The increasing use of heat pumps to cool homes during summer is putting a strain on electricity supply.

The Commissioner for the Environment says it's creating an unprecedented summer peak in energy consumption and could cause problems for future electricity supply.

Energy Efficiency and Conservation Authority chief executive, Mike Underhill, says heat pumps shouldn't be used during summer.

''If you have new summer loads coming on, your system isn't as well able to cope with it as if it came on in the winter.


"That's the whole question about whether you'd use a heat pump in summer, and our view is that you don't."