installing tub/shower

[R.B.]

Howdy , I am in the process of doing some remodeling. I am installing a new shower/tub 1 peice. I have the unit in place and am hooking up faucet. I am redoing the supply lines with cpvc. I plan on running 3/4 inch then reducing to 1/2 for connections .

Now for question #1. Do I need to instal a vent pipe on the shower drain? The only vent is coming off the toilet drain and is steel pipe threw the roof. Now I could run threw the shower walll and tee into the vent pipe in the attic if i need to.

Kitchen sink has the vent under the cabinet. Also what about the vanity vent? Currently I have not installed the vanity or water lines. I have already sheet rocked the walls, but have not painted them. I was waiting to finish the shower job.Will the vanity need vented also and could i use the same type as the kitchen sink under the counter? I am not putting any water lines in the walls except for the shower. I will be going thre the floor in the cabinet. This is a wood floor house on pillars. Space is a bit cramped under house.

If i have been unclear please let me know and i will try to elaberate. Thanks I have been reading all the prior posts trying to get some ideas.

[HayZee518]

Although I am not a plumber, when I was doing renovations, I was told you have to be within six feet of a vent.

[LazyPup]

First off,,Unless your main water line from the street to the main water shutoff and on to the water heater is 1" diameter or greater, do not use 3/4" lines to the shower.

In a typical residential water service the main line from the street is 3/4". The 3/4" should be continued to the water heater where the inhouse distribution system divides into two separate but equal systems, the hot and the cold. From the water heater junction the lines should reduce to 1/2" to insure equal pressure on both the hot and cold systems.

When comparing the capacity of two lines we cannot use diameter but must compare cross sectional area, thus the formula is:

Large Diameter squared divided by small diameter squared.

(3/4 x 3/4)/ (1/2 x 1/2) = (.75 x .75) / (.5 x .5)= 0.5625 / 0.25 = 2.25

Thus one 3/4" line can carry the volume of 2.25 lines of 1/2" and the pressure will remain equal on all lines. If you run 3/4" lines downstream of that junction either line is then capable of carrying all the volume and pressure, which leaves the opposite side starved.

The second problem you would encounter is that if the lines are increased to 3/4" the velocity of flow is reduced to 1/2 and it doubles the amount of radiational cooling of the hot water on the water lines.

IN RE: the vent for the tub/shower...The waste arm drain line from the tub/shower is a 1/2" line. Under the International Residential Code an 1 1/2 waste arm may run 6" without addiing a vent. (The Uniform Plumbing Code only allows 3' 6")

The code allows that the waste arm line may be increased one nominal pipe size larger, thus the 1 1/2" line could be increased to 2" which would allow 8' under the IRC or 5' under the UPC code.

[R.B.]

Huh ???? The bathromm is aprox. 8'x8'. vent is on oposite side of shower threw roof. Do I need a vent on shower?

Do i need vent on vanity? vanity will be on same wall as toilet.

I am bringing supply from meter 1".pvc. I live on a hill and pressure is weak during summer months due to people watering flowers/ gardens. I just want to have enough volume to offset weak preasure.Plus i have waterlines going to the barn anda couple other areas. I'm not a plumber, I'm a mechanical journeyman. Maybe i sniffed too much freon

[LazyPup]

RB....All fluids, whether liquid or gasseous exhibit the same characteristics so lets discuss pressure in terms of HVAC for a moment.

In an HVAC unit the compressor is the "prime mover" that generates the pressure in the system. As the high pressure gas is pushed into the condenser it condenses to a liquid, but the pressure remains constant until the liquid reaches the metering device (capillary tubes).

The combined volume of the capillary tubes are substantially smaller in diameter than the liquid line, thus the liquid has to increase velocity dramatically while passing through the capillary tubes. The "Venturi Principal" states that if the velocity of a fluid, either liquid or gasseous is increased, their is a proportional decrease in pressure, thus the capillary tubes are able to drop the liquid pressure to the suction pressure in the evaporator. An evaporator is actually a series individual tubes that are fed by the different capillary tubes then combined into one common suction line on the discharge side of the evaporator. Note that when the evaporator lines are increased in size by a common header on the discharge side, even though the line size is increased, the internal pressure remains exactly the same. The suction pressure then remains constant (with the exception of any superheat that may still be occuring in the suction line) until the pressure reaches the compressor where it is increased again.

A water supply system must be balanced in the same manner. The supply line to any given point must have the same volume as the lines exiting that point in order to assure balanced pressure. If the ratio of the line exiting the point is greater than the volume of the supply the result is an increase in velocity on the secondary side and a proportional decrease in pressure.

Consider the effect of reducing a 1" line to two 3/4" lines....

(1 x 1)/ (.75 x .75) = 1 / 0.5625= 1.77

Thus a 1 inch line can only supply the volume of 1.77 lines of 3/4inch. The result is a slight decrease in pressure on both the 3/4" lines.

Now consider the effect if the same 1" line was reduced to 1/2".

(1 x 1) / (.5 x .5) = 1 / .25 = 4

As you can see, the 1" supply line could supply 4 lines of 1/2" while maintaining the same pressure.

Now consider that the inputs to your shower mixer are 1/2" on each side. If you run 1/2" lines to the shower mixer your 1" line would supply full volume and pressure to your shower mixer while still retaining 50% capacity to supply your outbuilding, hose bibb or kitchen without any significant loss in pressure.

[R.B.]

I understand wht you are saying LazyPup, And i appreciate the time you have taken to explain.