gravity recirc. line

kevin

I have heard before some guys talk about the use of a gravity recirc. line on DHW lines (ie. w/o the use on a bronze or ss pump)... how do go about piping this to a faucet?...tia... kpc.

[Deleted User]

Here's...

an article the famous "Hollywood" Dave Yates wrote...





YATES ON PLUMBING


BY DAVE YATES, Plumbing Contractor

Put Newton's law to use for hot water

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 above. 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.

Remember this, though — the entire loop has now become an extended part of the vessel and its volume should be included in your calculations for the thermal expansion tank.

A number of years ago, we were installing the phc system in a huge home, something around 15,000 sq. ft. The plans called for a 120-gal. oil-fired water heater to serve the four bathrooms in the kids’ and guest wings.

A fair distance from the mechanical room was the second-floor master suite with a walk-in marble shower that had dual shower valves, first-floor kitchen with dual dishwashers, two double-bowl sinks and adjoining laundry with two clothes washers. These areas were to be served by a single 40-gal. electric water heater installed under the stairway with absolutely no access for future service! I’m not making this up.

A quick calculation showed that using the two high-volume shower valves alone would deplete the available hot water in less than five minutes. When I approached the architect and his mechanical engineer about installing a gravity hot water loop, they both told me it would never work. After much arguing, they grudgingly acknowledged that a small electric water heater wasn’t going to be an adequate source of hot water.

The mechanical engineer then drew up a fancy return loop rig for the oil-fired tank complete with a bronze circulator controlled by an aquastat. No amount of talking could persuade them to allow a simple gravity system.

After the job was completed, the owners moved in and the architect left. It was a simple matter of turning off the circulator and drilling a hole in the flow check. The owners never had to wait for hot water and they had a virtually inexhaustible supply from that hotel-sized 120-gal. oil-fired tank.

(Borrowed from contractormag.com)

ME

clammy

hot water recirc.

a few years ago i was re piping a older home with copper because the old galv. lines where shot as i progressed through the job i noticed 2 1/2 water lines lurking in the
joist bays above the d.h.w. heater.i unscrewed the plugs andand to my surprise after a minute i had hot water they where gravity re circ lines.i advised the home owner and added a 1/2 return lines from the second floor baths upon completion the re circ worked fine also this house was built in 1907 and had these re circ. lines from the start the original domestic hot water heater was a small hand fired coal unit.to think plumbers where re circ domestic hotwater way back then now every plumber is throwing in a domestic brass pump while gravity works fine i also like them pitched my lines back to the heater and did as mr. earthton had explained before.that job work perfect not to mention the bath where about 1 hundred ft. away and in opposite directions good luck

ScottMP

recirc.

Years ago I installed a guest bath that was connected to the main house by a green house. The guest bath was about 100 away and the water lines were run in the pipe chase loccated in the floor of the green house. This was all horizontal and the same floor.

I told the HO we would need a recirc line since she wanted to use the House's HWH in the basment of the main house. I hooked up a SS pump and waited for the electrican to wire a plug.

Came back about a week later and man that hot water was right there. And when I went to the basement .... You got it..... They had'nt wired the pump yet.

Gravity done right works just fine.

We allways go in the bottom of the tank with the return.

Scott

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Mike T., Swampeast MO

If you follow good plumbing practice...

...keeping the DHW "main" large with appropriately small branches to individual fixtures and groups (branch runs as short as possible) you will get rapid hot water.

Even with a 1" DHW main and 5 rather scattered baths, I have no more than a 14-second wait at 2nd-floor lavatories--showers/tubs are considerably faster. Before the loop (and before the 1" main) the longest wait at a lav approached 45 seconds!


Note that the main has sized "down" to ¾" at this point and that the "return" line is ½".
Photo shows temp of highest/farthest part of loop (before insulation) about 3 hours after completion.

kevin

Thanks Guys....

I will give it a shot...kpc

Unknown

Is there any problem creating a gravity flow

if you use a mixing valve ? We installed some heavy duty steam boilers in NYC , and originally there would be a big old steel boiler with a big old coil , usually hooked into a storage tank . The gravity return was usually 1/2 brass and connected into the bottom of the coil , or the tank , and there was no mixer in the system .

We usually replaced the whole system with a Weil Mclain 88 series , and used 3 or 4 internal coils for hot water . Everthing would be connected to a huge Watts 1 1/4 inch mixing valve before it went to the apartments . We would bring the gravity return to the bottom of one of the coils , with a valve and check . My question is , can you get a gravity flow of hot water through a big mixing valve ?

Bryan Hochheiser

recirc. line

I have seen recirculating lines that are continuously electrically circulated develop leaks from cavatation in a couple of years. Bryan Hochheiser

Unknown

Unknown

it depends

If the recirc line comes back to the tank in such a way that it can go to the cold port of the mixer, and through the tank, to push hot water to the hot port, you can do it.

If you just go to the tank, and neglect the cold port, the water going out will be straight hot from the tank. This eats mixing valve thermostats.

Do it something like this, without the pump.

Noel

todd s

recirc with pex

Would a gravity recirc work with pex? would make an easier retrofit.

hot_rod

PEX gravity flow

We've done several using PEX. Last one was a remote home run panel (remote from the water heater - in a new addition). We added a gravity return from the home run PEX manifold so both bathrooms and the laundry room enjoy virtually immediate hot water. Saved a ton of PEX by locating the home run H&C manifold close to the three points of use instead of in the basement.



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[Deleted User]

i should know this but i dont

so i better ask,,why drill the hole in the disc?