School me on hot water recirc?

[Caver Dave]

Tldr; In the middle of a total bathroom gut, the (overhead basement) plumbing shows numerous signs of multiple repairs AND shenanigans... like 1/2" copper feeding galvanized sections and judicious use of plastic compression fittings. All said, gonna redo all the water supply from pneumatic tank to endpoints (sinks/crapper/shower)...

Have the PEX tools, so thinking 3/4" "mains" (cold & hot) to 1/2" individual supplies...

Then wondered about recirculating the hot water (40' max run to furthest sink/dishwasher) with bath between there and water heater.

@shawn has stated (in 2015) a pump will use more juice than saved by letting the water run xx seconds to get hot to that point... just wondering if still the case?

 

[fourtrax]

A recirculate pump is more of a convenience. if your pretty consistent with your water schedule you could us a timer on the pump and just have it run when needed.
You could even use a motion sensor so when you walked into the bathroom or kitchen the pump would circulate for a couple minutes then kick off. pump doesn't need to run all the time. adding insulation to the hot water pipes would also help keep the pipes warmer longer.

 

[CasterTroy]

A residential recirc pump will pull about 14w
That's like burning a LED bulb in a lamp.
You won't notice a difference in a monthly bill.
To mitigate that you can place it on a time clock with multiple options. I.e. 5am-8am then 4pm-9pm M-F and 6am-10pm sat/sun
OR place it on a switch that you flip on when you wake up and go make coffee before your shower. Lots of options.
The best thing about this post is ditching the galvanized piping.

 

[orange150]

A residential recirc pump will pull about 14w
That's like burning a LED bulb in a lamp.
You won't notice a difference in a monthly bill.
To mitigate that you can place it on a time clock with multiple options. I.e. 5am-8am then 4pm-9pm M-F and 6am-10pm sat/sun
OR place it on a switch that you flip on when you wake up and go make coffee before your shower. Lots of options.
The best thing about this post is ditching the galvanized piping.

 

[DSM Turbos]

When we did our tankless they said you have it set on a timer to work at certain times. That seemed dumb to me so I didn't look into any further than that.

 

[RatLabGuy]

Just crank up the water pressure, then you'll get hot water faster...

 

[Shreddinlettuce]

You need a dedicated return line from the furthest faucet that goes back to the tank at the cold side with a check valve so the warm return water doesn’t enter the cold pipes, there is a weird doohickey they make that ties a cold and hot line under the sink, but it’s not very effective. Luckily with pex it’s really easy to make a return line since you can flex it around instead of needing elbows at every turn

 

[Caver Dave]

A residential recirc pump will pull about 14w
That's like burning a LED bulb in a lamp.
You won't notice a difference in a monthly bill.
To mitigate that you can place it on a time clock with multiple options. I.e. 5am-8am then 4pm-9pm M-F and 6am-10pm sat/sun
OR place it on a switch that you flip on when you wake up and go make coffee before your shower. Lots of options.
The best thing about this post is ditching the galvanized piping.

The galvanized is the least sketchy AF! The random combination of sweated joints and whacky compression fittings... I'd assumed the compression fittings were repairs? Regardless, breath on the copper lines now and they start weeping

@CasterTroy appears you might have such a pump... brands you like?

You need a dedicated return line from the furthest faucet that goes back to the tank at the cold side with a check valve so the warm return water doesn’t enter the cold pipes, there is a weird doohickey they make that ties a cold and hot line under the sink, but it’s not very effective. Luckily with pex it’s really easy to make a return line since you can flex it around instead of needing elbows at every turn

Yeah, my brother has one of those "things" under a distant sink and IIRC, isn't exactly thrilled/convinced it's doing shiite.

Was planning on a dedicated return from furthest branch... just wondering if I should keep it 3/4" or drop to 1/2"?

Given the amount of hard 90's (dozens) a 10-15# pressure drop wouldn't be a shocker... so hopping the sweeping pex 90's allow better flow?

Then there's ye old rusty shitstack... coming out as well

 

[OnlyOneDR]

The most distant faucet in my house is the kitchen sink and dishwasher. The location and the fact that it is on an exterior wall under a window and over a slab meant that a recirculation line was going to be a difficult proposition.

Instead I put a 2.5 gallon point of use water heater under the kitchen sink and get hot water instantly all the time. It is fed by the hot water line (40 gallon tank heater) so sometimes the temperature dips slightly if enough cold water dumps into it but more than tolerable. I did something similar with the bathroom addition years ago but that is a 20 gallon, also fed by the 40, so it never has that dip.

I am on a well so I do not meter the water consumption but I can assure you that we waste a lot less water because we never have to run it to wait for hot water. For me that offsets the obvious energy loss by having three tank heaters in the house.

 

[shawn]

You might could set it up like a gravity fed boiler system, no pumps needed. I probably wouldn't worry about the pump operating cost. The recirc system doesn't really make a difference for something like a shower or tub just because of the gpm rates involved (unless your runs are super long), but it's super nice for the sinks in the winter.

Keep in mind that pex crimp connectors are more restrictive than any nominally same-sized water pipe. It doesn't sound like any of your runs are long enough to make a huge difference, but it's a good reminder to minimize fittings and carry bigger pipe to branches than you might with copper. If you're borderline, size up.

keep it 3/4

If trying for a gravity system, bigger is better. If pumping, doesn't matter.

 

[CasterTroy]

@CasterTroy appears you might have such a pump... brands you like?

B&G
Grundfos
Armstrong

Top 3

 

[Hurley]

Do it! I did my setup at the same time as a water heater replacement. Got a grundfos running continuous, label says 4w power consumption. My master bath is on the opposite end of my house from the water heater, and with the return tee'd from that end I've got 4 seconds until full temperature water at that bathroom's shower (which is just the branch line volume off the main). I covered both lines with the 1" black foam insulation as well. 3/4" main and 1/2" return (PEX)

Based on what I've read, the under-sink arrangement is less than stellar. I've got my recirc pump mounted a few feet before the water heater in the loop (coldest location in direction of flow), with a check valve.

 

[Shreddinlettuce]

grundfoss is my recommendation

The doohickey under a sink is called a bridge valve, I have one setup that way and it is pretty much worthless. Will be redoing mine this summer

 

[jeepinmatt]

Keep in mind that pex crimp connectors are more restrictive than any nominally same-sized water pipe. It doesn't sound like any of your runs are long enough to make a huge difference, but it's a good reminder to minimize fittings and carry bigger pipe to branches than you might with copper. If you're borderline, size up.

I wish the guy who plumbed my house would have understood that. Trying to feed a 4br/3.5ba house through a 3/4" pex line at 150ft from the well is bad enough. Dropping everything except the tub down to 1/2" after it was in the house was even dumber. I reworked a couple areas it was so bad. I remember one section feeding the kitchen sink going from like 25 fittings down to 15, and using less toob. Went from a 45 second hot water delay to less than 30 seconds. Had I realized how bad it was before we moved in, I would have kicked him off the job and hired someone else.

 

[Caver Dave]

Keep in mind that pex crimp connectors are more restrictive than any nominally same-sized water pipe. It doesn't sound like any of your runs are long enough to make a huge difference, but it's a good reminder to minimize fittings and carry bigger pipe to branches than you might with copper. If you're borderline, size up.

Happy to go 1" ???, but figured the 1.25" black poly pipe from the well, and 3/4" thru the filters (cyclonic> 40mic> 15mic) had already "restricted" it enough that 1" mains wouldn't

If trying for a gravity system, bigger is better. If pumping, doesn't matter.

Give me the kindergarten version... assume it's a circuit/loop from furthest supply back to DWH with a checkvalve feeding back into the cold side (others Tee into the drain)?

 

[shawn]

Happy to go 1" ???, but figured the 1.25" black poly pipe from the well, and 3/4" thru the filters (cyclonic> 40mic> 15mic) had already "restricted" it enough that 1" mains wouldn't

I ran 1" from the pressure tank to the kitchen to both sinks. Stubs for each sink are 1/2". Tee'd from there headed north/south. 3/4" supplies south serve half bath and laundry. 3/4" North to WH and two full baths. Hose bibbs are on a separate 3/4" system with its own filter.

Give me the kindergarten version... assume it's a circuit/loop from furthest supply back to DWH with a checkvalve feeding back into the cold side (others Tee into the drain)?

Yup. I've never done it, but heard people do with success. The cost of recirc is in the extra pipe, fittings, and pump (and possibly labor). The ongoing cost to run the pump is minimal. Neat to think you can do it passively, though.