This article was originally published in the May/June 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online May/June 1996
Water Heaters and Energy Conservation- Choices, Choices!by Larry and Suzanne Weingarten
I think I should replace my water heater. What's the most energy-efficient heater I can buy? What brand is the best? What heater features should I look for? We get these questions all the time. The only quick answer is one of hydronics wizard Dan Holohan's favorite replies: It depends.
The most useful answers can be given if the questions tie into the broader context of getting the most from the whole water-heating system. People already know they should look for energy efficiency from the heater itself. But additional savings can be found in water distribution, equipment sizing and selection, and maintenance.
First, find out what's in place already. Look at the heater, distribution piping, fixtures, and appliances, and determine how hot water is used in the house. Try to ascertain the residents' ability and willingness to maintain the equipment. If you see much deferred maintenance when you look over the system, don't recommend high-tech equipment that needs to be programmed, balanced, descaled, and oiled.
During the assessment, find out if there are any complaints about performance, such as hot water delivery time, temperature fluctuations, or amount of hot water. This could be an opportunity to solve those problems, resulting in greater satisfaction with energy conservation measures. And remember always to keep safety in mind. Water heaters still blow up and cause fires, and people continue to get scalded by hot water and poisoned by carbon monoxide.
When you've determined what's already there, consider the following information and select the options for water heating and distribution that best suit the situation.
But tanks do deteriorate with age. You will need to inspect the water heater to determine if it is a good candidate to keep and maintain. A tank's age is usually encoded in its serial number. If it begins A-83 or 0183, the tank was built in January 1983. B-83 and 0283 mean February 1983, and so on. If it begins 8301, the tank was built in the first week of 1983; 8352 would mean the last week of that year. Knowing the tank's age is a start.
Inspect all tank fittings to get more information. Do you see any signs of rusting or leakage? Look into the combustion chamber and the flue of fuel-burning units. (A flashlight and an inspection mirror are a big help.) While slight rust or water marking from condensation are not a problem, heavy rust and water streaks are danger signals. A pile of rusty scale on top of the burner suggests that tainted air has damaged the flue.
Another indicator for both gas and electric heaters is the sacrificial anode rod. (This rod sacrifices itself to protect the tank.) Although it can be difficult to remove, the effort is worthwhile, because the anode provides the best clue to conditions inside the tank. The sacrificial metal (magnesium or aluminum) is formed around a steel core wire. Normally, the anode slowly corrodes away to protect the heater from rust. When enough metal has corroded away to expose 6 inches of the core wire, it's time to replace the anode. So if you pull out an anode and find little or no sacrificial metal left, some damage will have occurred in the tank.
If your inspection of fittings, combustion chamber, or anode suggests that the tank has undergone substantial damage, replacement is a reasonable choice.
Perhaps you found little or no evidence of tank deterioration. Then, assuming the tank has insulation and is correctly sized, the most cost-effective thing to do is probably to keep it going. But, you may be thinking, what about energy use? The main difference between most old and new heaters in terms of energy performance is the insulation level. Atmospheric combustion and immersion heating elements haven't changed a lot. So insulating blankets, heat traps, and pipe insulation can help keep heat where it should be and help old heaters perform more like new heaters.
Whether you keep the old heater or replace it, maintain it regularly (see Water Heater Maintenance Combats Tank Failure). This will avoid the cycle of replacement, saving the energy needed to produce new equipment and dispose of the old.
Gas Underfired Heaters It's not the most efficient type, but the gas underfired water heater is the most common. It is relatively inexpensive and can be maintained to ensure long service life. New models can include very heavy (up to R-25) internal insulation, multiple flues for greater heat transfer surface, or a submerged combustion chamber to prevent heat loss from the burner area.
Sidearm Heaters One type of heater has moved the burner and flue outside of the tank (just like the old sidearm heaters) to cut down on standby losses. Because the heating is indirect, the storage tank can be lined with plastic. Another type has moved the gas heating unit even further away from the tank and mounted it on an outside wall. This unit is used to convert an existing electric tank to gas, where space or plumbing problems are restrictive.
Direct-Vent Heaters Direct-vent heaters have their own combustion air inlet and vent routed through a sidewall. They are used where vertical venting is not possible or where tight construction may cause various appliances to compete for the same air. These units can save energy because they do not rob conditioned indoor air from the house. Also, they cannot backdraft combustion gases into the house.
Power Vent Heaters Power vent heaters use a fan to assist venting of combustion gases. Therefore they can use a long horizontal or vertical vent pipe, which allows them to be located almost anywhere, and they cannot backdraft while the burner is firing. The disadvantages are that the fan robs conditioned air from the house, and the water heater needs electricity to operate (so a power outage means no hot water).
Heat Pump Water Heaters Public acceptance of heat pump water heaters has been slow, probably because they are expensive and relatively difficult to maintain. A new unit, the E-Tech, by Crispaire Corporation, is about twice as efficient as electric tank-type heaters and should cost less than previous heat pumps.
Combined Systems If the resident uses a boiler for space heating, it can usually be combined with an indirect storage heater to provide hot water (see Once Heated, Twice Used, HE July/Aug '92, p. 14). This combined system offers reduced operating costs and improved efficiency over tankless coils or conventional water heaters. Unlike tankless coils, it does not require the boiler to come on each time you draw hot water (this is particularly unpleasant in summer), and the superinsulated storage tank retains heat very well. The higher the efficiency of the boiler, the more attractive this method looks. Making the Decision Many gimmicks are used to sell water heaters, but they don't necessarily give you a better tank. When you select a new tank-type heater, size it appropriately using the manufacturer's guidelines. Don't just automatically put in the same size heater as before-appliances and fixtures are replaced over time, and this may have reduced the demand for hot water. The efficiency (indicated by the Energy Factor on the label) gets lower as the tank gets bigger, so a smaller tank will use less energy per gallon of water heated. Insist upon a minimum of R-16 internal insulation. Internal insulation thoroughly covers the tank, including the top, which must be left exposed when using an external blanket on a fuel-fired heater.
Look for ease of maintenance and anode accessibility. Make sure the anode's hex head is visible on top of the tank, or that the tank has a combination anode/hot outlet. Don't pay extra for a longer warranty. Tanks with longer warranties are usually equipped with two anodes instead of one, but you can add a second anode yourself for a fraction of the cost.
Position the heater to facilitate maintenance. Provide easy access to the anode and sufficient overhead clearance for checking and replacing it. Make sure electric elements can be pulled out and thermostats can be adjusted. Be sure the relief valve and the drain are easy to reach. Place the heater near a sturdy wall if earthquake strapping is needed.
Add a Second Anode Most heaters have one sacrificial anode, often identifiable by the hex head visible on top of the heater. (Some tanks do not provide access to the anode; the hex head is hidden under a sheet-metal top. Avoid these.) A second type of anode is combined with the hot outlet port. Tanks with a hex head anode can be equipped with a second anode by adding a combination rod in the hot port (as many 10-year warranty tanks have).
Control Sediment Excessive sediment buildup can cause premature tank failure and element burnout, as well as noise and odor. Sediment can often be controlled by flushing if the proper parts are installed (see Water Heater Maintenance Combats Tank Failure).
Upgrade the Relief Valve Drain Line Because the temperature and pressure relief valve needs to be checked regularly, attach its drain line with a union or a flex connector to simplify valve replacement when it is needed. Drain lines must always lead away downhill, so water cannot be trapped where it might freeze or collect at the valve and corrode it closed.
If the heater is indoors, put it in a drain pan so that if there is ever a leak, the house won't be subject to water damage. You may wish to put a water alarm in the pan, especially if you cannot run a drain line from it.
However, older heaters (and even some new ones) have insulation rated R-7 and below. Consider installing a heavy blanket on these for a combined internal and external insulation value of R-16. Make sure all fittings are dry and in good shape before installing the wrap. Put a Gas Appliance Manufacturers Association safety sticker (available from GAMA or a plumber) on the blanket. Leave the anode, relief valve, and controlsexposed for routine maintenance. If your heater's R-value is not on the label, try this old rule of thumb: put your hand on the heater; if it feels warm, add a blanket.
Insulate Pipes Help keep the heat in the water by insulating all the hot plumbing lines you can get to (and the cold line back 3 ft from the heater). Use a good-quality plastic or rubber foam at least 34 inch thick. Do not cover unions or fittings at the ends of flexlines (these areas need to be clearly visible), and stay clear of the draft diverter on gas heaters.
Install Heat Traps Heat traps may also be used on the tank (see Figure 1) to help keep the heat where it belongs. Ball check valves work, though flow restriction and a chattering noise can occur at high flow rates. You can make your own heat traps by bending long flex connectors into an inverted U shape. In some circumstances, heat traps can save as much as a blanket.
Options beyond the Water Heater Hot Water Distribution Inadequate hot-water distribution can make even the best water heater's performance unsatisfactory. Distribution is best considered during new construction, but remodeling or repiping are the next best times. People do not want to wait for hot water. They would also prefer not to waste water or energy. Conventional long runs of branched piping manage to do all three. They contain gallons of cool water that must be wasted before hot water reaches the user. If the runs are not insulated, they can easily lose 20oF between the heater and the point of use, requiring the heater to be set hotter-which is both wasteful and dangerous. Also, water remaining in the pipes quickly cools when use is finished.
Consider the advantages of using a manifold system instead of a main line with branches. With individual direct runs of 3/8-inch tubing, this system contains much less water than a 3/4-inch main with 1/2-inch branches, so less water is wasted and less time is spent waiting for hot water to arrive. (It takes 40 ft of 3/4-inch, 82 ft of 1/2-inch, or 133 ft of 3/8-inch copper pipe to hold 1 gallon of water.) This new idea was mentioned in a 1950 book. (Bear in mind that smaller-diameter runs may take longer to fill bathtubs or spas, and they should not be used if water pressure is low.)
Solar Heaters A tempering tank located in a sunny spot is similar to a solar batch or bread box heater. Both active and passive solar systems can preheat water for a conventional heater, and at the right time of year, solar alone can provide all the hot water the house needs.
Solar is capable of delivering much of a household's hot water needs flawlessly for decades if the system is well designed, well built, and capably installed. Unfortunately, many systems have been net energy losers because they were overly complex, poorly installed, and not maintained. We do have the know-how to build efficient, long-lived systems (see Efficiency and Solar Water Heating: Untapped Potential, HE July/Aug '92, p. 21). With solar, it's particularly important to keep it simple and not install more than the resident can deal with.
In order to have hot water at the faucet faster, many people install systems to keep hot water circulating in the pipes. If the major modifications to the plumbing system mentioned above cannot be made, a recirculation line can save water and make for happier users. However, don't use a gravity system or simply plug in the circulating pump to run 24 hours-these options waste energy.
The Metlund System Probably the most efficient recirculating system is one made by ACT Metlund Systems. It gives the benefit of recirculation without the added plumbing. It's called a demand system, as hot water is only delivered when called for, greatly cutting plumbing heat loss. Using a pump and a motorized valve mounted under a sink, hot and cold lines are joined long enough for cool water to be pumped from the hot line. Once a sensor picks up rising temperature, the pump shuts off and the valve closes. Hot water is then available at the taps. Usually, the system is activated by push buttons, which can be wired in parallel and placed conveniently at any fixture. The system can also be operated by a wireless remote control.
Whatever water-heating choice you make, safety, simplicity, low cost, and ease of use should be your major goals.
Larry and Suzanne Weingarten operate Elemental Enterprises in Monterey, California, which services conventional and solar water heaters. They also manufacture a sediment removal tool and have written The Water Heater Workbook-A Hands-On Guide To Water Heaters.
-This article is part of a series on energy effcient remodeling, which is finded by the Environmental Protection Agency and The Department of Energy.
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