Hot Water Sensor in Kitchen

[Greenthumb77]

Hello!

I put in a hot water recirc. pump and want to add a hot water sensor under the kitchen sink. It looked simple enough. However, when I look under the sink I saw an additional hose to the dish washer. The sensor valve has only 4 inputs. Do I hook this up the regular way and just not worry about the dishwasher hose. Or am I missing something here?

Big thx for any advice.

Jim

 

[Jadnashua]

Without seeing your exact configuration and the type of sensor, you'd probably be fine if your sensor only monitored the water feeding the sink. But, depending on where the DW taps off, you may be able to sense it before they break out.

 

[Sponsor]

 

[Terry]

If the kitchen sink faucet has hot water, the dishwasher will also.

 

[Phog]

Hi Greenthumb, can you tell us if the house is plumbed as a "home run" type system? And by this I mean: with separate lines for every single fixture and appliance, all connecting back to a manifold in your basement (often with separate shutoffs for each line)?

Or do you have a more traditional system, which would be a Y-connection under the sink, containing one line incoming into the cabinet and splitting off into two outgoing lines, one each for the dishwasher and the sink faucet?

 

[Greenthumb77]

Hi Greenthumb, can you tell us if the house is plumbed as a "home run" type system? And by this I mean: with separate lines for every single fixture and appliance, all connecting back to a manifold in your basement (often with separate shutoffs for each line)?

Or do you have a more traditional system, which would be a Y-connection under the sink, containing one line incoming into the cabinet and splitting off into two outgoing lines, one each for the dishwasher and the sink faucet?

Thx to everyone for the help. There is no better information than information from people on the ground.

The short answer is I have one hot water line coming to the kitchen sink and then a short one on the angle valve to the dishwasher. I did not know if putting a sensor valve on the hot and cold would somehow have to be joined to the dishwash line.

I have a single story with water heater on outside of house futherest away from kithen island. I believe it loops to the bathroom to far side of the house that is near the island and then to the kitchen sink. (With all the problems we have had getting hot water to the kitchen sink I think the original plumber and the inspector were together smoking something LOL) I installed a grunfros pump and a dedicated return line from the water heater to the far bathroom supply. The pump was initially set for a timed usage. It did not seem to get the water as hot as it should so I went to 100% on. We are stilll having some problems although it is better than without the pump and return line. So I thought this sensor valve might give me the victory.

Thx ahead of time for your advice.

Jim

 

[Reach4]

It did not seem to get the water as hot as it should so I went to 100% on.

Your water from the WH may be passing through a mixing valve at the WH. If that is the case, the piping can need to be more complex to work properly.

 

[Phog]

In addition to what reach said above, also consider insulating the hot water line from where it comes out of the water heater, all the way to the kitchen. But place *no* insulation in the sink cabinet.

Insulation will help ensure that the water in the pipe stays hot, instead of just warm, while it's waiting in the pipe. Leaving the insulation off under the sink (near the recirc sensor) will cause the pump to kick on more often, frequently refreshing the pipe with new hot water & not giving it a chance to cool down as much in the pipe.

Insulating pipe is an easy DIY job, they sell several types of pipe insulation at hardware stores specifically for this task. I like the black spongy foam stuff best but it's the most expensive. Fiberglass pipe wrap is cheap and will do the trick just fine, it is just itchy during installation

I do agree that you do not need an extra sensor for the dishwasher branch, since there's only a single line coming in.

 

[Reach4]

While insulating the hot pipes, it is usually recommended to also insulate the return pipe. That saves some fuel. Not as much as insulating the hot however.

 

[Dana]

In addition to what reach said above, also consider insulating the hot water line from where it comes out of the water heater, all the way to the kitchen. But place *no* insulation in the sink cabinet.

Insulation will help ensure that the water in the pipe stays hot, instead of just warm, while it's waiting in the pipe. Leaving the insulation off under the sink (near the recirc sensor) will cause the pump to kick on more often, frequently refreshing the pipe with new hot water & not giving it a chance to cool down as much in the pipe.

Forcing the pump to short cycle doesn't make any sense. If the control is set to an adequate temp it'll just do it's thing, but at a much lower cycling frequency than if the sensor is on a section of uninsulated pipe.

Insulating the full length of both the supply and return makes a lot of sense, and is required under IECC code on recirculation systems in new residential construction, often harder to fully implement as a retrofit. (See page 103. ) CA Title 24 and the CA plumbing codes both have a different set of requirements on pipe insulation than the IECC (and each other). I'm not sure if the return line must be insulated in CA the way it is under the IECC.

The insulation exception under IECC rules is if it's a "demand" system, that only turns on the pump if/when flow is detected or hot water is called by manual switch. But even with a demand type recirculation system at least the supply pipe would need R3 if it's 3/4" or larger.

 

[hj]

If what you call a "sensor" is what I think it is, it will NOT work with your dedicated return line. It is a "bypass" valve which uses the cold water system as part of the return line, and as such is completely incompatible with your system

 

[Phog]

Forcing the pump to short cycle doesn't make any sense. If the control is set to an adequate temp it'll just do it's thing, but at a much lower cycling frequency than if the sensor is on a section of uninsulated pipe.

I agree that short-cycling is not desirable. This may not be intuitive, but my suggestion is based on the assumption that the control reference (the temperature activating the recirc pump) is offset from the temperature in the upstream pipe (which is what the user really cares about).

For example, maybe the pipe passes on a long run through a cool basement, followed by a shorter stretch through a warmer area (like the back of a fridge) just before it hits the recirc sensor. The recirc now thinks the temperature is warm enough, while the balance of water in the upstream tube is in reality not. This sounds like what Greenthumb is describing.

By raising the temperature in the upstream pipe (via insulation) while keeping the final section untouched, now the temperature is more uniform throughout the pipe length & as a result the pump finds its proper duty cycle. That's not the same thing as short-cycling

I do agree that changing the temperature setpoint for the recirc would potentially achieve the same effect -- as long as the recirc temperature can be set high enough.

 

[Jadnashua]

Depending on how the piping really is run, you may need a return line from the furthest bathroom group and another one from the kitchen area.

 

[Greenthumb77]

In addition to what reach said above, also consider insulating the hot water line from where it comes out of the water heater, all the way to the kitchen. But place *no* insulation in the sink cabinet.

Insulation will help ensure that the water in the pipe stays hot, instead of just warm, while it's waiting in the pipe. Leaving the insulation off under the sink (near the recirc sensor) will cause the pump to kick on more often, frequently refreshing the pipe with new hot water & not giving it a chance to cool down as much in the pipe.

Insulating pipe is an easy DIY job, they sell several types of pipe insulation at hardware stores specifically for this task. I like the black spongy foam stuff best but it's the most expensive. Fiberglass pipe wrap is cheap and will do the trick just fine, it is just itchy during installation

I do agree that you do not need an extra sensor for the dishwasher branch, since there's only a single line coming in.

Thx guys!

As for the insulation, I have already insulated the dedicated return line. The house sits on a slab and the copper pipe is looped under it. If I did not have an island I would have had it re plumbed with pex, with the island it would very very expensive.

Summary

So based upon you guys advice do not need a sensor valve under the kitchen sink?

 

[Phog]

Greenthumb, it sounds like your incoming supply lines to sink are buried in the concrete slab & inaccessible? But, you have also separately installed a dedicated return line for the recirc, above the slab, & then insulated that line only? Is that correct?

My short response to your post is that you definitely DO need a sensor valve under this sink if you are not getting the water temperate you want. You can tee off to both the sink & the dishwasher (either upstream or downstream of the sensor valve, doesn't matter) and both will get recirculated hot water.

The longer response is that you do not need a dedicated return line for the type of sensor valve that you have shown in your picture. It is designed to push water from the hot line back into the "incoming" cold line, eliminating the need for a separate return line. To get the recirc system to function properly you need to have one (and only one) of those sensor valves on each main trunk branch. Also, if you have a dedicated recirc return line elsewhere in your system, it may actually interfere with the recirculation to other branches with sensor valves, such as your kitchen, depending on how it is plumbed.

And apparently I have misunderstood your previous posts -- I thought you *already* had a sensor under this kitchen sink, but were struggling to get it to work properly. Since you apparently don't have one there, start by putting one in, and see how it works. Get back to us if the results aren't satisfactory.

 

[hj]

You not only DO NOT need it, but it would be completely worthless and ineffective. In fact, it could create more problems than what you think it would solve. It is NOT compatible with a dedicated circulation pipe system.

 

[Phog]

You not only DO NOT need it, but it would be completely worthless and ineffective. In fact, it could create more problems than what you think it would solve. It is NOT compatible with a dedicated circulation pipe system.

It's a little unclear what you mean by "it" -- the sensor valve, or the recirc line?

The Grundfos pump that greenthumb said is installed is part of an integrated system that eliminates the need for a recirc loop. The pump is intended for use with the Watts valve in the picture.

https://www.freshwatersystems.com/specifications/L-UP-TL-043.pdf

If there is a dedicated recirc line installed, (aside from being unnecessary), it very much depends on exactly how that recirc section of the system is plumbed to know what will happen. There are a couple different ways it could have been installed and each would have a different result.

And in any case, adding a sensor valve at the kitchen should at worst require a tweak of the timer setting in the Grundfos pump but that's it. And it might actually fully fix the problem.

What would be really helpful is system diagram showing the branches of the hot & cold plumbing, the recirc loop, and the location of any sensor valves. And also a picture of how the installed sensor valves are connected to the hot/cold/recirc lines.

Greenthumb, if you can provide that I am confident we can get everything working to your satisfaction.

 

[hj]

quote; It's a little unclear what you mean by "it" -- the sensor valve, or the recirc line?

Actually, it could refer to EITHER, depending on where, and how, the pump is installed. But, based on what he has written previously, I meant the "sensor valve", but it is NOT a "sensor" it is a thermostatic bypass valve.

 

[Jadnashua]

With a recirculation return line, several things must be considered:
- you don't want the flow to be too fast...IOW, you don't want or need a huge pump as it takes more power, can tend to become noisy, and can literally wear out the pipes and shorten the life of the WH
- you do need a check valve to prevent sucking water from both the hot and return line at the same time when drawing water. AFter you've used some hot water, the bottom of that tank where the return usually goes will be cold, or at least tepid. Without a check valve, you'll be sucking it from both pipes, diluting your hot water.
- you want the lines insulated
- depending on the layout, you may need more than one return line so water will flow to each fixture, or at least close enough to minimize the waste and time to get it there
- for economy, it can help if you have a thermostatic control to stop the flow
- water will take the path of least resistance, so if you do end up with multiple loops, you may need balancing valves so all get hot water.
- sensing the water temperature at the fixture can be less expensive than back at the WH, since you don't normally need the return line to be fully hot..just hot at or close to the point of use.
- if you're using a tempering valve, unless you're running hot water, the tempering valve may allow full hot out into the hot line...IOW, it may not be able to actually temper that water coming out of the tank. some tempering valves have a port on them for use with a recirculation system to overcome that problem. When drawing hot water, some cold goes into the tank, and some will mix with the hot to the house, limiting the maximum outlet temperature. WHen recirculating...there's NO flow in from the cold line to the WH, so there's no tempering action. It will either block flow, or let all hot from the tank out. If it has a recirculation port, the cooler, recirculation water will temper the outlet. Running the pump constantly without a sensor in the system would eventually get that hot line the same temperature as the WH, and that may be too hot per code. Returning the water to the bottom of the tank may not work properly without some futzing around if you have a tempering valve. You could simply put a T in before the tempering valve for it verses going into the bottom of the tank.

The system I have, once it gets things primed after the first timer activation of the day, only needs to run maybe 1-minute 4-5 x per hour to maintain it since I was able to insulate most of the pipes. Some systems run the pump constantly and use sensors at the point of use (POU) to block it once hot there, some just have a sensor that remotely turns the pump off (this can get more complicated if you need or want to sense at multiple locations), and, there are options about where to actually install the pump. The most common place is back at the WH since you often have power readily available, but the simpler way, is to put the pump and control at the POU. In my case, everything was a short run off of a main line, with the upstairs vanity the last POU. It was easy to drop a line down, install a receptacle from the one above the vanity into the cabinet, and once there, it took all of about 10-minutes to install it. Mine's been running fine for about 13-years now with no problems or maintenance. It has an integrated check valve, pump, and sensor in a small box. You could use either the cold line as the return, or a dedicated one. I can only hear it if I really am listening for it, but some will put it at the WH to avoid any possibility of that. It does take up a little space underneath the vanity, but that hasn't been an issue for me. It would have been a major pain to use a dedicated return line. I find that flushing the toilet essentially flushes all of the hot/warm water out of the cold line. Part of that is the way I have mine adjusted...it has an adjustable aquastat (most don't) that I set to get that vanity warm. Since everything else in the house is before it, those are hot, and hot's not far away, but I usually don't need immediate full hot at that vanity. Warm works just fine to wash my hands.

 

[Greenthumb77]

Update

My gas water heater needed to be replaced. My neighbor suggested I get a on demand Nevian with a recirculation pump built into the system. I took his advise, keep the dedicated return line, and removed the Grunfros pump. Since doing this it takes 5 minutes to get hot water from the on demand to my island sink. What a mess! Maybe I need to have him replace the Nevian on demand with a pump and get the one without the pump and then put back the Grunfros. At least then it might work like it did with the regular hot water heater.

Any ideas?

Also, I am tired of this problem. The plumber who plumbed the house at inception did not do his job. Is there a way I can have a repiper just repipe the island with pex? If this can be done can it be done with our cutting the slab floor. I read somewhere that sometimes 3/8 pex is slide inside the 1/2 inch copper so the slab does not have to be cut.

Any ideas and wisdom would be muchly appreciated.

Thank-you

Greenthumb.

 

[Jadnashua]

I've not tried it, but if there are any fittings on the copper pipe, you will not be able to slide pex through it, and, while pex tubing is smoother on the inside, the ID of 3/8" stuff over any distance, will add a lot of dynamic pressure loss versus 1/2" copper. If there are any burrs on the ends of the copper that weren't dealt with, it will score the tubing, which also is not a good thing. If there's no pole or other support from the ceiling to your island, about the only way to replumb it is to either add one and run the pipes through the attic or second floor and come down, or tear up the floor to run new lines.

I've not investigated how the tankless systems with a built-in recirculation pump actually work. Using it in combination with an external recirculation system may not flow enough volume to turn the tankless system on, which complicates things, but MIGHT work.