Water saving device

September 24, 2007 10:14 AM

I remember reading about a device that measures the temperature of the water at a bath or shower faucet and opens the water valve when the temperature reaches a preset temperature. Purpose is to reduce water wastage while one is waiting for the warm water to reach the bathroom from the tank. Can anyone link me to this product?
posted by lapsang to home & garden (6 comments total)

Where does this 'waste' cold water go so that it's not wasted?
posted by DarkForest at 10:20 AM on September 24, 2007

If the water isn't flowing, how does the hot water reach the faucet?
posted by mr_roboto at 10:21 AM on September 24, 2007

They don't work quite the way you're describing, I think, but it sounds like you're shooting for a hot water recirculator. These guys make one and take a shot at explaining how it works.
posted by wemayfreeze at 10:27 AM on September 24, 2007

wemayfreeze's second link is interesting, a probably what you have in mind. With a thermostatic control and time-of-day controls, it's possible this setup saves money -- but only if the hot water line is well-insulated along its entire length. If a lot of the pipe is non-insulated and not-reachable inside of walls, it's like leaving a radiator on all the time when you don't need one, and the wasted heat would outweigh the costs involved in letting the water run while waiting for hot water.

They peg the amount of waste at 20000 liters, which is probably reasonably accurate (about 14 gallons a day). But heating that water, with a reasonably efficient oil furnace, costs less than $100 per year. Against this, with the recirculator, you have the cost of the device and installation (probably $1000 worth of plumbing, if the return line is not there), the annual cost of running the pump, and the seepage of heat from the loop, even if insulated. If it's not a wash, so to speak, it's a very low return on your investment.

A smarter investment, IMO, would be a grey-water heat recovery device (which takes the heat from all your wasted hot water, like shower water that goes down the drain, dishwasher water, etc., and recaptures it to preheat water going into your water heater). This can recover as much as 90% of the heat from water going down the drain.
posted by beagle at 10:51 AM on September 24, 2007

We use a Metlund on-demand system in our house. It works very well.
posted by jaimev at 10:53 AM on September 24, 2007

I talked with an old neighbor about implementing a recirculator with one interesting twist-

I wanted to put the recirculating line through the toilet seat to make a heated seat with relatively little wasted energy. Instant hot water plus a heated toilet seat.... Actually, my wife and I DID just buy a house.... hmm....
posted by JMOZ at 11:50 AM on September 24, 2007