Domestic Water Heaters - return and make-up water

Cesar

Dear Dan,

I think you're the only one who can help me to understand how to pipe hot water return and make-up water to domestic water heaters.

Where is the the best location for the hot water circulating pump? Does this pump run continuosly? What element in the system control the operation of this pump?

Should I use a tempering valve? If so, where should this valve be installed? Why to use tempering valves if I already have mixing valves in every fixture (shower, hot tub, sink...) in the building?

Do you have any piping diagrama for this type of applications?

I look forward to hearing from you.

Yours sincerely,


Cesar Villavicencio

Mad Dog

I'm sure he does, but he's eatin Lamb at this moment

George Firedragon Lanthier has a great book on that with all the diagrams. I'll try to get his attention. Mad Dog

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Unknown

Firedragon website

is WWW.firedragonent.com

Mark Eatherton1

Generally speaking...

The pump should be on a timer. The timer allows the pump to run approximatley 1 hour prior to first use, and shut off 1 hour after last use. The pump should also have an aquastat on it so that if the water comes back adequately hot during a timed ON period, the pump will shut off.

The pump should have a check valve to guard against backflow through the circ return.

As for tempering valves, that is dictated by local code.

I know Dave Yates has some valid reasons behind not wanting a timer on the circuit, but I will let him expound on them.

ME

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Weezbo

Larry Weingarten

another option

Hello: Suggest having a look at www.gothotwater.com . You don't need a recirc loop at all and this is a much more energy efficient way to do things if a pump is to be used. Hope this helps!

Dave Yates (PAH)

Here tis!

Two things don't pass these lips: lamb & liver!

Timers are sort of OK in my book, just depends on the system. The concern centers around Legionella bacteria & their needs for rampant growth. Needs a good judgment call IMHO. But, on the other hand, there's my favorite system - the gravity circulation system with no moving parts - unless you count the water(G).

Put Newton's law to use for hot water.
Contractor, Feb, 2000, by Dave Yates
Copyright - Dave Yates

AN OUTBREAK of the Plague in 1665 forced Cambridge University to close, and Isaac Newton, a 23-year-old student there, returned to his family's farm for the next 18 months.

A portion of the farm was an orchard, and it is widely believed that an apple fell on Newton's head one day while he sat underneath a tree. From this observation, Newton developed his theory regarding gravity and its effect on objects.

Specifically: "If object A has mass Ma and object B has mass Mb, then the force F on object A is directed toward object B and has magnitude." He wrote like an engineer, didn't he?

In our modern day times, no one wants to wait for anything, much less his hot water! Most of the means employed to shorten the wait for hot water use circulators with some form of time or temperature control. Another way to accomplish this task in residential or light commercial applications involves applying Newton's law.

Let's put Sir Isaac Newton's formula to practical use. You can follow this on the drawing on this page. When heat energy is absorbed by water, the molecules expand and become less dense. Gravity (the force F) causes the denser, and therefore heavier, water molecules to seek out the lowest elevation inside the vessel.

All that is needed to set up circulation between the hotter (mass Ma) water at the top and the colder (mass Mb) water at the bottom is a loop that returns from wherever the demand is located to the lower connection of the storage tank or water heater. Gravity works its magic on the water and causes a thermal circulation flow that gently works its way out to the end of your loop and back through the return.

The entire loop must be well insulated to prevent wasting energy and short cycling.

You can easily set up a gravity loop by installing a 1/2-in. return connected to the hot water line at the point nearest the fixture that your customers identify as being the one where they want instant hot water; typically it's the master bath shower. Run this line back to the mechanical room and connect it to the lowest port on the hot water tank.

New homes are a natural, but this works equally well in a retrofit application. If you can't easily access the point of use on an upper floor, a connection at the base of the hot water riser will help minimize the wait for hot water on a long run.

Remove the boiler drain and install a brass nipple, 3/4-in.-by-1/2-in. tee and reinstall the boiler drain in the end of the tee. Install the tee with its outlet to the side and then a ball valve, swing check and a second ball valve laid level. I prefer using threaded brass fittings, but copper with sweat fittings could easily be substituted.

The brass swing check valve will need a hole drilled through the center of the swing check gate prior to installation. This hole doesn't normally need to be larger than 1/4-in. and will work quite well with smaller drill sizes, provided you insulate the entire loop. Install this swing check so that the gate opens with flow toward your water heater return port. The second ball valve will give you the ability to access and service the swing check.


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Mike T., Swampeast MO

Newton Works Well!!!

About 2 hours after the loop became active. Time is DEFINITELY on your side when it comes to gravity DHW recirculation. Whether it "costs" or "saves" energy is really difficult to determine, but good pipe insulation is most certainly a plus.

Allied

Constant Circulation

And if included on current installation at the hot side of the tank, remove the following?

1. Thermal trap. 2. Ball Check.

Cesar

Domestic Water Heaters - return and make-up water

Thanks to everyone for your comments and suggestions.

Cesar