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I am re-piping the water supply lines in my house. I have a 1 inch supply line coming from the main. This will travel about 30 feet before being split into 2 lines, one supplying the hot and the other supplying the cold.

My intention is to run the 1 inch into the "top" of a copper tee then having 3/4 inch lines coming out from the two branches.

I could use a 3/4 x 3/4 x 1" reducing tee, but I am wondering if having a bigger tee would help in reducing pressure loss at the split.

For example, if I used a 2" x 2" x 1" tee with fitting reducers then taking the 2 inch down to 3/4 for the branches, would that help at all?

Or is there a better way than a tee to split the flow equally?

Thanks.

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    I suspect you are over thinking this. The impact this early in the system is going to be trivial. You'll see much bigger impact based on how your outputs are configured, and the volume of the feed to same.
    – The Evil Greebo
    Jun 13, 2016 at 18:40
  • Way over-thinking it - "split the flow equally" would only apply if the hot and cold flows were equal (flush toilet - no; dishwasher - no; sink - maybe sometimes), and the resistance between them also equal (it's never equal - nobody puts a turned-off water heater on the cold side of the line, for a start...)
    – Ecnerwal
    Jun 13, 2016 at 18:55
  • I accept that actual flow through the tee will be affected by the components downstream of the tee. However, assuming we consider just the outcome from the tee, what would be optimal? In addition a 2x2x1 tee is much more expensive than a 3/4x3/4x1. But if I can minimize pressure loss I would like to.
    – James McDowall
    Jun 13, 2016 at 20:03
  • A rough calculation at flow rates rather high for a house (10 gallons/minute) shows a pressure drop of less than 1 PSI for the 30 feet of pipe AND the Tee, so I'm going to stick with overthinking. If you want to tweak a bit, use a 1x1x1 tee and 1x3/4 reducers after it. If you have a particularly high-flow cold subsystem (sprinklers or unrestricted hose bibbs) consider separating that out before the general use hot/cold split.
    – Ecnerwal
    Jun 14, 2016 at 2:32

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James most of the Sinks and toilets in your home have 3/8 plumbing many homes are plumbed with 1/2 pipe through the entire house. The places you will see a pressure drop is usually hose bibs, showers and most kitchen faucets have water saving restrictors built into them. It all comes down to how many faucets will you have going at the same time and the size of pipe and distance of the pipe feeding them. If your home is plumbed with 3/4" that's all you need when you split the 1". I state this as I have never plumbed a house with anything larger than 3/4", but do use 1"pipe to feed most houses larger pipe 1-1/4" for over 100' and 1-1/2" for anything over ~150'. With this said I think you would be wasting $ to go bigger than 3/4" T from your 1" main.

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  • Thanks for your answer. I guess there are several aspects to my question. 1. Would a large diameter tee reduce pressure drop from the 1 inch pipe to the 3/4 inch branches? 2. If so would the difference be actually noticeable in day to day operation? And 3. Is it worth the extra cost? The answer to 2 and 3 it seems is "not really", but I would like to know the answer to part 1
    – James McDowall
    Jun 14, 2016 at 2:56

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