I have read at least a dozen threads about connecting a small tank water heater in-line with the tankless to buffer out cold spikes. I have not yet plumbed a return line for the recirculation pump. Should I wait until I run the return line and activate the recirculation pump, and then assess the performance, or install the tank now? If I install the tank, should I put it in series or parallel. Just to clarify, the sole purpose of the tank will be to buffer out cold spikes. In series, the tank will be supplied with hot water from the tankless, and will, hopefully, run sparingly. In parallel, it will be part of the supply. If I do put it in parallel, should I install a ball valve to regulate the volume of water I pull from the tank? I don't want to install point of use heaters. Thanks. Also, I made the mistake of posting on "Plumbing Zone," not realizing it is a forum for professionals. My ego still hurts.
Tankless water heater with tank
- Thread starter Joe0735
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John Gayewski
In the Trades
What brand is tankless? Navien A2 has a tank inside of it why not buy one of those?
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GL77
Member
This is how I used to have mine set up, just a 6 gallon WH after the tankless, and it was the best system I ever had for hot water. Hot water as soon as you needed it, even if you are barely running the water, and it never runs out. When the WH had to be replaced, my plumber talked me into getting rid of the small WH, he said these new Rinnai tankless heaters work so well, you won't need that small tank anymore. Well, he was so wrong and I am running gallons of water down the drain waiting for hot water every day. I am seriously considering adding a tank again when I can afford it. But I have never had it set up with a return loop so I don't know how that would compare.
PS Mine was in series, it worked great for me.
PS Mine was in series, it worked great for me.
Breplum
Licensed plumbing contractor
We used to do little electric tanks before Navien. The NPE A series solved that, plus have excellent pumps with air purge built in. Navien is the only mfr with the insulated mini-buffer tank and it works very well.
I am on Plumbing Zone, and yes, they are nasty. Don't take it personally.
I am on Plumbing Zone, and yes, they are nasty. Don't take it personally.
John Gayewski
In the Trades
The tankless water heater manufacturers are starting to realize having a bit of a tank is best. Even some point of use water heaters are starting to have little tanks.
I have worked in stamping plants for 30 years so I have thick skin. Guys with knowledge and tools can be harsh when their stomping grounds are invaded. I get it. It will be a month or two before I have time to plumb the return because people are buying cars right now and I am on 12's, and the return line needs to extend upstairs. If the return will solve this issue, I will wait. If I will still suffer with cold spikes even with the return, I will install the tank now, because it will only take a couple of hours. My wife decided on a tankless Rheem platinum with a recirc. pump, which is currently set on internal recirculation. I came home from work to a surprise. Merry Christmas!
John Gayewski
In the Trades
I'm not familiar with your model of heater. If there's an internal pump then the hot and cold spikes should be evened out by any type of circulation. External will get the water to you quicker. Without a detailed search on my part I don't know if you should add a tank.
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GL77
Member
My Rinnai has an internal recirculating pump. I don't know if yours is similar but I have not found it to make a difference at all. The problem is, you turn on the hot water. You have to turn it on a strong enough blast to trigger the tankless water heater to turn on. A trickle of water will not activate it. So, it turns on. It takes a bit of time to heat up, then start really heating the water good and hot, and then that hot water has to travel to the faucet you are using. I live in a very small house and I find it can take a full 60 seconds to 2 minutes to get really hot water out of the faucet. Repeat this every time you need hot water all day, if there is enough time in between for the tankless to cool off again. Or, say you start the washing machine or the dishwasher. I run the hot water at the sink so that the washer will start out filling with hot water, but by the time it gets to the rinse the tankless has got to heat up again and by the time that happens, the washer or dishwasher will have filled with cold water. It's very frustrating. I did not have this problem when I had the 6 gallon tank and also I could get hot water when running just a trickle of water. That's just my experience, I have never had a recirculating loop so I don't know how well they work. I will say that the Rinnai is a condensing water heater and it sounds about like a freight train when it turns on so I would not like to hear it turning on all the time. I really really miss my Bosch and my 6 gallon tank, if I had the money I would tear this thing out and put it back like it used to be.
John Gayewski
In the Trades
I don't think we are talking about normal time it takes to get hot water to a fixture. Internal recirculation won't help that and I don't think anyone says it will. The internal recirculation is to keep the coil hot and a consistent temperature.
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I installed a backflow preventer and expansion tank on the water heater cold water inlet, and installed a bridge valve on farthest fixture. This has made a significant difference. The 6 gal. electric tank will be here in several weeks. When I install a dedicated return line, within the next several months, is there any concern with backflow from the return line when I turn on the fixture? Do I need a check valve on the return line at the fixture?
John Gayewski
In the Trades
Yes you need a check valve.
John Gayewski
In the Trades
Flapper is more serviceable.
I opened up the wall below the sink in the upstairs bathroom. The supply lines are 3/4" diameter below the floor/ ceiling joists, then downsize to 1/2" before going up. The total length off the main run is about 15 feet. On the opposite side of the house is the downstairs kitchen. There is a 1/2" run of about 20 feet off the main 3/4" line. I plan on running dedicated return lines to these two fixtures. Should I run 1/2" or 3/4" line? Also, I have a Bosch shower fixture in the downstairs bathroom, with mixing and balancing valves. I replaced them in the fall after attempting to clean them. They have worked ok since then, until I activated the recirculation pump. I now cannot seem to control the water temperature. I am struggling to get it to level off between hot or cold. Did my mixing or balancing valve coincidentally go bad in my fixture again, or is this a recirculation problem?
John Gayewski
In the Trades
I think you'd be better off posting a diagram of what you have.
People used to use 1/2"pipe for recirculation lines. Nowadays 3/4"is the recommend minimum size for velocity reasons.
People used to use 1/2"pipe for recirculation lines. Nowadays 3/4"is the recommend minimum size for velocity reasons.
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