Two weeks ago, I discussed in my post water pressure about how water moves throughout the home - cold and hot. This week, I wanted to focus on the means by which water goes from cold to hot which is, of course, made possible by water heaters. Operating water heaters besides being essential to any home are also, on average, the second largest expense in a home, accounting for 14-18% of utility bills or roughly $400 - $600 a year. The average home uses approximately 64 gallons of water a day with much of this being hot water heated by a conventional storage water heater. While a storage water heater is the most common there are four other types of water heaters that can be suitable for residential use. Each type offers its own pros and cons and it is a good idea to review your options and be aware of your personal selection criteria. When comparing water heaters a few key things to consider are:
- Fuel type, availability and cost
- Energy efficiency
It is also important to realize that most water heaters last on average 10-15 years and for many of us this means we will soon be in need of a new one (according to energy.gov roughly 27 million households in the U.S. have a water heater that is more than 10 years old).
Below is a brief break down of the five major types of water heater:
Conventional Storage Water Heater: As its name indicates a conventional storage water heater "stores" hot water. Most residential heaters of this type store between 20 to 80 gallons of water while commercial grade heaters store up to hundreds of gallons. The heater can be fueled by natural gas, propane, fuel oil and electricity. The most common fuel source is natural gas followed by electricity. A natural gas sourced, storage water heater essential works like this - a gas burner heats the tank from below - controlled by a thermostat, the gas valve closes and opens as the water temperature rises and falls around its setpoint. The main issue with this type of heater is standby heat loss meaning energy can be wasted even when the hot water tap isn't in operation. However, this can be reduced by having a heavily insulated tank which will also in turn lowers operating costs. Costs can also be lowered by performing simple upkeep measures such as flushing a quart of water from the tank every three months and checking the temperature and pressure valve every six months.
Tankless or On Demand Water Heater: An on demand water heater provides hot water as needed. When a hot water tap is turned on cold water travels through a pipe into the heater where it is warmed by either a gas burner or electric element. This form of water heating is consider more energy efficient as standby heat loss is not an issue, there are lower operating and energy costs, and they have a longer life expectancy of more than 20 years. The trade off, however, is flow rate and cost. With no reserve or tank, an on demand water heater is limited in its flow rate (typical rate is 2-5 gallons per minute). This means that several units may be required for simultaneous, multiple uses of hot water. To resolve this problem you can have two or more tankless water heater, connected for simultaneous demands or you can install separate tankless water heaters for specific appliances or fixtures. This type of unit can also be cost prohibitive depending on how many you would need although their long term performance might make up for this upfront cost.
Heat Pump Water Heater: Heat pump water heaters are geographically specific in that they will only work for locations that remain in the 40-90 degree fahrenheit range year round so probably not St.Louis. Most commonly heat pumps are used to heat and cool homes however they can be used to heat water as either part of a conditioning system or as an independent water heating solution. Heat pumps work by moving heat from one place to another rather than producing heat on demand for a specific function. Essentially, they pull surrounding hot air into the heater to warm the water while expelling cold air into the adjacent space. This is why heat pump water heaters must be installed with at least 1,000 cubic feet of air space around them. Without going into too much more detail, it is useful to know that heat pump water heaters are roughly 2-3 times more energy efficient than a storage water heater, performance is very dependent on location both geographic and where it is installed within a home and the life expectancy of is 10-15 years.
Solar Water Heater: Again another location specific system that usually requires some form of a back up heater. Solar water heaters involve a storage tank or tanks and solar collectors. The storage tank can be a conventional water storage tank, however, a larger much more insulated tank would be more effective. There are three types of solar collectors used in water heating systems: flat-plate collectors, integral collector-storage systems and evacuated tube solar collectors. There are also two types of solar water heating systems: active and passive. Active and passive systems are further broken down which you can read more about here if you are interested. Solar is considered the most expensive in terms of equipment required however its fuel source, the sun, is free. It is also 50 percent more energy efficient than gas or electric.
Tankless coil and indirect water heaters: Lastly, this form of heating water uses your home's space heating system to warm water. Together, they are part of what is termed an integrated or combined water and space heating system. This combined system is most commonly used in colder climates as it can be inefficient in warmer places where a boiler or furnace is not needed for a large majority of the year. In tankless coil heating systems, water is heated on demand by sending cold water through a heating coil or heat exchanger in a main furnace or boiler. In indirect water heaters (usually a more efficient choice), the furnace or broiler heats a fluid that is passed through a heat exchanger in the water storage tank. When used with a high-efficiency boiler and a well-insulated tank this can be the least expensive form of heating water out of all the types available.