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Raising utility water temp?  Rating:  Rating
 Posted: Mon Nov 7th, 2011 12:24 am
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Joined: Wed Nov 2nd, 2011
Location: Ontario Canada
Posts: 10
My 40Gal Hot-water-heater is connected to the utility water line via a 7/8" OD cooper pipe. (Distance is 8Ft-to the hot-warer heaters cold water intake.
The watertemp. measures only 10C/50F.
My question: How many additional ft of cooper-pipe would be required, to raise the water temperature by 2C/36F or even up to 5C/41F before the water reaches the heater?
I also would consider addional insulation. Like "Tundra Seal", 3/4"wall with a Rvalue of 3.6. Also 30 ft Tundra-Seal"on the hot water side.
The heater is set at 120F.
Can I expect to lower my annual energy bill? (Family of two).
Your suggestions are welcome.

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 Posted: Mon Nov 7th, 2011 01:38 am
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Joined: Thu Aug 24th, 2006
Location: USA
Posts: 782
I want to think this would depend on your demand. The water is going to pass through the pipes at a faster rate not benefiting from the longer intake run with more demand. Maybe I don't understand your question.

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 Posted: Mon Nov 7th, 2011 01:48 am
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Joined: Mon May 22nd, 2006
Location: Asheville
Posts: 738
I am somewhat confused with your desired increase in temperature. An increase of 2C = increase of 3.6F. An increase of 5C = increase of 9F.

A flow rate of 2 gpm through the water heater is a flow rate of 17.43 inches/second through a 3/4 inch ID pipe.

How much heat transfer occurs is proportional to the differential temperature. If the space where the cold water line runs is relatively cool, you may well have to install over 1000 feet of copper pipe to pick up only a few BTUs. And how is the heat in the space provided? If you take heat out of this space, the space will have to be reheated. Reducing hot water use, WH and hot water line insulation, and a gravity film drain heat exchanger to reclaim heat normally thrown away makes a lot more economic sense than trying to pickup a few BTUs on the front end.


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 Posted: Mon Nov 7th, 2011 04:01 am
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Joined: Sat Sep 11th, 2004
Posts: 4131
Hello:  If you have a warm place somewhere in your home, like an attic, greenhouse, or equipment room where a big pipe could go: that large diameter line with many gallons in it could preheat your water heater.  Otherwise ( or in addition to), I like the idea of shower heat recovery, as David suggested.

Yours,  Larry

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