Hot water is one of the biggest electricity users in a South African home, and geysers are one of the most regulated parts of a plumbing installation. This guide covers sizing a geyser, working out the energy it uses, the regulation that asks new buildings to heat at least half their hot water without an electric element, and the certificate a plumber must issue.
Sizing a geyser
Kwikot’s rule of thumb is about 50 litres of hot water per person per day, and its guide by household is:
| Household | Geyser size |
|---|---|
| 1 person | 50 to 100 L |
| 2 people | 100 to 150 L |
| 3 to 4 people | 150 to 200 L |
| 5 to 6 people | 200 to 250 L |
| 6+ or a guest house | 250 L or more, or two geysers |
Within each band, size by 50 litres a person: four people need 200 L, and six people 250 L rather than 300 L. Beyond six people, split the hot water over two geysers rather than adding a small one.
For affordable (low-rental) housing, the NHBRC’s energy efficiency guidelines use a higher figure from SANS 10252-1 table 5: 80 to 115 litres per person per day, of which they use the lowest, 80 litres, with storage 1.1 to 2.5 times the daily use. The table gives other figures for other kinds of home. For four people that is 320 litres a day and at least 352 litres of storage. The NHBRC’s example meets it with a 200 L and a 150 L geyser (350 L, just short); rounding up to two 200 L geysers gives at least the 352 litres.
How much energy?
The NHBRC guidelines give 4.55 kWh to heat each 100 litres of water from 16 °C to 60 °C. A household using 200 litres of hot water a day uses about 200 × 365 ÷ 100 × 4.55 = 3,322 kWh a year just to heat it. Multiply by your tariff to see what that costs, or use the electricity cost calculator.
The 50% rule
Regulation XA2, in the energy-efficiency part of the building regulations, states that at least 50% (by volume) of the annual average hot water heating requirement must be provided by means other than electrical resistance heating: for example solar heating, heat pumps, heat recovery or renewable fuel. It applies to new buildings, so plan a solar geyser or heat pump from the start of the design. The NHBRC’s example: for four people, half of the 352 litres, about 176 litres, is heated by the alternative system, which suits a 200 L solar tank. SANS 10400-XA adds that solar water heating systems must comply with SANS 1307, SANS 10106, SANS 10254 and SANS 10252-1, and that hot water pipes must be insulated to the R-values in its table 1.
Installation and the PIRB CoC
Geysers are installed to SANS 10254, and water installations generally to SANS 10252-1. The Plumbing Industry Registration Board says a PIRB Certificate of Compliance must be issued on all plumbing work done by a licensed plumber, including geysers, solar water installations and heat pumps. Price the CoC into the job, and give the client a copy.
Where the geyser goes in the roof, SANS 10400-L says geysers and water tanks should, wherever possible, sit on timber bearers over internal walls. Where that isn’t possible, a geyser of up to 150 L may stand on a timber platform across trusses with a clear span of up to 8 m, with only one geyser per three trusses.
Working it out
Heat pumps heat the water in a tank too, and Kwikot notes that the tank is sized the same way as for an electric geyser. The geyser size calculator gives the size for your household by either method (Kwikot’s household guide, or the NHBRC’s affordable housing example), the yearly energy, and the share the XA2 rule asks for from solar or a heat pump.
Saving energy with any geyser
- Insulate the hot water pipes and fit a geyser blanket where the maker allows it.
- Set the thermostat no higher than you need.
- A timer that heats the water before the household needs it avoids heating it all day.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check SANS 10400 (the National Building Regulations) and your local municipality’s building control officer for your project.