Tool list

Water Heater and DHW Recirculation Calculator

Building and usage profile

The profile loads suggested demand and storage factors; both remain editable for project conditions.

Building type

Demand factor Between 0 and 1.

Storage factor Equivalent storage-hours multiplier.

Number of heaters

Fixture loads

Enter quantities. Flow rates are editable starting values for the selected profile.

Important: ASHRAE table values are intended for preliminary sizing and may not represent some modern low-flow fixtures. Replace L/h with manufacturer or project data when available.

Fixture	Count	Unit load (L/h @ 60°C)	Row total

Source cells shown as a range or “—” require a project/manufacturer value. Use “Add custom fixture” for each fixture not listed.

Temperature, coil and capacity settings

60°C is the hygiene default; outlet temperatures from 45–60°C are compared with the catalogue for the selected coil type.

Cold-water inlet temperature (°C)

Hot-water outlet temperature (°C)

Coil type For double-coil units, only the upper-coil duty is evaluated; lower-coil duty is not added automatically.

Recovery time (h)

Recirculation Pump CalculationOptional Open and enter the lengths; pipe heat loss, pump flow and closed-loop head are calculated.

Static building height is not added to the head of a closed recirculation loop. Critical length is the piping route in the most unfavourable closed circuit.

Total supply + return length (m)

Critical line length (m)

Pipe heat loss (W/m)

Return temperature difference (K)

Pipe pressure gradient (Pa/m)

Equipment pressure loss (kPa)

Safety margin (%)

Results are preliminary and must be checked against catalogue data, heat-exchanger duty and the pump curve.

Recommended water-heater volume

—L

Water-heater results

Hourly hot-water demand: —
Required total heating capacity: —

Calculation report

Copyable short selection summary

Selection summary text

Method, sources and limitations

ASHRAE Handbook 2019 — Service Water Heating, Table 10
Fixture demands and building demand/storage factors.
ASHRAE Handbook 2023 — HVAC Applications
Current chapter context; this tool does not claim compliance with the full 2023 text.
ASHRAE — Service Water Heating / Recirculation, Grundfos, Caleffi idronics 21
DHW return-loop heat-loss and pump-sizing approach.
Republic of Türkiye Ministry of Health — Legionnaires' Disease Control Guide
E.C.A. — Boyler Teknik Dokümanı / Water Heater Technical Document
Comparison source for common single- and double-coil catalogue volume series.
Alarko — Sıcak Su Boyleri ve Akümülasyon Tankı Broşürü
Reference for the conservative coil-duty values and 10/60°C operating data used by the brand-neutral recommendation.
Baymak — Aqua Hızlı Boylerler Broşürü
Comparison source used to cross-check single- and double-coil nominal-volume steps.
Usable-volume allowance comparison: Buderus 2025, Reflex single coil, Reflex double coil.
Used to compare nominal model names with actual water content.

This tool is for preliminary sizing and information only. Final selection must be verified by a qualified engineer against the usage profile, current regulations, hygiene strategy, manufacturer data, heat-exchanger approach temperatures and pump curves. The calculated pump is the DHW return pump; the primary/charging pump is outside scope.

Step 1 / 5