Water Usage

Based on Estimates, the Average Household uses between 80 & 100 Gallons of Water per Person per Day. The Shower is 2nd to Flushing the Toilet. Heating Water is on average 20% of the Total yearly Utility Costs. There 5 Ways to Heat Water in the Home, 3 of the Most Common Methods are - Water Heater & Storage Tank, Tankless Water Heater and Solar.

Water Heater & Storage Tank

Water Heater/Storage is the most common method used. This type of Heater can be Natural Gas, Propane Gas or Electric. Electric under Counter Heater/Storage Tanks can start at 5 Gallon and go up to about 15 Gallon. Under Counter Tanks are only to give Instant Hot Water at a Sink while the Water from the Main Storage or Tankless Arrives.

The Main Water Storage Tanks for a Home or Apartment Size could be 30 Gallon for a Small Apartment. 30 Gallon Size will serve maybe for 1 Short Shower, A 40 Gallon could Serve for 1- 2 people but not likely to be satisfactory with 2 Showers running simultaneously.

A 50 Gallon Size is the most common but may not be satisfactory with 3 Showers running simultaneously. A 60 Gallon Size would be common for a Family of 6 but may still not provide Hot Water if 2 or 3 were to take long Showers at the same time or one right after the other.

Making Estimates for available Hot Water is based on a Larger 2.5 Gallon per minute Shower Head. We also consider that while the Hot Water is going Out the Cold Water is coming in. At some point all the Water in the Tank Equalizes in Temperature and may begin to Cool until the Hot going out is Stopped. Now there is a Waiting Period before all the Water Rises to the Level of Hot Water. (see draw efficiency below)

Some say that you can compensate a little is by setting the Temperature in the Tank Higher so you are Mixture Hot at a lower rate. The Problem could be that if someone was not use to the High Water Temperature, one could get Burned. The other consideration is that the Tank will maintain that Temperature all Day even while you are not Home.

Calculations

A Certified WaterSense Shower Head Flow Rate is 2 Gallons per minute, non-Certified is 2 1/2 Gallons per minute.

Average Shower time is 10 minutes, Total is 20 Gallons with a WaterSense Shower Head and 25 Gallons with a WaterSense Shower Head.

The Hot Water Portion of the Total is only about 60%. For a 10 minute Shower you use only 12 or 15 Gallons.

Factoring in Average Draw Efficiency and First Hour Ratings you would Typically have about 40 Gallons of Hot Water.

There can be Variables like Thermostat Temperature Setting, Inlet Water Temperature, Distance from the Tank to the Shower and Ambient Air Temperature.

Flow Rate Chart in Gallon per Minute

Appliance	Energy Star	Non Energy Star
Dish Washer	6 gpm	16 gpm
Washing Machine	14 per load	20 per load
Kitchen Faucets	N/A	2.0 gpm
Bath Faucets	1.5 gpm	2.2 gpm
Shower Heads	2.0 gpm	2.5 gpm

Draw Efficiency

The Amount of Hot Water that can be used from the Tank before the Temperature begins to Cool. Most Gas and Electric Heaters are rated at 70%. 30 Gallon Tank is 21 Gallons, 40 Gallon Tank is 28 Gallons, 50 Gallon Tank is 35 Gallons.

First Hour Rating

The Amount of Hot Water that can be Heated in the 1st Hour. The Draw Efficiency plus the Amount of Water that can be Heated in 1 Hour.

Temperature Rise

The Difference between the Inlet and Outlet Water Temperatures. In Northern Climates the Cold Inlet Water Temperature increases the Recovery Time.

BTU Rating

BTU is a British Thermo Unit or Heat required to raise 1 Pound of Water 1 Degree Fahrenheit. This is Pretty Much related to the Size of the Burner. A Larger burner will use More Gas but the Water will raise in Temperature Quicker.

Tankless Water Heaters

This Type of Water Heater solves most of the Problems we pointed out above. Tankless Water Heaters Heat Water on Demand and Turn Off when the Demand Ends.

Tankless Heaters have some Advantages over the Storage System like Endless Hot Water and Efficiency, making them less Expensive to Operate and take up about 25% of the Space of a Storage Tank.

The Biggest Disadvantage is the Initial Cost of The Heaters plus the Installation. See Our Tankless Water Heater Articles in the Links below.

Solar Water Heaters

Solar Water Heaters use the Sun to Heat Water and can be used in any Climate. There are Two System Types - Passive and Active.

Passive

Passive Systems are the least Expensive & least Efficient of the 2 and may have a Longer Life than the Active System.

The Passive also has 2 Types - Integral Storage & Collector and Thermosyphon.

The Integral Collection System has the Storage Tank Built-In with no Pumps, Sensors or Controls.

This Passive System has a couple of Disadvantages.

The Weight of the Unit along with the Stored Water can Prevent the Installation on the Roof Top. The Unit may have to be mounted on the Ground.

The Integral Collection System has a Faster Heat Loss when the Sun is Not Out. There are Units that are more Insulated to Slow Down the Heat Loss.

The Thermosyphon System Heats the Water in the Collector on the Roof or Ground Mounted and Stores the Heated Water. When the Hot Water Faucet is turned on, the Water Flows through the Collection Tank to the Home. A continuous Flow of Cold Water enters the Collector and Storage Tank, usually 40 Gallon Capacity.

Active

Active Systems also have 2 Types - Direct and Indirect Circulation. These System require Circulation Pumps, Controls and Sensors.

The Direct Circulation System Circulates Water from the Home to the Collectors then Returns. This System is Best in a Climate that Rarely Freezes.

Indirect Systems uses a Non-Freezing Fluid that Passes through the Solar Panel (Collector) then through a Heat Exchanger that Heats the Water from the Heated Non-Freezing Fluid.

There are 2 - 3 additional Methods of Heating Hot Water for the Home that we did not cover, we may research them if we have any request to do so.