I am re-piping a 4600 square feet home on 3 levels. I have designed a passive return system that will feed 4 full baths, 2 half baths, kitchen with 2 sinks, 2 dishwashers, bar area, and a dog bath area.

My question is the size of the pipe to use. I was thinking of 3/4", but now thinking that 1" may be better. Does anyone know which would be better for my situation? (pros and cons). Thanks! I guess for the cold water it should be the same size as well?

We have very strong water pressure from the street and I will need to install a pressure regulator, fyi.

How many people living in the house? Women? Men? The systems I've installed have been 1/2" but in your case I think 3/4" would handle all the draws, Good luck, Tom