With us, the hot water has always been supplied by a tankless water heater - the oil heating system will be turned off in spring.
Mother-in-law has hot water via the oil heating system - and therefore also a considerable oil consumption every summer. The hot water storage tank is also quite poorly insulated. In spring, we therefore "made short work" and installed a small tankless water heater at the shower. So now the heating is off and she can still take warm showers at any time - washing hands only works with cold water.