tankless hot water heaters with recirculation

AlphaGJanuary 22, 2011

Looking at possibly going tankless, but, there are considerations. The home is 5.5 baths and has a dedicated hot water recirculation line. I've looked over a couple tankless heaters (Rheem and Navien), and one of them, the Navien, has what looks like a recirculation pump built in? Navien NR240A. I'm not sure how this works with a recirculation line. I thought the benefit of a tankless system was that when there was no demand, there was no gas being used. With a recirculation line, wouldn't the hot water heater be on whenever the recirculation pump is on? Thus negating it's efficiency to some degree? I understand that the pump could be on a timer, so on off hours the recirc pump could be off, so saving some energy there. Because the home has a recirculation return line is one of the big reasons I was considering NOT to get a tankless.

Any thoughts are welcome. Thanks!

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justalurker

The flow of a recirc pump may not be enough to trigger the tankless heater to turn on.

I have seen this discussion before and IIRC it is an either recirc or tankless decision with current technology.

    Bookmark   January 22, 2011 at 8:52PM
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wisehvac

Your right the navian has a circ pump build into the machine, I am a takagi rep you need a 26-99 grundfus or a 00-9 if you didnt have the pump already in the sytem. What you really want and it makes sence as a long term goal is have a takagi unit. I will assume your going to have at least 2 units to keep up with the use of water. having he demand system from taco. Look atthe taco-hvac website. going tankles and with the deman d system is a big purchase but you will be happy in the long run....
the demand system is a button or motion detecter on a wireless remote. You only push the button as you need the hot water circulated. so it only usedas you need it. which is an estimate of 15 to 25 minutes of recirluation at a time.
or get a high eff water heater by a. o. smith with the demand system which willalso be great.

    Bookmark   January 27, 2011 at 9:46AM
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antss

You could also use the tankless to feed a tank heater to run the circ. system and provide most needs. The tankless would kick in for high demand periods or filling large tubs.

Basically , a 5.5 bath house + a recirc pump and efficiency do not belong in the same conversation.

    Bookmark   February 13, 2011 at 2:00AM
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fatlady

Did you check out "Eternal Water Heater". It is what we installed, and it works with the recirculating pump.

    Bookmark   February 14, 2011 at 3:46PM
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zl700

Hey the master chimed in

    Bookmark   February 14, 2011 at 7:06PM
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ionized_gw

Tankless natural gas and tankless electric are generally expensive ways to heat water. Crunch your numbers, initial cost, fuel cost and efficiency go into lifetime cost.

    Bookmark   February 14, 2011 at 9:26PM
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wizard19

We were recently going to install a Rannai unit in our home but decided against it. While a great idea, the cost and practicality didn't seem to make sense. Some of the reasons we decided against it included dedicated 1" gas line run up the outside wall of our house (two stories), needed the recirculation to provide hot water to HE washer (uses small bursts of water), discussions of intermittant bursts of cold water, more stringent annual flushing requirement, need soft water and the total cost. Talked to a few installers and Rannai seemed to be the preferred choice. Considered Navian for the included recirculation but they are still fairly new on the market. Just seemed better to replace our two tank water heaters. I think tankless water heaters will eventually become the standard but right now they are still an expensive option.

    Bookmark   March 14, 2011 at 9:41AM
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mhudson

I have a little Takagi-Jr tankless and I put it on a recirculating loop so I could have "instant" hot water at all the faucets. Like WiseHVAC, I thought that a motion sensor would be a smart way to trigger the recirc pump. But years later, and I haven't got around to doing that upgrade. I'm sure I've wasted some gas pumping 24/7.

Here is a link that might be useful: another post with pic

    Bookmark   January 6, 2012 at 11:55PM
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