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
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?
Whirlpool: 3/4" as valve inlets are 3/4"
Thanks so much for your help.
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
Hint: not much, since there isn't much water in 1' of pipe, so it cools fast
between uses, even with lots of insulation.
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.
On Apr 4, 7:08�am, firstname.lastname@example.org wrote:
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
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
you will likely save more:)
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