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Author Topic: Union fittings inside furnaces  (Read 736 times)

Offline ze-hawn

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Union fittings inside furnaces
« on: November 16, 2016, 10:48:22 PM »
Why do they have to be there? Also why a union I don't really see why it has to be that fitting at all?, why not a straight pipe to the elbow and shut off valve . . .

I guess I am really wondering why use a union at all if it can be avoided? sorry if this is a dumb question but I am not grasping it.

Offline rmuntz

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Re: Union fittings inside furnaces
« Reply #1 on: November 17, 2016, 10:30:17 AM »
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Offline walker

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Re: Union fittings inside furnaces
« Reply #2 on: November 17, 2016, 12:01:47 PM »
Without a union how would you thread the pipe into the final fitting?? you need to have a spot where you can separate the pipe to allow yourself to thread in the final fittings, otherwise you wouldn't be able to complete the piping, unless that is you're using copper with flare fittings or CSST.

Offline Attavior

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Re: Union fittings inside furnaces
« Reply #3 on: November 20, 2016, 05:49:05 AM »
My understanding is that csst still needs a union as the csst fittings are not to designed to be used as a union. 

Offline walker

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Re: Union fittings inside furnaces
« Reply #4 on: November 20, 2016, 09:38:37 AM »
My understanding is that csst still needs a union as the csst fittings are not to designed to be used as a union.

you are right, I do see copper and csst used without unions all of the time though.

I was just simply stating why you need to have a union with black pipe as its impossible to install without one,

Offline Porcupinepuffer

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Re: Union fittings inside furnaces
« Reply #5 on: November 20, 2016, 09:56:05 AM »
We've been rejected on new installs with copper for the simple reason that the owners manual mentions the use of a union in the gas connection instructions.

To help you grasp it, Just picture your dirt pocket connection facing the valve and all you need to do is simply put in a piece of black iron between that dirt pocket and the valve. Well this now requires threading in both connections at the same time. Of course threading two connections at once seems quite efficient and a very good idea. Except that you'd need reverse threads on one end of the pipe and reverse threads to mate with. So it's completely impossible to thread in both ends at once.

Try piping it in and you'll grasp the concept pretty fast  ;D

Offline Admin

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Re: Union fittings inside furnaces
« Reply #6 on: November 20, 2016, 12:00:35 PM »
Technically If you had only one single gas appliance, you could use rigid and pipe back from the appliance gas valve to the gas meter and not need a union to do so.

The first person who needs to replace the gas valve might not be very happy though.  I'm sure you could use Clause 4.4.1 to issue a warning tag in that case.

Here's an interesting discussion about gas connectors and unions,

http://www.hvactechgroup.com/hvacforum/index.php?topic=1463.msg4029#msg4029

I think it's always best to use rigid from the appliance gas valve into a dirt pocket.  Then continue with copper, CSST, rigid or a gas connector.  It seems only certain types of CSST and any rigid piping would require a union.

If you look at any gas dryer or range you will probably only find a shut off valve and gas connector, but no union.  If the furnace manual allows the use of a gas connector there should be no need for a union as well.  Enbridge, in my experience, has always allowed copper flare fittings, CSST fittings or gas flex connectors to be used instead of a union.

Some furnace manuals want a union installed inside of the furnace casing and some require the union to be installed outside, unless there is a clearance issue then it's normally allowed to be installed inside.  Some manuals only require a union if there are local Codes to do so.  Some appliance manuals specify to use a union or gas connector.

I do not know of any Gas Code that requires the use of a union.  It's the appliance manual that may require a union.