Usually conserving water is a painful process. Low flow toilets conserve water, but most people who have used them complain about their operation…needing to flush multiple times etc. How about low flow shower heads and faucets? Again, for most of us it’s not a painless way to conserve water. It’s emotionally painful, at least for me. How about all those brown yards with dead lawns? And not being able to wash your car…that’s painful isn’t it?

Well the good news is there is a way to save a lot of water without the pain and it’s called a hot water demand system! In fact, this way of saving water is actually a convenience for the user. It’s called a hot water demand system (or demand hot water system), and it can save a typical family of 4 up to 16,000 gallons of water per year according to one manufacturer, and 10,000 gallons per year according to another.

A hot water demand system consists of a small pump that mounts under the sink in a bathroom or kitchen. When the user “demands” hot water, by pressing a button, the pump begins pumping water out of the water heater, and when the hot water reaches the pump, the pump shuts off. The cooled-off hot water in the hot water pipes is pumped into the cold water line, and back into the water heater inlet. It just pumps the water in a big loop out of the heater and back in. Since the pump shuts off when hot water reaches the pump, little if any hot water makes it into the cold water line.

Since the pump only runs for a very short time, typically less than a minute, it uses very little electricity. Usually these pumps use less than a dollar or two per year of electricity. With some of the systems the pumps are powerful enough that you get your hot water in half the normal time.

If you have a tankless water heater then you are probably wasting even more water waiting for the hot to arrive, since a tankless water heater takes time to heat the water and a storage tank type heater does not. However, it takes a certain amount of flow to turn on a tankless water heater so you must be sure the pump you purchase has enough power.

There are a number of hot water circulating systems on the market, and not all of them are “demand” systems. Traditional circulating systems require a separate return line for the hot water, and the pumps run continuously. These traditional systems use a tremendous amount of energy keeping the hot water pipes full of hot water. The water heater has to work a lot harder and can wear out much more quickly. Tankless systems won’t work with traditional hot water circulating systems.

There are also a class of circulating systems that are kind of half way between the traditional system and the demand system. They use the cold water line as the return line like real demand systems, but they operate on a temperature cycle like some traditional systems. That is, when the water cools down to a pre-determined temperature the pump turns on, and when the water reaches a pre-determined high temperature the pump shuts off. The pump cycles on and off continuously keeping the water in the pipes kind of luke warm. These systems will not work with tankless water heaters either. The pumps are too small to pump enough water to turn them on.

These temperature controlled cold water return line systems also use a lot of energy since they keep the hot water (and cold water) pipes full of warm water. They aren’t as bad as the full time traditional systems, but they consume one heck of a lot more energy than a true demand system.

When considering purchasing such a system be sure to check with your local water company and or city government to see if any rebates are being offered. There are water companies that offer rebates, and some rebate as much as $200.00 per home. That’s actually more than the retail price for at least one brand of demand system.




By: William Lund