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Water Heaters 101> Save Water, Save Energy

What you'll find on this page: If your water heater is at one end of the house and your bathroom at the other, you'll have a long wait for hot water -- and waste a lot of cold water in the meantime. Here are tools to solve that problem and home-building strategies to prevent it in the first place.

Once upon a time, there wasn't much of a wait for hot water because the water heater was not very far from the fixtures it served. Often, homes were two-story, and typically the water heater was in the basement. Convection heated the water in the pipes part of the way toward the fixtures, and the fixtures themselves were a short run away anyhow.

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Then came suburban sprawl, with the water heater at one end of the house, often in the garage, and bathrooms at the other end. That meant that you could go into the shower, turn on the hot tap, and hold your hand under the spigot for eternity, waiting for some hot water to flow out. That water had to come all the way from the water heater, sometimes a hundred feet away, and pass through plumbing that had cooled off since the last use. You'd waste a lot of time in frustration, and a lot of water would be wasted, running down the drain.

There are several solutions to this. Some are design solutions, others mechanical ones.

 

Recirculation Systems

One of the most common solutions is to install a recirculation system. That ties the farthest point of the system back to the water heater with a plumbing line, usually smaller-diameter piping than the main system, and returns cooled-off water to the heater, while pulling hot water through the lines. It can be either gravity-feed or pump-driven.

Their chief advantage is instant hot water. Because hot water is always circulating through the system, it's available at every faucet immediately, no matter how far that faucet is from the water heater.

A big disadvantage is that heat is continually radiating away from the piping, especially if it is uninsulated, so a recirc system can dramatically raise your utility bill. If pump-driven, the pump needs to be carefully sized or the constant flow of water can scour away the inside of copper piping.

Thermostats or timers can be used to shut down the system during off-times and lower the amount of energy being used.

See our Recirculation-Pump Valving page for the optimal way to install the pump.

 

Demand Systems

Demand systems are an alternative to recirculation systems. They solve the issue of wasted cold water, while also providing quick hot water without the attendant energy costs. However, they do not deliver hot water as instantly as a recirculation system.

They consist of a pump, some piping and a switch. One presses a button, or passes a motion sensor to activate the pump, which then pulls hot water from the water heater and may push cold water into the cold line. Then the pump turns off. Examples are the Metlund D'MAND and Chilipepper.

 

Heat Exchangers

One of the more interesting products on the market is the shower drain heat exchanger. It is a device that sits below a shower drain. When you take a shower, about 60 percent of the heat in the drain water is returned to the water heater or water flowing into the shower. This is the equivalent of adding a solar system to your home for a whole lot less. Some brands are GFX Heat Exchanger, Power Pipe and Retherm. They vary in length and type of construction.

 

A manifold system for distributing cold water
Manifold Systems

Manifold systems use a pipe with many outlets leading from it, each connecting to one end use, be it a washing machine, showerhead or faucet. There are cold manifolds (2) and hot manifolds (1). These images are from the House on Hummingbird Hill. The hot manifold sits on top of the water heater and individual PEX lines serve different parts of the house.

The cold manifold is in the basement and works similarly. Each line has its own shutoff valve. If there is a leak, any one line can be shut off without affecting any other fixture in the house.

There are several advantages to this type of setup. The PEX lines are small-diameter, which means less water flows through them. Greater pressure with less water loss can be had at each fixture.

 

Structured Plumbing

Structured Plumbing is a concept created by Gary Klein when he worked for the California Energy Commission. He was the one who noted the trend described in the introduction to this page -- away from two-story houses with the water heater in the basement, and toward ranch-style houses with the water heater at one end and the bathrooms at the other.

Structured Plumbing puts the water heater at the center of the house instead of on one side in the garage, as with a lot of new construction, and usually uses a demand pump. There is also a 3/4-inch recirc return, or maybe even a one-inch main line, that runs throughout a home, never more than 10 feet from any fixture, and back to the water heater, but with 3/8-inch branches to each fixture instead of half-inch. What does this do? The smaller branches and close main line mean minimal water runs down the drain during the wait to get hot water.

The larger-diameter main line means a very short wait after hitting the pump button, as hot water flows quickly.

The pump means no radiant heat losses in off-peak times, since it draws water to its fixture and then shuts off. And the insulated main line stays hot up to 30 minutes, long enough for a batch of morning showers. Structured plumbing is a possibility for new construction or anyone considering replumbing their home.

Another of its goals is to provide hot water to each fixture with no more than one cup of water running down the drain during the wait.

 

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