What size hot water pipe should I use?

[NoSpam]

I need to run hot water pipes to the various appliances in my home. Some of the appliances (lavatories, and sinks) will use relatively small amounts of water at a time but will be used frequently, while others (tubs & showers) will be used less frequently but will use much more hot water at a time.

I would like to minimize wasted energy and the time spent waiting for hot water at sinks and lavatories while still providing sufficient flow. At tubs & showers, having a good flow rate is more important and the wasted energy & wait times do not matter so much because of the less frequent use and large amount of water per use.

Running different size how water lines to the same room is no problem at all. I realize that, occasionally this will result in having to fill two pipes but in our situation this will seldom happen. A recirculating system is not ennergy efficient so I don't want to go that way.

Given the above, what size pipes should I run to: Sinks & Lavatories: Tubs/Showers: Dish washer: Washing machine: (Whirlpool tub: 3/4" since valve inlets are 3/4")

Many thanks for any help!

[Big_Jake]

1/2" for all. At typical pressure, you can get 5-7 GPM from a 1/2" pipe.

JK

[Bill]

I prefer 3/4 for house piping and 1 1/4 for a main line to the house and to outside water valves (idea with large main is that you can water outside and also get good flow inside).

I lived in house once which had all 3/4 pipes. It was great. Water flowed fast everywhere. I have preferred this ever since.

Keep in mind that crud builds up on the inside of water pipes. So perhaps with all the crud, the 3/4 pipe actually has 1/2 of remaining space whereas the 1/2 pipe has maybe 1/4.

[Edwin Pawlowski]

Where do you live? Over 30 years and my copper tubing is a clear as the day it was installed. You do get buildup in galvanized pipes.

[S. Barker]

1-1/4 is unrealistic for a supply. It's just not done. IF you really did it, you wasted money. The meter (at best) will only be 1". And it's probably a 5/8". A one inch feeder line would be optimal, and 3/4 is most common. (unless you're going over a hundred feet)

s

[nicksanspam]

SMALLER pipes to outdoor valves would make more flow indoors.

Nick

[RicodJour]

Not unless the outdoor valves were open when you went to use the indoor plumbing. As in most things, it's better to plan ahead and use a head, than forge ahead.

R

[hallerb]

PEX is so cheap your better off running larger diameter......

[Nick Pine]

Doh :-)

Nick

[NoSpam]

Thanks to all who replied. I used 3/8" pipe home runs to all sink & lavatory hot water valves. Water flow decrease was measurable, too small to notice in normal use. Wait time for hot wated decreased sharply due to shorter runs and the fact that a length of 3/8" pipe holds only 56% as much water as the same length of 1/2" pipe.

I d>I need to run hot water pipes to the various appliances in my home. Some

[NoSpam]

After about two months in my new home, I re-installed new PEX hot water pipes to all locations. I used 3/4" to the whirlpool tub, 3/8" all sinks and lavatories, and 1/2" elsewhere. I measured flow rates before and after and found no (or insignificant) decrease in maximum flow from the sink/lavatory faucets but substantially reduced wait times for hot water in every case. Since I made more home runs to the water heater, some wait times were decreased because of shorter length of pipe. However, even where the distance was the same, hot water arrives at the sinks lavatories much faster than it did before because of the smaller volume of water in the pipe.

I am not a plumber, but just from the physics of the flow I thought I would be a good move and we are very happy with the result.