Instant Hot Water: Installing a Re-circulating System

DIY network will be airing how to install a Re-circulating system at 9 am eastern time today. They'll be demonstrating the re-circulating valve which is known to bleed cold water from the hot water line when homeowners "only use the cold water" in their home. This occurs due to the crossover / re-circulating valve always being open anytime water which is less then 94F is in the hot water line. It's this bleedover that causes homeowners to complain about waiting for cold water as well as high gas bills. Here's the best explanation I've seen on this topic
I don't understand how this almost always openned valve passed through the approval process. When cold water is used in a home, then only cold water should be drawn from the city cold water supply, not some from the city and some from the hot water heater line.
If you've got one of these Grundfos Comfort Series Re-circulating systems in your home perform this test. When the pump is not scheduled to run, measure the temperature of the water coming out of the hot water line....since, the pump is scheduled off, the water should be around room temperature. Then open only the cold water faucet for 2-3 minutes...fully open. Now close the cold water faucet and open the hot water faucet and check the temperature of the water coming out of the hot water line. Because the valve is open when the water in the hot water line is cool....the water in the hot water line feeds thru the valve to assist in the fulfillment of the cold water usage. Not a good thing...because cold city water must enter the hot water heater to replace the water which bleed through the valve. Why would anyone want to consume gas when they brush their teeth or flush their makes no sense to me.
I'd think twice about installing one of these models. The only way to keep that valve closed is to always have hot water in your hot water pipes.
That's my two cents.
episode DETP-109,2046,DIY_19138_34692,00.html,2037,DIY_13929_3347744,00.html
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