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Old 01-02-2015, 06:08 PM   #16
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A union is for dis-assembly of a piece of equipment. Code requires them(or most do).
They come in different forms. In the case of a water heater, dialectics are needed if you are piping with copper and do not have dialectic nipples at the heater itself. These can be identified by a groove around the outside of the nipple, a plastic liner inside the nipple, or both.
Flexible heater connectors will also serve the purpose if your code allows them.
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Old 01-03-2015, 03:02 AM   #17
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The reason the code exists is you would not want someone turning both shut off valves closed. That would basically give you a pressure cooker. In theory you would have the temp pressure valve to blow. If that valve were to fall, you could have big trouble.
There is no code that prevents you from having a valve on both hot and cold.
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Old 01-03-2015, 06:28 AM   #18
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The reason the code exists is you would not want someone turning both shut off valves closed. That would basically give you a pressure cooker. In theory you would have the temp pressure valve to blow. If that valve were to fall, you could have big trouble.
Maybe I'm missing something, but I'm not seeing that it's an additional hazard than without. Even without a shutoff valve, the hotwater side has no room for expansion (unless there is an expansion tank installed) the hotwater side is a completely closed dead end (unless you have a faucet open and running) and is filled with an incompressible fluid (water) In either case, if you have some sort of malfunction which causes an overheating, you are depnding on your T&P valve to releive the pressure, or *something* is going to rupture, catastrophically.

Not really seeing why having the heater outlet closed 6 inches away by a valve is any more dangerous than having it closed 50 ft away with multiple valves.
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Old 01-03-2015, 09:48 AM   #19
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Dielectric unions are used to keep copper pipe from touching steel pipe--if the are conected without the dielectric union--the pipes will corrode,due to electrolisis--you are making a battery---
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Old 01-03-2015, 10:19 AM   #20
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The expansion tank if there is one may be above the shutoffs. If you have 2 valves and leave the tank running it may cause you t&P to blow off. If the T&P fails then it may launch through your roof. Besides not everyone has an expansion tank they are a relatively new requirement in the code. And only required if you have a back flow device or a PR valve on the main water.
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Old 01-03-2015, 10:26 AM   #21
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The expansion tank if there is one may be above the shutoffs. If you have 2 valves and leave the tank running it may cause you t&P to blow off. If the T&P fails then it may launch through your roof. Besides not everyone has an expansion tank they are a relatively new requirement in the code. And only required if you have a back flow device or a PR valve on the main water.
So you are saying IPC allows H&C valves on a water heater?
I cannot recall anywhere in the UPC that says you can't. I used to do it all the time on commercial applications
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Old 01-03-2015, 10:54 AM   #22
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Dielectric unions are used to keep copper pipe from touching steel pipe--if the are conected without the dielectric union--the pipes will corrode,due to electrolisis--you are making a battery---
And I don't think I have ever seen one actually work properly. They're a waste of money. The gap between the 2 halves is too small and crud eventually builds up over the gap and effectively connects them.

We changed forty tanks in one of our complexes about 8 years ago and every single one of those dielectric unions are showing signs of eventual failure.

A flex line does a MUCH better job at isolating.
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Old 01-03-2015, 10:59 AM   #23
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I cannot recall anywhere in the UPC that says you can't. I used to do it all the time on commercial applications
We do it all the time in our apartment buildings so we can repair/change out a tank without too much disruption the to tenants.
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Old 01-03-2015, 11:05 AM   #24
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We do it all the time in our apartment buildings so we can repair/change out a tank without too much disruption the to tenants.
I totally agree with the practice.
It seems to be a belief among members that you can't use 2 valves though....
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Old 01-03-2015, 11:13 AM   #25
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I totally agree with the practice.
It seems to be a belief among members that you can't use 2 valves though....
I'm not aware of any code which prevents isolation on both sides. If someone can produce such a code then I would truly love to see it.
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Old 01-03-2015, 11:14 AM   #26
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The expansion tank if there is one may be above the shutoffs. If you have 2 valves and leave the tank running it may cause you t&P to blow off. If the T&P fails then it may launch through your roof.
Ok, you really haven't made the case for a shut off on the hit side being more dangerous than not having one.

Let's consider two hot water systems. System A and System B

To keep it simple, neither have expansion tanks.

To keep it simple, each system has 50 ft of pipe and one faucet.

System A has a cold side shutoff only,

System B has shutoff valves on the Cold and the Hot side.

Both systems have a failed thermostat so that they keep heating the water past the boiling point.

Both systems have a failed the T&P valve that will not relieve and will hold a dangerous amount of pressure (I can't imagine what kind of failure would cause that, but let's assume for the sake of the discussion that it is possible)

The Cold water shutoffs are closed on both systems.

The hot side shutoff on System B is closed.

So there we are.

The heaters are overheating. Pressure is building. The relief valves are not relieving.

The pressure can't escape through the cold supply lines on either system, because the cold side shutoffs are closed.

The pressure in System B can't escape though the hot water side because there is 3 inches of pipe then a closed valve.

the pressure in System A can't escape, because there's 50 ft of pipe, then a closed valve.

How exactly do you think the pressure will be relived in System A ?

Serious question. What is it that keeps system A from blowing up?

You seem certain that system A will not blow up, but system B *will* blow up. I am curious to hear your explanation of why you believe this is so.
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Old 01-04-2015, 07:37 PM   #27
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Ok,Serious question. What is it that keeps system A from blowing up?

You seem certain that system A will not blow up, but system B *will* blow up. I am curious to hear your explanation of why you believe this is so.
Because we read it on the internet....?
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Old 01-06-2015, 01:25 AM   #28
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Because we read it on the internet....?


Yep, the "It will blow up" guys got awfully quiet when they were asked for a code reference or to explain the physics behind their theory, didn't they?
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