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 http://www.redytemp.com/Bypass_valve.jpg

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 toilet...it 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
http://www.diynetwork.com/diy/shows_..._34692,00.html
http://www.diynetwork.com/diy/hi_plu...347744,00.html