Comparison of Water Heaters and Important Metrics Best Climates
High-Efficiency Water Heater Type
High-Efficiency Storage (Tank) (Oil, Gas, Electric)
Demand (Tankless) Using Gas or Electric
Heat Pump Solar with Electric Back-Up
Energy Savings Vs. Minimum Standards
10%–20% 45%–60%
65% (compared to electric resistance)
70%–90% Any Any Mild-Hot Mild-Hot
Expected Energy Savings Over Equipment Lifetime
Up to $500 Up to $1,800 Up to $900 Up to $2,200
Expected Lifetime
8–10 Years 20 Years 10 Years 20 Years
Major Advantages Lowest first cost Unlimited supply of hot water Most efficient electric fuel option
Largest energy savings using a renewable energy source
First-Hour Rating (FHR). FHR measures how much hot water will be available during the busiest hour of the day. A large tank does not necessarily translate to a higher FHR. The recovery rating is important as it indicates the water heater’s ability to replenish hot water as it is drawn from the tank.
Efficiency. The water heater’s efficiency is measured as an Energy Factor (EF), which is usually listed beside the EnergyGuide label; the higher the number, the more energy efficient the water heater.
products in the same category. That said, simply selecting low-flow
fixtures doesn’t cut it. Ultimately, if we expect our occupants to behave respon- sibly in terms of their water use, we have to recommend truly sustainable installations as well as low-flow fixtures. Three shower heads or a 102-gallon tub are not the picture of sustainability, even when the fixtures themselves are water- efficient. Hot water delivery to fixtures by means of the water heating and distribu- tion systems is critical in the energy and water profile of the home. Lengthy (and uninsulated) distances or “runs” be- tween water heaters and fixtures cause a significant amount of water to be wasted simply waiting for hot water to arrive at a shower or faucet. When the tap is turned off, the unused hot water in the pipes causes energy to be lost. According to Klein, the problem
started with a well-intentioned solution, building regulations. “There were two sets of regulations,” says Klein. “The plumbing codes and the federal energy regulations. Plumbing codes required bigger diameter pipe to maintain proper pressure when there are more fixtures on a given line. Federal energy regulations limited fixture
flow rates, plus other federal regulations reduced flow rates to appliances. As bigger houses were built, more pipe and fixtures were needed, requiring bigger diameter pipe.” This poorly engineered solution resulted in occupants having to turn the tap on and then wait for warm water to arrive. Now, instead of 5 seconds to get hot water it takes about 18 times as long, or 90 seconds. In addition, supply and drain issues
were introduced, as piping remained the same while flow from fixtures decreased. There’s no other polite way to phrase the real problem here—there often simply isn’t enough water to flush the poop without changing drain pipes or slope. Strategies to address problems in wa-
ter distribution clearly vary in new and existing housing. In new construction, there are a slew of strategies to ensure ef- ficient hot water distribution, since you’re starting from scratch. Of these, creating a central core plumbing system is the simplest, most effective method. Stack- ing second floor bathrooms on top of first floor baths, kitchen, and/or laundry areas creates these central cores and helps to reduce the amount of time it takes for hot water to reach the desired end. Main trunk lines feed the central areas from
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GreenBuilder October 2010
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