low pressure water flow

[golfinaway]

Hello and thank you very much for this site, I just learned several things toight surfing it

Ok this is a longstanding problem: I have a very long sgl story rancher about 80' long.

The h/w heater is in the far back corner of the house and it takes about 10-15 min to get it to the laundry and bathroom on the far front end of home.

I have checked aerators, drained hw water tank out for any problems there, have tediously traced all 3/4" main lines and 1/2" feeder lines for a twist or bend,etc. I get water in the front half of home, just slow for hot and not near the pressure of back half.

just bought a smaller hot water heater for enclosed porch, about halfway down the length of home, anticipating that this will help the front half.

I am going to cap the hot right about halfway down the length of pipe (main lines 45'), so the front half hot lines will feed off hw heater #2.



Have been asking diff hardware stores around here and got two diff answers, so:

1) with the main cold source near to hw heater #1 ihaving to push wtaer clear down to all lines in front of house, do I run a second complete line all the way down to hw heater #2 to directly feed that system?

2) tee into main cold line for the cold feed on hw heater #2.

Have heard both things, really want to get this straight and only do it once.

Thanks very much again

[mrcaptainbob]

Water heater...

Why not tap that new heater into the existing hot water line? That way, the first water heater would act as a preheat. Would think it would be an economical/efficient way to get hot water to the farther part of the house...

[LazyPup]

The problem is not the volume of available hot water, but rather the time it takes to get the water to the point of demand. Adding another water heater may offer a solution but it definitely is not the most efficient nor is it the most cost effective solution.

The problem is that the hot water in the lines from the water heater to the point of demand is cooling so in order to get hot water all the water standing in the line must first be replaced with a fresh supply of hot water from the water heater.

The first step would be to insulate all accessible hot water lines to minimize the rate of heat loss to radiation from the pipes.

An even more effective permanent solution would be to install a circulating pump to keep the lines continually full of hot water.

The most efficient circulating system would have a dedicated return line from the furthest point of demand back to the water heater. The plumbing codes require that when we install a recirculating pump in new construction we must insulate all hot water lines and return lines, however when retrofitting an existing system installing a return line can present a challenge.

There is another option, although not quite as economical as a dedicated return line, non the less, it does work good. They now make small circulating pumps that use the cold water line as the return line.

Quite often when people install the recirculating pumps they make the mistake of allowing the pump to run full time. While that method is used in larger commercial structures it is not necessary in residential applications. A much more efficient method is to install a strap on thermostat on the hot water line to control the pump. In this manner the thermostat monitors the temperature of the line and only runs the pump when the temperature falls below a set point. The pump then only runs long enough to circulate a sufficeint amount of water to keep the lines full of hot water. The question then becomes, how big of a pump do we need?

From the information in the post the house is 80' long. The water heater is on one end and the furthest point of demand is on the opposite end. It does not state whether the lines run under the house of through the attic space but either way we must allow an additional 5' or so for the rise or drop from the water heater to the main hot water line on each end, thus the line is a minimum of 90' long plus any additional length for offsets from the main to the tank or from the main to the point of demand. The post states that the main hot water line is a 3/4" line so we can then compute the volume of that line as:

Cross sectional area of a 3/4" pipe=
Pi x radius squared
Radius equals 1/2 the diameter therefore the radius is .72/2= 0.375".

Area equals:
A= 3.1416 x (0.375 x 0.375)
A= 3.1416 x 0.140
A= 0.439 sq.in

The pipe is 90' long so allowing 12" per foot it is 90' x 12" = 1080" long.

Volume equals cross sectional area x length
volume equals 0.439 x 1080 = 474cu.in.

On gallon of water occupies 231cu.in
therefore the line holds 474cu.in / 231cu.in =2 gallons.

Typically the pumps will move 1 to 4gal/min so we can anticipate 30 seconds to 2 minutes run time to move a sufficent supply of water to keep the lines full of hot water. If the hot water lines are not insulated we can expect this action to occur approximately 4 times per hour. If the lines are insulated the pump duty cycle is typically reduced to not more than 2 times per hour.

Now let us consider the efficiency of these systems.
Typically the first hour rate of a gas water heater is to deliver 70% of the tank volume at a temperature approximately 10degF below the thermostat set point. (Electric water heaters deliver 60% of their volume at 10degF below set point)

Assuming the water heater to be set at the standard code temp of 120degF we can then expect the water at the demand to be 120degF at the initial start but only 110 degF continually until we have consumed 70% of the tank volume. We would not need the circulating pump to run while we are in the shower so we set the start temp of the circulating pump slightly below the continual load temp, thus in this example we could set the pump to start at 100degF and turn off when the line reaches 115 or 120degF.

One BTU(British Thermal Unit) of energy will raise one pound of water one degree of fahrenheit and water weighs approximately 8 lbs per gallon so we can then say that we need 8 BTU's per degree per gallon of water.

If we have a dedicated return line the water returning to the water heater will enter the heater at approximately 100 degF and needs to be heated to 120degF so the energy consumed by the water heater is 8 BTU per gallon x 2 gallon x 20 degF differential. 8 x 2 x 20 = 320BTU.

If we use a pump that uses the cold water line as a return path the water entering the water heater will be at the ambient cold temperature, which is typically 55degF. The differential between the incoming water and the water heater set point is then 120 - 55degF(avg ambient temp) = 65degF thus the energy required by the water heater per cycle is 8btu/gal x 2 gallon x 65degF differential equals 1040 BTU.

As you can see a dedicated return line is much more energy efficient than using a cold water line as a return line, however we do gain the luxury of instant on hot water.

Now let us compare this to the cost of simply running the hot water until it arrives at the point of demand as you are doing now.

Here again, for each gallon we pull off the water heater it must take in a gallon of cold makeup water so the water heater energy is the same as for the pumps that utilize the cold water pipe as a return line, however, when simply running the water we are wasting the first two gallon of water. Now consider how many times per month this occurs and compute what the cost of purchasing that water from the municipal supplier or operating a home well pump system to obtain that water, and don't forget that if you have a municipal water supply you are also paying sewer tax on that waste water.

The question then becomes what is the initial cost of the pump and what is the operational cost?

You can generally find a self contained hot water recirculation pump complete with thermostat control at most of the larger home supply centers for about $80 to $100 and dedicated return line can be run with continous roll copper so that is generally an easy task.

They are now even making a circulating pump that uses the cold water line as a return path with two short flex lines on the pump and 3/8" compression tee's on the end of the pump lines. You simply mount the pump in the lavatory cabinet then cut the supply lines ot the faucett and install the tee's on the supply lines. The only thing you need then is a place to plug the pump in.

As far as operational cost, they pumps typically only require about 60watts of electrical energy so the operation cost would be equal to leaving a 60watt light bulb on a couple hours a day or less.

[golfinaway]

thank you pup and captbob for your quick replies!

[golfinaway]

thank you again both so much for answering. Lazypup you lost me in the math



I thought it thru again, and did this:

kept the cold line to feed both hot water heaters, cut the hot line as it existed and capped it off (going both ways) , so with regards to the hot lines, they were two diff.systems.

Pressure came right up and everything works great.