver only lukewarm water when pushed, so it is a sink-and-shower unit at low flow rather than a comfortable shower unit. Owners who expected a full replacement for a tank heater are the group most likely to be disappointed, because the 2 GPM rating assumes a generous temperature rise.
There is also a cluster of reports about repeating warranty replacements and element scaling in hard water, and about the electrical connections being inside a sealed case so the unit must be opened to wire. If your building is on hard water, budget for descaling and a filter rather than assuming a maintenance-free appliance.
4. Rheem RTEX-11 11kW Multi Fixture – Most Versatile with the Clearest Brand Support
Rheem 11kW Multi Fixture Tankless Electric Water Heater – 240V
240V
11 kW
2.68 GPM
80F to 140F in 1F steps
8.25 x 12.63 inch
Pros
- 2.68 GPM handles a small household load
- Works on a 100A main panel
- No venting required
- Long reported service life
Cons
- Lowest rating in this group at 4.0
- Cover secured from the back
- Supplied adapters prone to slow drips
Among plumbers and service technicians, the Rheem name carries more weight than any efficiency number, and that shows up in how owners talk about this unit. The most common comment we saw across reviews was longevity, with people running multiple RTEX models over several years. That matters more in an apartment than in a house, because the cost of getting a replacement in and out is paid by whoever owns the unit.
Capacity is the strongest argument for it. At 11 kW it delivers up to 2.68 GPM, the highest flow of any electric unit in this roundup, which is what allows it to carry a full small household load on a 100 amp main panel without tripping. Digital thermostatic control in 1 degree increments from 80 to 140 degrees is a level of control that matters when a shower is shared with a kitchen tap.
Installation is straightforward by tankless standards. It needs 240 volt single-phase power, a 50 amp double-pole breaker, number 8 AWG copper and a 100 amp minimum service panel, and it requires no venting at all. The body is roughly 90 percent smaller than a traditional tank heater by the manufacturer’s own figure, which is the reason it exists.
Apartment-specific note: this is the pick for a two-bedroom or a two-bathroom condo where two people could reasonably shower at once. Mount it close to the fixtures to cut the wait, and note that it is a multi-fixture unit, so a kitchen, a main bath and a powder room can all draw from it within the flow limit.
Why the Rheem RTEX-11 suits a shared building
Parts availability and technician familiarity are the practical advantages here, and they are not marketing. A brand with an established service network means a failed part is a same-week fix rather than a weeks-long search, and in a building where you are not the owner that difference decides whether an outage becomes a complaint. The warranty is 5 years on leaks and 1 year on parts, which is thinner than some rivals but backed by a much larger service footprint.
The 100 amp panel requirement is also more achievable than it sounds. Apartments with 40 amp sub-panels are the problem case, and this unit sidesteps that only if the main service has headroom. Check the panel label before you fall in love with the flow rate.
What buyers should know before ordering
This model has the lowest rating in our set at 4.0, and the reason is build quality rather than performance. Owners point to mostly plastic construction and supplied adapters that drip slowly over time, plus a recurring group of delivery-damage reports involving broken cover tabs and missing dials. A slow drip inside a closet in a high-rise is a real problem, so budget for quality fittings rather than the supplied ones.
Two more practical notes. The cover is secured from the back, so the wiring has to be finished before the unit is mounted, which changes the install order. And a low-flow or clogged showerhead can cause the unit to stop heating entirely, so clean the aerators before blaming the appliance.
5. Rheem RTEX-08 8kW Multi Fixture – Best for Studios and Tight Closets
Rheem 8kW Multi Fixture Tankless Electric Water Heater – 240V
240V
8 kW
1.95 GPM
80F to 140F in 1F steps
5/8 inch compression
Pros
- No storage tank in a very small space
- Accurate digital display
- Easy 240V install for a confident homeowner
- Handles a kitchen and a bath
Cons
- Barely carries a shower on its own
- Needs throttling for usable temperature
- Scale shortens life in hard water
Compare this to the RTEX-11 one size down and the difference tells the whole story. At 8 kW and 1.95 GPM it is a smaller machine, and reviewers converge on the same sizing lesson: it serves a kitchen sink well, it can just about carry a shower at a restricted flow, and it will not comfortably run two fixtures at once. Owners who understand that up front rate it well; owners who expected a tank replacement rate it badly.
What it does have is the same digital thermostatic control in 1 degree increments from 80 to 140 degrees as the larger model, and reviewers report the display holding a measured 120 degrees accurately. The body is 8.25 by 12.63 inches, which is small enough for a studio apartment, a tiny home or an RV, and the endless supply means no tank to leak onto a neighbor below.
The electrical requirement is friendlier than the 11 kW model, and that is why it earns a place in this roundup. It runs on a 40 amp double-pole breaker with number 8 AWG copper and a 100 amp minimum panel, so on a moderately sized apartment service it can often go in without a service upgrade. No venting is required either, which removes the single biggest install complication on the gas models below.
Apartment-specific note: if your lease permits a hard-wired personal unit at all, an 8 kW on a 40 amp breaker is the least disruptive version of that conversation. Documented connection size is 5/8 inch compression rather than the 1/2 inch stated in the paperwork, so confirm that with your installer before parts are ordered.
Who should look at the 8kW Rheem
A studio, a one-bedroom where the hot water use is genuinely modest, or an RV or mobile home. Owners report that a 1.25 GPM showerhead performs comparably to a tank heater when paired with this unit, which is the practical trick: install a low-flow showerhead and the effective capacity goes up. It also handles a dishwasher or washing machine demand within its flow budget if you stagger them.
It is a good landlord unit for a furnished short-term rental where the goal is no tank leak risk and no standby loss rather than luxury flow. The digital control also means tenants cannot crank the temperature past a safe setpoint, which is a small operational win in a managed property.
Where the 8kW model frustrates owners
At full flow it needs a limiter or a partly closed valve to deliver a usable temperature, and that workaround is not obvious to a first-time buyer. Several owners describe the transition from acceptable to frustrating as soon as a second person uses hot water. The fitting documentation mismatch is the other recurring complaint, and it delays installs.
Hard water is the long-term risk. Owners report heating element scale shortening service life without a filter, and an apartment resident may not be the person who does the descaling. If your building is in a hard-water area, budget for an annual flush and a scale filter, or pick a model with a separated heating chamber instead.
6. MIZUDO 120,000 BTU Natural Gas – Best for Smart Control Where Gas Exists
MIZUDO 120,000 BTU Natural Gas Tankless Water Heater,Max 5.1 GPM,WiFi&APP
Natural gas
120,000 BTU
5.1 GPM
WiFi and app
Indoor or outdoor
Pros
- WiFi and app control with alerts
- Converts from indoor to outdoor
- Quiet operation
- Holds temperature within about 1F
Cons
- Gas fittings and vent hardware not included
- Error codes reported at high elevation
- No fresh-air intake
Most apartments have no gas line, so this pick only applies to a specific group: a condo or a single-family rental where gas is available, or a building where the owner has already run gas to a utility space. If that describes you, this is the most capable gas machine in the roundup. Five point one GPM from 120,000 BTU is real whole-unit capacity, and owners report sustained very hot water indefinitely for a single shower.
The differentiator is the app. WiFi and app control covers temperature, energy monitoring and maintenance alerts, and the flow monitoring with gas modulation holds output within about 1 degree. For a landlord managing a rental remotely, the maintenance alerts are the part that actually saves money, because they flag a scaling or freeze issue before a tenant complains.
The convertible installation is unusual and useful. Indoor mounting needs a 3 inch outside-diameter vent pipe, and outdoor mounting uses a conversion kit sold separately. That flexibility matters in an apartment utility space where a wall penetration may be difficult but an exterior patio or balcony wall is available. The heat exchanger is phosphorous-deoxidized copper with a stainless steel combustion chamber, and the warranty is 2 years on the unit and 5 years on the heat exchanger.
Apartment-specific note: the anti-freezing protection is a real advantage in a balcony or exterior closet in a cold climate, but the unit must be drained if it will sit unused through freezing weather. The 1 degree temperature stability also makes it the easiest of the gas models here to live with in a wall shared with a neighbor, since it does not modulate loudly during draw.
What makes the MIZUDO worth the gas line
Capacity and control together. Five point one GPM covers a shower, a laundry load and a dishwasher without anyone feeling the difference, and the app gives you the data to prove it. Owners consistently report quiet operation and heat-up within seconds, which matters in a unit mounted near a bedroom wall or a shared mechanical space.
The indoor-outdoor convertibility is the quiet advantage. Most competitors force a choice at purchase, and choosing wrong is expensive. Here you can install indoors, and if the building later objects to the vent penetration, a kit converts the unit rather than replacing it.
What could go wrong with the MIZUDO
The loudest complaint thread is cold-climate and high-altitude error codes, with one owner reporting recurring codes and short bursts of hot water at elevation. Gas appliances are derated for altitude, so if your building is above roughly 5000 feet, verify the unit is rated for your elevation before you buy.
Gas fittings and vent hardware are not included, and the instructions do not clearly state the required gas line capacity, so confirm both with your installer. There is also no dedicated fresh-air intake, which is a genuine limitation in a tightly sealed space. Budget for a landlord conversation about combustion air in an attached unit.
7. Rinnai V53DeN Natural Gas – Best Gas Capacity with the Longest Heat Exchanger Warranty
Rinnai V53DeN Natural Gas Tankless Water Heater
Natural gas
5.3 GPM
Outdoor rated
33 lb
10 year heat exchanger warranty
Pros
- Highest GPM in the roundup at 5.3
- Serves up to four appliances
- 10 year heat exchanger warranty
- Established installer network
Cons
- Professional installation required
- Outdoor install still needs a specified vent
Among the brands plumbers actually name when asked which they trust, Rinnai appears alongside Navien and Stiebel Eltron, and this model is the reason. At 5.3 GPM serving up to four appliances its flow rating is the highest in this roundup, and the heat exchanger coverage is the longest we found: 120 months on the heat exchanger, 60 months on parts and 12 months on labor.
That labor term has a condition worth knowing. Register the unit within 90 days of installation or the labor warranty defaults to a single year. Set a reminder, because it is an easy step to miss and it is the difference between a ten-year protection and a one-year one on the most expensive component.
The body is compact at 33 pounds with a 7.9 inch depth and an outdoor-rated installation footprint, which makes it easier to place in a small mechanical area than a 40 gallon tank it would otherwise replace. Because it heats only on demand, there is no standby energy loss, and the compact footprint means it can sit where the tank stood without rebuilding the space.
Apartment-specific note: Rinnai maintains a national professional installer network through Rinnai PRO, and in a building where you are not the owner, having a documented installer path is a genuine advantage. Confirm the building allows a gas appliance in the space first, since venting and gas line work almost always requires owner sign-off.
Why the Rinnai earns a spot in an apartment
Two reasons, both about risk rather than speed. The first is that it is a capacity unit: 5.3 GPM means an entire apartment can run hot water simultaneously, which is exactly the case where a smaller unit disappoints. The second is the heat exchanger warranty at ten years, which in a rental or condo is the number that makes a building owner comfortable approving the install.
It is also the safest gas choice for a shared mechanical room, because the compact depth means it fits in a standard recess without pushing into a hallway or a neighbor’s storage space. Owners cite size and brand warranty backing as the two main draws, and both matter more in an apartment than in a house.
What the Rinnai costs you
Installation and venting. Rinnai recommends professional installation, and gas work plus vent work is the single most expensive part of any tankless project. Outdoor installation still requires a vent system specified for the unit, so the outdoor-rated label does not mean ventless.
The second cost is process. A gas appliance in a rented or associated unit needs approval, and in most buildings it needs a licensed gas fitter as well. Buyers who treat that conversation as a formality are the ones who get surprised by the schedule.
8. ThermoMate 75,000 BTU Natural Gas – Best for Small Gas Spaces
ThermoMate Natural Gas Tankless Water Heater, Up to 3.06 GPM 75,000 BTU
Natural gas
75,000 BTU
3.06 GPM
98% efficiency
UEF 0.81
19.8 lb
Pros
- Comfortable shower even at 52F incoming water
- Under one third the volume of a tank
- Plug-in 120V control wiring
- Eight-layer safety protection
Cons
- Vent hardware not sold and docs unclear
- Some temperature swing reports
- Class 3 vent can be costly
This is the gas pick when the space is the problem rather than the capacity. The body is 21 by 13 by 7 inches and 19.8 pounds, under one third the volume of a conventional tank heater, and at 75,000 BTU and 3.06 GPM it is sized for a small apartment rather than a house. Owners report a comfortable single shower at 2 GPM and 105 degrees even with 52 degree incoming water, which is an honest test of a gas unit in a cool climate.
Two design details make it apartment-friendly. The oxygen-free copper heat exchanger is rated at 98 percent thermal efficiency with a UEF of 0.81, and the control electronics run on a UL-approved 120V plug rather than hard-wired current, which simplifies wiring in a space where the gas line is the only thing a plumber wants to touch.
The safety package is unusually thorough, with eight protections including boil-dry, freeze, flame-out, overheat, pipe blockage and excessive air pressure, plus a 3.5 inch LED diagnostic display that shows error codes and adjusts from 90 to 140 degrees. Four ceramic heating cores with frost protection activating at 41 degrees add another layer against a cold closet.
Apartment-specific note: flow and temperature sensors hold output within about 1 degree, with the control chip adjusting 20,000 times per second. That stability is what makes a unit in a wall next to a neighbor less likely to produce complaints about temperature swings. Water connections are 3/4 inch NPT with a 1/2 inch NPT gas inlet and a 3 inch outside-diameter vent connection.
Where the 75,000 BTU ThermoMate fits
A one-bedroom or a two-bedroom with one bathroom, where gas is available and the closet is genuinely tight. The sub-one-third volume figure is the useful one here, because it is what lets the unit occupy a shallow recess that a 40 gallon tank physically cannot fit into. Owners also report responsive manufacturer and seller support, including a credit issued to resolve a venting issue.
It is also the pick for a landlord who wants a visible diagnostic display. When a tenant reports a problem, the error code on the front panel narrows the diagnosis before anyone opens a cover, which reduces service call time in a managed building.
What buyers complain about most
Venting, consistently and from several directions. The vent pipe and vent type documentation is unclear, the required parts are not sold with the unit, and Class 3 vent requirements can add significantly to the installed cost. Confirm the vent specification with your installer before ordering, not after.
A few owners report temperature swings between cool and too hot, and a small number of units arrived with a control panel that would not power on. Neither is common, but both point to a tighter quality-control question than the Rinnai or Rheem equivalents, and that is the trade for the smaller footprint and the plug-in controls.
9. APUS 80,000 BTU Natural Gas – Best for a Straightforward Gas Install
APUS Natural Gas Tankless Water Heater, 80,000 BTU, 3.6 GPM Indoor
Natural gas
80,000 BTU
3.6 GPM
95F to 149F setpoint
19.2 lb
Pros
- Vent pipe included in the box
- Low-flow start at 0.53 GPM
- Confirmed operation at 6300 ft
- Holds within 1F when another tap opens
Cons
- Some units run without heating the water
- Flow drops with cold incoming water
- Must be drained before freezing weather
The APUS is the pick when the priority is a predictable install rather than a feature list. At 80,000 BTU and 3.6 GPM it is sized by the manufacturer for 2 to 3 water points in a one or two person home, apartment or tiny home, which is an unusually honest sizing statement. Owners describe installation as close to plug-and-play for a licensed installer, largely because the vent pipe is in the box with the heater.
Two details stand out. The low-flow start threshold is 0.53 GPM, so it will fire in an apartment with lower water pressure than a high-threshold unit would, and the temperature holds within about 1 degree even when another faucet opens. It is also one of the few models here with documented high-altitude operation, confirmed at 6,300 feet.
Controls are a 95 to 149 degree setpoint range on an LED display, and the unit carries a 2 year manufacturer warranty. Dimensions are 20.55 by 13.27 by 5.91 inches at 19.2 pounds, so it mounts on a wall in a standard utility alcove without the depth a tank would need.
Apartment-specific note: the included vent pipe removes the most common source of install delay and cost overrun, which is a practical advantage in a building where a vent termination has to clear an association rule. Anti-freeze protection activates near 41 degrees, but the unit must be drained below that or during any extended non-use period, so ask about winter shutoff in a vacant rental.
Why the APUS is a good landlord unit
Everything that costs money at install time is accounted for. The vent pipe ships in the box, the assembly kit and installation card are included, and the low-flow start means it will work in an older building with modest supply pressure. Customer support resolved a vent blockage issue quickly for at least one owner, which is the kind of responsiveness that matters when a tenant is waiting.
It is also the easiest of the gas models to spec for a rental because the manufacturer states the intended household size plainly. A property manager can match 3.6 GPM to a one-bedroom without running a calculation, and the 0.53 GPM start threshold protects against older piping in the building.
Where the APUS falls down
There is a cluster of reports of units that run without meaningfully heating the water, and flow drops noticeably when incoming water is in the 40s or 50s. That is a sizing and climate problem rather than a random defect, but it will look like a failure to whoever is living there, so spec conservatively for a cold region.
The installation and use manual contains no contact information for the manufacturer, which is a small thing that becomes a large thing when a unit needs support. The unit must also be fully drained before freezing temperatures or long non-use periods, so it is a poor fit for a seasonal or occasional-use apartment without someone responsible for it.
10. SIVUATEK 14kW 240V Electric – Best for a Sink and Shower at Once
14kW Tankless Water Heater Electric 240V, Sink & Shower,Gray
240V
14 kW
3.3 GPM
86F to 131F in 1F steps
ETL certified
Pros
- Highest electric rating in the set at 4.4
- 3.3 GPM covers two usage points
- LED shows inlet outlet temp and GPM
- No standby losses
Cons
- Requires a 60 amp breaker
- Maximum outlet temperature capped at 131F
- Not sized for whole-home demand
This is the highest-rated electric unit in the group, and the only one here whose reviews describe sink and shower use together as a solved problem rather than a compromise. At 14 kW and 3.3 GPM it carries one to two simultaneous usage points, and the review distribution is 73 percent five star with only 6 percent one star, the lowest negative share of any model we compared.
Interface quality is a genuine feature here. The LED display shows inlet temperature, outlet temperature, GPM and kW at once, with control in 1 degree increments from 86 to 131 degrees, so you can see what the unit is actually doing instead of guessing. Thermal efficiency is rated at 99.8 percent and heat-up is reported at three seconds, and wiring can be completed without disassembling the housing.
Design choices target longevity. Water and electricity are physically separated to limit scale buildup, and the unit includes leakage, overheat and automatic shut-off protection. Dimensions are 12.2 by 17.25 inches with a 15.87 inch depth, so it mounts on a wall or under a sink depending on the space you have rather than a fixed orientation.
Apartment-specific note: this needs a dedicated 60 amp breaker, which is the highest electrical demand of any unit in this roundup. If your panel has the headroom it is the most capable electric option for a two-bathroom apartment. If it does not, the 11 kW models on this list are the realistic ceiling for most apartment service.
When the 14kW SIVUATEK is the right size
It fits the apartment scenario that defeats the 8 kW class, which is a real shower plus a kitchen sink at the same time. Owners highlight exactly that combination in their feedback, and the 3.3 GPM rating is the number that makes it possible. It is also the pick for a condo with two full bathrooms, where a lower-flow unit would be a permanent annoyance rather than a minor one.
The 3 second heat-up and the diagnostic readout make it a good fit for a shared building where a tenant will call about a slow shower. The visible GPM and temperature numbers let a maintenance conversation stay factual, which reduces the number of service visits a small property has to make in a year.
What to check before you commit
The 60 amp circuit is the gate. Some apartment electrical panels cannot provide it, and a service upgrade is a landlord decision that takes weeks. Confirm the panel rating and available breaker positions first, because that answer determines whether this is your unit or a 40 amp model.
Maximum outlet temperature is capped at 131 degrees, which is fine for showers and hand-washing but limits uses such as very hot laundry or sterilization. The unit is also unsized for high-demand whole-home simultaneous use, so in a three-bedroom where two showers could run together you would be undersized and would see it in the winter.
Can You Install a Tankless Water Heater in an Apartment? Ask Before You Buy
The honest answer is that in most apartments you cannot install one at all, and that is a lease and building question rather than a shopping question. A hard-wired heater, a new breaker, a vent penetration and a gas line are all alterations to structure and common systems, and virtually every lease and condo document requires written owner or association approval before any of them happen. A thread on r/Plumbing about adding a tankless heater to a three-flat owner draws exactly this advice, and the conversation centers on feasibility and permission rather than which model to buy.
There is a second blocker that catches people first: in most apartment buildings the water heater is building-owned. Replacing it is not your decision, and adding a second heater to a rented unit means the previous tenant has to remove it at move-out. That removal cost, plus any damage to the walls during installation, is why most landlords say no.
What does tend to get approved is a point-of-use unit serving a single personal fixture, installed by a licensed plumber, on a tenant-owned circuit, with the understanding that it comes out at move-out. The CAMPLUX 4.5kW at the top of this list is the most common shape of that approval because it is small, runs on 120 volts and does not touch the building’s hot water supply.
Ask these five questions before you spend anything. Is the existing heater building-owned? Does my lease or association rules require written approval for a hard-wired appliance? Is electricity in the target space on a tenant meter or the building meter? Is gas available in the unit or the utility space, and is there a vent route? And who is responsible for annual maintenance and for removal at move-out?
One more, and it is the one that quietly decides the savings math. In a sub-metered building your savings are yours, but on a shared building service the hot water cost is spread across every unit, and a more efficient heater in your apartment does not lower your share. If the building already owns an efficient heater, tankless may not pay back for you at all, which is a perfectly valid reason to skip it.
How to Choose a Tankless Water Heater for an Apartment: 7 Decisions
1. Size by GPM, not by marketing horsepower
Gallons per minute is the only sizing number that matters, and the figure is always quoted at a temperature rise. A unit rated at 3 GPM delivers that flow at roughly a 35 degree rise; ask for the flow at your actual rise and the number falls. As a practical guide, a single sink wants about 1 to 1.5 GPM, a low-flow shower plus a sink together wants about 3 GPM, and two showers running at once wants 5 GPM or more. In a colder climate, subtract meaningful capacity because colder incoming water needs a bigger rise.
Sizing down is the most common expensive mistake. A too-small unit in a two-bathroom apartment produces lukewarm water in winter and gets blamed on the brand, when the actual problem is the buyer’s spec. If you can only afford one number to check before ordering, check rated GPM against simultaneous fixtures.
2. Confirm the electrical panel before you fall for flow rate
This is the apartment gate that kills most purchases, and it is a pass or fail check. Roughly: a 4.5 kW 120V unit needs a 40 amp circuit; 8 kW units need a 40 amp double-pole breaker; 11 kW units need a 50 amp double-pole breaker; and 14 kW needs 60 amps. Most of the electric models in this roundup also specify a 100 amp minimum service panel. Older apartment buildings frequently have 40 or 50 amp sub-panels, and adding a 50 or 60 amp breaker to one of those means a service upgrade, which is a project, a permit and a landlord approval.
Read the panel label rather than the breaker sizes you can see. If the main service is already 100 amps or higher and there are two spare breaker slots, you are fine for most of this list. If the label says 40 amps, only the 120V point-of-use unit on this page is realistic, and that is not a failure, it is the correct answer for that building.
3. Treat electric as the default and gas as the exception
For apartments, electric wins on process even when gas wins on output. Electric units need no vent penetration, no combustion air and no gas line, which removes the three items that most often require association sign-off. Condensing gas units recover heat from exhaust and can run at higher efficiency, but the payoff in a studio or one-bedroom is small compared to the installation friction.
Gas makes sense in three situations: a condo or single-family rental with an existing gas line and a vent route, a landlord upgrading a building-owned unit where one gas heater serves several apartments, or a very cold region where incoming water temperature is the limiting factor. For everyone else, an electric point-of-use or 11 kW unit is the lower-friction path. Our gas water heater guide covers the conventional side of that comparison if the building already runs gas.
4. Ask about venting, clearance and where the unit will actually go
Electric units need no flue but do need clearance and accessible shutoff. Gas units need a vent, and the three gas models here vary widely on what arrives in the box: one includes a vent pipe, one requires a conversion kit for outdoor mounting, and one does not include vent hardware at all. That difference is a bigger cost driver than the appliance itself, so ask for the vent specification in writing before ordering.
Measure the actual alcove, including service access. In an apartment, a unit that can be isolated and drained matters more than a unit that is slightly more efficient, because whoever services it may need to reach it from a shared corridor. A 2 to 3 inch service clearance around controls is the minimum we would accept.
5. Plan for hard water and for who does the descaling
Mineral scale is the most common tankless issue reported by owners, and the answer that comes up repeatedly in forums is descaling. In an apartment the complication is not the technique, it is access and responsibility. A tenant may be able to do a monthly vinegar flush and nothing more, and a building-owned unit is the building’s problem whether or not you want it to be.
Prefer designs that fight scale. The ThermoMate 11kW uses a cast aluminum chamber with the element separated from the water lines, and the SIVUATEK separates water and electricity paths, and the Rheem units benefit from a scale filter. In hard-water buildings, an annual professional flush is a reasonable line item to include in any budget conversation with an owner.
6. Consider noise and recirculation in attached units
Electric tankless units are quiet, because there is no burner. Gas units modulate combustion, and a unit sharing a wall with a neighbor or mounted near a bedroom is worth testing before installation. The MIZUDO and the APUS both report about 1 degree temperature stability through flow and gas modulation, which is the mechanism that keeps a gas unit from cycling loudly during a shower.
For long pipe runs in an older building, the real problem is not the heater, it is the distance. A recirculation loop fixes a slow tap far more effectively than a bigger unit, and it is worth asking the building owner about before you buy anything, because it is a common-measure improvement that benefits every unit in the stack. If noise is a live concern in a high-rise, our notes on isolation for shared-wall equipment cover the general principle of mounting in attached spaces.
7. Know when to skip tankless entirely
Do not buy tankless in an apartment if any of these apply. You cannot get written permission and you are not the unit owner. Your panel cannot support a 40 amp double-pole breaker without a service upgrade nobody will approve. Your building has hard water, no annual service access and a landlord who will not commit to descaling. Your household uses very little hot water, in which case the savings never justify the install. Or your electric rate is high enough that a resistive heating element costs more per shower than the tank unit it replaced.
There is one more honest case: if the building already has a reasonably efficient heater with a short pipe run to your fixtures, the change may not pay back. Buying the best tankless water heater for apartments is the right move when your constraints are space, age and standby loss. It is not a substitute for permission you do not have.
Frequently Asked Questions
Can I install a tankless water heater in an apartment?
Only with written approval from your landlord or condo association, because installation usually means a hard-wired circuit, a vent penetration or a gas line connection. In most buildings the existing heater is owned by the building, so adding a second one is usually refused. The most commonly approved option is a small point-of-use unit serving one personal sink, installed by a licensed plumber and removed at move-out.
What are the downsides of a tankless water heater?
The main drawbacks are upfront install cost, a fixed power requirement, and maintenance. Electric units need a dedicated 40 to 60 amp breaker, which can mean a service upgrade. Flow rate is a hard ceiling, so a unit that is too small gives lukewarm water when two fixtures run. Scale buildup in hard water also needs periodic descaling, and gas units add vent installation cost and constraints.
Why are plumbers against tankless water heaters?
Most are not against them, but they are against undersized units and unpermitted installs. A unit bought for its kW rating rather than its rated GPM disappoints in the first cold month, and the plumber takes the blame. They also object to vent hardware specified but not supplied, and to panel upgrades discovered only after the unit is already on the wall.
Can you replace a 50 gallon water heater with a tankless water heater?
Usually yes, and it is the case tankless handles best, because the saved floor space is the whole point. The constraint is flow: a typical shower needs about 2 GPM and two showers need 5 GPM or more. Check that the unit’s rated GPM covers your simultaneous use, and confirm the electrical panel can carry the required breaker before buying.
What size tankless water heater do I need for an apartment?
For a studio or one-bathroom apartment serving a sink and a low-flow shower, 1.5 to 2 GPM is enough. For a one or two-bedroom with a shower and a sink running together, target 3 GPM or more. For two simultaneous showers, look for 5 GPM or more. These figures assume a roughly 35 degree temperature rise, and cold incoming water in winter reduces usable output.
What is the most common issue with tankless water heaters?
The most common reported issue is mineral scale building up on the heating element, especially in hard-water areas. Symptoms are declining flow, longer heat-up times and eventually an error code or shutdown. The fix is a periodic flush or descale, and prevention is a scale filter plus a unit design that keeps the element separated from the water path.
Do I need landlord permission to install a tankless water heater?
Yes, in nearly every apartment. A hard-wired heater, a new electrical breaker, a vent penetration or a gas connection all alter the building, and leases and association rules normally require written approval before any of them. Ask specifically about ownership, who pays for the install, who handles annual maintenance and what happens to the unit when you move out.
Do tankless water heaters work in cold climates?
They do, but cold incoming water reduces usable capacity because the unit must deliver a bigger temperature rise. That means a unit that performs well in summer can feel undersized in January. Sizing for your coldest-month incoming water temperature is the fix, and gas units need altitude and freeze protection verified if they are installed outdoors or in an unheated closet.
Our Verdict for Apartment Dwellers in 2026
Pick the CAMPLUX 4.5kW 120V point-of-use unit if you are a renter and need one fixture. It is the only model in this roundup that runs on a standard apartment circuit, mounts inside a cabinet and gets approved as a personal appliance more often than anything else we reviewed. Pick the ThermoMate 11kW if you own the space and can get a 50 amp double-pole breaker, because 2.15 GPM at a 35 degree rise is the first capacity in this list that actually covers a one-bedroom properly. Pick the SIVUATEK 14kW if your panel has the headroom for a 60 amp circuit and you need a shower and sink running together.
For a building owner replacing a shared tank, the Rheem RTEX-11 gives the best balance of capacity, a 100 amp panel requirement and a service network that technicians already know. If gas exists in the space, the Rinnai V53DeN carries the strongest heat exchanger warranty and the highest flow in the group.
Our pick this if space is the constraint and you are the owner, a large service or 2026 electricity rates are the constraint, or the tank keeps failing. Skip tankless entirely if you cannot get written permission, if the panel needs an upgrade nobody will approve, or if the building’s existing heater already runs efficiently with a short pipe run to your taps. That is the complete picture for the best tankless water heaters for apartments in 2026, and the permission conversation matters more than the model choice.
If you want the technology explained without the apartment lens, our general tankless water heater roundup goes into how the units work, and our electric tankless picks and heat pump water heaters cover the alternatives worth comparing if your building has no gas line.