If you’ve decided that it is best for your household to use a storage tank style water heater (most traditional type), it is then time to determine what size of unit you will need.
You want to make sure the storage and heating capability of the unit will produce enough hot water for your household needs. Buy too small and you will never have enough hot water, but too large and you waste what can be a significant amount of money.
A hot water tank that receives a continual supply of fresh water and stores it in a tank where it is heated is commonly called a hot water tank but can also be known as:
- Storage Hot water heater
- Boiler
- Heat exchanger
- Geyser
- Calorifiers
The water in a regular hot water heater is continuously heated to a certain temperature determined by the setting on the thermostat, which is adjustable for your comfort. Most commonly, a water heater tank is set for 120-140 °F.
Most tank hot water heaters hold anywhere from 20 to 100 gallons of water.
Small tank water heaters can be installed in kitchens and bath cabinets. They generally hold from 2 to 6 gallons of water.
Generally, one person uses 15 to 30 gallons of hot water per day to wash clothes, do dishes, clean, and for bathing.
Taking that figure, if you have one person in the household, you need 30 gallons of hot water produced from the time the person wakes up to the time they go to bed. If your water heater tank holds 100 gallons of water, you can see that is more than three times the amount needed, plus it is being heated to the set temperature every minute of the day.
The one person may use 5 gallons here to wash dishes, 8 here to bathe or wash a load of clothes, etc., so for on demand need during only a certain period of day, a 100 gallon tank water heater is incredibly large for one person. Realize, 100 gallons of water is ready for that one person to use at any point of the day or night.
Based on that information, it would therefore be reasonable to say that for a 100 gallon tank, three people would have more than enough hot water to use throughout the day…3 x 30 gallons = 90 gallons
Generally for a household of four, an 80 gallon tank would be more than sufficient for 20 gallons of hot water to be available, at any given time of day, per person per day.
In sizing the tank you will need, the peak hour of usage comes into play. That is, at the most common hour of the day when everyone uses the hot water, how much water is needed during that one hour. When you figure that out, you can be sure to get a tank that will hold at least that much hot water.
So, let’s say that a household of four all take showers, run the dishwasher, run a load of clothes, and clean some floors, all at the same hour of the day. How much in that one hour would be used?
| 4 showers | 10 | × | 4 | = | 30 |
| 1 cleaning | 2 | × | 1 | = | 2 |
| 1 dishwashing | 4 | × | 1 | = | 4 |
| 1 clothes washing | 45 | × | 1 | = | 45 |
| Peak Hour Demand | = | 81 |
24 gallons of water generally held in a bathtub
45 gallons for typical washing machines (not modern machines that are high efficiency)
So in this case, it is fair to estimate that about 81 gallons of hot water is needed for a household of four during their peak hour of usage.
Unfortunately, there is no one answer as to exactly how much hot water a household needs. Calculations could be more exact if you measure to obtain the cubic feet of water your bathtub, washing machine, dishwasher, etc hold for each use.
Plus, your household may have a much lower estimate of peak hour usage if the hot water usage is more scattered throughout the day and evening.
Hick’s Plumbing Service is a well-known plumbing repair and installation company here in Fairfax, VA and surrounding areas.
If you would like help determining the size, style, and type of water heater you need for your household or business, please give us a call. We would be happy to help you with any plumbing need you may have.