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Tanklets > Recirculation System Issues

Where to Place the Return to the Tank

Q: Good evening, I'm trying to install a recirculation pump system to an existing electric hot water heater and I'm wondering if I should tee the recirculation line into the cold water line to the tank from up top or should I connect to the water heater drain line below?

Some pump manufacturers show the bottom connection with the drain valve while talking to the heater tank manufacturer they recommend connecting up top to the cold water line. Has anyone done either method and found one better than the other?

The tank manufacturer recommends to connect to the cold water line because the recirculation line water temperatures can give the tank thermostat a false high temperature reading if connected at the bottom drain line therefore the tank won't heat up.

From what it sounds, it makes sense, but I thought it was strange how I found at least two pump manufacturers showing their recirculation system to connect at the bottom? Any opinions? Also, are there any suggestions if I have to and where to place an air vent for the recirculation line? Thanks for any help.

A: There is probably no single answer on this. I've seen it both ways, with the giant preponderance in commercial water heaters in apartments having the return going into the bottom of the water heater. One advantage to putting it on top, though, would be that sediment on the tank bottom couldn't drift into the recirc line/pump and clog it. Larry Weingarten (Eleent) recommends a spring check valve on the line to prevent that, but every time I ever saw a check valve there, it was a swing, and they stick open easily. -- Randy

Q1: Randy, Thanks for the reply. Since you mentioned about sediments with the bottom connection as a possibility, I think I will try to connect the recirculation line to the cold water line up top of the tank. However, do you have any suggestions where I should place any air vents? I am assuming the highest piping point? So whether the recirculation line or regular hot water line is highest, I should put a vent there? Currently my hot water line is above the sinks before it drops down to it, so I'm curious if it should have a vent as I don't see one? Thanks.

A1: The air vent I'm not so sure about, which is why I didn't answer. When Larry Weingarten logs in, I expect he can answer that one, and will also have something to say about return line placement. -- Randy

A2: Hello: Forget the air vent. It will only clog/fail with time. I would plumb things so you can use water pressure to flush the recirc loop. Also, I would not put a check valve in the cold supply should you choose to tie into that line. It will create thermal expansion problems. I prefer to tie into the drain, provided a spring check is used in the recirc line to have good control of water flow/sediment. -- Larry (1/7/10)

Gravity-Feed Recirc

Q: We recently had a new 50 gal gas water heater tank (State Select Model # GS650YBRT 200) installed in our 45-year old, one story house. We have a recirculating system (gravity flow, no electric pump) that until this new installation would circulate warm water from the water heater in the garage to the bathroom in the far end of the house.

The hot and cold lines are on the top of the tank, there is a pipe in the attic to the other end of the house, and there is a smaller pipe coming out of the wall (below the hot water line side) about 11 inches above the floor leading to the T at the bottom of the tank also 11 inches above the floor. At first there was a valve between the small pipe and the T....if the valve was open we were getting cold water mixing with hot...if it was closed we did not get any circulation, had to run the faucets long before hot water.

The plumber changed that valve to a swing check valve...still no circulating warm water. I think the check valve flow is going in the direction toward the bottom of the tank. There is a valve between the tank and the T marked Webstone 600 WOG and on the other side of the T is a faucet for draining. I have tried turning the temp up on the tank to pretty hot. I have tried turning all hot faucets on at the same time in case there was air in the line. Neither has helped.

A: Hello: You can't use a check valve on a gravity system. It creates too much restriction. There does need to be a valve for throttling the flow. I use a ball valve; set it and remove the handle. (tape handle to pipe) This allows the very slow gravity flow, yet does not allow a lot of backflow when water is drawn. It'd best to valve things so you can use water pressure to flush the recirc line to remove sediment or air. -- Larry

A1: Apropos to the valving, go to the Commercial Water Heater section and read the page on recirc valving for more on Larry's ideas on this.-- Randy (1/12/10)

Homerun System Dilemma

Q: I have a situation as a plumber that has me scratching my head. Let me explain: This house is equipped with 3/4" homerun water lines going to mechanical room by request of homeowner. He wants the ability to be able to shut off H/C to any given room at mechanical area. This is no problem. There are 7 rooms with H/C. He also wants 4 of these rooms with hot water recirc lines back to water heater. How do I do this? Can it be done?

How can I maintain equal flow through all 4 loops with one being only 15' and the longest being 70'? As I understand water takes the path of least resistance; therefore only circulating in the shortest loop. What size pump? Where should pump be located? Do I need swing check valves and where? Can I tie all 4 lines together as I return or do all need to return to water heater? Thank You in advance for any help that can be offered? I love this challenge; but haven't got it yet.

A: You may not like my answer. The reason for building a home run system in the first place is to keep as little volume of water in the hot lines as possible. This way there is little cool water to flush out of the hot line and you get quick hot water. The lines should be sized for flow, where bigger is not better.

My place, for instance, has a home run system using 3/8" PEX tubing. I can't easily imagine needing 3/4" tube. I'd do the math to figure what size lines should be run. If they are much smaller than your client has now, there will be no need for recirc as the hot water will arrive much faster. Vanguard/Viega makes the Manabloc system and they have a sizing calculator which would be useful to you. See http://www.vanguard.ca/mbloc.html Best of luck on your exams.

PS: If you Google "Gary Klein" and "structured plumbing," you'll find another plumbing method that works well for spread out systems. -- Larry (11/1/07)

Metlund and Alternatives

Q: I plan on installing a hotwater recirculation pump, due to the length of the run from the hotwater tank to the shower (3-4min to hot water) the simplest seems to be the Metlund recirculation pump. It requires little modification and is almost a "plug and play" the Grunfos and the laing require cutting the hot water line and soldering the pump in place. do-able but not the first choice.

A: We like the Metlund.... -- Randy

A1: The Laing Autocirc doesn't require any cutting or soldering. Neither does the Grundfos Comfort System if you have flexible piping to the wh. We've been quite happy with our Autocirc for at least five years. Recommend you insulate your hot water line, to reduce standby losses between pump runs. -- PGMR

A2: I still think the Metlund is the easiest to install, but I would like to "visit" with someone that has one installed.. -- Lonewolf (10/31/07)

Sediment Drawn Back Through Recirc Line

Q: Hi, we got a new water heater a year ago, and from the day it was installed, all our hotwater faucets got clogged with bluish white grit. We checked all the hot water pipes to see if there was a reaction (is it where a new copper pipe is joined?) but nothing wrong there. Someone suggested the dip is broken, but the plumber said no, the sediment is not plastic and it is blueish, so its not a dip.

The water heater company said it was the anode reacting with the chemicals in our water and suggested replacing it with a zinc/tin/alumium one. We did, and there has been even MORE sediment than before. I have a feeling it is a problem with the metal of the anode. Would anyone have any suggestions, pleease?

Q1: In reading more on your site, I just discovered that I think it could be the hot water recirculator pump. We have one. So it needs a spring check valve. Do you think that could be it? Your site is AMAZING. Thanks!

A: You've got it! Your tank has an aluminum anode and corrosion byproduct from that is being pulled back through the recirculation connection at the bottom of the tank. Try turning off the pump and closing a valve on the line. The sediment should stop shortly. If it does, than installing a spring check valve will fix the problem. I'd also suggest putting in a magnesium anode. They produce far less sediment. -- Larry