Residential hot water conservation is one of the last frontiers of available water conservation. Most homes waste tremendous amounts of water with their existing hot water plumbing. Every time you have to wait for hot water you are needlessly running water down the drain.
Most water conservation measures in the home are flow limiting or volume limiting devices and or appliances. Low flow fixtures reduce the flow and thus can reduce water wastage if the home owner would otherwise leave the water on at a high flow rate. It doesn’t save you any water if you are just filling a pot or a glass, it just takes you longer.
Low flow fixtures can actually cause you to waste more energy. As the hot water travels from the water heater to the fixture is loses some of its heat to the cold piping material, causing the hot water to warm up more gradually at the fixture. With very long pipe runs this effect is very evident.
For long pipe runs the low flow fixtures result in more barely-warm water from the hot water plumbing to be run down the drain. That means you are running heat energy down the drain too. That is wasting energy and costing you money.
Many folks who have slow hot water problems turn the faucet or shower on and go do something else while they wait, coming back a few minutes later to use the hot water. Often when they get back the water being run down the drain is hot water. It’s like running Btu’s down the drain, not to mention all that extra water being wasted.
In large homes where long hot water runs are more likely and hard to avoid, often a hot water circulating system is used. A hot water circulating system continuously circulates hot water through the hot water piping, keeping instant hot water always available at the hot water faucets.
This saves a lot of water and is a nice convenience, but it is a huge waster of energy. Your hot water piping is in effect, a large radiator. Even with heavy insulation you will be using a lot of heating energy to run such a system. You are also running a pump which also consumes a modest amount of energy.
A number of products are on the market to remedy this situation. One common system is what I call the luke-warm hot water circulating system. It is similar to the standard hot water circulating system, except the pump is controlled by the water temperature at the fixture. In some systems the pump is located under the sink and some locate the pump at the water heater with just a valve at the sink. There are also pumpless systems that rely on thermo siphon effects to operate.
I personally can’t understand why anyone would want one of these warm water circulating systems. They are virtually the same as the old full time circulating systems except instead of running continuously they run for a short time periodically all day. These systems monitor the water temperature at the fixture, and when the temperature drops to a pres-set temperature, usually around 85 degrees, the pump comes on and pumps until the water temperature reaches say 95 degrees and then shuts off. At the moment the pump shuts off you have 95 degree water available, not exactly hot, but not cold. The hot water will be probably be only a few seconds behind it.
The water will begin cooling down immediately and so after about 10 or 20 minutes the temperature of the water will drop below the lower set point, and the pump will again turn on and run until the warmer water arrives and it shuts off. Now all the 85 degree water that was in the hot water pipes is in the cold water line. If you want a drink of cold water you will have to purge the warm water out of the line. This will waste water.
If you happen to turn on the hot water faucet when the hot water has cooled down almost to the set point but not quite, your hot water will actually feel cool to the touch… and you will have to run luke warm water down the drain until the hot water arrives. Now you are wasting energy and water at the same time.
The thermo siphon systems lose energy in the same way. These systems require the water heater be below the fixture, relying on the principle that hot water rises, and thus don’t need a pump. They still waste the heat energy which is much larger than the pumping energy anyway.
You can put such a system on a timer to reduce the energy consumption, by not running it during time you normally don’t use hot water. During those times however, you won’t have the benefits either.
Most of these types of systems are incompatible with tankless water heaters. They don’t produce a high enough flow to turn on the heater.
These luke-warm hot water recirculation systems are available from Grundfos, Taco Pump Company, RedyTemp, Watts, Armstrong, and others.
There is however a better way. It’s called a hot water demand system and it eliminates the wasted water completely, eliminates the wasted energy, uses less than $2.00 a year in pumping energy, and doesn’t need any special plumbing or a dedicated return line. This makes it very easy to retro-fit into existing homes.
The hot water demand system typically locates the pump at the fixture furthest from the water heater and will thus may service other fixtures along the way. To activate the system you push a button which starts the pump. The pump then speeds the water from the water heater to your fixture, returning the cooled off hot water to the inlet of the water heater through the existing cold water piping. When hot water arrives the pump shuts off preventing warm water from entering the cold water line.
Now when you turn on the tap you have instant hot water. Since the pipe had to get filled with hot water anyway, you don’t waste any extra energy, in fact, you often get your hot water much more quickly and thus you actually save a little energy. Because the pump only runs for a few seconds and only when you demand hot water, it consumes very little electricity; typically for a family of four it would be less than $2.00 per year.
Most demand hot water systems produce enough flow to turn on a tankless water heater. Demand systems are especially nice with tankless hot water heaters since tankless units require longer to deliver hot water and thus waste more hot water than storage tank type hot water systems.
By installing a hot water demand system you will be going green with your hot water plumbing. You will be reducing not only the amount of wasted water and energy, but you will be reducing your carbon footprint and reducing greenhouse gas emissions.
The best part is you will feel good every time you use your hot water.
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