A working electric water heater can heat 40 gallons of water in just under an hour and a half. The most efficient heaters can reduce this time to about an hour. If you want an efficient water heater that heats your water for as long as you want (after the hot water runs out) and stores a good amount of hot water, these are the specifications you should keep in mind. If you want to run a lot of hot water at the same time, you'll need a more efficient system than if you just want a daily hot shower.
Even so, if you have a 30-gallon capacity water heater, you won't wait as long for it to warm up as if you had a 50- or 80-gallon unit. An average 50-gallon gas water heater may have an FHD rate of 80 to 90 GPH, but a 50-gallon electric water heater will have an FHD rate of approximately 58 to 66 GPH. However, as we have seen, tankless water heaters work much faster than this, heating water in just 15 seconds on average, although they cause the additional problem of slower water flow. From the moment new water comes in, an electric water heater would take about an hour to heat the 40-gallon tank explained above.
If you have a 5500-watt electric water heater set to 120 degrees and the incoming water temperature is about 50 degrees, you will have hot water after waiting a little longer. However, not all water heaters are created equal, so it is important to know how long you should wait when the supply runs out. Remember that temperature rise, tank size, and BTU rating will affect the amount of time it takes to heat water from the water heater. The average shower uses approximately 10 gallons of hot water, so in theory, your home should be able to take 4 showers with a 40-gallon hot water tank.
If you want an efficient water heater that heats your water as long as you want (after the hot water runs out) in addition to storing an excellent amount of hot water, these are the requirements you need to keep in mind. This is why homes with higher water demands generally choose to purchase a whole-house gas tank water heater rather than an electrical design. Unfortunately, despite all the other benefits of electric water heaters compared to gas heaters, electric models generally take longer to heat up. Simply put, a BTU is the amount of heat needed to raise one pound of water by one degree Fahrenheit.
A tankless gas heater heats the water immediately, so it should only take a couple of seconds before the hot water reaches its component through the pipes.