# Simple DHW heat trap question...



## maple1 (Apr 2, 2014)

How much up & down should the trap have to be effective?

Is a foot enough?


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## woodgeek (Apr 2, 2014)

maple1 said:


> How much up & down should the trap have to be effective?
> 
> Is a foot enough?



yes.  I did 8"


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## jebatty (Apr 2, 2014)

If you have space, a foot is good, or a little longer.


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## velvetfoot (Apr 2, 2014)

That should be good.
This is what I did. 
Of course, it's probably going to come out with my pellet boiler project.


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## maple1 (Apr 3, 2014)

Thanks for the feedback - I haven't actually measured how much convenient space I have for one, but was guessing a foot. Sounds like I'll be good.

Part 2: Is there really any benefit to be had in also putting a trap on the inlet pipe of a bottom feed DHW heater? I was only planning on putting one in, on the top outlet.


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## velvetfoot (Apr 3, 2014)

On the other hand, don't all new dhw heaters have built in heat traps?


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## maple1 (Apr 3, 2014)

Mine is new (well, almost 2 years old), and I'm not sure about built in - if so it's not apparent. But I got the least expensive one I could find - if that might matter. But I can feel warm piping for quite a ways down the line out the top of my tank.


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## velvetfoot (Apr 3, 2014)

I just read the manual on the cheapest unit HD sells.  Apparently they MAY, or MAY NOT have internal heat traps, or they MAY, or MAY NOT have external heat traps.  Then they show a diagram of a piping heat trap.  Makes it all real clear.  

example:

Heat Trap
For increased energy efficiency, some water heaters have been supplied with factory installed internal or external heat traps in the hot outlet and cold water inlet openings.


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## jebatty (Apr 3, 2014)

I have a hw htr that supposedly has built-in heat traps and I still felt warm to hot water up both the cold and hot water pipes, thus put in my own external heat traps.


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## Highbeam (Apr 3, 2014)

When they say heat traps they don't seem to mean a loop in the pipe but a little device that goes inline. Seems to be like a spring loaded valve to only allow larger flows.


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## woodgeek (Apr 3, 2014)

Yeah, even in my high-end HPWH there are no internal traps.  I also heard they often stick open...so I added loops on the outside...nothing to break.


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## DBoon (Apr 5, 2014)

I had an off-the-shelf heat trap put in by my plumber a few years ago with a new Marathon hot water heater.  Still feel warm water in the piping above it.  Next time, I'll use a U trap of copper pipe.


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## semipro (Apr 5, 2014)

Its relatively easy to create a heat trap using corrugated flexible copper tubing also.  A simple loop of sufficient diameter works.


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## BoilerMan (Apr 5, 2014)

The factory heat-traps I've seen in the electric water heaters I've installed were little black rubber flaps.  A few had a clear plastic ball which sat on a seat to stop the hot water from rising.  Either way a real copper heat trap is a failsafe way to do it with no moving parts! 

Side note:  After installing 1" fiberglass insulation on all of the connections (there are 6 on my dual coil) I've seen a noticed extension in the hotwater retention time.  I'm only firing every 48 hours now and still have hot water, whereas before the last shower was warm. 

TS


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## Highbeam (Apr 7, 2014)

DBoon said:


> I had an off-the-shelf heat trap put in by my plumber a few years ago with a new Marathon hot water heater.  Still feel warm water in the piping above it.  Next time, I'll use a U trap of copper pipe.


 
Don't expect these heat trap ideas to be 100%. The pipe material will still conduct heat and while the loop may slow down the circulation of hot water it can't stop it. Heat rises. Heat is the engine causing this thermosiphon. I can siphon water through a loop so why does this loop slow the thermosiphon?


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## maple1 (Apr 7, 2014)

I think the principle is that with the loop, the cooler heavier water at the bottom of it will prevent the warmer lighter water above it (on the heater side) from working its way around the loop.


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## Highbeam (Apr 7, 2014)

I would expect to feel heat from conduction quite a ways away from the heater but maybe less flow if the heat trap works as you describe.

Like running water down into a trap under your sink. If enough lift is provided by the hot water rising it will rise up to the top of the water heater trap and then be pushed downward through the trap by the endless supply of rising hot water in the tank. Obviously you guys believe the concept from experience. I've only ever owned homes with water heaters on the same floor as the living space so the trap is sort of built in.


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