Unused water heater, leave full or empty?



wrote in message > 000yqz.googlegroups.com... >>> A friend has a house that came with two identical water >>> heaters hooked up in parallel. He doesn't need all the capacity, >>> so we turned one of them off and turned off the water going >>> into it. This was several years ago. The water heater was >>> about 4 years old at the time, it's now 7 years old. >>> >>> Given that a tank has already had some service, what would >>> you guys do to try to keep the spare tank available for as long >>> as possible? >>> >>> Leave it full of water? >>> >>> Drain it? >>> >>> My thought was that draining it would be worse, because >>> allowing air in, it would rust....... >>> >>> >> >> Fill it with water, add a rust inhibitor? >> >> As an aside, shouldn't two water heaters be hooked up in series? >> Been meaning to post that to the group. The rcm peeple should have >> some insights into both Qs. > Having a second tank that's unpowered, uninsulated, and plumbed in > series so that cold water passes through it first will reduce > summertime AC and water heating costs by naturally warming the inlet > water up to room temp. I am not sure, but I think that technically speaking that approach won't save any money on energy costs. The reason is that for the water in the first tank to be brought up to room temperature, it needs to draw its heat energy from the room. So, it will cost that much more to heat the room because some of the room heat is going toward heating the water in the first tank. In other words, there is no free heat -- it either gets its heat from being heated by at working hot water tank, or it gets its heat from the room and that heat energy needs to be replaced by the heating system for the room.

But the proposed tank isn't going to be sitting outside in the summer air. It's typically going to be in an unfinished basement, or inside the living space. So, if you take city water at 45F in winter and get it up to 60F in a basement, I guess it will help some, but doubt it's worth the trouble. In summer it would make even less difference, because the incoming city water is going to be closer to basement or living space temp.
For the guy asking if there are tanks suitable for the purpose, that would seem to be any water tank that's suited for a well pump. Preferably without a bladder inside, but that could be removed. Might find one on craigslist....

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jamesgang wrote:

You are correct. He wrote,
"Having a second tank that's unpowered, uninsulated, and plumbed in series so that cold water passes through it first will reduce summertime AC and water heating costs by naturally warming the inlet water up to room temp."
I didn't catch that part - that he meant in the summertime with the AC on etc.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


I believe he said "reduce summer time costs". And it does do that since ground water and city water are usually a lot cooler than summer air temps.
I run two wh in series with the 1st one on a 30amp switch in the hall. When I anticipate guests or otherwise needing extra hw I just turn it on. ============================================= Staged water heating.... what a neat idear!!
--
EA



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Which is why I said that energy savings occur during summertime through a reduction in AC usage.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@optonline.net wrote:

I don't know the answer, but given the choice, I think I would drain it. My thinking would be to drain it and leave the drain valve open to hopefully let it completely dry out over time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/3/2013 8:44 AM, snipped-for-privacy@optonline.net wrote:

I would put them in series using the inactive heater as a tempering tank but it would need to be drained on a schedule too as I think it could catch some sediment from the incoming water. It would be available as a ready backup and not that hard to bypass the other heater if/when it failed. Assuming it a gas fired unit, it could be left on on a low setting to keep the burners moisture and insect free. ^_^
TDD
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Rust and what the anode is there for are two seperate things. Rust involves oxygen combining with iron. The sacrificial anode involves two dissimilar metals in an electrolyte. Think about boats. They use a similar approach, with zinc being used as the sacrificial anode to protect the underwater metals. Zinc is more reactive than bronze, stainless steel, etc so it comes off instead.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Rust and what the anode is there for are two seperate things. Rust involves oxygen combining with iron. The sacrificial anode involves two dissimilar metals in an electrolyte =================================================== A good observation, BUT the (dissolved) oxygen would/should combine with sacrificial magnesium, zinc etc first, as well.
Magnesium, zinc, alum appear not to "rust" because the nature of those oxides is *mechanically* stable, whereas iron oxides are not, constantly exposing more fresh iron, ergo a deterioating process.
--
EA




. Think about boats.
They use a similar approach, with zinc being used
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It 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.