Most homes had electric water heating but some used gas and some used solid fuel to boost supply. Original hot water cylinders and low pressure systems may need replacement.
The traditional low pressure electric hot water system (based around a header tank feeding an open vented cylinder) was taken over by medium pressure systems using a pressure reducing valve, and eventually by mains pressure systems. Gas-heated storage systems were also available.
A standard hot water cylinder had a 135 litre capacity and was installed in a cupboard, usually in the hallway or laundry. The cupboard usually had enough space for drying or airing clothes.
Open-vented wetback systems could be used with a low-pressure system, and where a solid fuel stove or wood burner was installed this could also be used for water heating or boosting the water temperature.
Storage cylinders typically have a life of 30-40 years, so in many 1970s houses a replacement may be necessary if it hasn't already been done. Even if the cylinder hasn't reached the end of its life it may have become less efficient, and its thermostat may no longer be working - so replacement may be a good option.
Other possible issues with hot water cylinders include:
- lack of insulation. EECA (the government’s Energy Efficiency and Conservation Authority) recommends adding a thermal wrap around any cylinder installed before 2002. Wraps can be bought from most larger building and hardware stores
- temperature set too high – installations during the 1970s were not fitted with a tempering valve to regulate the hot water delivery temperature to 55°C at bath, basin and shower outlets in order to prevent scalding
- lack of earthquake restraints – cylinders should be restrained to prevent them from toppling during an earthquake
- inadequate hot water storage capacity.
Hot water delivery temperatures for new installations should be meet the requirements of NZBC clause G12 Water Supply which says in G12.3.6 "where hot water is provided to sanitary fixtures and sanitary appliances, used for personal hygiene, it must be delivered at a temperature that avoids the likelihood of scalding".
If the low-pressure system is still in use, it may not provide sufficient pressure to run modern bathroom fixtures such as showers controlled with a mixer.
If renovations are being carried out, consider converting the hot water system to a mains-pressure system or, depending on use patterns and availability of gas, a continuous flow system.
Where a mains-pressure system is being installed using existing pipework and fittings, they should be checked for their ability to cope with the additional pressure and they may require replacement.
A continuous flow system which has the water heating unit outside will require additional plumbing work to connect into the existing pipework, and again the pipes will need to be checked.