Demand pump or small HWT for far bathroom?

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Brianslink

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I'm building and now in sheetrock phase. I have a long DEDICATED run from HWT (not tankless) to far bathroom (approx. 75' of 3/4 inch pex). My plan was to not have a dedicated recirculating line and install a Metlund D'mand pump or similar type pump with the diverter valve to dump into the cold side. I'm not sure of how I will like luke warm water in the cold line though. Maybe you guys could comment on this? I'm also here to ask about the possibly another alternative to this.

FYI This bathroom will be used by 3 people and it has a tub/shower + toilet + two sinks.

I'm wondering about doing an electric 2.5 gal hot water tank (not tankless) under the sink instead of the demand pump. I already have a dedicated 110v under one sink. Obviously I'm not going to supply this entire bathroom with the 2.5 so I would use the hot line coming from main HWT as the supply for the 2.5. I calculate 1.5 gallons of cold water would be sitting in the 3/4" pex pipe. When the little 2.5 gal tank runs out will enough hot water have will have entered from the main HWT to keep from getting a cool water blast?

Thanks in advance for your advice!
 
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Jadnashua

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I have had a RedyTemp unit installed now since around 2005. I have it on a timer so it only runs when I'm likely home, but there are other ways to run most of these, including that one. I bought it because it allows you to adjust when it shuts off. I have mine adjusted so that the water is just warm, not at all hot, but my shower tap off is closer to the WH than the sink where I have this unit. I find that a flush of the toilet and I've also flushed out the vast majority of the warm water in the cold pipes. From an energy viewpoint, you'd need to run the small WH 24/7 and be adding heat to the room all of the time. The recirc won't do that. Try to make sure you've insulated all of the hot water lines you can access - it will make a difference in both comfort and economy.
 

Brianslink

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Jadnashua, thanks for your input. I just finished looking at the RedyTemp website and I like what I am reading. Which model do you have? Also, I never thought about a HWT adding unwanted heat load to the bathroom. That's exactly why I asked my question here because I get experience and knowledge. Thanks.
 

Jadziedzic

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If you can install a dedicated return line now by all means do so. The recirculating pumps available now - particularly the Bell & Gossett (or Laing) "ecoCirc" series - use very small amounts of energy and can be outfitted with thermostatic controls and/or timers.
 

mangoManFT

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I have two D'MAND (Metlund) recirc pumps in my house. One uses a dedicated return and the other sits under the sink and uses the cold water for the return. I would recommend an insulated dedicated return if you can do it. If you use the D'MAND system, also run a control wire along with the dedicated return so you easily wire up the push-button activation at your sink (assuming the pump will be at the hot-water heater).

I have a portion of my return line in the attic, and in the summer it gets hot. Since the D'MAND system shuts off when it detects a temp rise, the pump will turn off after only running a few seconds as that hot plug of water in the attic hits the pump. After a few seconds, I can hit the button again and it will run again, usually completing a full recirc cycle, but sometimes a third button press is required. Something to think about if you run the return thru the attic.

The pump that uses the cold water return shuts off as soon as the temp rises at the sink where the pump is located, so I don't usually have a problem with hot water in the cold line. However, the water at the hot tap is not fully hot either, and this is after adjusting the shut-off temp higher. The one with the dedicated recirc line doesn't have this problem since the hot water is cycled all the way back to the water heater, so the water at the tap is fully hot.

Finally, I had a somewhat unusual situation with the pump using the cold water return that caused a problem that was a pain to solve. I explain that in this thread: https://terrylove.com/forums/index....ecirc-pump-sprinklers-and-check-valves.56982/.
 
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