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Heat Trap - Function?


Konrad
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Ok, this is a commercial design question, but I can't get a straight answer out of anyone at my firm, so I'm gonna ask it here and see if some here can enlighten me.

Mixing valve - Lawlor 801 I believe, but can't remember at the moment. 140 deg water ahead of it on the hot side, and regular cold on the other side, to get to 120 deg tempered water.

On the hot side, before the mixing valve, the water is specified to be 140 deg. The schematic diagram shows an S type piping layout, minimum 2 feet, then the piping enters the mixing valve. The S piping is labeled "Heat Trap".

WTH is the purpose of trapping heat inside a stud wall cavity?

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Hi Konrad,

The connector pipes above a water heater are sometimes configured in an S bend with a drop of at least six inches, so that, when the water is turned off, there is an air pocket trapped at the top of the high portion that will prevent heat from migrating out of the water heater up the pipe.

A lot of the time this isn't necessary if the plumber uses a matched pair of pipe nipples at the top of the tank that have heat traps inside that are essentially little nylon one-way doors that close when the water is off.

I'm guessing that the S-bend you are seeing in the drawing is to prevent the mixing valve from remaining heated to 140 degrees day in and day out, so it won't be too hot to grip when making adjustments.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi,

Yeah, it is all above the water heater or on a manifold array next to it on the wall. I see them used with bio-radiant hydronic systems all the time.

The air pocket (maybe is should be termed a vacuum pocket) is formed when you turn off the water. The weight of the water on either side of the high loop causes the water to fall away and leaves the air gap - sort of like what is expected to happen with a high loop on a dishwasher.

That detail shows a drop of 2ft. but you're only supposed to need a fall of 6 inches to create the gap.

Another thing, the S-type heat trap isn't supposed to work unless there is one on both pipes entering and leaving the water heater. Otherwise, heat migrates up both pipes when no water is being drawn.

Perhaps in this case they were worrying more about overheating the valve than wasting energy.

ONE TEAM - ONE FIGHT!!!

Mike

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One of my mech guys piped up and said the new IECC will be requiring this in residential after July, so check your local authority having jurisdiction, and find out.

Not sure if that will be a universal standard for everyone or not. Me = never seen it in residential here in the midwest. [8]

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