Plumbing: What size hot water pipe do I need?

[NoSpam]

I need to run hot water to lavatories, sinks, tubs, showers, washing machine, dishwasher and a 60 gallon whirlpool tub in my home. Especially for the sinks and lavatories I would like to use the smallest size pipe that will provide sufficient flow. Lavatories and sinks often use relatively small amounts of hot water at a time (wash hands, rinse something). I think a smaller pipe would result in less waste and less waiting for the water to get hot.

Appliances such as tubs, etc. are used less frequently and use much more hot water at a time, so the initial wait and the waste of the hotwater left in the pipe should not matter so much and a high flow rate is more important.

Running separate pipes of different sizes to the same bathroom is no problem if it will improve performance & save energy. I realize that running the lavatory faucet and a tub/shower would require filling two pipes, but this will seldom be done at the same time so the water in the pipe would cool down between the uses.

Question: What size pipe should I run to each type of appliance?

Lavatory: Sink: Tub/Shower: Whirlpool: 3/4" as valve inlets are 3/4" Dishwasher: Washing Machine:

Thanks so much for your help.

[hallerb]

are you running PEX ? individual lines to each outlet has lots of advantages, and be certain to insulate all hot water lines

[nicksanspam]

How much energy would we save by adding R2 insulation to 100' of 1/2" pipe, with 6 10 gallon hourly 110 F water uses per day at 3 gpm (an SRCC standard test condition)?

Hint: not much, since there isn't much water in 1' of pipe, so it cools fast between uses, even with lots of insulation.

Nick

[RicodJour]

All you'll need to know.

R

[nicksanspam]

The pipe is only used for about 3 minutes per hour...

... 62.33Pi(0.5/24)^2 = 0.085 pounds.

L' of ri' radius pipe with an r' insulation radius and a k Btu/h-F-ft insulation conductivity and an airfilm conductance h Btu/h-F-ft^2 would have thermal resistance R = (1/(hr)+ln(r/ri)/k)/(2PiL), so 1' of bare 1/2" pipe with ri = r = 0.3125/12 = 0.026' and an h = 1.5 slow-moving airfilm would have R = 1/(1.5x0.026x2Pi) = 4.1 F-h/Btu, so RC = 4.1x0.085 = 0.35 hours, ie 21 minutes. After 57 minutes in 70 F house air the 8.5 pounds of water would cool from 110 to 70+(110-70)e^(-57/21) = 72.7 F, losing (110-72.7)8.5 = 317 Btu of heat.

With 1/2" of R4 per inch (R48 per foot, ie k = 0.021) foam insulation, r = 0.6875/12 = 0.0573' and R = (1/(1.5x0.0573)+ln(0.0573/0.026)/0.021)/2Pi = 7.8, so RC = 0.67 hours, ie 40 minutes, and the water cools from 110 to

70+(110-70)e^(-57/40) = 79.6 F, losing (110-79.6)8.5 = 258 Btu.

The net savings is 6(317-258) = 352 Btu per day or 129K Btu (38kWh) per year, worth $3.80 at 10 cents/kWh.

OTOH, some pipe insulation near the heater where the pipes are warm most of the time could pay for itself quickly.

Nick

[hallerb]

remember in the winter the lost heat helps warm your home............

in summer it can be a loser if you air condition.

definetely insulate the lines but PEX is much less conductive heat wise than copper, so its naturally a insulator.

life is full of standby losses..........

every electrical device in your home thats not 100% off when off.......

cable boxes, computers, pilot lights, clocks, night lights, security lights, TVs, the list is endless..........

one shouldnt get too concerned wany single one.

better to insulate and weatherstrip your home for better savings............

you will likely save more:)