Five quick steps to an indicative SIRAC heat pump selection, sized to SANS hot water allowances. Already know your storage volume? Enter it directly instead. ← All tools
Select the occupancy type and usage profile. We apply the SANS hot water storage allowance for that category.
We calculate your storage volume from the SANS allowance. Adjust the allowance or add capacity for laundry, kitchens or other loads if needed.
Choose the heat pump range and operating conditions. The heating load is sized over your selected recovery period with a 10% allowance for line losses.
Your sized plant needs hot-water storage. Pick a vessel form factor and we’ll size it to your design volume and heat-pump flow — or skip to view the heat pump on its own.
The calculator follows the same route a consulting engineer takes on paper. It starts with how much hot water the building has to store, converts that into a heating load over the recovery period you are prepared to accept, and then matches the load against published SIRAC unit capacities.
SANS 10252-1 is the South African standard for water supply installations in buildings. It sets the hot water storage allowance for each type of occupancy, expressed per bed, per person, per unit or per meal. These are the allowances this calculator uses.
| Occupancy group | Usage profile | Storage allowance |
|---|---|---|
| Clinic | Clinic | 35 L/bed/d |
| Colleges/ Schools | Day School | 6 L/capita |
| Boarding School | 50 L/capita | |
| Dwelling Houses | House Low rental | 150 L/unit |
| House Medium to high rental | 50 L/capita | |
| Factories | Staff | 7 L/capita/d |
| Ablutions | 60 L/capita/d | |
| Flats (Blocks) | Flats Low rental | 25 L/capita |
| Flats Medium to high rental | 35 L/capita | |
| Hospitals | General | 30 L/bed/d |
| Infectious | 50 L/bed/d | |
| Infirmaries | 25 L/capita/d | |
| Infirmaries with Laundry | 30 L/capita/d | |
| Maternity | 35 L/bed/d | |
| Mental | 25 L/capita/d | |
| Nurses Homes | 50 L/capita/d | |
| Hostels | Hostels | 35 L/capita/d |
| Hotels | With resident Staff | 70 L/bed/d |
| Without resident Staff | 60 L/bed/d | |
| Kitchens | Full meal preparation | 6 L/meal |
| Offices | With Canteens | 25 L/capita/d |
| Without Canteens | 7 L/capita/d | |
| Shops | Staff only | 6 L/capita |
| Sports Pavilions | Participants only | 40 L/capita/d |
Allowances cover normal occupancy only. Laundries, commercial kitchens and process loads are additional, and the calculator has a separate field for them.
A hotel with resident staff is allowed 70 litres per bed per day. For 112 beds that is 7,840 litres of stored hot water. Recovering that volume through a 45 °C temperature rise over a 6 hour period needs 7,840 ÷ (6 × 3600) × 4.187 × 45 = 68.4 kW, and with the 10% line loss allowance the plant must deliver 75.2 kW. That is comfortably met by three 30 kW modules, and the design volume matches a Thermocube TC-085 vessel with a three-coil 32NB heat exchanger kit.
It is built for consulting engineers, mechanical contractors, developers and facilities teams working on hotels, hospitals and clinics, high-rise residential, student accommodation, social housing and commercial buildings across South Africa and the wider region. It gives a defensible indicative selection in a few minutes, which the SIRAC engineering team then confirms.
Start from the daily hot water storage volume the building needs, then work out how much heat is required to raise that volume through your design temperature rise inside the recovery period you are willing to accept. The calculator does this as volume ÷ (hours × 3600) × 4.187 × ΔT, adds 10% for line losses, and then matches the result against published SIRAC unit capacities.
SANS 10252-1 sets out how much hot water storage to allow per person, per bed, per unit or per meal for different building types. A hotel with resident staff is allowed 70 litres per bed per day, a general hospital ward 30 litres per bed per day, and medium to high rental flats 35 litres per person. The full table used by this calculator is published above.
Multiply the number of beds by the SANS allowance for that hotel type: 70 L/bed/day with resident staff, or 60 L/bed/day without. A 112-bed hotel with resident staff therefore needs roughly 7,840 litres of stored hot water before any allowance for laundry or kitchens.
Yes. Air source heat pumps lose capacity as ambient temperature falls. The tool offers an optional COP de-rate for the Modular (MF) range, interpolating published capacity against your design ambient so an inland winter design is not sized off a mild-day rating.
No. It produces an indicative selection for early stage planning and budgeting. Final model selection, redundancy, pipework, controls and commissioning must be confirmed by the SIRAC engineering team for the specific project.
The tool can match your design volume to a SIRAC Thermocube (rectangular, 1,600 to 17,500 litres) or Thermotube (cylindrical, 500 to 2,500 litres) vessel, and sizes the heat-exchanger coil kit from the confirmed peak hot water flow.
Need the coil side as well? Use the coil sizing calculator to work out coil length, count and pressure drop for the storage vessel, or talk to the SIRAC engineering team about a full design.