A friend recently wrote us asking about running out of hot water during showers, and it reminded me of a simple fix. She wrote:
"Hello friends and family. Can you please help me out? We are having trouble getting enough hot water for showers at our house. We just bought a new hot water heater, 50 gallons, and we still can only take two SHORT showers one after the other if we want hot water to last.
I have been doing a lot of research and calculations. Can you tell me about your own household? I'm wondering if my expectations are too high.
1) How many gallons is your heater?
2) Gas or electric?
3) Brand?
4) FHR #? (First hour recovery number is located on your tank) This number is important.
5) How long are your showers?
6) How many showers can your family comfortably take in a row?
Do you run out of hot water? I am going nuts!!!! I think we need an 80 gallon tank!!"
Generally speaking, gas and oil heaters can heat water faster than an electric heater, but this is just a common product engineering trade-off, not a law of physics. I replied that a 50 gallon gas or oil heater is a bit small for a family of four, and that it is definitely too small if it is electric.
Either the shower needs enough BTU/Hour (British thermal unit is the amount needed to raise 1 pound of water 1 degree Farenheit) to keep up, or it needs a large thermal reserve in the tank to compensate for the gap between production and usage. The legal limit for a shower in the United States is 2.5 gpm (gallons per minute), although you might have a higher flow rate if you are using an older showerhead or someone removed your flow restrictors for a high pressure shower (this article describes how it is done, so it should help you check to see if the restrictors are in place in your shower).
If your shower is running at 2.5 gpm and your water source is 40 - 50 degrees (meaning 60 degrees increase is required to boost the temperature to over 100 degrees), you need a heater with a minimum 75,000 BTU/hour to keep up with demand, according to this handy calculator. If you are using a shower that produces 4 gpm, you will need 120,000 BTU/hour to keep up. So if your pressure is more than you need, one solution to hot water capacity is to reduce the water usage using a reduced flow shower head.
Most people are looking for more pressure, not less, so this probably isn't a practical solution. Another option is to add a tankless hot water heater to one of the showers. You can also add a storage tank (e.g., SuperStor) to an existing hot water heater for less than buying a new higher capacity hot water heater. However, before upgrading the hot water system, there is a simple solution for getting the most out of the heater that many people overlook: turn up the temperature on the heater.
We have a 80 gallon gas fired heater. We can take an unlimited number of showers without running out of hot water. However, when we first moved into the house, we had the same problem. The water temperature on the heater was set to the minimum. After I turned up the heat to the maximum we problem went away completely. This is for two reasons that are mutally reinforcing:
1) If the temperature is set higher you will need less hot water to mix in with the cold (e.g., 170 degrees hot + 40 degrees cold mixed 50%/50% = 105 degrees, whereas 120 degrees hot + 40 degrees cold must be 80% hot water to get 104 degrees).
2) If the tank can't keep up with your usage, it has a bigger head start if the temperature is set higher. As the cold water refills the hot water tank, the tank temperature falls, and when it is below the 100 degrees, the shower will no longer feel hot, even with the cold turned off. So if your temperature is set to 120, when 20% is depleted, the tank water drops to 104 degrees. If the temperature is set to 170 degrees, the temperature will not cross the 100 degrees threshold until more than half the water is depleted. This is an oversimplification because even as the heater is falling behind, the heater slows the rate of temperature decrease - this static temperature mix calculation does not reflect the heating done during the decline. However, it is also follows that the tank will have more time to raise the temperature when it has until 50% depletion instead of 20% depletion.
There are several drawbacks to increasing the temperature of the heater, but they are not dealbreakers to me:
1) Heat loss from the tank to the surrounding room is greater, but modern tanks are very well insulated so this is less of an issue than older tanks. Also, my hot water heater is in my basement, so the heat loss warms the unheated basement a little.
2) You can scald yourself on the tap water, but everyone gets used to it so really you just have to warn guests. If you are concerned, you can try turning up the water in increments to give everyone time to get used to it.
3) If you have hard water, the minerals come out of solution more, so you might need a water softener. If you have hard water, you should get a softener anyway, because your pipes, valves, and showerheads will fill with minerals over time which is very difficult to fix.
So while not high tech, it is technology (definition: applied science) that we appreciate every morning.
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