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We are building a new house. The master bath is the furthest spot from the tankless water heater. The builder is specifying the WaterQuick Premiere circulation pump with the bridge valve. It looks like it has a water flow sensor. So to activate it, it looks like you give the faucet a quick turn on/off on the hot water side. Which activates the pump and will run until the bridge valve shuts down the flow (meaning the hot water is reaching the bathroom). My issue with the bridge valve is that now I'm pumping warmed water into the cold side, so if I want to get a drink from the sink while this is running, the water will be almost hot coming from the cold side, right?

I have asked the builder to do a dedicated return from the furthest point and then put the pump on it, with a smart outlet that I can then either time when the pump will run, and/or a button in the bathroom when we walk in.

Am I thinking too much into this? Which would you do in a new build?

Thanks

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    A circulation pump on a tankless water heater ? – Alaska Man Jul 9 '20 at 18:43
  • Yes. It's pretty common, in fact more common. Since a regular water heater can actually heat the copper pipe up a bit. But in a tankless, when you're done with water it turns the heater off, so water in the pipes start to cool right away. – Matt Winer Jul 9 '20 at 18:45
  • So it only circulates left over hot water with out turning on the thankless heater ? Wont the water cool down after a few hours, or is there a thermostat that will fire it back up to keep the loop hot ? – Alaska Man Jul 9 '20 at 18:52
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    Why is the tankless water heater so far from the point of use? Circulation pump schemes basically defeat the purpose of a tankless, since it’s now a tanked heater. (The tank being 3/4” x 75’ x 2 pipes or whatever, and it’s going to lose all that heat quickly, so it’s energy wasted). And I can’t believe you have to explain to the guy not to return the tepid water on the cold pipe, how cynical are these people, they’re just selling you stuff for an easy markup? The whole “circulation pump” concept is just kludgey as can be. – Harper - Reinstate Monica Jul 9 '20 at 18:53
  • If it is a new build then you can give the master bath its own, closer, Tankless WH. NO ? – Alaska Man Jul 9 '20 at 18:58
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Too much over thinking. The set up the OP is describing is that the pump turns on when the hot water is turned on in the master the master. Once the water starts to warm up, the temperature bridge closes and pump shuts off. The bridge closes before the water gets too warm. I have a re-circulating hot water pump, and the water out of the cold faucet never feel hot or warm. It is just not "cold". So if you are looking for "cold" water out of the faucet, then a recirculating would be out of the question.

No- the water will NOT be hot coming out of the cold-side faucet, just not cold or cool.

If you think about it, The water out of the cold side of the faucet will be the normal temp of the cold faucet water until the existing water on the hot water side has been expelled and heated water has reached the bridge.

If you want to spend the additional money for a separate return line to the pump to have cold water to drink, the builder will most likely accommodate you.

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  • I appreciate your concise answer. And the fact of the mater is, we live in FL. 9x out of 10, the water coming out of the cold side is "warm" anyway. Thank you. – Matt Winer Jul 9 '20 at 19:37
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    Actually the recirculating system if using the cold will make the cold water hot! A new install just use a dedicated line for return. – Ed Beal Jul 9 '20 at 22:46
  • Recirculating system may not be the correct term for this system. The therma-bridge which connects the hot water to the cold line and it is NOT a true loop back, shuts off when the water reaches a pre-set temperature. It cuts off way before the water gets warm. When the faucet is turn completely to cold, the water feels the same as any other faucet receiving cold water directly. – Programmer66 Jul 9 '20 at 23:55
  • I do agree if the cost of a return line to the hot water is not a factor, and this is a new build, the separate return line to the hot is the best design. Just stopping the notion that hot water is being pushed into the cold line. It is the cold water in the hot water pipe that is being pushed into the cold line. Once a preset temp in the bridge is reached. the flow is cut off. If hot water is being pushed into the cold line, then the bridge thermocouple is defective. – Programmer66 Jul 10 '20 at 0:08
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No, it won't go into the cold - that is usually a hot loop back into the tank.

Another option is to have the hot water pipe sleeved with an electric water heater to keep the water at, or above, a given temperature.

You have to consider what priority you want - instant hot water with associated electricity use or a pump recirculating cooler water into the tank or into the cold.

Both will work.

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  • If you're using a bridge valve wouldn't it run the warmed water into the cold side. Unless I use a dedicated return. – Matt Winer Jul 9 '20 at 18:32
  • Is this designed by the builder or you? – Solar Mike Jul 9 '20 at 18:34
  • The builder will do it however the plumber does it or unless I request otherwise. They are suggesting a pump with a bridge valve at the furthest point. So the warming water would flow into the cold side via the bridge valve. I'm asking for them to do a dedicated return instead of a bridge valve so that while the pump is running it's only circulating hot water and not putting warm water down the cold supply to the sink. – Matt Winer Jul 9 '20 at 18:38
  • "recirculating cooler water into the tank" The question is about a tankless system. – Alaska Man Jul 9 '20 at 19:33
  • @AlaskaMan well I would be starting with solar water heating anyway... – Solar Mike Jul 9 '20 at 19:36

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