Preheating water by running pipes through attic?

those 150 b uck point of use with a shower? you must be joking, at most hand washing.

Reply to
hallerb
Loading thread data ...

Most of which consist of you saying "does so" and everybody else saying "you're full of it".

Reply to
J. Clarke

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

Reply to
nicksanspam

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

Reply to
sno

Attic air can be full of all kinds of nasties. Lots of dust, insect and animal excrement....

Jimmie

Reply to
JIMMIE

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

Reply to
sno

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.

Reply to
Chuck

I hope the copper pipe was protected. Plastic pipe would be better, all in one large coil.

Reply to
News

Heh! That's a great idea. Sort of a poor man's geothermal power station.

Reply to
HeyBub

Cute idea, but up north here in frost heave country, those copper pipes wouldn't make it through one winter. PEX, maybe. And you'd have to fill with antifreeze and use a heat exchanger setup, to keep them from freezing solid, unless you put them so deep that it was residual ground heat you were sucking instead of solar.

When I lived in southern Indiana, with abandoned water-filled limestone quarries all over the place, I had a dream of buying one, and dropping a heat exchanger on the bottom to get free cooling for a/c. Of course, I was a broke student at the time, so it stayed in the dream stage.

-- aem sends...

-- aem sends...

Reply to
aemeijers

That reminds me of a funny story I guy once told me. He had lived for a while in a trailer park in southern Arizona. The service lines to the trailers were only buried about 6 inches deep, in ground that baked in the sun all day, so the water supply that came into the trailer was HOT. This was a problem in that you could not take a shower without getting scalded -- no cold water to blend in with the hot. Finally his neighbors clued him in -- the solution was to turn off your water heater. Then the water in it would cool down to your air-conditioned indoor temperature and be your cold water supply. -- H

Reply to
Heathcliff

When I read the subject I had to laugh. No one around here would contemplate the idea. Something about sub-zero temperatures for a couple of month a year...

But I suppose if freezing is never a concern (even Florida gets an occasional frost), then go for it.

daestrom

Reply to
daestrom

There is something disturbing about making something that gives you an incentive to continue to have poor attic ventilation, or even to make your attic ventilation worse in order to raise the efficiency of the water heating system. That is like a government basing its budget on having a tax on prostitution.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

You might try a few numbers for a draindown system like this in your neck of the woods...

Nick

Reply to
nicksanspam

Why ? What's so good about ventilating an attic rather than using it as a heat trap.

Everywhere prostitution is legal it is taxed just like any other income. I don't think it's a substantial part of any governments income though.

Reply to
Steve O'Hara-Smith

It encourages the formation of ice dams in the winter, which causes snow melt to back up under the shingles and leak into the decking, which rots the decking and rafters, leading to premature roof failure.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

Well, for one thing heat is the enemy of shingles--if you don't have proper ventilation and are in a hot climate they'll very likely fail prematurely.

Then there's elimination of moisture--without adequate ventilation you can get enough moisture buildup in the attic to result in mold on the structure, and where there is mold there is shortly after rot.

Then there are ice dams in winter.

There's a reason that every new roof that goes on in most of the US has a ridge vent, and the reason is not that it looks snarfy or makes big profits for the roofer.

Reply to
J. Clarke

Hmm good point - I'm too used to slate.

Not seen that happen in unventilated lofts but it makes sense.

Also too used to mild winters where below freezing is rare.

Reply to
Steve O'Hara-Smith

OK, for people in your type of climate, the reason against using the attic to pre-heat domestic water is to limit air-conditioning costs. The money you save on hot water by using the attic to pre-heat it is more than cancelled out by the extra money you spend on AC, as compared to what you could have saved by passively venting your attic.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

It might be if air conditioning were common here - which it isn't. Round here the temperature gets below 0 C or above 25 C maybe two or three times a year - almost a perfect climate, apart from the rain.

What we do in these parts usually is put insulation in the loft so as to thermally isolate it from the house. In summer it gets hot up there and in winter it gets cold (range perhaps 5-40 C).

It does strike me that it may well be reasonable to use the loft as a solar collector here.

Reply to
Steve O'Hara-Smith

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.