What would the difference be in water pressure with a 1" main compared to a 3/4" main?

Question

I currently have a three baths in my place.

Answer 1

It all depends on the supply coming into your house, I only have a 3/4 supply, I would run 3/4 to all of you bath rooms, then break it down to 1/2 to supply the sink, toilet, shower/bath, I't not a pressure problem, beings you have 3 baths, it will end up being a volume, and if you can get a 1" supply coming into your house, I would do that, but you will lose it at the water heater, they are mostly all plumbed for 3/4 inch, might help with your cold supply.

Answer 2

boy, the answers here amaze me...

first off it all depends on the pressure from the street.  your local building code specifically has a chart for just this.  depending on your demand, too large of a pipe will kill "VELOCITY" and you'll regret it.  

size your pipes according to the chart and you won't have any problems.

remember the difference between all the values.

there is:

pressure --> how hard it's pushing your water <this is constant>

volume ----> how much it's pushing your water

velocity ----> how fast it's pushing the water.

Answer 3

What bilko said is exact

Answer 4

it's not really a pressure situation, but a flow volume capability as the main difference.

if you have 3 bathrooms and are concerned about maintaining pressure/volume for all... go with the 1" or 1-1/4" meter size.

Answer 5

Bilko has it, the pipe size does'nt affect the pressure, just the flow.

Just for the record.........A 2" pipe carries 4 times the volume as a 1" pipe.           A 1" pipe carries4 times the volume of  a 1/2" pipe    therefore  a 2" pipe carries 16 times more volume than a 1/2" pipe, so if in doubt go for the larger pipe.

Answer 6

To calculate the specific pressure difference in flowing water at a faucet for a 1" main as compared to a 3/4" main is impossible without knowing specifics of where you are measuring pressure... like the distance of pipe from the city main to the location you are measuring pressure and the number of bends (90s, 45s, TEEs, valves, reducers, etc.).  Each of these fittings reduces the pressure head of water when it is flowing.

Velocity is only an issue to make sure you don't have settling in the pipes.  This really isn't a big deal in home plumbing because your piping network isn't that long and there will be times when no water is being used so velocity will be zero.

Like you suspected, pressure is the issue.  Sure, when there is no flow, static pressure across the system is the same as long as every where you check is the same elevation.  The size of pipe certainly affects the pressure when you have flow despite what you've read here.  The smaller the pipe, the more headloss (pressure loss), so the less volumetric flowrate of water you will see at each faucet because the pressure head will be less.  Larger pipe reduces the headloss less (so does smoother pipe), so you will get more flow at the different fittings in your home.  

Large pipe is good, but you just don't want large sections of stagnant water.  The smaller pipe reduces this effect.  Your best bet is to review a plumbing reference, or your local code, or talk to a plumber yourself.  

Good Luck