An un-wrapped electric cylinder loses around 1,000–1,200 kWh per year in standing losses — that's about $400/yr at today's NZ power rates, just to keep water hot when nobody's using it.
A standard cylinder wrap from Mitre 10 / Bunnings costs $40–60. Done in 30 minutes with a Stanley knife and some duct tape.
How to do it
- Turn off the cylinder at the switchboard (safety first)
- Wrap the sides — never cover the temperature/pressure relief valve, the element cover, or the thermostat access
- Tape the seams
- Wrap the first 1 m of both hot and cold pipes coming out the top with foam pipe lagging
Don't wrap if: the cylinder is already an A-grade insulated tank from the last 10 years (you'll see the rating on the label), or it lives inside a hot-water cupboard with the rest of the home's plumbing.