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milicifet · Jan 3, 2013, 02:40 PM

I found out that my main water line coming into my house is 3/4". I had already bought 1" pipe so I put a converter from 3/4" to 1" and ran the lines to my water heater, whole house sediment filter and water softener which all have 1" direct lines in. It then goes into all 3/4" pipes from there. My question is: Should I remove all of the 1" pipe? I've been told that going from a smaller pipe to a larger pipe decreases pressure, but I've also had a plumber tell me that running 3/4" pipe throughout my house (that replaced 1/2") is much better because it's not all about pressure, but volume as well. My water pressure is ok, but not great (probably due to my water softener and sediment filter). I'm on a community well of about 15 houses. Is there going to be a benefit or will I see a difference positively if I switch to all 3/4" pipes? Any help would be greatly appreciated!

ebaines · Jan 3, 2013, 02:52 PM

Inserting a section of 1" pipe in the middle of all the 3/4" pipe will have no effect at all on pressure at the tap. The pressure in the 1" pipe will be the same as in the 3/4" - it's just that the velocity of water flow will be less in that section. Consequently there may actually be a minor improvement in pressure at the tap, as there is less loss due to friction in larger diameter pipes (though it's unlikely you can actually notice a difference).

mygirlsdad77 · Jan 3, 2013, 04:32 PM

I agree with ebaines. I would not waste my time changing out the one inch. It won't hurt a thing.

PS, nicely put, ebaines.

massplumber2008 · Jan 3, 2013, 05:29 PM

You said, "I've been told that going from a smaller pipe to a larger pipe decreases pressure"...

In terms of Bernoulli's principle and the venturi tube experiments, the opposite is actually true. Here, when you increase the pipe from 3/4" to 1" you have a slight increase in pressure and a decrease in velocity.

However, since you increase the pipe size and then reduce the pipe size again, you have effectively negated the issue as I understand it and as Ebaines stated, you "will have no effect at all on pressure at the tap".

It's been a long time since I studied fluid dynamics/principles/theorems, for sure, but you are definitely all set here!

Mark