What Hot Water Heater is Best for You?

Ecologically sound solutions for heating your home’s water supply can also save you money.

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The AquaStar Model 125B on-demand (tankless) water heater provides instant energy savings.

Photo courtsey Gaiam Jade Mountain

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Many people are not aware that hot water doesn’t come cheap. Consider this: Over its 13-year lifespan, a $350 electric water heater will cost you more than $5,500 in energy bills and will emit more than 32.5 tons of carbon monoxide. But you don’t have to sacrifice hot showers to live an environmentally conscious lifestyle. Today, you can choose from a variety of efficient water-heating options. Depending on your location and budget, you can find a system to supplement or provide all your hot water needs that uses significantly less (or no) fossil fuel energy.

You may even decide to give your old tank-style system early retirement. In most cases, hot water heaters consume more energy as they get older; for example, a sediment-filled 10-year-old water heater may be running at just 50 percent efficiency.

Sun showers

Solar water heaters are a sound environmental and economic choice. Although they cost more up front—from $1,200 to $4,000—solar systems cost less when you consider annual energy costs and realize that they can outlast two or three tank-style water heaters. The Florida Solar Energy Center (FSEC) has found that solar systems can pay for themselves in four to eight years (and will continue to operate for an additional seven to thirty years). In addition, some state and local governments offer rebates and tax incentives to encourage residents to invest in solar technologies, so check with your local energy office before you buy.

Solar water heaters can be grouped into two subcategories: passive or active. Passive systems have no breakable electric components; consequently, they’re more reliable, easier to maintain, and less expensive. The downside is that they are generally less efficient than active systems, which use electric pumps, valves, and controllers to circulate the heat-transfer fluid through the solar collectors. Because of the extra hardware, active systems are generally more expensive, but they can produce more hot water per square foot of collector space, and can be adapted for areas that are subject to extended freezing temperatures. Active systems are also easier to retrofit on existing homes because the collectors can be located away from the storage tank.

Passive and active solar water heaters can be either “open-loop” or “closed-loop.” Open-loop, or direct, systems circulate household water through the collector. Closed-loop systems circulate water or another heat-transfer fluid (such as antifreeze) through the collectors, then transfer only the stored heat to the water supply through a heat exchanger (double-walled heat exchangers prevent the heat-transfer fluid from mixing with the drinking water). Closed-loop systems are more complex and more costly, but they protect the collectors against freeze damage.

If you live in an area that doesn’t experience hard-freeze winters, the simplest and least expensive solar heating system available is the batch, or “breadbox,” heater. This open-loop, passive system consists of one or more storage tanks within an insulated box. The tanks are designed to absorb solar energy and limit solar loss. Combining the collector and storage tank eliminates pumps, controllers, and wiring. Batch heaters start at about $1,000, but you can build one yourself for as little as $300.

Because they can generate more hot water and can be adapted for use in colder climates that do experience winter, flat plate collectors (systems start at about $2,000) are more common than batch heaters. Most flat-plate collectors require some electricity to run the circulation pump and the temperature controller that tells the pump when to run. A few models use a photovoltaic module instead of an electric motor and controller; sunlight heats the water and produces the electricity needed to run the pump.

The smaller tubes within the flat-plate collectors are prone to freezing. To address this problem, many units use a freeze-proof fluid (such as antifreeze) that must be flushed and replaced every few years. Although you can find less toxic heat-transfer fluids, a safer option is to stick with water and choose a drainback system. In this case, the heat-transfer fluid (water) drains out of the collectors and collects in the storage tank whenever the system is off. When empty, the tubes within the collector are safe from freeze-related damage.

Solar water systems aren’t perfect. Unless you live in the middle of the Sunbelt, you will still need a fuel-fired backup system (most building codes require it). In addition to working with Mother Nature, you may also need to deal with zoning laws and covenants, which may restrict where you can place collectors.

Hot water on demand

Tankless, or on-demand, water heaters go to work only when someone turns on the hot water tap. Because they don’t heat water needlessly, tankless systems use 20 percent less energy than conventional tank-style water heaters. In a one- or two-person home, standby heat loss from conventional heaters can be even greater, because the stored hot water sits around longer.

Tankless heaters aren’t a good solution for every household. Most units provide only two to three gallons per minute (gpm), just enough to run one high- efficiency showerhead. Larger units, such as the AquaStar 125 ($600) and the Takagi TK-1 ($1,100) can provide up to 5 gpm. Although both of these units can easily support a low-flow showerhead, the pressure and/or temperature may drop if you try to do a load of laundry in hot water at the same time. The volume of heated water will also decrease if the temperature of the incoming water drops. One way to avoid these disadvantages is to pair a tankless heater with a solar heater. In this case, make sure your tankless heater is designed to modulate down to a zero-setting for those times when it only has to add a few extra degrees to the preheated water.

In addition to taking a few water-conservation steps, many of the drawbacks of a tankless heater can be resolved if you install additional tankless heaters to serve different zones. Also, because tankless systems require a minimum flow to start heating the water, you may want to consider a small point-of-use electric water heater for washing hands or other minimal tasks.

Storage tank heaters

If you choose to stick with conventional tank-style water heaters, there are ways that you can reduce energy consumption. According to Michael Lamb, an energy consultant with the Energy Efficiency and Renewable Energy Clearinghouse (EREC), in Merrifield, Virginia, “Tank size is important, but consumers should pay more attention to the first-hour rating (FHR) that’s listed on the heater’s Energy Guide Label.” The FHR is a measure of how much water the heater can deliver to meet peak demand. For example, a thirty-gallon high-efficiency gas heater has a FHR of 67 gpm; in comparison, a fifty-gallon electric heater has a FHR of just 58 gpm. In this case the smaller water heater can supply more hot water, with lower standby losses than the larger unit.

Water heater efficiency can also be measured by its energy factor (EF). The EF is based on recovery efficiency, standby losses, and how much heat is lost incidentally during operation. In general, the higher the EF, the better; however, it’s important to consider the price of fuel as well. Electric resistance heaters with an EF rating of 0.7 to 0.95 may seem to outperform gas water heaters (EF 0.5 to 0.6), but in most cases, electric heaters cost almost twice as much to run. For a list of the most energy efficient heaters, check out the American Council for an Energy-Efficient Economy’s website (below).

Finally, when you’re installing a new heater, be sure to ask your plumber about anti-convection or one-way valves. These inexpensive ($5 to $10) devices prevent the loss of convective heat through the heater’s inlet and outlet pipes.

For more information

American Council for an
Energy-Efficient Economy (ACEEE)
Washington, DC
(202) 429-8873
www.aceee.org
For a list of the top-rated energy
appliances:
  www.aceee.org/consumerguide/topwater.htm  

The Energy Efficiency and Renewable
Energy Clearinghouse (EREC)
Merrifield, VA
(800) 363-3732
www.eren.doe.gov  

Florida Solar Energy Center (FSEC)
Cocoa, FL
(321) 638-1010
www.fsec.ucf.edu

Solar Rating and Certification
Corporation
Cocoa, FL
(321) 638-1010
www.solar-rating.org