Ask Me Help Desk - Sizing Water Lines

Tom,

It's me again. The guy finishing his basement. I've made it all the way to being ready to run water pipes for my basement bathroom and wet bar.

Here's my question. Our house is about 3 years old and the builder or plumber was nice enough to stub out the water lines above where our bathroom is going. Since the cold water will be servicing 2 sinks, a shower/tub, and toilet I'm going to use 3/4 inch type M Copper other than the wall stub outs. Should I do the same with the hot water? It will obviously service the same fixtures minus the toilet.

Thanks in advance.

I'm not saying its right or wrong, but my house has 3/4 run until the first branch, which feeds the water heater and other lines. At and after that first branch its 1/2 in all around. Unless tom says there's a need for more volume or some other issue that a DIY'er like me has no clue about (and I'm pretty clueless sometimes), id say it's a waste of good money and copper to run any more 3/4 than you need to... but I've got no pressure issues, so the 1/2 in seems fine here. I imagine the smaller volume can be an issue in some cases. We rarely run more than a couple of fixtures at a time, so our demand doesn't require the larger pipe, at least not yet!

*edited* after I posted this I got to thinking that maybe I'm just wrong. I know I've seen bigger pipe run to the water heater and other fixtures... and maybe the only thing worse than spending extra money on the front side to maybe overbuild is to spend more money and time after you have to rip out that small pipe because of water pressure issues or noise. Again... I haven't had a problem with pressure, but I have had some water noise where pipe is near a register... and ill bet that's in part because the lines are smaller..?

Quote:

Originally Posted by kp2171

im not saying its right or wrong, but my house has 3/4 run until the first branch, which feeds the water heater and other lines. at and after that first branch its 1/2 in all around. unless tom says theres a need for more volume or some other issue that a DIY'er like me has no clue about (and im pretty clueless sometimes), id say its a waste of good money and copper to run any more 3/4 than you need to.

Thanks KP... I'm not sure either but I've been told that the more fixtures a line will service, 3/4 is the way to go. I guess my dilemma is that I have 3/4 inch water lines, which service the rest of the house right above where the bathroom will go. The rest of the fixtures in our house are teed off this main line with 1/2 piping but that's 1/2 inches to each fixture. In my set up, one branch will be servicing multiple fixtures.

Thanks again for the fast reply. I hope you're right... it would save me about $50.

Hi Kevin, Welcome back!

"Here's my question. Our house is about 3 years old and the builder or plumber was nice enough to stub out the water lines above where our bathroom is going. Since the cold water will be servicing 2 sinks, a shower/tub, and toilet I'm going to use 3/4 inch type M Copper other than the wall stub outs. Should I do the same with the hot water? It will obviously service the same fixtures minus the toilet.

Let me tell you how we size our pipes, by code, in our new construction
First off type "M" copper is thin wall copper and not to be used in residential water piping. Go with type "L" ridged copper.
We make our mains 3/4" and our branches 1/2" with NOT OVER 3 FIXTURES ON A 1/2" BRANCH.
You are planing on 4 fixtures that will need cold water. A suggestion here that someday someone taking a shower will thank me for. Since you're held to 3 fixtures off a 1/2" branch make those 3 fixtures the 2 lavatories and the tub. Run a dedicated 1/2" line off the 3/4" main to the toilet. That way if someone's going rub-a-dub in the shower and you flush the potty the person taking a shower won't get parboiled. All the other fixtures using hot water may be serviced by one 1/2" branch. Sound like a plan? Regards, Tom