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Don't Let Your Money and Hot Water Go Down the Drain

December 9, 2008 - 4:00am

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Do you look at your retirement savings statements and feel like you're sending your money down the drain? Do you deposit more money each paycheck into your retirement account, but find the balance goes down, not up?

Pssst, want to invest in a "sure thing?" No, this isn't a scam. It's a device that has no moving parts to break down, but is certain to save you energy, and thus save you money by lowering your utility bills. When we all take showers and baths, wash the dishes or clothes, and wash our hands, we send heated water literally down the drain. That typically represents 80%–90% of the energy used to heat water in a home. Drain-water (or greywater) heat recovery systems capture some of this energy to preheat cold water entering the water heater or going to other water fixtures.

How It Works

In its simplest form, a drain-water heat recovery (DHR) unit is simply a copper heat exchanger that replaces a vertical section of a main waste drain. As warm water flows down the waste drain, incoming cold water flows through a spiral copper tube wrapped tightly around the copper section of the waste drain. This preheats the incoming cold water that goes to the water heater or a fixture, such as a shower. Some units also contain a storage tank.

Drain water heat recovery technology works well with all types of water heaters, including demand and solar water heaters. They generally have the ability to store recovered heat for later use. You'll need a unit with storage capacity for use with a dishwasher or clothes washer.

Most DHR systems are installed in the main waste drain of the house by an experienced plumber. Be forewarned, however, that many plumbers are not familiar with DHR installation. Most systems use common equipment and tools, and installation is relatively simple, so your local plumber should be able to figure it out.

By preheating cold water, drain-water heat recovery systems help increase water heating capacity. This increased capacity really helps if you have an undersized water heater. You can also lower your water heating temperature without affecting the capacity.

There are several residential drainwater heat exchangers commercially available.

According to the National Association of Home Builders Research Center's Toolbase Services, DHR systems typically cost $300 to $500 plus installation—contact the manufacturers for their current prices. I never said they were cheap, did I? Consider it as an investment, one that's sure to stop throwing money and hot water down the drain.

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