Attic Hot Water Holding Tank???

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  #1  
Old 10-20-11, 07:24 PM
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Attic Hot Water Holding Tank???

Hello All,
I was wondering if anyone had tried installing a water holding tank, even if just 20 gallons, in an attic space (garage) to collect heat upstream of the hot water tank? Not a solar type system but instead just a holding tank.

It would seem you could install such a tank, which would heat up naturally, that would replenish the hot water tank as water was used from it. Instead of having 55 degree tap water replenishing the HW heater as water is being used, you'd have maybe 85 or 90 degree water replenishing it.

Any insight or direction on this?

Thanks, Ralph
 
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  #2  
Old 10-20-11, 07:33 PM
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What do you do in the winter?

Mike NJ
 
  #3  
Old 10-20-11, 10:54 PM
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Hey Mike,
It wouldn't be usable during the winter but that may only be three to four months in south Alabama. It could be viable for up to 8 months or more here.

You could bypass the holding tank, with valves, and have the tap water feed the HW heater as normal during winter. Otherwise, insulate the holding tank over the winter months in order to avoid any bursting of lines.

I had a rough drawing but do not know how to post it here?

Ralph
 
  #4  
Old 10-21-11, 05:39 AM
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Hi Ralph,
That 55 water does not grow undesirable things as well as 90 water and once it gets to the water heater it goes high enough to again afford some protection. Luke warm water can be a breeding ground you should avoid. If you are on treated city water there may be less of an issue, but well water comes complete with lots of things that like to grow. Those that have filled their swimming pools from a well have learned all too well.

I'm certainly not a pro on this and some solar reading might disagree with my concerns. Just me .

Bud
 
  #5  
Old 10-21-11, 05:52 AM
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About 25 yrs ago I read an article that said you could take an old tank, paint it black and set it where it would get a lot of sun and use it to preheat the water going into the water heater..... but Bud makes a good point about 'stuff' growing in the tank I don't remember that article mentioning anything about that.
 
  #6  
Old 10-21-11, 08:52 AM
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Hey guys,

That's an excellent point I hadn't thought of Bud!

1) We are on city water though which will contain chlorine and should significantly eliminate such.
2) The water would be flowing regularly through the holding tank versus being stagnant for long periods of time.
3) There would be no air pockets which seems to contribute to algae or such growth. I used to manage a detail business and we had a 150 ga. tank that would have to be cleaned occassionally. The algae would mostly grow at the top where air pockets resided or where water often less present.

I think the above may eliminate the issue, or greatly curtail it, but would have to research this a little more. I can see where there may be a requirement to clean the tank on occassion and possibly install a filter.

Ralph
 

Last edited by Ralph III; 10-21-11 at 09:30 AM.
  #7  
Old 10-21-11, 08:37 PM
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Ralph,

You might also want to be sure that any tank you install doesn't overload the attic and/or roof framing. Water weighs 8.33 lb. per gallon, plus the weight of the tank. Not trying to scare you, but rather just reminding you of things to consider. A 300-lb. point load on the bottom chord of an attic truss may be more than it was designed to handle.

Also, if you go ahead with this project, make sure you thoroughly insulate all water lines in the attic. Even though you may be located in a warm climate, an occasional cold spell can cause a lot of damage (I'm speaking from experience, having dealt with a frozen water line in an attic in NM--big mess! Lots of soggy insulation and sheetrock floating through the house). Another thing to consider would be a piped drain valve for the tank, along with a top relief valve for letting air in as the tank drains.
 
  #8  
Old 10-22-11, 05:29 AM
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Doesn't algae need sunlight to grow?

My thoughts are that a 20 gallon tank isn't going to provide much for you. When using hot water, it will quickly be replace with cold water and tank a long while to heat up again. Once it gets cold water again, it will sweat like crazy. I think a better approach would be to avoid the tank completely and just run the water line through the attic. The more surface area you have exposed to the attic, the more heat will transfer. Maybe a coil of pex tubing up there like they do for ground source heat pumps. Overall, you don't have a terrible idea, but I don't think you are going to get much of a gain from it.
 
  #9  
Old 10-23-11, 11:36 PM
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Hey guys,

I apologize for responding so slowly but have been out of town. Several of ya'll bring up good points which I considered and will address.

1) Yes, weight is a factor and why I was considering a smaller 20 gallon tank. That won't be an issue for where I will locate it.

2) A pan would have to be installed with a drain line for any possible minor leaks and/or sweating. Just like an attic AC air handler.

3) Measures must be taken to protect against freezing in winter. I figured on insulating the lines and either draining the tank or covering it with an insulated box, for winter preparation.

4) A drain line would have to be installed. I hoped to be able to drain the tank, gulping-like, without having to actually go into the attic and opening a relief valve. That may still be required but would be a minor inconvenience.

5) Drooplug, I have to completely dissagree the savings potential couldn't be significant. In testing, it took a full hour to completely reheat our 50ga tank filled with colder tap water. That meter is flying the entire time. In contrast, it only takes 20 minutes to completely reheat the tank (turned off 9hrs) filled with luke warm water.

Twenty gallons isn't much but it would mean one full bath or two showers, or a shower/dishwasher/washing machine. We don't use a lot of hot water at once, so there would be plently of recovery time. However, even if we benefited only once per day that would still add up to quite a bit over a calendar year. TO YOUR LAST POINT.....

6) I've thought about just using 3/4 copper tubing, as you mention, but it would take a lot to amount to any volume and the upfront cost would be quite a bit higher. The problem with a tank is incoming cold water would tend to mix with outgoing warm water. A larger multi-chambered tank would be better as smaller tanks will prove challenging. That wouldn't be an issue with tubing. On the other hand, a water tank will hold heat longer so it would be more beneficial at evening time when we use the most.

God Bless
 

Last edited by Ralph III; 10-23-11 at 11:52 PM.
  #10  
Old 10-24-11, 06:29 AM
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I will take drooplug's comment about not getting much return from this effort and put some numbers to it, but experience tells me $5.00 a month would be on the high side. Now, I'm not trying to discourage you, but thinking that your efforts might be better directed to an actual solar water heater system of the DIY style and there are many.

Here's some concerns:
1. No fins. With just the simple surface area of the tank to exchange heat from the attic to the water it will be slow. It takes a lot of degrees from the air to equal one degree in that tank and with only convection to power the process it will take a while. Put that tank in the sun, painted black, and it will heat much faster.

2. If we ignore the heat transfer time and just look at the energy captured. With a full 20 gallon tank at 90�, you have 5,845 btu's of free energy. It takes one btu to raise one pound of water one degree F.
(167 lbs of water raised 35� = 5,845) So whats that worth?
If we use electricity at 10 cents a kw, and we get 3,412 btu's per kw we have captured $0.17 worth of energy. One tank full per day for 200 days and your yearly savings would be $34.

As stated above with my guess, this would be on the high side.

Bud
 
  #11  
Old 10-24-11, 07:18 AM
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Bud, thanks for crunching those numbers but indeed a little dicouraging.


I think I can get maybe 250 days, or more if it could be conveniently drained/re-routed for expected cold days; versus completely shutting it down for months on end. Winters in south Alabama aren't quite like New England, ha.

Anyhow, I hoped the savings would be higher but hadn't crunched any numbers. A solar type system, or outdoor painted tank, would be great but not practical for our home and an eyesore.

I had considered installing the tank or lines nearer the attic rafters, somewhat boxed in to capture heat and with a hanging lid. The heat is much greater there versus simply placed on attic ceiling joists.


Hmmmmm, any salvaging this idea?
 
  #12  
Old 10-24-11, 07:45 AM
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Here's some reading, BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution
Gary has some great information on DIY solar and lots of illustrations, so perhaps something will hit a hot spot for you.

My first venture into solar will probably be pv and then hot water. Mine is more of a learning experience than actual savings as energy is my business, but my family is down to 2 so we don't use a lot. In time, if I live long enough, I hope to reach net zero. It will be tough as -20 is common up here so may need to supplement some wood at times.

As for saving your approach, there are still issues. Heat transfer is based upon a difference in temperature. As your tank warms up the transfer process will slow down. Add to this, your attic is probably vented, so most of that heat up there is designed to escape. Closing off the vents to capture heat would not be good as you might also be capturing moisture.

Now, before I add more, what is your objective? If it is saving energy, that list is long and some quick fixes will show up on your next bill as savings. Happy to review some options.

Bud
 
  #13  
Old 10-24-11, 07:17 PM
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Bud,
Yes, savings is the goal and as heated water is one of the major costs with utility bills, on average. I'm in the process of replacing my shower heads with low flow types, aerators on faucets and will look to blow in more insulation over the winter. Numerous other such cost saving things, etc etc.

The previous homeowner (contractor) who built the home did an excellent job to begin with but then tightened the budget as he and his wife ended up seperating and eventually divorcing. The home was part of the settlement. So there are some things he didn't quite finish or could have put a little more money into, as was his initial pace. I'm now looking to finish my improvements to the property within the next two years.

My major project will be to replace our aging central air/heat unit(10 seer) with a high efficiency heat pump and possible desuperheater. I'd love to go geothermal, as we have the land for it, but depends on how much work I can contribute and tax breaks, etc. That would be awesome but the savings might not justify the upfront costs due to our milder climate.

Take care, Ralph
 
  #14  
Old 10-25-11, 02:52 PM
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I know some geothermal units offer hot water preheat as an option. Can you get an air source heat pump to do the same thing?
 
  #15  
Old 10-25-11, 03:14 PM
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The first step in what you outlined should be an understanding of where your heat loss and gain are occurring. There are five major areas, walls, ceiling, floors and foundation, windows and doors, and air leakage. Once you divide up the energy loss and attach a dollar figure to it, sequencing your improvements becomes easier. There are different way to break down the heat loss but I chose those as Build it solar happens to have a nice little heat loss calculator with those general groupings. There are more sophisticated if you would like.

Then you decide what should come first. like air sealing should be done before you bury the attic any more than it already is. If you have access to your basement ceiling some of the air sealing is quick, easy, and rewarding.

As for purchasing a new heating/cooling system, the usual advice is to wait until the improvements are done so you don't install something that is way oversized.

One of the most important aspects of becoming familiar with the potential options is to combine them when other work is being done. So many times people install new siding when they could have easily added an extra layer of insulation.

There are many threads here on the forum dealing with all aspects of upgrades so enjoy.

Bud
 
  #16  
Old 10-25-11, 10:25 PM
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Originally Posted by drooplug View Post
I know some geothermal units offer hot water preheat as an option. Can you get an air source heat pump to do the same thing?
Yes, air source heat pumps can have desuperheaters and really is better for the system in general. That is the system I will most likely end up getting.



Bud,
Yes, yes, I undestand all that and have addressed much already.

We have a brick home on a concrete foundation so no realistic improvements can be made there. The home already has high efficiency windows, doors are fine, and I spend hours in the attic foaming every hole in the top plate. I doubled the amount of attic insulation the previous owner had installed but am still short of the r-40 value I want, so will add more soon. I will also be adding insulated gaskets to interior faceplates(ext. walls).

So the home is quite well sealed but am now looking to address two major contributors to energy costs, the central heat/air system and hot water heater. I just don't believe in wasting money when some simple things can be done to save on energy costs.

I appreciate all the input which was given to the thread.....

take care
 
  #17  
Old 04-25-12, 07:28 AM
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Ralph III

I like where your going with this. I had the same idea 2 days ago. Was going to make a solar tank breadbox but with the HOA it wont happen. SO I thought putting the tank in the attic to heat the water before it gets to the water tank would save. I like to know where you went with this idea. I would put the tank inside a 55 gal plastic drum with a drain line to catch any water or drips. I know the attic gets pretty hot with the summer sun so my water heater would have to heat up 50 degree water to 120 but take around 100 degree water to 120 would save big time. I know in some parts of the world they put water heaters in the attic so it is not new. If in the winter it gets under 50 degrees in the attic I would just by pass with ball values. Let me know where you are on this.
 
  #18  
Old 04-25-12, 09:30 AM
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Welcome to the forums Shawnkkk!

Your idea should work well but before you start you need to make sure where you place the tank the attic framing can handle the extra load.
 
  #19  
Old 04-27-12, 09:57 AM
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Based on the numbers and location specifics, if cold weather can be an issue, maybe consider waste water recovery instead.
There is no maintenance and really it's taking some heat from your waste water to warm up your HW feed.
This might be something to consider in combination with your idea.
 
  #20  
Old 04-27-12, 11:05 AM
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I think your best bet is to have the water flow through a heat exchanger and have a fan blow air across it. Much like the way forced air systems would work. The water flows through the tubing and the fan blows hot air across it. No matter what you do, that cool water entering the attic is going to cause the pipes, tank, heat exchanger, to condense. Need to deal with that condensate. As I believe I stated earlier in the thread, I don't think the cost of the rig will justify the savings in energy with this.
 
  #21  
Old 05-02-12, 06:55 AM
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I suspect a continuously running fan might also kill off any energy savings.
A fan that is configured to turn on and off would add a fair bit to the up front cost as well.

What about a roof top heat exchanger system? Something similar to what is used for pools?
 
  #22  
Old 05-02-12, 03:57 PM
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You mean solar panels?

More characters.
 
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