The ID (inside diameter) of the pipe should be 1/2" - what ever kind of pipe you use.

Faucet is 1-2 gpm. 3/8 will work fine. Ain't filling a tub.

There are better ways of getting hot water quicker if you decide to weigh the options.

@stoveguy: "3/8 will work fine." Then why did you ask the question?

I said 1/2" id because that's usually the minimum size for a fixture. Check with your local permit department to find out the minimum for a single fixture in your town.

Permit?

Permit? Really how the heck should I know?

Probably in a phobic world you should have a permit. However, if you install the water line with the appropriate clamps ( every 4 feet or so ) who's to know?

My advice is learn to think ahead, before asking a question.

I installed a tee/shutoff valve on WH outlet. Now I am thinking a passive hot water return loop might be better? Real easy to run poly to sink though.