Using old electric water heater as tempering tank?

I will probably be purchasing a new "energy star" electric hot water heater for my house in the not too distant future. I was wondering what the issues would be (good or bad) to gut out the old one, remove the insulation and pipe it just ahead of the new one to act as a tempering tank?? I also have a wood stove in the basement for heating the house and I would place the old heater tank close to the wood stove to add heat to the tank. I'm thinking I could preheat the water in the old tank up to about 100 degrees F overnight especially. Do others here think this could be a worthwhile project to do? Thanks for any input on this! Steve
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I did that with an electric but was to lazy to strip the insulation, it still helps a bit, but I think it will sweat in summer and you will need a pan and drain hose under the tank. If you have ng or propane consider a gas tankless, i cut my bills maybe 60% by going gas tankless vs electric. One other consideration is the tank is old and will someday leak, I put in valves to I can bypass the tank without removing it.
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We went tankless but the cold water is now really, really cold. It was being tempered in the basement by the warmth of the water heater as it sat in the pipes. Unfinished part of basement is now much colder too. An advantage during the summer but disadvantage during the winter.
wrote:

I did that with an electric but was to lazy to strip the insulation, it still helps a bit, but I think it will sweat in summer and you will need a pan and drain hose under the tank. If you have ng or propane consider a gas tankless, i cut my bills maybe 60% by going gas tankless vs electric. One other consideration is the tank is old and will someday leak, I put in valves to I can bypass the tank without removing it.
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If you have ng or propane

most of this savings is by going gas.
tankless heaters have downsides like delay from flow starting till hot water arrives.
tankless must detect flow turn on burner before water starts heating.....
tankless have ;lots of downsides
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old tank might leak.........
might be better to some how plumb and circulate water around your wood stove, and send to a insulated storage tank like a solar storage tank.
someone must sell this
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I doubt if it is going to save you enough to bother.
If it did work, it would mean you would also be burning more wood or you will have a colder basement, which could convert to a cooler home.
--
Joseph Meehan

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wrote:

Any savings is an investment, and what will NG cost in 20 years? maybe 4x more, so it is worth it as plumbing will last 60 yrs + and payback goes down, J.M. penny foolish as is America and most of the world.
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...
Maybe, but then if that tank decides to leak some night in the next 60 years and does a couple hundred dollars of damage .....
--
Joseph Meehan

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replying to Joseph Meehan, Gabby_Jim_41 wrote: Maybe, but then if that tank decides to leak some night in the next 60 years and does a couple hundred dollars of damage .....
--

Cute, Joe - but that is what homeowners' insurance is for - protecting people
who are too stupid to pay attention to their home appliances. Actually 10 years
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replying to ransley, Gabby_Jim_41 wrote:

more, so it is worth it as plumbing will last 60 yrs + and payback goes down, J.M. penny foolish as is America and most of the world.
Ransley is also correct - with the codicil shown in my reply to Joseph Meehan - For example, circa 1960 the monthly payment for my mortgage in Barstow, CA was approximately the same as the monthly cost of my natural gas bill circa 1980! Energy costs will continue to rise - ANY investment made today that will reduce the cost of energy in as little as three years is a wise decision. (My home made solar air heater - cost abut $300 - has a three year Return on Investment. In three years, it will start EARNING me money above the initial cost. In six years it is expected it will SAVE me $600 a Year in heating costs - and the amount it will save me will increase with inflation every year thereafter (life expectancy is 30 years).
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I'm sure it would, with an electric water heater.

The ceiling could contain more pipes to make a greywater heat exchanger.

Nick
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replying to Joseph Meehan, Gabby_Jim_41 wrote:

Joseph Meehan is right! I've been "surfing" this topic today (looking for a cheap tempering tank) and the one thing they all seem to have in common is ignoring the fact that a tempering tank has to get the heat from SOMEWHERE and if that source is the heating system of the house you get a zero sum situation, HOWEVER, if you heat the tank using some sort of solar or geothermal source, (or ambient air OUTSIDE your home) you get a positive result. Back in the 1970's a bunch of us college students (Salt Lake City Solar Energy Society - morphed into Utah Solar Energy Society) made an extensive research project out of solar energy. The long and short of it is, a simple box with a transparent cover and any sort of energy transfer system will produce a theoretical gain of about 1BTU per square foot of collector surface. The better the cover, the better the adsorber, the better the transfer medium - the higher the efficiency and the more "heat" you gain. ALSO, the "accepted" concept of thermal siphon has it backward. Don't bother trying to designate top or bottom of tank for (working fluid) input/output. The flow will run what ever direction it wants to - depending on which "leg' is hotter. Try this simple experiment. Take a (metal) coffee can (or "number ten tin") and braze/silver solder a drop loop (about 2' should do) of copper tubing such that it is physically lower than the can. One end goes into the side near the bottom of the can and the other end into the side near the top. Fill the system with water and heat the tubing. (A bit of food color will help you see the action) Then move the heat source from one "leg" to the other and watch the direction of flow - just for the fun of it, move the heat source to the CENTER BOTTOM of the loop. Finally, move the leg from the top of the can to a position at the bottom matching the first leg and repeat the experiment. If top and bottom are your only choice, so be it - but if you have a choice, both legs in the bottom is best. (Of course, take your output from the top and put the inlet at the bottom, standard water heater style). Questions/ comments welcome
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Sounds good to me. An alternative is 3 or 4 10'x4" PVC pipes tucked up under the joists, if they are exposed. You might use close nipples and rubber washers as bulkhead fittings between them, with garden hose adapters at the main inlet and outlet, like this, viewed in a fixed font: --------------------------------------------------- |in out| --------------------------------------------------- --------------------------------------------------- |out in| --------------------------------------------------- --------------------------------------------------- |in out| --------------------------------------------------- --------------------------------------------------- |out in| ---------------------------------------------------
The main outlet could connect to the water heater drain.
The pipes would hold about 220 pounds (26 gallons) of water with 40 ft^2 of surface. In slow-moving air with a 1.5 Btu/h-F film conductance, RC = 220/(40x1.5) = 3.7 hours. After 4 hours in 100 F air, water would warm from 55 to 100+(55-100)e^(-4h/3.7h) = 85 F. A foil wrap around the pipes and insulation above them would help.
Nick
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On Mar 12, 4:54pm, snipped-for-privacy@ece.villanova.edu wrote:

Thanks! That sounds like a good plan also. But my ceiling joists are pretty full or covered with ductwork and stuff. Especially over my wood stove which would be the best place for something like this. And I wonder about a dripping of condensate problem in the summer?? With my wood stove going strong in the winter months, my basement near the wood stove is easilly close to 90 - 100 degrees F and I don't think it would make me have to burn any more wood because of it if I put my old hot water heater tank (which is fiberglass vintage 1978) close to the wood stove. Do you think it would cause a loss of or problem with water pressure? I have a well system with 35 - 45 psi. Thanks again! Steve
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In summer heat is free, as in the water will come in at 50f and heat free to 70f, a big savings, PVC wont transfer heat like Copper, Copper will absorbe summer heat more efficiently Do it but Copper is best.
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Thanks! I think I will do this. My plumbing is mostly copper already so I plan to stay with it. If I can save up to 5 kwh/day (about 30% less on time) with this @ .10 / kwh, it could be a savings of up to $180 / year. Enough to payback the new heater! Steve
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Not in the basement :-)

No, given the much larger limiting airfilm resistance.
Nick
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Warm air rises, so the pipes might work well anywhere in the ceiling. I removed most of the wooden cross blocking in the basement ceiling of my neighbor's house and tucked 60 50-pound capped 4"x10" thinwall PVC pipes between the joists with 1x3s beneath to add 3K Btu/F to the house thermal mass and make the basement woodstove heat last longer. A few more thickwall pipes to make a tempering tank would be useful.

You might catch any condensation with a piece of plastic stapled beneath. If it happens a lot, the basement may need airsealing or dehumidification.
Nick
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My brother did something like this several years ago. Two old non functional hot water heaters in front of the working one. They are in his garage. He doesnt have a freeze problem where he lives but he still bypasses them in the winter, about 3 months. cut his LP gas usage by a third.
Jimmie
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