tankless hot water output pipe size?


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Old 10-07-09, 08:32 PM
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tankless hot water output pipe size?

I put in a tank less system and ran 3/4in pex pipe for the hot water supply and branched to 1/2in to the different fixtures.
The hot water takes 50 to 60sec. to get to the far fixtures, when I have the recirculation running then it is pretty fast, 10sec or so.
I am thinking that when the recirculation is running of course the system is not being as efficient as it is rated.
I only have the recirculation running at peak usage times though.
Of course the recirculation system still has to heat all the water in the 3/4in line.
I am thinking that I could change the 3/4in line to 1/2in and in that way not have to move as much water. It seems that the 3/4in line contains more then 2wice the amount as the 1/2in line.
The only draw back in doing so would be the supply volume would go down, so if I had to many things running at the same time the pressure would drop.
Is it a good choice to go to the 1/2in line?
Thanks
 
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Old 10-09-09, 08:50 AM
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I would have expected it to be 1/2" in the first place. What does the manufacturer recommend?
 
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Old 10-09-09, 09:21 AM
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Back in the days when galvanized pipe was king water heaters were supposed to have " pipe. Then along came plastic and in many early articles " PVC was said to give water flow equivalent to " galvanized because it was smoother inside, reduced friction increased flow.. If that is still true then you may have been misled by a connection adequate for galvanized but which can be reduced when PVC is used.
 
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Old 10-09-09, 01:12 PM
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Pipe History

Originally Posted by ray2047
Back in the days when galvanized pipe was king water heaters were supposed to have " pipe. Then along came plastic and in many early articles " PVC was said to give water flow equivalent to " galvanized because it was smoother inside, reduced friction increased flow.. If that is still true then you may have been misled by a connection adequate for galvanized but which can be reduced when PVC is used.
Most codes that I know of still require 3/4in. to the water heater.

The next piping that succeeded galvanized was copper tubing with a little side-road of brass pipe.

PVC is not used inside houses on the water lines; the OP is talking about Pex tubing which the i.d. of 1/2 Pex is approx. 3/8in., not something that you want to run to a water heater without having major supply problems.
 
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Old 10-09-09, 02:04 PM
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The real way to minimize hot water heat losses is to heat the water you need in a pan on the stove, then walk it to where you will use it immedietely.

If you are truly frugal, you will draw the water from your rain barrel and heat it on your wood stove.

Otherwise, expect some heat losses or compromises with you hot water system.
 
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Old 10-09-09, 02:52 PM
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PVC is not used inside houses on the water lines
Not to argue but here if not copper PVC for cold and CPVC for hot is what is most commonly used. Pex is seldom seen except in a mobile home. I will correct my own general statement by saying the outlet of a water heater would be CPVC but inlet is sometimes PVC. Another thing that would probably shock the northerners the PVC/CPVC is run in the attic.
 
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Old 10-09-09, 03:33 PM
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Sorry for thr off topic but if may comment on my original posts. I did some Googeling and it seems that at least half of the homes I have seen in my years of doing home repair may not meet current plumbing code in regards to use of PVC. Strange. I wonder if it is a local exception or just blatant code violation.
 
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Old 10-09-09, 08:54 PM
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Lets clear things up a bit.
The cold supply to the heater is 3/4in.
The hot output is also 3/4in. dropping down to 1/2in at the fixture.
The recirculation line is 3/4in as well.

As for using Pex, it is made for potable installations.

It is interesting to see how things get off subject.
In my OP the basic question was about what size pipe to use for my hot water.

I think Pulpo pretty much summed it up in one sentence.

Thanks for the input.
 
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Old 10-10-09, 09:09 PM
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rrekih,

You're only interested in getting one answer -- the right one for WHERE YOU ARE AT. For that, go talk to your local building dept.

I don't know what the code says about it in B.C., but in the 4 counties around here that I know allow PEX, they all require the same thing. A 3/4" line to feed the WH, a 3/4" line at it's outlet that goes to the manifold. From there, you can reduce it to 1/2".
 
 

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