to work as hard to bring water up to temperature. Because on-demand water heaters heat water only when needed, they don't waste energy keeping a tank warm when no one's using it, and they work quickly and efficiently, so you shouldn't notice an interruption in hot water supply as long as your heater is appropriately sized. For example, someone could take a shower while another member of the household runs a dishwasher or does a load of laundry. They also have a lower profile, which can be useful in a structure with limited space for appliances. It's important to make sure the heater has enough room for safety clearances to reduce the risk of fire or water damage, but it should fit under a sink or counter if necessary, unlike a large tank, which requires far more surface area and vertical space. The disadvantage to flash heaters is that they tend to have a higher up-front cost. Sometimes it's possible to get a rebate or qualify for cash assistance if you can demonstrate that you are making your home more efficient with a flash heater, but otherwise, you may need to budget ahead for the higher price. Tank water heaters are available in both gas and electric versions; further, electric heat pump water heaters save money by using less energy. All designs keep the water heated in a large storage tank, but have the obvious drawback of allowing a home to run out of water during periods of heavy use.