Preheating water by running pipes through attic?

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My brother-in-law and his wife are planning to retire and build a custom home with as many energy-saving and eco-friendly features as possible. Since they're likely to be stuck with HOA rules about exterior appearance, solar panels on the roof are probably out, but they were wondering about simply running water pipes through the roof space.
Does this have possibilities?
Perce
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I am inclined to think that you're pulling our leg, but here is my answer anyway. You did not tell us where the house will be built. If ever winter temp drops below freezing, the copper pipes will bust like you have never seen, sort of like cutting butter with a knife. Get the picture?
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snipped-for-privacy@uark.edu wrote:

With creative use of tees and valves, this doesn't necessarily need to be a problem. Just need to remember to drain down the "attic loop" before the outside temp. gets near freezing.
nate
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On 08/05/08 06:59 pm snipped-for-privacy@uark.edu wrote:

No, I am not pulling your leg. This is what they told me they are thinking of. And, yes, I should have said where: "Hotlanta" area.
And also I omitted to repeat in the body of the message the word I used in the subject line: "preheating." They are not thinking they are going to get water hot enough for washing dishes from such a system, but they are hoping to use less gas to heat their water.
Perce
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Hot water really only costs about $15 a month anyway. So how much do they plan to save. Even if you had 200' of 1/2" pipe up there, you're only talking about preheating 2 gallons of water. Now if you put a properly supported 50 gallon tank up there..........
s
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Steve Barker DLT wrote:

How about a flat roof built like a shallow swimming pool, say 3 to 6" deep ?? Would that warm up enough ?? Would also catch the rare Atlanta rain every now and then (BTW, catching rain like this is illegal in some states, mostly Western, where "water laws" prohibit such.)
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If it is hot out and the water coming into the pipes is cool, wouldn't that cause a lot of condensation on the pipes?
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just like the law preventing HOAs from stopping satellite dishes there should be one allowing solar panels, to help the envirnment........
I wouldnt live in a HOA community because of such issues
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Yes, possiblility it will freeze in winter. Where we talkin' 'bout?
s

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I doubt they'd get much benefit from preheating the water in the pipes. There's just not a lot there. However, it's not uncommon in large buildings to install a "tempering tank" in the boiler room. It's basically a large holding tank that allows water to reach boiler room temperature BEFORE it hits the water heater. That way the water heater only has to raise it from 70-80 degrees to 140.
I have a friend who uses old water heaters (the non-leaking ones) as tempering tanks in all of his rental properties. He removes the insulation and installs them in the boiler rooms. He figures whatever heat they absorb is that much less heat he has to pay for.
I wouldn't recommend his method if they're putting it in an attic--at least not an old tank.
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A very creative HVAC tech may be able to use some of the heat from central AC to preheat a tank of water. The attic seems possible, but who can tell? Might be more trouble than it is worth.
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Christopher A. Young
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On Aug 5, 10:04pm, "Stormin Mormon"

Where my woodstove is a primary source of heat in my home I have the copper line to my HW boiler coiled under the stove before going to the boiler. Been preheating HW boiler water like this for years, and it works.
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On Tue, 5 Aug 2008 20:04:55 -0400, "Stormin Mormon"

Obviously that leaves you out Stormy. Bubba
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I'd never want to live in such an area where Gladys Kravitch can tell me what to do. Abner! Oh, Abner!
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A newer home should have a well ventilated attic, building codes call for attic no more than 15 degrees warmer than outside air temp.
It might not gain you as much as you believe..........
Our homes attic temperature used to be 140 with outside at 90 till we replaced the roof with a lighter color shingle and added ridge vent.
its now about 110 with outside at 90.
I have a recording thermostat for work I put it up there for a few days out of curosity while on vacation
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I'd put a $35 used car radiator with its 12 V fans under the ridge and make the south roof transparent. It seems to me there's a federal law that prohibits HOAs from outlawing this form of renewable energy.

You might get 5 Btu/h-F per $2 foot of fin-tube, vs 1000 for a car radiator, which might also circulate some warm attic air through the house on a winter day, with a couple of motorized dampers.

Which code? Section R806.2 (Roof Ventilation--minimum area) of the 2006 International Residential Code (used in PA, NJ, and lots of other states) says an attic can have 1/300 of its floor area as ventilation if upper vents have 80% of that and vents at least 3' below them have 20%. So my 24'x32' attic might have a total vent area of 24x32/300 = 2.56 ft^2 with 0.512 ft^2 of low vents.
In full sun on a still day the roof might absorb about 24x32x250 = 19.2K Btu/h of sun and lose heat to outdoor air with a 24x32xU.5 = 384 Btu/h-F thermal conductance, with an equivalent circuit like this, viewed in a fixed font: T 1/384 | --- ------www-------|-->|---| | --- | 125 F I --- - | | -
One empirical chimney formula says I = 16.6Asqrt(H)T^1.5. A = 0.512 ft^2 and H = 3' make I = 14.72T^1.5, which makes T = 0.0383(3261-T^1.5). T = 91 F on the right makes T = 91.7 on the left. Repeating makes T = 91.3, so the air in an IRC-code attic could be 91 degrees warmer than outdoor air.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

When I blew the hot air out of attic (Georgia....dark green roof) on any kind of clear day could get a 20 degree rise in house above outside.....on a bright day could easily get 90 degree inside no matter what outside temp...had a differential thermostat that turned on box fan when attic temp rose above inside temp... usually turned on around 0900 and turned off around 1800....and could usually coast all night with morning temp in low 60's....
hope helps...have fun....sno
hope helps...have fun.....sno
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Attic air can be full of all kinds of nasties. Lots of dust, insect and animal excrement....
Jimmie
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JIMMIE wrote:

Jim...you are right...every year when I first turned fan on dust and other things blew all over.....wife complained like crazy....if did it again would use fan with filter....
have fun....sno
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JIMMIE wrote:

Why don't you bury the pipes in the driveway? I did this in Florida and had very hot water all the time. I had a black asphalt driveway and before they installed it, I buried copper pipe in the sand. After the asphalt was put down and cured, I found that I had plenty of very hot water. Since the water heater tank was just inside the garage, it was easy to get the water back into the tank.
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