About this calculator
What size geyser a household needs, how much electricity heating the water takes, and what the 50% solar or heat pump rule means for a new house.
How it’s calculated
The household method uses Kwikot’s rule of about 50 litres of hot water per person per day and their household guide: 50 to 100 L for one person, 100 to 150 L for two, 150 to 200 L for three or four, and 200 to 250 L for five or six. The size is 50 litres per person, kept inside that range, so six people get 250 L. For more than six, Kwikot suggests over 250 L or two geysers, so the 50 litres per person is split over two geysers of 100 to 250 L.
The affordable housing method follows the NHBRC’s energy efficiency guidelines, which use the low-rental figure in SANS 10252-1 table 5: 80 litres per person per day (the lowest of 80 to 115), with storage 1.1 times the daily use. For four people that is 320 L a day and 352 L of storage. The NHBRC’s example uses a 200 L and a 150 L geyser (350 L); the calculator rounds up to two 200 L geysers so the storage is at least 352 L. Above 250 L it always picks the fewest geysers of 100 to 250 L that hold the storage.
Energy uses the NHBRC figure of 4.55 kWh for every 100 litres heated from 16 °C to 60 °C. Regulation XA2 asks for at least 50% of a new building’s hot water to come from other than electrical resistance heating: solar heating, heat pumps, heat recovery or renewable fuel.
Worked example
With these inputs:
- People in the household
- 4
- Sizing method
- Household guide: about 50 L per person (Kwikot)
the result is:
- Geyser size
- 200 L
- Hot water per person per day
- 50 L
- Storage needed
- 200 L
- Kwikot’s guide for 3 to 4 people
- 150 to 200 L
- Energy to heat it (16 °C to 60 °C)
- 3,322 kWh a year
Tips from the trade
- Fit a geyser blanket and insulate the hot water pipes to cut standing losses.
- A timer on the geyser element, set around the household’s use, saves electricity.
- Size up if the household runs baths more than showers.
Common questions
What size geyser for a family of four?
About 200 litres, at the top of Kwikot’s 150 to 200 L range for three or four people. For affordable housing, the NHBRC’s example (80 litres per person, from SANS 10252-1) works out 352 litres of storage, split between two geysers.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.