Plumbing Water Heater Sizing Calculator
Budget actual peak useful draw under explicit ideal hot/cold mixing and independent recovery/usable storage; not energy-reheat duration, thermostat instructions or scald/legionella safety.
Description
A storage heater mixes hot water with colder supply water to meet a draw.
A storage heater mixes hot water with colder supply water to meet a draw. Recovery during the draw offsets the required usable storage.1
The returned values include Modeled hot storage fraction of draw, Required usable hot storage liters, Required nominal hot storage liters. The How section below explains the calculation, input rules and interpretation.
When to use Plumbing Water Heater Sizing Calculator
Use Plumbing Water Heater Sizing Calculator when you need to evaluate the supplied records under the calculation and evidence rules below. No peak timing, stratification, safe delivery temperature or actual recovery curve is established.
Prepare measured flows, pressures, temperatures or inventories with consistent units. For catalog tools, use independently verified capacities at the stated operating conditions and supply the explicit design demand.
How to use Plumbing Water Heater Sizing Calculator and understand its results
- Prepare measured flows, pressures, temperatures or inventories with consistent units. For catalog tools, use independently verified capacities at the stated operating conditions and supply the explicit design demand.
- Enter callerPeakUsefulDrawLiters, observedStoredHotC, observedColdFeedC, callerDeliveredWaterC, callerRecoverableStorageFraction, callerRecoveryDuringPeakLiters using the field table and calculation rules, then run the tool.
- Read modeledHotStorageFractionOfDraw, requiredUsableHotStorageLiters, requiredNominalHotStorageLiters. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| callerPeakUsefulDrawLiters | Caller peak useful draw liters | number | Required |
| observedStoredHotC | Observed stored hot c | number | Required |
| observedColdFeedC | Observed cold feed c | number | Required |
| callerDeliveredWaterC | Caller delivered water c | number | Required |
| callerRecoverableStorageFraction | Caller recoverable storage fraction | number | Required |
| callerRecoveryDuringPeakLiters | Caller recovery during peak liters | number | Required |
Enter finite temperatures with hot above cold and delivery within their closed interval, nonnegative draw and recovered hot-water liters, and usable fraction in (0,1]. Return mixing fraction, net usable liters and required nominal liters.
hotFraction=(delivery−cold)/(hot−cold); usable=max(0,draw×hotFraction−recovery); nominal=usable/usableFraction Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| modeledHotStorageFractionOfDraw | Modeled hot storage fraction of draw | number |
| requiredUsableHotStorageLiters | Required usable hot storage liters | number |
| requiredNominalHotStorageLiters | Required nominal hot storage liters | number |
{
"input": {
"callerPeakUsefulDrawLiters": 100,
"observedStoredHotC": 60,
"observedColdFeedC": 20,
"callerDeliveredWaterC": 40,
"callerRecoverableStorageFraction": 0.8,
"callerRecoveryDuringPeakLiters": 10
},
"output": {
"modeledHotStorageFractionOfDraw": 0.5,
"requiredUsableHotStorageLiters": 40,
"requiredNominalHotStorageLiters": 50
}
}Limitations and assumptions
No peak timing, stratification, safe delivery temperature or actual recovery curve is established.
Numeric inputs, where present, must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Plumbing Thermostatic Mixing Valve Setting Calculator: Ideal mixing balances hot and cold water to a requested delivery temperature. Equal heat capacities and negligible heat loss make the balance linear. For a complementary task, use Plumbing Water Heater Recovery Time Calculator: Recovery time divides required heat by net delivered heating power. Concurrent draw loss reduces that power.
References
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Plumbing Water Heater Sizing Calculator — tool.io
Similar or alternative tools
- Plumbing Thermostatic Mixing Valve Setting Calculator
Ideal mixing balances hot and cold water to a requested delivery temperature. Equal heat capacities and negligible heat loss make the balance linear.
- Plumbing Water Heater Recovery Time Calculator
Recovery time divides required heat by net delivered heating power. Concurrent draw loss reduces that power.