As an estimate, the water in your tank should stay hot for a day or two. The larger the tank, the greater the heat loss will be, and it depends on the quality of your tank as well as the form of insulation you have.
If your hot water runs out too fast, you may have an issue with: Too much hot water demand from multiple sources at the same time. Sediment build up inside of your water heater tank. A broken dip tube.
The average adult uses about 10 gallons of water per shower (at a rate of 2 gallons of water per minute). If you assume that an 80-gallon tank has about 55 gallons of hot water to dispense before refilling, that means you have 27 or so minutes of total shower time before running out of hot water.
For instance, a typical shower uses about 10 gallons of hot water. So, if you have a 40-gallon hot water tank, you should be able to get four average-length showers out of your hot water tank. This also depends on how much hot water you use for other things.
Say your electric heater is 30 gallons. If the previous shower lasted 15 minutes, you're looking at about four minutes of hot water remaining. If you want to loll in your own 15-minute shower, you'll need to wait 47 minutes before stepping in.
A 30 gallon water heater should be able to supply enough hot water to meet the needs of a household of 1 -2 people with only one bathroom. A good way of measuring your hot water requirements is calculate your peak hot water usage and compare it the first hour rating of a water heater.
With a low-flow showerhead, you can expect to use about two gallons of water each minute, equating to 10 gallons over a 5-minute period. If a standard showerhead is fit, the shower will likely emit around an extra half gallon of water per minute, so a 5-minute shower will use in the region of 12.5 gallons.
One of the easiest ways to make a hot shower last longer is by using less hot water while it's at a higher temperature. To do this, turn up the temperature on the thermostat that's attached to the hot water heater tank. (Not the thermostat on the wall.) Use a low-flow shower head.
If you have a low-flow showerhead installed, you can expect to use about two gallons of water per minute, equalling 20 gallons throughout a 10-minute shower. With a standard showerhead, around half a gallon more water will emerge each minute, so a 10-minute shower would use somewhere close to 25 gallons.
A broken dip tube may be the culprit if your shower quickly runs out of hot water. The dip tube is a long, plastic tube that stretches from the cold water inlet to the bottom of the water heater. It directs cold water to the heater, where it's warmed up before being distributed throughout the home.
Water Heater Issues
A malfunctioning thermostat, broken dip tube, and sediment buildup are the most common repair issues that can explain why your shower quickly runs out of hot water.
The Hot Water Temperature Needs Adjusting
If your shower seems to take a frigid turn pretty quickly, you may need to adjust the temperature of your water heater. The recommended temperature for hot water is 120 degrees Fahrenheit with a maximum of 140 degrees Fahrenheit.
Low water pressure
If the water pressure to your house drops, this can affect how the hot water pressure is working in your system too. If your shower goes cold after a few minutes, it might be that you've been unlucky enough to be showering just as the water pressure dropped.
Faulty or burned out heating elements is one of the main reasons why your hot water goes cold quickly. Old or burned out elements account for the reduction of hot water and will cause your hot water to go cold quickly or not have any hot water at all.
Your water heater has a thermostat that controls the temperature of the hot water. If the thermostat is set incorrectly or if it's malfunctioning, that could explain why you run out of hot water in the shower. Solution: Check the temperature on the thermostat and make sure it's set to 120° F.
According to the U.S. Environmental Protection Agency (EPA), a full bathtub requires about 70 gallons of water, while taking a five-minute shower uses 10 to 25 gallons. You might argue that very few people fill the tub to the top, but a simple calculation shows that either way, baths use more water.
Typically, draining a 40-gallon water heater takes somewhere between 30 and 45 minutes. The overall time is heavily influenced by the size of the unit and the rate at which the water can exit the tank through the drain valve.
A broken internal heating element
If the water is constantly lukewarm, it usually indicates a problem with the upper heating element. A short-lived supply of fully hot water points to a problem with the lower heating element.
Whether you are genuinely concerned about the state of the environment and saving energy, or more worried about your ever-rising energy and water bills, making your hot water last for longer can help significantly. One way that you can save on water and energy is by using a low pressure shower head.
So if you're in a family of four, a 50-gallon water tank should cover all those showers and washings. Another number to calculate when buying a new water heater is the First Hour Rating (FHR).
With the standard shower head flow rate of 2.5 gallons per minute, a 45 minute shower uses 112.5 gallons of water at a cost of $1.68 per shower. Compare that to a ten minute shower that uses just 25 gallons of water for a cost of $0.375 and see the savings of $1.30 per shower.
If you've got that big a house on a slab then we would say yes, it's a good idea to have two tanks to service individual sides of the house. And it won't cost a whole lot more to have two smaller tanks rather than one big one.