Quick copper sizing question

[Dostoy320]

I'm replumbing my house, have 1" into the house, 3/4" from the meter across the basement to the water heater, and am now running the branch lines to the bathroom and kitchen.

My run to the kitchen is about 15ft, then a 4 ft climb to the sink. The only fixture in the kitchen is the sink, but there will be a dishwasher eventually.

My question. Is there any reason to run a 3/4" branch to where the supply pipes head up to the main floor, or can I just run 1/2" from near the water heater?

I was gonna do 3/4" because I have the pipe for it, but then I got to thinking about how, for the hot run, I have to heat up the extra copper and the water takes longer to get from the heater to the faucet. So now I feel like maybe 1/2" is the way to go.

Also, a 1/2" to the utility sink/washing machine branches from the 3/4" coming off the water heater. Does the placement of the kitchen branch matter with regard to this branch? Before? After?

Ok, that wasn't really a quick question...

[Gary Swart]

I would use the 1/2 for the hot water for the reason you gave. You could use a recirculation pump with a return line that would provide virtually instant hot water, but there is a fair amount of added expense. I don't think the branch location for the kitchen would matter much, but best let the pros chime in on this. These is a charter on pipe sizing on the home page of this site that might give you a bit more factual data.

[Ian Gills]

I have a half inch pipe serving a washer, utility sink, kitchen sink, outdoor faucet and a dishwasher. It seems to work just fine.

I suggested to my neighbor that this might be under-sized on our 1950s houses. His reply, which was strangely intuitive, was that it's fine given that none of us run all these things at the same time.

So, I think you will be just fine.

I would worry more when multiple bathrooms are involved.

[shacko]

Eyeball engineering is to run 3/4 main and 1/2 branch. Some codes require 3/4 min. on a riser. If you reduce the line to 1/2 you have to realize that you also reduce the volume. The difference in time is minimal, but the difference in volume could be problematic, your call.

[Terry]

Water pipe sizing

Use the chart and work backwards.

[Dostoy320]

Thanks, guys. I'm gonna run 1/2" from the water heater to the kitchen. Should be more than sufficient for a sink/dishwasher.

[tjbaudio]

I ran 3/4" copper trunk lines to the kitchen. Then each fixture got 1/2" pex. The only exception is the main shower. I ran 3/4" copper from the heater and reduced to 1/2" copper inches before the pressure balancing valve. In our house NOTHING affects the shower. we can flush, run any faucet in the house, run the dish and clothing washers. The shower temp and pressure stay stable.