Takes too long to get hot water

jan1227

I just built a new house in NC and my builder installed a Rinnai tankless water heater (gas). I have no problems in my bathrooms but it takes over a minute to get hot water at my kitchen faucet and it never really gets hot enough to do dishes. Once I turn the faucet off for a minute and try it again, I start all over again with cold water. All I'm doing is wasting water. I will add that my house is build on a concrete slab so the water travels through this concrete about 50' to my kitchen sink from the tank. I need some suggestions on a fix for this? It there something available that could go under my kitchen sink to make the water hotter, quicker? My plumber is suggesting putting a hot water tank in my garage with a recirculating pump yada yada and this fix is going to cost me $1600.00. It seems to me that there has to be a better way as I already HAVE a hot water tank.

Dave H_2

I would just add a recirc pump under the sink. If you already have a disposer here at the kitchen sink, then you already have power. The kit comes with everything you need. Your water heater can handle this. Lots of these tankless units would require the storage tank when adding a recirc pump, but this system is a little different, use the 008 model http://www.taco-hvac.com/products/systems/instant_hot_water/genie/index.html

Dave H.

Rich_49

Using the installed cold water line certainly does work . It is not complicated at all . You enter bathroom , kitchen wherever , motion sensor or on demand switch engages pump and uses cold water line to return the cold water in the line to point of roigin . What is so complicated ? Sometimes it is just that simple . Have many of these retrofit systems with a diverter type tee under farthest fixture . Simple and effective . It's not always about price . does everyone need an electric water heater under their sink and risk the incidence of relief valve release ? Another water heater installed due to poor planning is just more poor planning . Someone was already cheap once , let's not perpetuate the folly .

Bob Bona_4

Dave's idea is great, and Grundfos's Comfort System with the diverter T/pump is another excellent choice.

hot_rod

But on a slab system like this, wouldn't the "pumped" bandaid fix take almost as long as running the faucet? It's the cold slab, in this case that is the issue

Those recirc thru the cold piping just seem to swap problems. Now you need to run the cold water for a minute to flush the hot out if you want cold at then tap?? The motion sensor no doubt helps limit how warm the cold line gets. Probably is less water down the drain, but still a compromise system.

I think Hatters idea, in this instance is a better solution, if small quantities of instant HW is the goal.

BobC

That water line shound not have been run through the slab. Either a new line has to be run out of the slab or a water heater has to be installed near the problem sink.

be thankful it's not the bathroom with this problem.

Bob

hot_rod

The dishwasher probably has a water heater function, it's good to use that to sanitize anyways.

Usually 103°- 105 is all you can put your hand in. If the tank under the sink is at 120° f (code compliant) 6 or 7 gallons under the sink would be plenty to fill both sides of a sink. The more water that is used at the faucet, the warmer the supply gets, as it warms it's way thru the slab.

Jack

What model Rinnai? There are, depending upon model things you can do.

jan1227

The model #RU98e (REU-KB3237WD-US) and I am being told that the suggestion by Dave H to add a recir pump under the sink would void my Rinnai warranty???

jan1227

Also, I have turned the temp up and it makes no difference in the amount of time I wait for hot water to get to the kitchen sink and dishwasher and the water is then way too hot in the bathrooms. I have to let this water run for at least 2 minutes to get it so I feel it's hot enough to do dishes, yet I can still comfortably put my hand under it so I know it's still not hot enough.

Jack

Re-reading the whole thread this morning I am siding with HG on this. The problem is the heat loss from the mass of the floor and length of run in the slab. I can't imagine running a hot water line in that way without some very $pecial treatment. The range of options is covered in this thread, but again concrete never saw a btu it wasn't willing to absorb. It is unfortunate you find yourself in this position with a new home and installation. Recirc on Rinnai's does not void the warranty...If the recirc is done correctly. There is a right and wrong way not only on hot water lines but recirc as well.

jan1227

Well I went with the plumbers suggestion and now have an additional hot water tank in my garage and something under my kitchen sink. I now have hot water much quicker but it created a problem with the cold water. It now takes forever for the cold water to get cold. I also am finding that the instant hot water that I am getting doesn't stay hot very long. Looking for suggestions as to why I'm now having an issue with the cold water along with why I am running out of hot water? I think this fix just created additional problems

hot_rod

What exactly is under the sink? A valve, a pump, a tank?

Recirculating through the cold line is not a good way to fix this problem, especially with a slab. You just moved the problem from one pipe to the next, possibly both.

Did you suggest to your plumber a small tank under the kitchen sink? Doesn't sound like that is what you got?

ChrisJ

I would've installed a 20 gallon electric heater under the sink or as close as possible and likely stopped using the hot water line that is heating the slab.

Problem fixed.

Sometimes KISS is best.


That said, I read a lot of the comments and I can't agree with many. The homeowner wants hot water at their kitchen sink. This isn't too much to ask. I like 130-140F at my faucet as does my dishwasher and even though the dishwasher does have a calrod heater, feeding it hotter water allows it to finish much faster.

If you think 103F is sufficient at a kitchen sink you've never washed a cast iron skillet.

njtommy

I think you've been ripped of twice now. Like every one stated above a small hot water heater would of done the trick under the sink.

I can't believe they wouldn't of insulated the lines under the concrete, but after being in the trade I will almost believe anything.

jan1227

Well the good news is - I did fire the plumber and had him come back and take the hot water tank, pump etc with him so at present I'm not out any money. I also contacted Rinnai and they are telling that I should only lose about 10 degrees as the hot water flows through the concrete. I am losing much more. I want the water at my sink to be at least 130 and I'm lucky if I get 105 with the tank set at 140 so obviously either something is wrong or Rinnai is way off base. I am back to the drawing board with the suggestions above but now have to find another plumber.

jan1227

I'm not sure if the lines are insulated or not but every time I suggested a small tank under the sink - I was told that this wouldn't work.

njtommy

I'm not sure if you have city water or well water either. The temperature rise from your tankless unit may never reach the 130-140 supply temp even for your showers. Due to what the max water temp and flow rates acrossed the unit is.

If the tank is sized properly for under your sink I don't think you would have a problem.

If the tank is piped in line or in series with the tankless unit. The under sink hot water would only have to bring the water temperature up 30-40 degrees assumeing your getting 100 dgrees out of the tankless unit. If sized wrong you could be getting what is called a "cold water Sandwich". The water will be hot then go cold and back up to hot again.

And remember tankless isn't instant hot water. You have a long run of cold water to get rid of first. It's normal to wait a min or two for hot water.

I hope this helps.
Where at in NC are you?

jan1227

City water, Wilmington, NC.

4Johnpipe

May be a silly question...Has any of the plumbers or you attached a long flexible supply line to the hot side valve under the sink and fill a pail of water to check temperature that way? You may have an issue with the faucet mixing temp if it is a single handle style.
Also I had a slab situation a few years back with a problem with temperature at 1 sink. I found a bad washing machine valve (in the washer not the wall). I closed one of the supply valves to the washing machine and presto hot water as designed!

Jean-David Beyer

Is this problem all year, just in summer, or just in winter.

My house is on a concrete slab (used for radiant heating downstairs), with the water pipes run through the slab. I estimate that the hot water pipes run through 30 feet of the slab, and the rest outside it. I have no trouble getting hot water from the taps if I let them run long enough. In winter, my main problem is the cold water is too warm as it absorbs the heat from the slab that is heated.

In the summer, the slab is not heated, so it measures 80F on the top. I do not have any trouble with the hot water being too cool in the summer.

On the more distant taps, it takes too long to get hot water, but when it gets there, it is hot enough.

jan1227

I have only lived in the house since April so I haven't even encountered winter yet. I don't have radiant heating in the floors so I don't expect to encounter the same issues as above. Right now my issue is hot water at the kitchen sink. If I let the water run long enough it does get hot but I don't believe it gets hot enough. As soon as I turn it off, wait maybe 30 seconds or more and turn it back on, it's right back to being cold and I then have to let it run again to get hot. I am seriously concerned about what's going to happen in the winter when the slab is even colder. I do have an issue with the cold water in the master bath - it's always warm and I have to let it run until it's cold!

And for the other suggestion - no the plumber has not run a flexible supply line so I will try that next but will probably end up having a tank installed under the sink as it seems to be the overall best suggestion

Zman

4Johnpipe said:

May be a silly question...Has any of the plumbers or you attached a long flexible supply line to the hot side valve under the sink and fill a pail of water to check temperature that way? You may have an issue with the faucet mixing temp if it is a single handle style.
Also I had a slab situation a few years back with a problem with temperature at 1 sink. I found a bad washing machine valve (in the washer not the wall). I closed one of the supply valves to the washing machine and presto hot water as designed!

A cross connect is a very real possibility here. It is possible that it is at the sink. I think it is more likely the problem is in another part if the house. Janitor style faucets with Y splitters attached are common culprits....

4Johnpipe

@Zman That is what I was trying to get at. It really sounds like he has cross connection somewhere. I have seen this in washing machines, laundry faucets with creative hose connections and shower valves....

hot_rod

A cross connection is sounding more likely. Isolate any places where H&C connect, if possible. Turn off the washer valves.

Any H&C hose bibs in the building?

Some single handle tub and shower valves has isolation screw valves under the trim ring. Just keep eliminating the potential cross connections. It's a time consuming job, but it needs to be eliminated from the equation.

ChrisJ

Couldn't you just disconnect the outlet from the water heater, let it drain, turn the water main back on (with the water heater cold supply shut off) and then see if you continue to get water out of of the hot water supply?

If you do, it's a cross problem, if you don't, it's not?