Replies

1. 
   DanH | May 11, 2009 11:00pm | #1

   It's known as a "tempering tank". Sometimes just an old water heater with the insulation removed. It makes sense so long as you're not paying more to heat your air than you are to heat your water. Especially makes sense when on a well, since the water tends to be colder.

   However, the money savings may not be worth the added space consumed, etc.

   Another trick is a drain pipe with copper water pipe wrapped around it. Put the drain pipe on, eg, the shower drain, and run the cold feed to the water heater through the copper pipe. Someone makes these commercially, but I don't remember the brand.

   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
1. 
   Hudson Valley Carpenter | May 12, 2009 08:38am | #3

   I was thinking about using off-peak electricity to pre-heat well water to room temperture.  I suppose that using a 50gal HWH as a pre-heater would work OK but I'd probably add a header tank also, to make sure that there was enough for a full day.

   Thanks for the description of the drain heat recovery system.  That's a new one for me.

1. 
   DanH | May 12, 2009 02:02pm | #4

   Yeah, I've thought of doing essentially the same thing with wind power. You'd in theory be able to use "low-quality" unregulated power, so you'd have a cheaper installation than if you tried to go the backfeed route. So even a small wind generator would be worthwhile.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   peteshlagor | May 12, 2009 05:04pm | #5

   Remember that solar siting comment I made?

   This is where you use some of the highest efficiency solar collectors to preheat that water you got in mind.

   But it's gotta be designed in up front so it's unobtrusive and leakproof.  

    

1. 
   Hudson Valley Carpenter | May 12, 2009 06:04pm | #6

   That's a good idea for an area like the Mid-Hudson, where winter brings two days of clouds for one day of sun.  Solar water heating on sunny days, using plastic tanks of 500gal to 1000gal, would be a workable system.   Definitely worth thinking about.

   BTW, I'm planning for about 1000sqft of roof area facing south in order to be prepared for whatever solar systems come along.  I'm betting that photovoltaics will take off pretty soon, using some totally new approach to achieve much greater efficiency.

1. 
   DanH | May 12, 2009 07:36pm | #7

   In Mexico and south Texas the "water heater" is commonly a black plastic tank on the roof. Fills with a valve like a toilet fill valve, feeds the shower via gravity. Makes for miserable showers on cold, cloudy days.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   Hudson Valley Carpenter | May 12, 2009 08:42pm | #8

   When I lived in th City of Durango, Mexico back in '67, the city water system was something like that, a big concrete tank on a hillside.  The water arrived luke-warm, year-round, without much pressure, strings of green algae hanging from the shower head.  We boiled what we drank. 

    

2. 
   reinvent | May 12, 2009 01:44am | #2

   This is what DanH was talling about.

   http://gfxtechnology.com/contents.html#selection

3. 
   GaryGary | May 16, 2009 04:41am | #9

   Hi,
   Something to think about:

   Buy a 300 ft coil of 1 inch diameter HDPE (black poly) water pipe, and use it as a preheat tank.

   Cost is about $70.
   If the OD of the pipe is 1.25 inches, the surface area is 98 sqft.

   The surface area of a 50 gallon water tank is about 21 sqft.

   So, the pipe would give you 4 times the surface area to transfer heat, and cost a lot less??

   As was pointed out, if the heat for preheating the water is coming from an area that you have to heat anyway, there does not seem to be much benefit. So, maybe put the coil in a crawl space?

   Or, just use my $1000 solar water heater:
   http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

   Gary

1. 
   Hudson Valley Carpenter | May 16, 2009 05:52pm | #10

   Thanks for your interest and for the link to your design.  I'll have to find some time when I'm wide awake, to study your system and ask questions.

   I first ran across black poly pipe when I began sub-contracting the installation of vinyl liner in-ground swimming pools.  It wasn't my choice but it had the advantages of being cheap and easy to install. 

   Anyway, I found an extra 100' roll at one job so I tried it out as a cheap pool heater, just expanding the coils and laying them on the south facing embankment next to the pool. 

   I had an old pool pump that I used for a sump pump so I hooked it up to one end of the coil and ran the other end through a cement block, back into the pool.

   It worked very nicely, raising the 20,000 gals of 55 degree water by about one degree per hour in full sun.

    

   Edited 5/16/2009 10:55 am by Hudson Valley Carpenter