All About Water Heaters
Buying a new water heater isn’t necessarily the best way to lower your energy expenses for domestic hot water
If you want to save energy, there are lots of exciting appliances and building materials that you might want to specify for your home: triple-glazed windows, an efficient refrigerator, and compact fluorescent or LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. lighting, for example.
When it comes to choosing a water heater, though, clarity evaporates. Simple, affordable water heaters aren’t very efficient, and efficient equipment is complicated and costly. So how do you go about choosing a water heater?
Most homeowners ignore their water heaters. About once every ten years, the average homeowner goes down to the basement or out to the garage and notices that the water heater is sitting in a pool of water.
Since the family needs to replace the leaking water heater right now, the $350 special at Home Depot (or whatever model the nearest plumber is willing to install) looks good. Although a rush replacement job is understandable under the circumstances, it's not the wisest way to choose a water heater.
Choosing a water heater
The overwhelming majority of water heaters sold in the U.S. are tank-type water heaters heated by natural gas, propane, or electric resistance elements. Tank-type water heaters are widely available and inexpensive. Of the three most common fuels, natural gas is by far the cheapest, except in a few areas of the country with very low electric rates.
If natural gas is unavailable, an electric-resistance water heater makes more sense than a propane water heater, since electric water heaters avoid potential problems with backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney. and flue-gas spillage.
What if you want to heat your water more efficiently — or in a more environmentally friendly way? Well, there are many options, all of which require a much bigger investment in equipment.
Most of these high-tech water heaters are more efficient than typical tank-style heaters. Unfortunately, all of these options have disadvantages:
- Condensing gas water heaters require a condensate drain, have a long payback period, and are expensive — generally $4,000 to $8,000 for a unit with a stainless-steel tank, or $2,100 for a unit with an enameled steel tank (the Vertex). Paying that much would only makes sense if you plan to use your water heater to supply space heat as well as domestic hot water.
- On-demand water heaters require an oversized gas supply line, are mechanically complicated, may have trouble keeping up with simultaneous demand from several fixtures, have a long payback period, and are expensive.
- Heat-pump water heaters are noisy, mechanically complicated, rob space heat from the house during the winter, require a condensate drain, have a long payback period, and are expensive. According to energy expert Marc Rosenbaum, monitoring shows that the efficiency specifications provided by manufacturers of heat-pump water heaters are probably exaggerated.
- Solar hot water systems require regular maintenance, complicate roofing replacement, have a long payback period, and are expensive — generally $5,000 to $9,000. Although these systems make a lot of hot water in June — in some cases, more than a family can use — they don't produce much hot water in December.
- Indirect water heaters require a boiler — an appliance that most homes lack. During the summer, the efficiency of these systems plummets, especially for households that don't use a lot of hot water; according to Marc Rosenbaum, the summer efficiency of an indirect water heater may be as low as 10% to 20%.
- A desuperheater requires a very expensive ground-source heat pump — an appliance that most homes lack.
What about Energy Star water heaters?
Some of the water heaters mentioned above — condensing gas water heaters, solar water heaters, on-demand gas water heaters, and heat-pump water heaters — can be purchased with an Energy Star label. However, it’s worth noting that Energy Star-labeled non-condensing gas water heaters aren’t particularly efficient (minimum EF, 0.67).
Moreover, while indirect water heaters and desuperheaters aren’t eligible to receive an Energy Star label, that doesn’t mean that these methods of water heating don’t make sense for some homes.
In short, while the Energy Star labeling program for water heaters has some logic behind it, it shouldn’t be the main criterion for choosing a water heater.
If you can put it in your garage, an inexpensive gas water heater makes sense
Atmospherically vented gas water heaters have a major disadvantage: when installed inside the conditioned envelope of your house, they are subject to backdrafting whenever a strong exhaust fan is turned on. So atmospherically vented gas water heaters are a no-no in a tight house.
If you live in a warm climate where pipes don't freeze in your garage, and if you are lucky enough to have access to natural gas, it makes perfect sense to install an inexpensive atmospherically vented gas water heater in your garage. The water heater is outside of your home's thermal envelope, so there is no backdrafting risk, and natural gas is ridiculously cheap.
Power venting reduces backdrafting — but imposes an energy penalty
One of the advantages of old-fashioned atmospherically vented gas water heaters is that they don’t need any electricity to operate. While power-vented water heaters reduce the chance that an exhaust appliance causes backdrafting, the energy required to operate these venting systems is a new electrical load.
A research report from the Saskatchewan Research Council (Robert Dumont, Case Studies of Major Home Energy Retrofits) noted, “It appears that the power-vented water heaters deliver very little energy savings when you factor in the use of the power-vent motor.” Since the electrical consumption of power-vented gas water heaters is not subject to regulation, manufacturers have little incentive to address the issue. The American Council for an Energy-Efficient Economy does not compile data on power-vent consumption. “We’re doing some testing of power-vented water heaters,” Skip Hayden, a senior research scientist at Advanced Combustion Technologies in Ottawa, told me in 2004. “In terms of electrical consumption, they are all over the place. We’ve seen some that draw 100 watts, and some that draw 200 watts.”
Scott Pigg, a senior project manager for the Energy Center of Wisconsin, has reported (in a residential ventilation study) that the median operating time for residential power-vented water heaters was 80 minutes a day, although the water heater in one monitored home ran for over 240 minutes per day. If a water heater has a 200-watt power-vent, an average family might see an annual electrical consumption of about 100 kWh, and a high-use family might see an annual electrical consumption of almost 300 kWh. “I will say this about power-vented water heaters: they’re noisy little buggers,” Pigg told me. “And any time you hear a lot of noise you know there is some energy going to waste.”
A direct-vent gas water heater that doesn't require electricity
If you are wary of the backdrafting risks of conventional gas water heaters, but are still attracted to the simplicity of a tank-style gas water heater without power venting, a good solution might be a direct-vent gas water heater from GSW Water Heating of Fergus, Ontario.
GSW makes a direct-vent sealed-combustion gas water heater that operates without electricity. Its efficiency is no better that similar conventional gas water heaters, but it is protected from backdrafting risks. According to the manufacturer, this gas water heater complies with Canada's R2000 home requirements.
A lot of hot water gets wasted
When it comes to calculating how much energy Americans use to heat water, water heater efficiency tells only a small part of the story. A large percentage of the hot water produced by most water heaters never reaches the faucet.
Because many faucets and fixtures are a long way from the water heater, it can take anywhere from 30 seconds to 3 minutes for hot water to reach a distant sink. For example, when you turn on the hot tap to wash your hands, you probably begin by using the cold water that first flows from the pipe. Just as the hot water is about to reach the tap, you shut it off because you’re done. Now all of the hot water in the pipe begins to cool off, assuring that the next time you wash your hands, you will again be using cold water — but paying for hot water.
James Lutz, a research associate supervisor at Lawrence Berkeley National Laboratory, researched hot water waste; he reported his findings in a paper, “Estimating Energy and Water Losses in Residential Hot Water Distribution Systems.” His summary: “From these calculations, about 20% of total hot water use in single-family residences seems to be wasted. Although these calculations are based on many assumptions and simplifications, the results do seem reasonable to this author and point to a significant opportunity for increasing residential energy efficiency.”
Why it takes so long for hot water to reach the faucet
If Lutz’s calculations are correct, and the average house wastes 20% of its hot water, then some houses waste much more.
The factors that affect the amount of wasted hot water include:
- Whether the house has a compact design: stretched-out single-story homes are likely to have more waste than compact two-story homes.
- Whether the water heater is in a basement (making it easier to locate the water heater in the center of the house) or in a garage (in other words, at one end of the house rather than the center).
- The number of bathrooms and fixtures in the house. (Homes with many fixtures waste more water than homes with few fixtures.)
- The diameter of the tubing supplying hot water to remote fixtures. (Small diameter tubing is preferable to large diameter tubing).
As Gary Klein, managing partner of Affiliated International Management, has pointed out in a useful series of articles (“Hot-Water Distribution Systems”), all of these factors have been trending in the wrong direction in recent years, and as a result our wait times for hot water are getting longer. In Part I of his series, Klein wrote, “Since houses are generally stretched out from the driveway to the back yard on long, skinny lots, the distance to the furthest fixture has increased to over 60 feet. … There are twice as many fixtures in the current median home as there were in 1970. The distance to the farthest fixture has more than doubled. And there are a lot more fixtures served by the trunk line. In consequence and in accordance with the plumbing code, the diameter of the trunk line has increased from 1/2 to 3/4 inch for much of its length and to 1 inch for a significant portion. This means that the cross-sectional area of the pipe has increased by a factor of 2.25 to 4.0. … In addition, water utilities have taken additional steps to reduce water consumption by promoting more-water saving fixtures. They also have reduced supply pressures, both to reduce leaks in their aging systems and pump costs and to effectively increase supply for the ever-growing population in their service areas. … In short, it now takes 18 times as long for the hot water to arrive. For example, if it used to take 5 seconds to get hot water, it now takes 90 seconds.”
In Part II of his series of articles, Klein explained why small diameter hot water tubing is preferable to large diameter tubing: “Compared to the time it takes hot water to arrive in 3/8-inch-diameter pipe at a given flow rate, it takes roughly 1.5 times as long in 1/2-inch-diameter pipe, three times as long in 3/4-inch-diameter pipe, and six times as long in 1-inch diameter pipe.”
Other ways to reduce the cost of hot water
If you want to reduce the amount of energy you use to run your old refrigerator, it makes sense to shop for a new refrigerator with a higher efficiency. But you can’t really apply the same logic to your hot water system.
If you’re not happy with your run-of-the-mill water heater, you could spend thousands of dollars on a fancy new water heater that might reduce your energy use by 15%. But if your house is wasting 25% of the hot water produced by your new equipment, it’s clear that fancy equipment alone won’t solve your energy waste problem.
Here’s a list of seven things you can do to reduce the amount of energy used for domestic hot water:
- Design your house for an efficient pipe layout. Designers should create compact designs with as few bathrooms as possible. Bathrooms should be located close to the kitchen — directly above or below the kitchen, if possible, or close to it in a horizontal direction if the rooms are on the same floor. The water heater should be centrally located. Hot water lines to remote fixtures should be small diameter lines; in most cases, home-run manifold systems make more sense than trunk-and-branch plumbing systems.
- Insulate your hot water pipes. Pipe insulation has only limited value, since it helps keep water hot for only 30 minutes or so. Nevertheless, insulated pipes are preferable to uninsulated pipes.
- Install a drainwater heat recovery device. These devices consists of a coil of copper water-supply tubing wrapped around a large-diameter vertical copper drain pipe. The devices extract heat from hot water flowing down the drain and transfer the heat to cold water flowing to a showerhead. Brands include GFX, Power-Pipe, and WaterCycles. Studies show that these simple devices can save 16% to 34% of the energy used to heat domestic hot water.
- Install low-flow fixtures and efficient appliances. If you can find a 1.75 gallon per minute showerhead that you like, you’ll use a lot less hot water than your neighbor who uses a 2.5 gallon per minute showerhead. It’s also important to consider hot-water usage specifications when choosing a dishwasher or clothes washer.
- Consider installing a demand-controlled hot-water circulation pump. If you are stuck living in a house with a bad plumbing layout — for example, a stretched-out single-story house with a water heater in the garage, and a master bath on the opposite end of the house — consider installing a demand-controlled hot water circulation pump. This type of pump won’t turn on unless you flip a switch located in the remote bathroom. Whatever you do, however, don’t install a hot-water circulation pump that is controlled by a timer or one that runs 24 hours a day; these pumps will just increase your energy bill.
- Wash your clothes with cold water.
- Change your behavior. If it takes you 2 minutes to wash your hands, and it takes 2 1/2 minutes for hot water to reach your bathroom sink, it probably makes sense to use the cold-water tap instead of the hot-water tap for most hand-washing activities. Retrain yourself!
The lower your hot water usage, the fewer reasons there are to buy expensive equipment
Many American households use a lot of hot water, and our inefficient plumbing systems result in a lot of waste. However, it doesn't make much sense for families that use average or below-average amounts of hot water to invest in an expensive high-tech water heater. The savings are too small to justify the investment.
For example, energy consultant Marc Rosenbaum lives in a two-person household in Massachusetts. Marc and Jill heat their water with an electric resistance water heater that requires only about 1,100 kWh per year. (They recently hooked up a heat-pump water heater, but that's another story.) It's possible to generate that much electricity with a 1-kW photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system that costs only $4,500 to install — even less with a tax rebate — so their household is a poor candidate for a $5,000 condensing gas-fired water heater.
That said, the more hot water your household uses, the more sense it makes to install efficient but expensive equipment.
A few radical ideas
Can we imagine better ways of reducing the amount of energy we use to make hot water?
A few years ago I visited a small town on the Caribbean island of Dominica, and stayed in a simple guest house. The house had no water heater. However, the showerhead was fat, and it had a cord dangling from the end that was plugged into the nearest outlet. An electric resistance element in the showerhead (controlled by a flow sensor) raised the temperature of the water flowing through the showerhead. Since the electrical draw of the resistance element was fixed, the user controlled the temperature by adjusting the water flow. If the flow was adjusted to a trickle, the water was very hot; if the water flow was fast, the shower was lukewarm at best.
Of course, this device looked a little frightening, but it worked. It had several virtues:
- It only worked with low flows, so you had to save both water and electricity if you wanted a hot shower.
- Obviously, there was no hot water wasted, because no hot water ever sat in a pipe.
It turns out that these point-of-use electric water heaters are widely used in the Caribbean and Latin America. Common brands include Marey, Coral, and Lorenzetti. (If you want, you can buy such a unit in the U.S. The Marey Heater Corporation will sell you a 110-volt model for $75, and a 220-volt Lorenzetti model is available from Casa Excel in Miami for $79. Disclaimer: I'm not sure that these water heaters meet U.S. building code requirements, so experiment with these devices at your own risk.)
The main disadvantage of these units: most of them are made for tropical countries that have incoming cold water temperatures of 70°F or 80°F. These units advertise a temperature rise of 10 F° to 30 F°; that means that they won’t heat water in Vermont to shower temperature. (The better-quality 220-volt models can provide a 122°F shower with 40°F incoming cold water, but only at a relatively low flow rate of 1 gallon per minute.)
But here’s my point: many builders of zero-energy homes are moving toward all-electric homes equipped with photovoltaic systems. If you don’t like the complexity of heat-pump water heaters, that means you’ll be heating your water with electric-resistance elements. And if you’re doing that, I think that the water-heating elements should be located at the tap to minimize hot water waste.
Calling all manufacturers: we need innovative point-of-use water heaters
Clearly, most of us can't use an electric showerhead that only raises the temperature of the incoming water by 10 F° to 30 F°. Even better engineered products, like the Stiebel Eltron Mini Tankless heater, probably cost too much to install at each faucet and only handle a slow flow rate of water. (You can buy a Stiebel Eltron Mini Tankless on the Web for about $130.)
However, I'm raising the idea of using point-of-use electric resistance water heaters for two reasons: in hopes that manufacturers will develop a wider variety of point-of-use water heaters, and to get builders and designers thinking of new ways to reduce hot water waste. (For more information on this type of water heater, see Point-of-Use Electric Tankless Water Heaters.)
The bottom line
In the meantime, I believe that there’s nothing wrong with installing an inexpensive electric resistance water heater — or, if you live in a hot climate, a heat-pump water heater. Just be sure to wrap the tank in an insulation blanket and use as little hot water as possible.
Last week’s blog: “New Green Building Products.”
- Claudio Secci - 40andnow.com
- Marey Heater Corporation
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