Designing Expansion PEX Layout and Brands to Use

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Tuttles Revenge

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For an application like this, what are the pros and cons of a dedicated 24' long return line, vs a point of use pump that dumps the hot water back into the cold line?
I've not much experience with the pumps used for dumping hot into the cold tho I do have one specified for an upcoming project. But if feasible a dedicated return is just the best way to keep the hot side hot and the cold side cold. And if they're repiping anyways an additional tube run is minimal work.

If the pump is manually activated, is there any concern about stale water in the recirc line if it doesn't recirculate for weeks or months for some reason?
Yes, just the same as that powder room that may never get used. Open heating systems are supposed to be setup to cycle 15 minutes at least once a day.. or something to prevent stagnation. So perhaps a control that cycles the pump periodically if a manual button were used. I still prefer the aquastat which is going to cycle the pump periodically and incedentally prevents stagnation.

How about pump location with a dedicated return line? If the pump is near the lav, and only runs until hot water reaches the pump, then I don't see any energy cost to the recirculation (other perhaps than foregoing washing your hands with cold water). The water going into the recirc line would otherwise have gone down the drain.
I'm sure theres an energy cost / benefit.. but I only consider the convenience when selling and designing a recirculating system.

If the pump is at the water heater end of the recirc line, and runs until it sees hot water, then I think the standby losses of the 24' of hot water line to the full bath get doubled. Of course, this is more about pump controls location than actual pump location.
Something I've never tried, but it makes sense. But pumps are noisy so to keep from getting sued, I like them in a mechanical room.

Lastly, how about pipe sizes in the diagram above? I can see supplying the kitchen sink with a separate 1/2" line from the tank, as it's so close. And the spur to the half-bath is 1/2". Is 1/2" adequate for the supply to the full bath, with an extension to the washer? Or a 3/4" supply to full bath and washer, with a 1/2" return line?
Yes, each branch could be 1/2 from the loop. Not sure how they're working the un-crawl area, but I'd feed that spot with 3/4 from the loop and half to the laundry

Just thinking this through out loud.
I believe its always a good idea to bounce ideas off other people. everyone adds their experience and expertise.
 

Jeff H Young

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24 foot return line is not a long way the tubing is cheap, the labor little, and the results of a proper system will be well received by the "Boss"
 

Taylorjm

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Yeah, but my reference was to the failures of the uponor brand of pex. The only time I've seen copper leak is if it freezes. I've worked with my father who was a plumber/pipefitter for over 30 years and he's just now coming around to pex, and so am I. Until then, it was copper all the way and none of those push fittings. To us, pex and anything with push fittings was for people that can't sweat a joint. I wouldn't have a single concern with any of my copper sweat joints or piping, but pex is scary especially with the uponor brand having failures and repiping homes. I just put in some 1" pex from my well to the bladder tank, water filters and softener. I had over 30 joints with all the valves and bypass loops for the filters and each joint was less than a minute compared to all the time spent cleaning, flux and soldering fittings. I just hope the brand I use isn't one that all the sudden fails in 10 years.
 

Reach4

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but pex is scary especially with the uponor brand having failures and repiping homes.
The problem was with the colored stuff with the coloring on the outside. Red and blue. Apparantly no problem with the "white" translucent kind. They also offer white with red or blue ink.
 

Wren

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I suppose that it boils down to is whether it is worth it to put in a recirculator pump for a shower that is 26' from the water heater. If I use 1/2" pipe, how much water will be saved by not having to wait on hot water for the shower vs. how long it would take to get hot water to the shower if no pump were used?

If I install a system, I would be interested in one that uses a return to the water heater. Using the cold water line as a return doesn't occur to me as a good idea because that cold line would be filled with water that had been in the water heater. That's not the most appealing idea for drinking water or for brushing teeth.

I like the idea of a push button system with return. Maybe something that cycles the pump for a minute then turns off that could be actuated when entering the bathroom.

What are some good manufacturers/models to look for?
 

wwhitney

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I suppose that it boils down to is whether it is worth it to put in a recirculator pump for a shower that is 26' from the water heater. If I use 1/2" pipe, how much water will be saved by not having to wait on hot water for the shower vs. how long it would take to get hot water to the shower if no pump were used?
1/2" PEX has an ID of 0.475" per random website. A 26' length has a volume of 0.032 ft^3 or 1/4 gallon. So you'd save 1/4 gallon. If your showerhead is 1.8 gpm and you empty the lines by going full hot, that would take 8-10 seconds (depending on your water heater temperature and thus the max % hot that your shower valve is set to to ensure a maximum shower temperature of 110F).

Cheers, Wayne
 

Wren

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I did some figuring and came up with this layout. I would like to wire in the pump so that it comes on when the bathroom light is on unless there's some compelling reason not to. I like the idea of the pump only running when someone is in the bathroom and not circulating hot water continuously through the house that adds to the heat load in the Summer that our HVAC has to work against.
I didn't include the half bath in the circulation loop as it's close to the water heater and it will seldom get used. As for the kitchen sink, it's right above the water heater so there's no need to include it.
Any feedback and/or suggestions would be appreciated.
Thanks!

Iwreffp.jpg
 

Too Ambitious

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I'm also looking at a recirc pump whenever I get around to repiping. Two options I'm considering are:
  1. Dumb pump plugged into a smart outlet. Gives the most flexibility and best efficiency since it only runs when needed. Can be triggered with occupancy sensors, switches, scheduled, geofence, etc. etc. I can figure out how long it takes to get hot to the farthest fixture & set it to turn out for that amount of time when triggered.
  2. Grundfos pump with temperature sensing. The less complicated option. Won't be as efficient. But with insulated lines in an encapsulated crawl space + heat pump water heater, maybe it won't be that bad.
Problem is my water heater is on one end of the house, and the ensuite addition bathroom is on the complete other side, around 50' away.
 

Wren

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I've decided to definitely install a hot water recirculation system for the full bath. I may add the half into the loop, but I fear that there might not be a real advantage in doing so. I'm mainly curious about the pump I'm considering.

The supply and return line (green in the photo) will be 3/4" with a manifold in the plumbing wall. I want to use a switch operated pump instead of a timer or sensor-controlled one. I found this Grundfos model UP15-10BUC7 that I believe will work well. Here are the specs:

Max Pressure (PSI): 145
Temperature Range (F): 36°F - 230°F
Connection Size: 3/4"
Connection Type: Union
Max Flow (GPM): 6.6
Flow Range (GPM): 0-6.6
Head Range (ft.): 0-6.6
Max Head (Ft): 6.6

I'm planning on having the return line (green line in drawing below) enter the water heater at the bottom using a tee fitting on the drain bib. I believe this pump has a bleeder screw to allow one to purge the air from the system. I was planning on mounting it vertically in the pipe that goes down to the drain bib or if that's not a good idea then somewhere near the water heater.
Does anyone see any problems with this pump or layout?

EDIT: From doing a little research, it seems that having the return loop enter at the drain bib might not be a good idea and that the return loop should enter the water heater on the cold inlet side with a backflow preventer valve in place to keep it from entering the cold supply. Which is correct?

Here's a photo:

59896241-4.jpg




Here's a photo of my layout:
Iwreffp.jpg
 
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John Gayewski

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For an application like this, what are the pros and cons of a dedicated 24' long return line, vs a point of use pump that dumps the hot water back into the cold line?

If the pump is manually activated, is there any concern about stale water in the recirc line if it doesn't recirculate for weeks or months for some reason?

How about pump location with a dedicated return line? If the pump is near the lav, and only runs until hot water reaches the pump, then I don't see any energy cost to the recirculation (other perhaps than foregoing washing your hands with cold water). The water going into the recirc line would otherwise have gone down the drain.

If the pump is at the water heater end of the recirc line, and runs until it sees hot water, then I think the standby losses of the 24' of hot water line to the full bath get doubled. Of course, this is more about pump controls location than actual pump location.

Lastly, how about pipe sizes in the diagram above? I can see supplying the kitchen sink with a separate 1/2" line from the tank, as it's so close. And the spur to the half-bath is 1/2". Is 1/2" adequate for the supply to the full bath, with an extension to the washer? Or a 3/4" supply to full bath and washer, with a 1/2" return line?

Just thinking this through out loud.

Cheers, Wayne
A pump that goes on and of and on and off is a pump that won't pump for half as long as a tiny well built pump thay hums along delivering hot water at any point at any time. Insulation on the hot side of recirc system is worth its weight in gold. Standby losses in my opinion are more of a talking point rather than a factor. Unless someone is trying to achieve a very specific goal that is.
 

John Gayewski

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I've decided to definitely install a hot water recirculation system for the full bath. I may add the half into the loop, but I fear that there might not be a real advantage in doing so. I'm mainly curious about the pump I'm considering.

The supply and return line (green in the photo) will be 3/4" with a manifold in the plumbing wall. I want to use a switch operated pump instead of a timer or sensor-controlled one. I found this Grundfos model UP15-10BUC7 that I believe will work well. Here are the specs:

Max Pressure (PSI): 145
Temperature Range (F): 36°F - 230°F
Connection Size: 3/4"
Connection Type: Union
Max Flow (GPM): 6.6
Flow Range (GPM): 0-6.6
Head Range (ft.): 0-6.6
Max Head (Ft): 6.6

I'm planning on having the return line (green line in drawing below) enter the water heater at the bottom using a tee fitting on the drain bib. I believe this pump has a bleeder screw to allow one to purge the air from the system. I was planning on mounting it vertically in the pipe that goes down to the drain bib or if that's not a good idea then somewhere near the water heater.
Does anyone see any problems with this pump or layout?

EDIT: From doing a little research, it seems that having the return loop enter at the drain bib might not be a good idea and that the return loop should enter the water heater on the cold inlet side with a backflow preventer valve in place to keep it from entering the cold supply. Which is correct?

Here's a photo:

59896241-4.jpg




Here's a photo of my layout:
Iwreffp.jpg
You want the return line to enter the bottom of the water heater. Not the cold inlet.
 

John Gayewski

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About 50 feet if I only include the full bath, and about 75 if I include the half bath.
You need to look at the pump curve. You have 4.5 ft. of head. What gpm does that pump at with 4.5 ft head?
 

wwhitney

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You need to look at the pump curve. You have 4.5 ft. of head.
Question: how did you come up with 4.5 ft of head? If just pumping around a loop, of a given (equivalent) length and fixed inner diameter, I would think the head the pump sees is just the frictional losses in the pipe. Which depends on the flow rate, so you'd need to take the two curves and find their intersection. But I've never actually had to select/check a pump before.

Second question: when pumping through a big water heater tank, does that add any head? Or is it negligible and you can just look at the piping length?

Thanks,
Wayne
 

John Gayewski

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Question: how did you come up with 4.5 ft of head? If just pumping around a loop, of a given (equivalent) length and fixed inner diameter, I would think the head the pump sees is just the frictional losses in the pipe. Which depends on the flow rate, so you'd need to take the two curves and find their intersection. But I've never actually had to select/check a pump before.

Second question: when pumping through a big water heater tank, does that add any head? Or is it negligible and you can just look at the piping length?

Thanks,
Wayne
Right. 75 ft. of pipe creates 4.5 ft of head. 75×0.06=4.5

That it's just a general multiplier used to approximate head. There is a much much more complicated way to do it that will get a more precise number. But the difference is negligible enough the industry (hyronics) uses 0.06. That figures in elbows and other restrictive devices such as a water heater or boiler.

For a run of pex with no fittings one could use 0.03. But remotely sizing a pump I use the better safe than sorry 0.06.

A pump curve should have the gpm along one axis and the head along another axis. If given a head OR gpm AND a pump you can easily find the third variable which is provided by the pump manufacturer.
 
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