Domestic hot water recirculation systems residential homes.

bob eck

Anyone selling and installing domestic hot water recirculation systems? What type are you using? Taco? Grundfos? Other? Do you sell many of these systems?

JUGHNE

This has worked for me, no pump needed. Pump could be added if needed later, but if installed correctly will work without.

rick in Alaska

I rarely get to do a water heater where there is the option of gravity circulation, but have down a few, and they do work great. Not sure about how energy efficient they are though as the hot water is always moving without any way of shutting it down. Insulation is a must, but to a point, or the circulation can be weak.
I had one customer who had someone come in to work on her system when I was out of town, and they wanted to sell her an expensive pump system to run her recirc, even though she told them it has been working without one for seven years now!
Needles to say, she did not have him put one on.
Rick

Mark Eatherton

I love gravity too, and as Rick pointed out, it can be wasteful, or NOT. By installing a zone valve and timer, you can limit the circulation within the system, keeping it off for extended periods of non use. Instead of using a swing check, which is prone to being limed shut or limed open, I prefer to use a restrictive orifice. I take a nickel ($0.05) and drill an 1/4" hole through its center. I then place that nickel into the receiver fitting of a 3/4" copper fitting.

Also, instead of bringing the return back to the bottom of the tank as shown in the PM article, I tie my return back into the cold water inlet. I then incorporate a venturi fitting into the tee, which when hot water is being drawn, will induce flow on the circulation return line, enhancing what gravity is already doing.

If you do decide to use this venturi tee method, be sure and note so on the pipe, because there is no external change in appearance and you will save some poor technician a lot of time in trying to figure out exactly how it works. http://kscdirect.com/item/NIB+621+1/NIBCO+INC_621+1+VENTURI+INSERT+WROT

While we are talking about hot water, one thing that really irks me is having to wait for warm/hot water to purge out of a given cold water pipe so I can get a cold drink of water. It is so simple to put the DHW supply and circulation return (both insulated) in one common joist bay, and place the cold water supply line in a completely separated bay. The water that is saved by having a circ return is lost by people trying to get a decent glass of cold water... And that water is hot, so it wastes, water, sewage and energy.

If gravity is not an option, then my suggestion would be to install one of the new self contained thermostatic flow controllers on the far ends of the system, and then install a DCECM Delta T circulator on a timer in the return system. Then, as the remote returns cool down, the pump moves water and satisfies the need for instantaneous hot water. It also lessens the piping standby losses because the hottest water stops at the remote control device.

ME

SWEI

Nice touch with the venturi insert, Mark.

Does the orifice disk go into the same tee as the venturi?

Mark Eatherton

No, the orifi just has to be in the return to create a path of greatest resistance. I guess if you used 3/4" for return, you could. You also need to set up a means of positive and complete purge, otherwise the loop will be air bound and circulation won't happen.

ME

SWEI

Thanks, Mark. I intend to experiment with this a bit. Smaller recirc lines are easier to route and (with proper sizing) can help balance flows.

I'm about to tool up for Viega Press PEX just so we can use 3/8" PEX (for more than just floor loops.) One of my few gripes with Uponor is their near-complete lack of 3/8" fitting options.

Mark Eatherton

In case you are not aware (and I assume you are) there are now numerous "grades" of PEX ratings for resisting the oxidative tendencies of treated potable water (chlorine). For circulation return lines, it is suggested that the highest possible rated tube be used to avoid embrittlement of the tubing due to constant exposure to the chlorine.

The more you know...


If you need the name of someone to complain to within Uponor, let me know. I know a few people up there :-) Ingrid Mattsson is the V.P. of our org., and a long time industry friend (like 20 years).

ME

SWEI

We use PEX-a for everything, regardless of the fitting system.

If you're not willing to pay a few cents more per foot to get a top quality product, you're probably not the kind of customer we want to deal with.

hot_rod

One of the biggest mistakes with DHW record loop is the lack of insulation. It is basically a hydronic loop and heat is transferred from that loop to the space.

A little insulation goes a long way.

On large buildings, hospitals, hotels, etc, balancing the loop is also an important step for energy savings and fast HW response.

JUGHNE

I've only used the gravity system twice and was very pleased with the results. I did slope the return line down as it went back to the WH. It is insulated, but not drastically. The last copper vertical drop of a few feet is not insulated, (in my mind it is a cooling leg to induce flow). I did use a check valve into the water heater (WO hole drilled) and have a ball valve ahead of the check that is choked down to slow the flow to where it just works by gravity. For vacation mode I can just close the ball valve and am soon reminded of it after returning.

I am sure this constant trickle flow wastes some energy. But the expense of a brass or SS pump and hydrostat control buys a lot of NG, and the pump cost some KW. Then replace the pump every few years, the reasonable ROI.... I doubt is there. IMO

vibert_c

Thank you @Mark Eatherton I shall embellish my system with your suggestion of a timed zone valve. Brilliant !

MikeJ

I remolded my house years ago, ran a extra copper line to the upstairs bathroom and the far bathroom on the main level. Installed circulating pump, check valve, pipe it to the bottom of the tank, insulated the lines. Worked great instant hot water at all the faucets. Then seen the article about the gravity system, so I shut the pump off that was 6 years ago and it still works great. keep thinking of removing the pump, maybe one day.