Easy Hot Water

Hot water cylinder sizing

Clear all entries?

This resets every field and clears the calculation. Your own details (assessed by, company and contact) are kept. It can't be undone.

Tap the ⋮ menu (bottom right), then Guide, for the full method, sources, manufacturer guidance, and customer talking points.

✎Report details▾

Shown on the report cover. Your own details are kept when you clear.

Property name or reference

Address

Assessment dateToday’s date for a new calculation — change it if the survey was on another day

Assessed by

Company

Contact

AHow much hot water?▾

Number of bedrooms

Number of bathrooms

Number of occupantsOptional — used if higher than beds + baths

Cold mains temperature (°C)Default 10°C for UK

BHow big a cylinder?▾

Storage temperature (°C)

Cylinder volume override (litres)Leave blank to use calculated minimum.

CHow long to reheat?▾

Heat input to water, P (kW)Lesser of heat generator output at DHW flow temp or coil rating

Cost to reheat

Select what reheats the cylinder and enter the fuel price to see running costs.

Electricity tariff (p/kWh)Check current Ofgem price cap or homeowner's actual tariff

Reheat efficiency (SCOP / COP)Select what reheats the cylinder

✓Summary▾

Complete Parts A to C to produce a full report.

+Additional Considerations▾

Outlet hot water use — mixing equation

How much stored hot water does a specific outlet actually use? Enter the outlet details below.

Flow rate (L/min)

Duration (minutes)

Outlet temperature (°C)Temperature at the tap/shower

Target reheat time — what P is needed for the entire cylinder?

If the client wants the entire cylinder (V_cyl) reheated within a specific time, this calculates the minimum heat input required.

Target reheat time (minutes)

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References: CIPHE (2025) | CIBSE DHDG (2026) | MCS MIS 3005-D (2025) | BS 8558:2015 | AD L 2021 5.11

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