# Can a Tankless Water Heater Work With a Private Well?

Source: https://brictale.com/water/pressure-tanks/can-a-tankless-water-heater-work-with-a-private-well
Published: 2026-08-30
Audience: Homeowner
Published by Brictale, a consumer home-intelligence publication. https://brictale.com

## Short answer

Yes, a tankless heater can work on a private well, but there is no universal pressure or flow pass mark. Record the exact model’s minimum pressure and flow, measure pressure at the heater while water is flowing, account for treatment pressure loss and simultaneous demand, then verify water-quality limits and warranty terms. Unknown or failed gates mean design review before purchase.

---

# Can a Tankless Water Heater Work With a Private Well?

Yes. A tankless water heater can work with a private well when the complete water path can deliver the exact heater’s required pressure and flow during the demand you care about, and when the well water meets that model’s water-quality and maintenance requirements. The pressure-switch numbers at the tank are not enough to decide.

The homeowner decision is therefore not “Does a well work with tankless?” It is:

> Does this exact heater, on this exact well system, still have the manufacturer-required flowing pressure and flow after the pressure tank, pump cycle, filters, softener, pipe losses, and simultaneous demand are accounted for—and is there a documented plan for water quality, service, gas or electrical work, and local requirements?

This worksheet produces one of three records:

- **Go to professional quote:** every model-specific gate is documented as passing, the test conditions are clear, and installation scope is still assigned to qualified trades.
- **Needs design review:** a gate may be workable but pressure, flow, treatment loss, chemistry, peak demand, or installation scope is unknown or marginal.
- **Do not buy this model yet:** a documented model requirement is not met, water quality is outside the manual, or the system is unstable under the intended demand.

There is no universal “40 psi means yes” rule. Bosch publishes different well-pressure recommendations for different covered heater cases, Rheem gives its Eagle manual specific minimum pressure and flow figures, and Rinnai directs the reader to the exact specification sheet for minimum flow. Keep those numbers attached to the model and manual revision that produced them.

## The decision in one sentence

Buy only after you can fill this record from the exact manual and measured conditions:

| Gate | Record this | Pass interpretation | Stop or handoff condition |
|---|---|---|---|
| Exact heater | Brand, full model, fuel, indoor/outdoor version, manual and specification-sheet revision | The numbers below are tied to one model | A family name, retailer title, or screenshot is not enough |
| Minimum pressure | Manufacturer minimum operating or inlet pressure | Measured flowing pressure at the heater is at or above the exact requirement under the intended demand | No model value, or a reading only at the tank with no flow test |
| Minimum flow | Activation flow and, if listed, continuous-flow minimum | Measured flow stays above the relevant model minimum without pressure collapsing | Flow is below or close to minimum, or the heater manual says performance changes near the minimum |
| Well cycle | Pump cut-in, cut-out, cycle behavior, and pressure-tank type | The cycle is stable and does not make the heater fall below its gates | Rapid cycling, unexplained pressure swings, or a proposed control change |
| Treatment | Filter, softener, iron or sulfur treatment, UV, bypass, and measured pressure drop | Treatment preserves the model’s flowing pressure and is compatible with its water-quality instructions | Pressure loss is unknown, media is exhausted, or bypass changes the water quality reaching the heater |
| Water quality | Certified lab results and date for relevant chemistry | Results fit the model’s limits or a documented treatment design does | No current results, corrosive or scale-forming water without treatment, or warranty uncertainty |
| Peak demand | Fixtures and appliances expected at the same time, with measured or rated flow | The system and heater performance table cover the combined demand and required temperature rise | Demand is based only on heater “maximum GPM” marketing or the pump’s horsepower |
| Installation boundary | Gas, electrical, venting, condensate, relief, drainage, permits, and local code questions | Qualified installer has reviewed the complete scope | You would need to open energized controls, change pump settings, modify gas or electrical systems, or alter a well |

The table is a record, not a guarantee. A pass means the evidence is adequate for a qualified installer to price and design the work; it does not turn a homeowner measurement into an installation approval.

{{visual:well-to-heater-pressure-path}}

## 1. Freeze the model-specific requirements before testing

### Capture the model, not the product category

Write down the full rating-plate information or the exact product-page model, including fuel type and the indoor or outdoor configuration. “Rinnai RX,” “Rheem tankless,” or “Bosch gas tankless” is not a model. A 130,000 Btu/h indoor natural-gas unit and a larger outdoor propane unit may have different flow tables, pressure guidance, venting, electrical, and water-quality instructions.

Download the current installation and operation manual and the current specification sheet before you compare your gauge reading with a number. Record the document title, revision or publication date, and page number for each gate. Keep the manual with the property file. The [Rinnai RX130iN product page](https://www.rinnai.us/residential/product-detail/rx130in), for example, identifies the model and links its 100000839 SENSEI RX manual and other documentation.

### Do not transplant a manufacturer’s number

The cited documents show why a universal threshold is unsafe:

- Bosch’s troubleshooting page gives 40–60 psi as the lowest recommended range for some private-well cases, while another Bosch case on the same page lists 30–50 psi. Bosch also says erratic home pressure can create hot-water temperature fluctuation. See the [Bosch gas tankless troubleshooting guidance](https://www.bosch-homecomfort.com/us/en/residential/service-support/technical-support/troubleshooting/troubleshoot-gas-tankless-water-heaters/).
- The [Rheem Eagle AP22009 Rev 04 manual](https://files.rheem.com/blobazrheem/wp-content/uploads/sites/2/AP22009-Rev-04-UC-Manual-Eagle-Tankless-Indoor-and-Outdoor.pdf) says its covered heater requires 14 psi minimum operating pressure, 0.4 gpm activation flow, and 0.25 gpm for continuous operation. It states that 40 psi is required for maximum flow and recommends stable minimum system pressure of 40 psi for well systems. Those are Rheem Eagle figures, not a rule for every tankless heater.
- The [Rinnai SENSEI RX manual (100000839)](https://www.rinnai.us/download/download?filename=100000839+SENSEI+RX+Residential+Installation+and+Operation+Manual.pdf.pdf&path=%2Fs--yMCYf7cd--%2F93f77a9585e0bf4429ca4bedfe5e24b38a6d0239.pdf) says the minimum flow rate is found on the exact specification sheet. It does not give you permission to substitute a number from another Rinnai series.

If the manual is missing, the specification sheet is unavailable, the model number is incomplete, or the seller cannot identify the revision, the right result is **needs design review**. Do not fill a blank with a number found in a forum or a different model’s manual.

### Record the heat-rise context

Tankless output is not only a pressure-and-flow question. The [U.S. Department of Energy’s tankless-water-heater guidance](https://bsesc.energy.gov/energy-basics/tankless-whs-gas-fired) says sizing should use the practical maximum flow needed at one time and the required temperature rise, which depends on incoming cold-water temperature and the setpoint.

For this worksheet, record:

| Input | Your record |
|---|---|
| Cold-water temperature used for design | ____ °F; source or season: ____ |
| Desired hot-water setpoint | ____ °F |
| Largest simultaneous hot-water demand | ____ gpm measured or rated |
| Heater performance-table result at that temperature rise | ____ gpm or ____ °F rise |
| Installer’s stated design condition | __________________ |

Do not infer that a heater’s advertised maximum domestic-hot-water flow will be available at your well’s winter inlet temperature and desired setpoint. A well may supply enough water but still not provide the selected temperature at the combined demand.

## 2. Measure the well cycle and pressure that reaches the heater

### What to observe first

Before changing anything, observe one ordinary cycle while no unusual water use is occurring. Record:

| Observation | Record |
|---|---|
| Pressure-switch cut-in shown by gauge | ____ psi |
| Pressure-switch cut-out shown by gauge | ____ psi |
| Time from pump start to stop with no fixture open | ____ seconds |
| Time from pump stop to restart during a steady draw | ____ seconds |
| Pressure behavior while one representative fixture runs | stable / falls / oscillates |
| Treatment equipment in service | __________________ |
| Water-quality or pump symptoms | sediment / air / odor / none / other: ____ |

Cut-in and cut-out are evidence about how your system is controlled. They are not the heater’s inlet-pressure requirement. A tank may start at one pressure and the heater may see less after the pressure tank outlet, house piping, filter, softener, check valve, elevation, or a partially closed valve.

### Static pressure is not flowing pressure

A gauge reading with every faucet closed is static pressure. A tankless heater is evaluated while water is moving. Rheem’s manual makes the distinction explicit by adding pipe and faucet pressure loss to its required operating pressure and by calling for stable pressure on a well system.

Use an accessible hose connection as close to the heater inlet as practical. With the system at rest, record the pressure. Then open a representative hot-water demand or a safe accessible test outlet and record the pressure while the target flow is running. If your gauge is upstream of a sediment filter or softener, repeat the reading downstream or measure the pressure drop across the treatment equipment at the same flow.

The worksheet arithmetic is:

{{visual:flowing-pressure-measurement}}

```text
flowing pressure at heater = pressure gauge reading at heater-side point while flow is running
available pressure after treatment = upstream flowing pressure − treatment pressure drop
pressure margin = available pressure after treatment − exact model minimum pressure
```

This arithmetic is a comparison aid, not a code calculation. If you cannot place a gauge at or near the heater, label the result as an estimate and hand it to the installer for confirmation.

### A safe homeowner observation sequence

1. Locate an existing hose-bib gauge or an accessible gauge point. Do not remove a fitting or open the heater cabinet to create one.
2. Confirm all valves and treatment bypasses are in their normal operating positions. Photograph the positions so the test can be repeated.
3. With no water running, record static pressure and the pressure-tank gauge position.
4. Open one ordinary fixture. Let the flow settle, then record the pressure and the pump state. Note whether the pressure falls smoothly or hunts between values.
5. Repeat with the representative peak demand you actually expect, such as a shower plus a sink, only if the fixtures can be used normally and no drain or overflow risk is created.
6. Record the treatment equipment’s before-and-after pressure at the same flow if two accessible gauges exist. If not, ask the treatment installer for a pressure-drop curve or a field measurement.
7. Stop if a gauge behaves erratically, a fitting leaks, water sprays, the pump runs continuously, the pressure approaches an equipment rating, or the test would require opening a pressurized enclosure.

Do not open the well cap, pull a pump, open a pressure-switch or control enclosure, touch live wiring, adjust cut-in or cut-out, change pressure-tank precharge, remove a relief valve, or loosen a pressurized fitting as part of this check. Those actions belong to a qualified well or plumbing professional who can isolate stored pressure and electrical energy and verify the equipment’s ratings.

### How to interpret the pressure result

| Finding | What it supports | What it does not prove | Safest next step |
|---|---|---|---|
| Flowing pressure remains above the exact model minimum and stable | Pressure gate may pass for that test condition | It does not prove peak-flow or heat-rise capacity | Test flow and document the manual page |
| Static pressure looks good but flowing pressure falls below the model minimum | The heater may not receive the pressure it needs | It does not identify whether the cause is pump, tank, treatment, piping, or demand | Design review before purchase; do not raise controls yourself |
| Pressure oscillates while a fixture runs | The water supply may be unstable for a heater that requires stable pressure | It does not prove the pressure tank is failed | Have a well/pump professional diagnose the cycle |
| Pressure is acceptable upstream but low downstream of treatment | Treatment is part of the compatibility problem | It does not mean removing treatment is safe | Review filter sizing, service state, bypass, and water-quality consequences |
| You have only a tank gauge or only a static reading | The record is incomplete | It does not prove heater-side pressure | Mark needs-design-review and obtain a heater-side flowing measurement |

## 3. Measure flow at the demand you actually need

### Separate three flow numbers

Keep these numbers separate:

1. **Minimum activation flow:** the flow at which the exact heater detects demand and starts operating.
2. **Minimum continuous flow:** a lower or separate value that may apply after operation begins, if the manual lists one.
3. **Peak simultaneous demand:** the combined flow of the fixtures and appliances you expect to use together.

Rheem’s Eagle manual provides all three kinds of gate: 0.4 gpm activation, 0.25 gpm continuous operation, and 40 psi associated with maximum flow for the covered models. Rinnai instead tells the reader to find minimum flow on the exact specification sheet. Bosch warns that a clogged inlet filter or another obstruction can drop flow below the activation point and that too much simultaneous demand can reduce pressure and flow. This is why the worksheet records the model’s values rather than publishing a Brictale universal minimum.

{{visual:model-manual-gate-map}}

### Build a peak-demand record

List only uses that could realistically overlap. Use fixture labels, appliance manuals, or a timed container at an accessible outlet. A simple flow measurement is:

```text
flow in gallons per minute = gallons collected × 60 ÷ seconds collected
```

Example: 1.5 gallons collected in 30 seconds is 1.5 × 60 ÷ 30 = 3 gpm. That is a measured outlet flow under the tested pressure, not a promise that the same fixture will draw 3 gpm in every condition.

| Concurrent use | Measured or manufacturer flow | Test condition |
|---|---:|---|
| Shower 1 | ____ gpm | temperature and pressure: ____ |
| Shower 2 | ____ gpm | temperature and pressure: ____ |
| Kitchen faucet | ____ gpm | aerator in place: yes / no |
| Clothes washer fill or other appliance | ____ gpm | manual or measured: ____ |
| Other simultaneous use | ____ gpm | __________________ |
| **Peak total used for comparison** | **____ gpm** | __________________ |

Do not add the maximum flow printed on a heater’s product page to the pump’s rated flow and call that capacity. The heater’s maximum is a product condition; the pump’s rating is not a guarantee at your well depth, pressure, treatment train, and current water level. Use the heater performance table and the installer’s pump-system calculation for the actual duty.

### Use a margin, but do not hide uncertainty

For a preliminary worksheet only:

```text
activation-flow margin = measured flow at the relevant fixture or test point − exact model activation minimum
peak-flow margin = model performance-table flow at the design temperature rise − measured peak simultaneous demand
```

If either margin is zero, negative, or based on an unverified number, mark **needs design review**. A positive activation margin does not establish hot-water capacity at a large temperature rise. A positive peak-flow margin based on a marketing maximum does not establish pump capacity. The qualified installer needs the exact well and heater records to finish that check.

## 4. Treat chemistry and filtration as part of the inlet system

### Get a current, certified water record

Well water has two separate roles in this decision. It must be safe and suitable for household use, and it must not damage or rapidly foul the heater. A clear glass is not a chemistry report.

The [EPA private-well guidance](https://www.epa.gov/privatewells/protect-your-homes-water) recommends annual testing for total coliform bacteria, nitrates, total dissolved solids, and pH. EPA also recommends additional testing after well repairs, flooding or land changes, or a change in taste, odor, color, or clarity, and directs owners to certified drinking-water laboratories. EPA’s suggested analytes connect local conditions with tests: hardness for scale clues, iron and manganese for staining, pH and corrosion-related testing for plumbing problems, and other panels based on nearby land use.

For the heater record, attach the lab report and mark:

| Water-quality item | Result and units | Exact heater limit or instruction | Treatment and maintenance consequence |
|---|---:|---|---|
| pH | ____ | ____ | __________________ |
| Total hardness | ____ | ____ | __________________ |
| Total dissolved solids | ____ | ____ | __________________ |
| Chloride | ____ | ____ | __________________ |
| Iron | ____ | ____ | __________________ |
| Manganese | ____ | ____ | __________________ |
| Copper, zinc, or corrosion indicators | ____ | ____ | __________________ |
| Sand, dirt, or sediment observation | ____ | manual instruction: ____ | __________________ |
| Other model-specific analytes | ____ | ____ | __________________ |

Rinnai’s SENSEI RX manual illustrates the model-first approach: it lists maximum levels for several parameters, including pH 6.5–8.5, total dissolved solids up to 500 mg/L, total hardness up to 200 mg/L, chloride up to 250 mg/L, iron up to 0.3 mg/L, and manganese up to 0.05 mg/L. It also says hard or scale-forming water must be treated and warns that water-quality damage is not covered by the warranty. Those numbers should be copied only when the selected heater is the applicable Rinnai model family and the current manual agrees.

### Include every treatment device in the pressure path

Draw the water path in order:

```text
well and pump → pressure tank → shutoff/check components → sediment filter
→ iron/sulfur treatment or softener → UV or other treatment → heater inlet
```

Your home may differ. The point is to name every component between the pressure source and the heater. For each one, record service state, bypass position, cartridge or media condition, rated flow, and measured pressure drop at the test flow.

Treatment can help a heater meet water-quality requirements while making the pressure-and-flow gate harder to meet. A filter that is dirty, undersized, or operating at a flow above its rating may create a larger pressure drop than the homeowner sees when all taps are closed. A softener or iron filter may also have a backwash or regeneration event that changes available water. Ask the treatment professional how the equipment behaves at the heater’s peak demand and whether any bypass or regeneration arrangement changes water quality reaching the heater.

Do not remove a treatment device merely to make a pressure number look better. EPA says treatment depends on the contaminant, its concentration, and the condition of the well; a lower pressure drop is not a safe substitute for water-quality control. If chemistry is outside the heater manual and no treatment design is documented, the decision is **do not buy this model yet** or **needs design review**, depending on whether a qualified designer can specify a remedy.

{{visual:water-quality-treatment-check}}

### Plan for scale instead of assuming a softener solves everything

Rinnai’s manual separates water hardness bands, recommends or requires treatment at different levels, and ties harder water to more frequent flushing. It also says lime or scale buildup can damage the heat exchanger and be excluded from warranty coverage if the heater is not flushed. The [Rinnai SENSEI RX manual (100000839)](https://www.rinnai.us/download/download?filename=100000839+SENSEI+RX+Residential+Installation+and+Operation+Manual.pdf.pdf&path=%2Fs--yMCYf7cd--%2F93f77a9585e0bf4429ca4bedfe5e24b38a6d0239.pdf) is therefore useful as a pattern: copy the selected model’s table into your record, then create a maintenance date from the measured water quality and the manual’s instruction.

Do not treat a “salt-free conditioner” label, a softener capacity label, or a generic whole-house filter rating as proof of compatibility. Ask for the device’s specific treatment claim, rated flow, pressure-drop information, discharge or regeneration requirements, and maintenance instructions. Match the treatment decision to the lab result and the heater manual.

## 5. Convert the worksheet into a go, no-go, or design-review result

### Use this decision matrix

| Situation | Verdict | Why |
|---|---|---|
| Exact model manual and specification sheet are saved; heater-side flowing pressure clears the model minimum; peak demand is supported at the required temperature rise; treatment and chemistry are documented; installation scope is assigned | **Go to professional quote** | The homeowner record is complete enough for a qualified installer to verify and price |
| Pressure clears the model minimum only with one fixture, treatment pressure drop is unknown, peak demand is estimated, or the manual/warranty is unclear | **Needs design review** | The condition might be solvable, but the evidence does not justify buying hardware or changing controls |
| Flowing pressure is below the exact minimum, flow is below activation, water quality exceeds the manual without treatment, or the system is unstable | **Do not buy this model yet** | A documented compatibility gate fails; select a design remedy or another model with professional help |
| The heater passes plumbing gates but gas sizing, venting, condensate, electrical supply, relief discharge, freeze protection, or local requirements are unreviewed | **Needs design review** | Water compatibility is only one part of a safe installation |
| The system uses a variable-speed pump, constant-pressure controller, storage tank, or unusual treatment sequence | **Needs design review** | Conventional cut-in/cut-out logic may not describe the system, and the equipment manuals control |

### Example: how not to overread a pass

Suppose a homeowner records 50 psi static pressure and 44 psi while a shower runs. The selected heater’s manual says 14 psi minimum operating pressure and 0.4 gpm activation flow. That is encouraging for the pressure gate if the 44 psi reading is genuinely at the heater inlet and the same test represents the intended use. It does not answer:

- whether the shower’s flow is above 0.4 gpm after the heater and treatment equipment;
- whether a second shower makes pressure fall below the requirement;
- whether the heater can produce the desired temperature at that combined flow;
- whether the pump can sustain the demand as the well water level changes;
- whether scale, iron, sand, corrosive water, or a filter cartridge will damage or restrict the unit;
- whether the exact indoor or outdoor installation can meet gas, venting, condensate, electrical, relief, freeze, and local requirements.

The correct record is “pressure gate passed for this test condition; remaining gates open,” not “the tankless heater is approved.”

### Do not repair the wrong system by raising pressure

If pressure is low or unstable, possible causes include a clogged filter, treatment pressure drop, pump or well-yield limitation, pressure-tank or switch issue, leaking plumbing, undersized piping, a partially closed valve, or an installation-specific control problem. The reading alone does not distinguish them.

Do not change pressure-switch cut-in or cut-out, alter pump controls, bypass a relief device, or increase system pressure to force a heater to pass. A pressure change affects the pressure tank, pump, piping, fixtures, treatment equipment, and relief protection. Give the professional the pressure log, photos of the gauge and treatment path, pump and tank model numbers, and the exact heater manual page.

## 6. Prepare the installation and maintenance handoff

### What a qualified installer needs from you

Bring one folder or digital record containing:

- exact heater brand, model, fuel, configuration, manual revision, specification sheet, and warranty;
- rating-plate photographs of the current heater, pump, pressure tank, pressure switch, filters, softener, and treatment equipment;
- static and flowing pressure readings, the gauge location, the fixture or flow used, and the date;
- pump cut-in and cut-out observations, cycle behavior, and any low-pressure or rapid-cycling symptoms;
- peak simultaneous flow list with measured or manufacturer-sourced values;
- well construction or pump records if available, including pump model and any known water-level or yield information;
- current certified laboratory water report and treatment equipment service records;
- gas type and available gas-service information for a gas heater, or electrical-service information for an electric heater;
- photographs and measurements of the proposed heater location, vent route, condensate route, drain, and service access;
- questions about permits, inspection, freeze protection, seismic or wind exposure, snow level, combustion air, vent termination, and local code.

The installer must determine the final gas or electrical work, venting, condensate, relief discharge, mounting, pipe sizing, treatment arrangement, controls, permits, and commissioning. A homeowner worksheet can expose missing evidence; it cannot approve energized, combustion, pressure-vessel, or well work.

### Maintenance record after installation

Use the exact heater manual to fill the final schedule. The following is a record template, not a universal maintenance interval:

| Event | Record or action | Date / reading |
|---|---|---|
| Commissioning | Model, manual revision, installer, setpoint, measured inlet pressure and flow | __________________ |
| Monthly or manufacturer-directed observation | Leaks, unusual noise, error code, sediment, pressure behavior | __________________ |
| Filter service | Cartridge or screen condition, before/after pressure, replacement date | __________________ |
| Softener or treatment service | Salt/media status, regeneration or backwash issue, bypass position | __________________ |
| Annual well-water test | Certified lab report for core panel and local analytes | __________________ |
| Heater flush | Exact manual procedure, reason, solution, and service provider | __________________ |
| Pressure review | Static and flowing pressure under the same test condition | __________________ |
| Event-driven test | After repair, flooding, land disturbance, water-quality change, or treatment change | __________________ |

Rinnai’s manual is an example of why the schedule must be model-specific: it provides a service indicator and warns that failure to flush when scale is building can damage the heat exchanger. EPA’s private-well guidance is the separate water-safety layer: test on the recommended schedule, use a certified lab, and test again after relevant changes or repairs. Keep both records; a heater maintenance log is not a substitute for a drinking-water test.

### Safety boundary for the homeowner

You may observe gauges, record accessible readings, photograph equipment labels, collect water from an ordinary fixture, and compare your records with the manual. Do not open energized electrical controls, test live wiring, open a well, pull a pump, enter a confined space, manipulate pressurized equipment, change pump controls, adjust a pressure switch, alter gas piping, modify venting, remove a relief valve, or disconnect treatment plumbing unless a specific manufacturer procedure clearly identifies the action as safe for a homeowner and the system is isolated as instructed.

If you smell gas, leave the area and follow the gas supplier or emergency instructions. If a well or pump area has been flooded, stay away from the pump because of electric-shock risk and follow public-health or qualified well-contractor guidance. If a water report indicates contamination, do not make a heater purchase the remedy; follow the local health or environmental authority’s direction for safe use and treatment.

The useful final decision is not a confident “yes” based on one pressure reading. It is a dated record that says exactly which model was checked, which numbers were measured at which point, which manufacturer gates passed, what remains uncertain, and who must resolve the uncertainty before equipment is bought or the well system is changed.

## Evidence

- [Bosch Home Comfort — Gas Tankless Water Heaters Troubleshooting](https://www.bosch-homecomfort.com/us/en/residential/service-support/technical-support/troubleshooting/troubleshoot-gas-tankless-water-heaters/) — Bosch U.S. troubleshooting guidance for the named heater cases on that page; ranges are not a universal well-system setting and do not authorize pressure-switch changes.
- [Bosch Home Comfort — Gas Tankless Water Heaters Troubleshooting](https://www.bosch-homecomfort.com/us/en/residential/service-support/technical-support/troubleshooting/troubleshoot-gas-tankless-water-heaters/) — Bosch U.S. troubleshooting guidance for the covered gas tankless heater cases; it supports checking demand and restrictions, not a universal flow or pressure value.
- [Rheem — High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual, AP22009 Rev 04](https://files.rheem.com/blobazrheem/wp-content/uploads/sites/2/AP22009-Rev-04-UC-Manual-Eagle-Tankless-Indoor-and-Outdoor.pdf) — Rheem Eagle noncondensing tankless models covered by AP22009 Rev 04; these figures are not a universal tankless or well-system threshold.
- [Rheem — High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual, AP22009 Rev 04](https://files.rheem.com/blobazrheem/wp-content/uploads/sites/2/AP22009-Rev-04-UC-Manual-Eagle-Tankless-Indoor-and-Outdoor.pdf) — Rheem Eagle installation guidance in AP22009 Rev 04; use the exact manual for the selected model and do not treat its arithmetic as a national code rule.
- [Rinnai — SENSEI RX Residential Installation and Operation Manual, 100000839](https://www.rinnai.us/download/download?filename=100000839+SENSEI+RX+Residential+Installation+and+Operation+Manual.pdf.pdf&path=%2Fs--yMCYf7cd--%2F93f77a9585e0bf4429ca4bedfe5e24b38a6d0239.pdf) — Rinnai SENSEI RX series manual; the minimum flow value must come from the exact model’s current specification sheet.
- [Rinnai — SENSEI RX Residential Installation and Operation Manual, 100000839](https://www.rinnai.us/download/download?filename=100000839+SENSEI+RX+Residential+Installation+and+Operation+Manual.pdf.pdf&path=%2Fs--yMCYf7cd--%2F93f77a9585e0bf4429ca4bedfe5e24b38a6d0239.pdf) — Rinnai SENSEI RX series water-quality table and warranty warning; values apply to that product family and are not a universal well-water standard.
- [Rinnai — SENSEI RX Residential Installation and Operation Manual, 100000839](https://www.rinnai.us/download/download?filename=100000839+SENSEI+RX+Residential+Installation+and+Operation+Manual.pdf.pdf&path=%2Fs--yMCYf7cd--%2F93f77a9585e0bf4429ca4bedfe5e24b38a6d0239.pdf) — Rinnai SENSEI RX series maintenance and water-quality guidance; maintenance frequency must follow the exact model and measured water quality.
- [U.S. Department of Energy — Tankless Water Heaters, Gas-Fired](https://bsesc.energy.gov/energy-basics/tankless-whs-gas-fired) — U.S. Department of Energy Building Science Education guidance; it is a sizing principle, not a substitute for the selected heater’s performance table or local installation requirements.
- [U.S. EPA — Protect Your Home’s Water](https://www.epa.gov/privatewells/protect-your-homes-water) — U.S. EPA private-well health and protection guidance; local health departments, state programs, and property-specific requirements may add tests or timing.
- [U.S. EPA — Protect Your Home’s Water](https://www.epa.gov/privatewells/protect-your-homes-water) — U.S. EPA private-well treatment guidance; it does not select a treatment train or establish a universal chemistry limit for a tankless heater.