The one-shower question
Some homeowners want a tankless unit for one bathroom, a basement apartment or an addition. A small electric or gas unit can do that, as long as you size it for the coldest water of the year.
Everything starts with two numbers: how many gallons per minute the shower uses and how many degrees the water must rise.
Calculate flow and rise
Find the flow
Check the shower head label. Many modern heads use about two gallons per minute, and older ones use more.
Pick the target
A comfortable shower is around 105 degrees at the head.
Find the inlet
Use the coldest incoming water temperature for your area, not the summer number.
Subtract
The difference is the temperature rise the unit must deliver at that flow.
A unit rated for 2 gallons per minute at a 70 degree rise works in summer, but may only manage a lower flow in winter.
The North Olmsted angle
The National Weather Service normals for Cleveland put the average January low at about 22 degrees. Incoming water in winter is far colder than in summer, so the temperature rise needed is much larger. A unit that looks fine on a summer sizing chart can deliver lukewarm showers in January. Size the unit using the winter rise, and ask the manufacturer for its winter flow chart.
Electric or gas for a single shower?
| Type | Pros | Watch for |
|---|---|---|
| Point-of-use electric | Small, no venting, near the shower | High current draw and a dedicated circuit |
| Whole-house electric | No venting, quiet | Large panel load, often too much for old panels |
| Gas tankless | High flow | Venting, gas line and condensate drain |
| Small storage tank | Simple, low upfront cost | Uses space and standby energy |
For one shower far from the main heater, a point-of-use unit is attractive. For a shower in the same house with a full heater already, you may not need a second unit.
Panel and circuit checks
An electric unit may need a 30 to 60 amp circuit or more. Older houses with 100 amp panels and no spare capacity may need an upgrade. Ask an electrician to confirm before you buy.
Gas units avoid the panel issue but need a vent, a gas line and a drain. Compare both before you decide.
Comfort details
- Minimum flow: tankless units need a minimum flow to fire, and a low-flow head may not trigger it.
- Cold water sandwich: a brief cold burst between hot water uses.
- Pipe length: a long run from the heater wastes water while it warms.
- Mixing valve: helps keep temperature steady.
- Scale: hard water scales small heat exchangers, so plan to flush.
When a one-shower unit is not the right fit
If you plan to add a second bathroom, a kitchen or a laundry, size for the future. A small unit that covers one shower will not keep up with two at once.
For a whole house, see our tankless water heater page. If you want to replace a failed tank first, water heater replacement is the page for that.
We can size it for you
We install in North Olmsted and in Westlake and Fairview Park. Tell us the shower head flow and where the unit will go, and we will talk through the winter sizing numbers.
Installing a point-of-use unit
A small electric unit mounts on the wall near the shower and connects to the cold supply and the shower line. It needs a dedicated circuit, a breaker sized to the heater and correct wire gauge. This is work for a licensed electrician in most cases.
On the plumbing side, install shutoff valves and a union connection so the unit can be serviced. Keep the pipe run short, because every foot between the heater and the shower holds cold water that you wait for.
Running costs and comfort
A small unit uses electricity only when water flows, so there is no standby loss. For a household that showers for a short time each day, that can be efficient. Longer showers and larger families push the bill up quickly.
Comfort depends on setting the temperature once and not fighting the controls. Use a thermostatic mixing valve if the unit supports it, so that temperature does not swing when someone flushes a toilet elsewhere in the house.
Alternatives worth comparing
A small storage tank heater under the sink or in a closet can serve one bathroom without the demands of a tankless unit. A mini-tank has a short run and no minimum flow, and it costs less to install.
A recirculation system on a whole-house heater can also solve slow hot water at a far shower. It moves hot water through a loop so the tap delivers heat quickly, though it uses energy to do so.
Think about how the shower is used. A guest bath used a few times a month is a very different job from a master bath used by two people every morning. Choose the option that fits the real pattern.
Final checks before you buy
Confirm the flow rate of the shower head, the coldest incoming water temperature and the circuit capacity. Ask the maker for the winter flow chart at your temperature rise.
Confirm warranty terms, and ask who services the unit locally. A great unit with no local service is a poor purchase when it breaks in January.
A simple decision path
If the shower is far from your main heater and used rarely, a small point-of-use unit may fit. If the shower is close to the main heater, fixing the existing heater or adding a recirculation line often makes more sense.
If you are building new, plan the circuit or gas line in the walls now. Adding power later is far harder than roughing it in.
Codes for power and plumbing
An electric unit needs a circuit installed under the National Electrical Code (NEC), and the plumbing side follows the Ohio Plumbing Code, which is based on the International Plumbing Code (IPC). Hire a licensed electrician for the circuit and keep the permit paperwork.
Questions homeowners ask
Yes, if it is sized for the winter temperature rise at the shower flow rate.
Incoming water is colder, so the unit needs a larger rise. An undersized unit cannot keep up.
Only if the shower is far from your main heater or you cannot run hot water to it easily.
It saves water, but the heater needs a minimum flow to ignite. Check the specification.
Yes. Scale builds in small heat exchangers, so plan on regular flushing.
Have a question that is not here? Call (440) 468-0237.