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Old 03-08-2018, 06:45 PM   #16
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Re: Tankless water heater recirc pump


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Originally Posted by ddawg16 View Post
My thoughts as well.

The idea behind a recirc pump is to take the hot water from tank and make sure the hot water lines are flooded with fresh hot water.

The tankless unit.....is well, tankless. It only heats up water when there is flow. Unless it's real sensitive, it's not going to sense the recirc pump flowing. If it does, it will be going on and off....I would hate to pay that utility bill. Ok....you have solar so you're not worried about it....until you see what the peak electrical draw does to your bill.

Being in SD, you would have been better off with a hybrid unit. It's basically a heat pump....heats up the same amount of water for about half the electricity. And, you could have also used solar heating. Small panel on the roof to pre-heat the water.

Then your recirc pump would have worked great.


Sorry....but I think you made a really bad decision going with the tankless
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Originally Posted by chandler48 View Post
Quote:
it's not going to sense the recirc pump flowing.
Why not? The water flows from the trecirculation unit to the furthest point and back. Once the unit senses the heat, it turns off. You can then use hot water on demand until you are through with it.
If you are going to quote me....make sure you do it correctly.

Typical recirc pumps have a flow rate of 0 to about 6 GPM.

Typical tankless units have a minimum flow of 1/2-3/4 GPM flow before they heat up the water.

Assuming the recirc pump is set up right, yea, it will work.

I'm also assuming the OP is using the type that pulls water from the hot side and pushes it back down the cold water pipe. Will it be able to get 1/2-3/4 GPM flow via the cold side?

But it sure seems like an expensive way to save water.
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Last edited by ddawg16; 03-08-2018 at 06:49 PM.
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Old 03-08-2018, 08:14 PM   #17
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Re: Tankless water heater recirc pump


I'd look into an electric 6 Gallon point of use water heater if power cost is not an issue. Place it near where you want instant hot water. If power cost is an issue, it can be placed on a timer and set to only run when you typically will be home. Feed the hot water from your thankless into it. The temperature difference from a couple gallons of room temperature water feeding into 6 gallons shouldn't have a noticeable affect on the temperature.
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Old 03-09-2018, 09:47 AM   #18
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Re: Tankless water heater recirc pump


Wow guys, some great feedback here, thanks.

So this morning I timed how long it takes for the water to get hot at the furthest point away from the tankless heater. I ran the Master Bathroom shower and it took 2mins 45secs before it was hot enough for a wimp like me :-) to get in. That's a lot of wasted water.

I'm thinking that the best option is a recirc pump local to the farthest point and have the pump run on a timer twice a day.
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Old 03-09-2018, 01:44 PM   #19
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Re: Tankless water heater recirc pump


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Originally Posted by welshie View Post
Wow guys, some great feedback here, thanks.

So this morning I timed how long it takes for the water to get hot at the furthest point away from the tankless heater. I ran the Master Bathroom shower and it took 2mins 45secs before it was hot enough for a wimp like me :-) to get in. That's a lot of wasted water.

I'm thinking that the best option is a recirc pump local to the farthest point and have the pump run on a timer twice a day.
technically Dawg is correct that pumping to 2nd story fixture
may not consistently cycle your tankless' minimum flow rate...

in which case you may have to install:
the higher priced Laing system and also provide electrical there
Or install a 6 gallon electric heater in series immediately down stream
of the tankless outlet with 3/4" ports and connect pump on hot outlet of
that tanked heater to compensate for the diminished flow rate or forego tank
& buy separate higher head rated pump & separate crossover sensor/components...

The good news with a tank & the Watts style system installed will be that the tankless will not cycle until you turn on a fixture but yet the hot water will be instant soon after pump cycles...
The bad news is a small electric tank should fail within 10-12 years...

this small tank will also absorb any cold water sandwich affects as well as not cycle when tankless is running if the thermostat is properly set below discharge temperature of tankless heater;
yes you will be maintaining 6-9 gallons of hot water via a 1650 watt element...
25 watt pump & 6 gallon tank should operate off a single 20 amp circuit with duplex outlet.


where is closest sink downstairs in relation to MB location?
if your baths are stacked I would definitely suggest you do a test
of pulling hot water to closest downstairs sink location,
then immediately go up to master & time how long it now
takes for hot water arrive at your shower...

All that said - may be that you can keep your energy footprint lower
& thereby not circulate any hot water through upstairs piping...
nor need the small 6 gallon tank nor buy a Laing system
that will cost 3 times more than the Watts... its a
given the Watts system & tank should cost the same as the Laing setup
so take your pick as to which route to take (pump with built in sensor crossover
vs an external crossover valve but with a limited life expectancy tank involved)
or install the 6 gallon tank upstairs (but this takes dedicated
space & needs to properly tie into the hot distribution piping)


Curious as to how long it took hot water to arrive with old 100
gallon tank setup since you are now taking almost 3 minutes?

Peace
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Last edited by DR P; 03-09-2018 at 01:46 PM.
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