Will adding a mixing valve increase the available hot water?

4Johnpipe

MIX RATIO=(TMix-TCold) / (THot-TCold)
T Cold is inlet domestic water=50*
T Hot is tank storage temp=140*
T Mix is usable mixed temperature=110*
(110-50) / (140-50)= 60 / 90 = .667
The mix ratio would be 33 gallons of cold, mixed with 67 gallons of hot water. This equals 1 gallon of cold to 2.03 gallons of hot. Then you plug and chug flow into the Universal Hydronics formula Which takes into account degrading tank temperature via BTU's and get to the 30%.
Remember also the mix at the shower is roughly 60/40 cold to hot.
The TMV starts out by slowing the flow of hot by mixing in cold at the tank because it closes to reduce the stored temp to the desired delivered temp. So to answer your question without a TMV nothing happens to the hot water at the shower. What happens in the tank is begins to cool quicker because the tank is filling with more cold because the hot is leaving at an un-metered rate.

Paul48

In this case, the storage tank temp(maximum) is available at the shower. You're confusing yourself with all the other BS.

4Johnpipe

No confusion the original question was does a TMV increase hot water availability. The answer is yes definitely. Will it be enough for this specific application...that depends.

Paul48

That was what he asked.........but once he explained his situation, it is clear that it will not help his situation. He already has the t-stat maxed out. His thermostatic mixing valve, for all intensive purposes is at his shower valve.

4Johnpipe

Lets say we have a single handle shower valve with a 2.5 shower head. The split between hot and cold water is 60/40. That leaves us with a possible flow of 1.5 GPM hot. The TMV will mix cold with the hot at a rate of (rounded) .5 GPM's. That leaves 1GPM of hot moving out of the tank. This means the tank is filling with 1GPM. If you did not have the TMV it would fill with 1.5 and leave at 1.5.
This alone without any consideration to tank firing is as follows...
A 30 minute shower remember that without the TMV the hot water will be cooling at the end of the 30 minutes quicker than with a TMV.
WITH TMV 1GPM x 30 minutes = 30 gallons still more to go
NO TMV 1.5GPM x 30 minutes = 45 nothing left in tank

These are conservative numbers I rounded down...Also as you approach the 30 minute time you will be turning the NO TMV hot side up to maintain a desired shower temp. This will quicken the hot water dump and lessen the amount of HW left.

Why is this so difficult for you?

Paul48

If he didn't have his tank at maximum temperature, a TMV would do that for him, and allow him to have a safe temperature at the shower. Or he can do the same thing, without a TMV and risk scalding someone. You either proportion it at the TMV, or proportion it at the shower valve. The tank is at maximum temperature, and the people will shower at the same temperature. Stop and look for what you missed in his posting. Apply clutch....disengage fingers.....engage eyes.

4Johnpipe

Yes I get that. There is more physics going in then just the obvious. The OP also said it takes 30-40 minutes for his next shower.
I see the scenario like this. The Mrs takes a shower about 8 minutes in she is turning up the hot (or the cold down), another 4 minutes she turns it up again, another 4 minutes again and so on. Now the water heater fired at the first 8 minute mark. But the flow through the heater has Been steadily increasing throughout the shower. The unit is flowing almost straight hot water around 2 GPM's at the 20-24 minute mark and she is done!
With the TMV she will get to that 20-24 minute mark uninterrupted with fumbling for tempurature control. Then part 2 the husband will be able to get a shower pretty much right away. Waiting 4 minutes wouldn't hurt.

fred9

I really appreciate your input don't want you all to get too worked up about my issue. :-))
I would like to install a low flow shower head but she says that won't happen.
Yes the WH is in the basement and the shower is on the second floor but horizontally they are only about 20 feet apart

The BTU's on the Boch are 104,000 and only 40,000 on my State gas heater.

SWEI

fred9 said:

The BTU's on the Boch are 104,000 and only 40,000 on my State gas heater.

The smallest of these fires at 120,000 BTU/hr. How hard is your water?

fred9

We are going to install a second 50 gallon in parallel, same model GS6 50 YBVIS. My plumbing company said parallel and also said piping will be the same length. I'm thinking each one should have cutoff's before they join so one can keep working if the other fails or leaks. They are considered the best plumbing company in the area, Farmington River Valley in CT, but what else should be done to make this setup work properly?

SWEI, I don't know how hard the water is but in the 23 plus years we have had six or more pin hole leaks in the copper pipes and no, the piping is not the "lightweight" variety. I decided against the tankless cuz my wife doesn't do change well and because I understand the tankless ones require annual maintenance but thanks for bringing up that option.

SWEI

Sounds more like you have low pH (corrosive) water, which is frankly tough on everything.

Reverse return piping is generally easier to install and service than the "perfect match" mirror image diagram shown in many of the install manuals.

Mark Eatherton

I just Googled "Hot Water Extender Valve"... Either there is a lot of false advertising going on by numerous major manufacturers, or they do work (my belief is that they do work, or they wouldn't be selling these things). But then again, who'd believe anything a manufacturers sales department produced....

And it is NOT a good practice to bull head flow in a tee, ever. In fact, prior to the introduction of primary/secondary piping, it was against the code to use bull head tees.

Pipe it parallel reverse return, or don't bother.

WWBS...

ME

Rich_49

TMVs definitely increase storage capacities of tank type vessels .
They also protect against something referred to as thermal shock , hint , this can be either hot or cold water that rapidly changes . These events cause other than scald injuries as one attempts to too quickly get out of the offending stream of hot / cold water and are often more injurious than a burn .

If your house has 2 handle faucets you'll need many POU devices , lots more maintenance , lots more first cost , many more headaches .

Allowing the valve at the fixture to do the mixing will soon be a thing of the past as this wastes energy from the standpoint that over the course of a year an extra average 2 gallons cooling to ambient from 140* on a daily basis results in a minimum increase of 425,000 BTU of usage . I know , that's not that bad and at 1.00 per therm it's only 4.25 per year but we are not the one's making the rules . Yes Brian , that little bit of use is of concern to those who would see us gone , I don't expect you to understand .

Not that any of this will help the OP since his Best in the area plumber saw fit to install something 1/3 the size of what was there and expected a positive result . I might be inclined to find another plumber . I might even be inclined to s&^%can the existing , offending heater and put in a single tank type heater with enough **** and a TMV to do the job right . It would cost less to operate also . Fact is that a single properly designed unit would suffice , but at least you'll have redundancy .

Everyone who has commented should acquaint themselves with ASSE white papers and research . It is not always black and white and it seems some may actually be placing the end user at risk all while trying to do the right thing .

Gordy

Rich, and Mark I don't disagree with what you are saying, but...

The original "story problem" the OP posted was that his replacement WH is not providing the amount of HW the old one did after the switch. Further clues to the original problem were his WH set point is maxed out. The OP wanted to know from this point would a TMV extend his usage. The answer is no.

IF the original problem was the WH was set to 120, and the OP wanted to know if the addition of a TMV would extend usage the answer would be yes. Because this would allow the storage temperature to be safely raised, and increase capacity.

From there things went on a tangent as to whether a TMV extends storage. Yes in the proper scenerio. Plus adds protection at point of use. Protection being the main driver....

fred9

Rich,
My wife NOW agrees with you that the plumber should not have sold us the 50 gall, 40,000 btu WH. Note that I started this thread saying I did not do my research. In some defense of the plumber, when he was here he offered to give me a quote on a 75 gall heater but I said I didn't want it. At the time I didn't understand the difference in BTU's.
This morning I sent him the diagram of reverse return piping but have not heard back yet,
Thanks to you all for educating me.

Rich_49

fred9 said:

Rich,
My wife NOW agrees with you that the plumber should not have sold us the 50 gall, 40,000 btu WH. Note that I started this thread saying I did not do my research. In some defense of the plumber, when he was here he offered to give me a quote on a 75 gall heater but I said I didn't want it. At the time I didn't understand the difference in BTU's.
This morning I sent him the diagram of reverse return piping but have not heard back yet,
Thanks to you all for educating me.

Fred ,

Just so you know , MOST plumbers suck and are woefully inadequate . The 75 gallon with a TMV and an = or > 75000 BTUh would probably suffice .

Fred

I'm going to guess that an additional 50 Gallon tank and the additional plumbing will cost about the same as replacing the current tank with a 75 gallon unit.

Rich_49

@fred9 .

Get a price on a 75 and a 50 and make your own decision on what the better value will be . Probably pretty accurate though , don't forget the TMV . IT WILL INCREASE storage capacity and allow a 75 gallon to perform as well as a 100 . THIS IS A FACT

jonny88

@ME when piping 2 water heaters I was taught to bring cold water into bull of tee directly exactly in the center of the two heaters.The run of the tees is exactly the same to the inch.On the hot side the two hot supplies again meet at the center of the two heaters and the bull goes to fixtures.I have just called 2 NYC lic plumbers and both have said this is how they do it.A.O. Smith even show it in their piping diagram.What are we all missing here .

hot_rod

another option for piping tanks for equal flow, is with balancing valves. This not only assures and indicates flow, with a 132 Quicksetter valve, but also isolation of tanks if need be.

This drawing shows indirect, ignore the coil piping for fired tanks.

4Johnpipe

...

Rich_49

Since when would ambient be 115* Genius ? Remember also that the ambient temp in most homes and buildings may change several degrees in an unconditioned space where most mechanical equipment is located .

Lest we not ignore the other fixtures in the house that have or should have temp limits . All those mixing devices cost money my friend and since they are smaller through the passageways present a much higher frequency of failure , repair .

My data is correct and there is no substitute for experience , whether it be repairing or replacing or hearing people's complaints . In case you didn't know , that's what many of us do for a living Sierra Mary Echo

jonny88

A.O.Smith diagram

SWEI

jonny88 said:

when piping 2 water heaters I was taught to bring cold water into bull of tee directly exactly in the center of the two heaters.The run of the tees is exactly the same to the inch. On the hot side the two hot supplies again meet at the center of the two heaters and the bull goes to fixtures.I have just called 2 NYC lic plumbers and both have said this is how they do it.A.O. Smith even show it in their piping diagram. What are we all missing here .

In a parallel reverse-return arrangement, as long as the total path lengths through each parallel vessel are equal, the flow will essentially self-balance. The "mirror image" layout they (and many others show) is really just a special case of reverse return piping -- one which can sometimes be difficult or impractical to install.

Rich_49

Am I to believe that water in hot water lines delivered from a maxed out water heater that is sitting there is not hotter than mixed water and that it will not waste more energy by losing temp than the water delivered through a TMV ?

I avoided all the nonsense that was discussed here , I know this gentleman's situation and opted not to get involved with the nonsense . This really only has to do with the fact that an uninformed consumer got screwed and now needs help . He puts himself and his family at risk running this system in the fashion he is at present . Advising to continue to do this is not only stupid but unethical .

I do not obfuscate , you know this . I choose to offer an opinion based on facts and practical knowledge , you exercise for the most part in symantics without concern for the safety and well being of the end user . You must have me confused with others on the forum .

If the OP is still around . I advise you to purchase a high quality water heater that has the capability of modulation and that offers a high efficiency , combustion and thermal . Store the water at 140* and use the TMV at the heater for your fixtures and utilize no tempering for washing machine , dishwasher , kitchen sink . A heater in the 75,000 range will probably suffice but going to a 100,000 , 55 gallon unit would be better . Try to get some reimbursement for the piss poor water heater your stupid plumber installed in an obviously uneducated attempt to provide the required hot water for your needs . If not . don't argue , bite the bullet and get the right water heater and protect your family from all sort of hazards that have not even been discussed .

JUGHNE

Fred9;
You probably never thought that your lack of hot water could start so many controversial fires here, it is very interesting and educational for all involved I must say.

So what I would do if you were my customer is try convince you to get another exact water heater tank, place next to the existing one. Connect it as shown in Jonny88..AO Smith diagram. (Many of us don't like AO Smith company but they have been in the water heater business a long time and I would follow their piping diagrams and probably not buy their products today; 20 years ago yes.) There would be no balancing valves or such gadgets, just keep all valves fully open unless there a problem with one WH.
I have a 6 unit motel with 3- 50 gallon residential electric WH set up in parallel piping as shown. The owners were happy as the customers would certainly mention lack of hot water. Imagine 6 or more showers going every morning!

First I would make sure the gas piping and chimney venting would handle 2 WH on at the same time. I would set the temps at the recommended 120 or so, but keep them both set the same.

The piping would be done with a future tempering valve in mind, that is minimal changes required to add the valve at a later date if these two tanks at the low (safe) setting would not fulfill your needs. Then with the temp valve added the WH tanks would be set up to 140 or so to extend the supply.

The isolation valves would be installed as shown should one burner/tank fail and you could have at least what you have now.

The hot water lines would be insulated where possible in the basement. The vertical inaccessible pipe does in effect provide recirculation up and down its riser length. The hot will migrate up the center of the pipe and as the outer layer cools and drops down there will be a chimney effect (or Ferris Wheel effect) to keep hot water at the top. Mind you this will only happen slowly as in overnight.

You could turn the temp of WH's up yourself at your own peril.
However no responsible tradesman would recommend that for you. There is a reason that WH's out of the box seem to be set almost always too low, someone else has to turn it higher and it wasn't the factory......that buck was passed to the next person whose fingerprints are left on the knob.
The temp you are running now is extremely risky, true there may be only the two of you in the house at the moment and you are both obviously aware of how hot your water is.
But any visitor may not realize what 150 or so water can do quickly, and maybe their brother-in-law is a lawyer.

Anyway that's what I would say if I were standing in your basement.

I'm waiting for the arrows to head my way.

Gordy

No arrows @JUGHNE . K.I.S.S.

Unless the plumber bucks up, and eats the cost of the 50 he installed which I doubt. Then ditching the 50 for a 75 is more costly than keeping the 50, and adding another 50 to have 100 gallons. Don't forget the OP's cost for the to small 50 on top of the 75. Its easy to give advice with other people's wallets. The driving element is the Exisiting 50 either goes in the corner, on Craig's list, or eBay as a used water heater to maybe recoup the losses.

JUGHNE

Gordy, do you think a 2nd 50 would fix the problem? With or without the TMV? I'm thinking the NG 50 is almost at bottom of the price range. They are simple and replacement down the road should be an economical replacement. Also doubtful both would fail at one time. The redundancy is there to not do a impulse buy from the first person to answer the phone with the promise to have it changed today.

The plumber was as simple as I would have been 20 years ago.
That has changed only in that I am 20 years older.
A 50 gallon NG would usually have taken care of most homes. (as I mentioned above for the family of 9). Today I would ask more questions. 50 gallon tubs, (I have one), multiple shower heads, (total of 4 in my house) etc.
I know of no trade school programs dedicated to plumbing. There is a union apprentice program with those usually headed to commercial work. HVAC school just touches on actual plumbing. Otherwise it seems to the school of hard knocks. And if you don't read up on simple things such as this subject then there are many surprises ahead. I have seen plumbers who only did installations and simple faucet repairs really get snowed with power vented water heaters and such. Those appliances step into the HVAC field and that is avoided by most pipe/pex plumbers. Just another trade, maybe more so than others, that is begging for people to learn and work with what they learn.

Note: Looking back and above, I realize I think too long and type to slow. (Hat stole my thunder as I attempt to compose).

Mark Eatherton

jonny88 said:

A.O.Smith diagram

Jonny, that is called pyramydic parallel. For two tanks, it is adequate. For more than two tanks, it poses many times more leaks than tanks piped in parallel reverse return. And, if you have a low ceiling, there is no possible way that you will be able to keep the isolation valves and unions out of the aperture of the tank if you had to remove it. Will it work, obviously, but if there is ANY deviation in perfect balanced piping, it will not flow equally through both, or multiple vessels. It looks really cool and simple in a drawing, but its practicality beyond two tanks is impractical.

What HR is showing is parallel direct return, and if done without the balancing valves, it's fairly obvious what will happen to the flow of the first and last tanks. I've seen numerous jobs piped like that where some unknowing technican opened the balancing valves completely open, thereby throwing the flow way out of balance. They know no better...

Piping in parallel reverse return has a much better chance of getting the isolation valves and unions out of the removal aperture of the tank without having to disassemble much, if any piping, and there s nothing to cause it to get out of balance on draw through the tanks.

IMHO AO Smith needs to review and augment their own drawings. This pyramid system will work if done perfectly.

A major manufacturer still shows a 2 valve bypass on their cast iron boilers installation drawings, but I haven't seen anyone do that in around 35 years. It doesn't provide proper protection for the boiler seeing a cool (<140) return that will cause it to condense. Just because it's drawn that way doesn't mean it will be installed exactly that way, unless of course YOU are doing the job

Another little known factor about bull heading tees, and the main reason it used to be illegal, is that as water hits the bull on flow, it's looking for the path of least resistance. As it finds it, the flow through that portion starts creating more back pressure, and it changes its mind and starts flowing more the other direction... Until the pressure drop in that circuit increases, and it goes to flowing more in the other direction. In other words, it's flow is sea sawing back and forth through the two tanks.

With a parallel reverse return, on draw the system locks into the hydraulic resistance values and flow does not deviate. John Siegenthalers very first article addressed this very same concern.

When the ICC filed paperwork to abandon that portion of the code due to a lack of understanding an misinterpretation, I attempted to educate the Technical Committee on the function of primary/secondary piping, which is where the confusion was coming from, and they decided it would just be easier to eliminate that portion of the code. In other words, they didn't understand it, so why should they expect their inspectors to...

Bull heading is not recommended. Period.

ME

jonny88

I understand what you are saying Mark.On Swei's diagram of reverse return piping second heater is still bullheading its hot out.Could you draw a sketch of how to pipe in 2 heaters the way you would like it done.I am not talking about 3 or 4 heaters, as in the real world nowadays there are to many options rather than using more that 2 heaters.Thanks.

hot_rod

jonny88 said:

I understand what you are saying Mark.On Swei's diagram of reverse return piping second heater is still bullheading its hot out.Could you draw a sketch of how to pipe in 2 heaters the way you would like it done.I am not talking about 3 or 4 heaters, as in the real world nowadays there are to many options rather than using more that 2 heaters.Thanks.

Here is an example of RR with multiple tanks.

A few small details... ideally the piping size should step up and down, probably not a huge deal with two tanks, however.

I do like the simplicity of balance valves and most are able to be locked in the set position, some even have provisions to tag, the one I showed is a simple ball valve type, with no handle to tempt someone to change the setting
.

Also put the reverse return loop on the cold piping side to eliminate heat loss potential that the extra piping would add on the hot side. Insulation, of course is advised, TMV may be code required if tanks are set above what the code states.

I would not fault the installing plumber, 50 gallons has been a standard size for the majority of families.

jonny88

To the OP sorry for the hijack but we are getting a good lesson here from some of the best.Agreed with HR a 50 gallon has been standard,now homeowners have to answer truthfully what their HW demands are.Show rooms love to show state of the art showers and tubs etc but water requirements come at a price.

hot_rod

jonny88 said:

To the OP sorry for the hijack but we are getting a good lesson here from some of the best.Agreed with HR a 50 gallon has been standard,now homeowners have to answer truthfully what their HW demands are.Show rooms love to show state of the art showers and tubs etc but water requirements come at a price.

The best takeaway, always ask. The plumber should ask about DHW expectations, and the HO should indicate their desires.

We will see more and more examples of the DHW loads exceeding the heating loads in energy efficient building designs.

Having a boiler that can step up to the higher output for DHW recovery is something to consider as we size down the boilers.

fred9

JUGHNE, Yes, I am somewhat embarrassed that I started all this but at least one of you said it was educational. And it has been for me too.
I have not yet fully studied the recent posts but will restate that on Sunday I emailed my plumber saying I needed to make a change and suggested a second WH in series as an option. He called me at 8:10 Monday morning and agreed getting a identical second WH was the best "bang for my buck " but said he'd install in parallel. I had said "series" before many of you said parallel was better for two identical WH's. Then yesterday I emailed him a copy of the reverse return piping by PVI Industries. (Thanks to SWEI!)
My email said Online a number of plumbers recommend using "reverse return piping" in the parallel setup as in the attached diagram. Their view is that it's difficult to get a perfect balance of the two heaters' water flow even when heaters are identical. Please consider this when planning the installation of our second water heater.
I have not heard back from him with a quote. Looking at the potential issues with having two WH's. If his price is "high", aka a lot more than the first WH, I will ask for a quote on a good 75 gallon, ie, one with 75,000 or 100,000 btu's. I will now add to you that the current WH is a power vent one , ie, pvc out the side of the house.
Thanks again.

JUGHNE

Fred9, not to worry. This happens here a lot. A lot of back and forth. IMO it is certainly a worthwhile discussion.
As to what I say about the WH you should remember that I am an old guy.....old school.....and not too active in residential plumbing at all any more. I would venture to say that everyone else is quite a bit younger and more tuned in for the present.

fred9

While I'm in kindergarten for hot water heaters, I'm 72. And glad I'm retired so I have enough time to read all the posts here.

JohnNY

I also have a boat load of mixing valves installed in all sorts of situations. I love mixing valves. Just love them.

They keep my clients safe at the point of use when I want to store water at temperatures that are hotter than can be safely handled by us humans.
In other words, they allow me to store more energy than I could without the mixing valve, which affords me the added benefit of making slightly more hot water available at the sinks, wash basins, dishwashers, pre-rinse stations, food prep areas, etc.
That additional benefit, however, is not realized at showers. Mixing valves at showers, practically speaking, are mixing valves at the source moved down stream.

ChrisJ

Only experience I had with mixing valves was one going bad. It was removed and replaced with another one which ended up just getting scrapped for unrelated reasons.

I also recall several sources, including professionals telling me mixing valves are known for failing often. Since that was my only experience with one, I tend to believe them of course.


If it is true, that they are known for failing then the cost of them is certainly not very appealing.

Mark Eatherton

Jonny, here is a simple parallel piping arrangement. The reverse return doesn't really show, but it is a reverse return piping configuration, minus the reverse return. I have drawings on an older PC showing all of the differences I will try and dig up.

An easy way to look at this is that if the in and the out flow in the same direction, it is reverse return. If they flow in opposing directions, it is direct return, which will require balancing on flow.

HTH. Share it with your other plumbing friends. I never intentionally try and offend my plumbing bretheren (or sisterens), but there are always better ways of doing pretty much anything. We just get too used to doing it a certain way that we are comfortable with, and don't bother to look around at other methods.

If you count the number of soldered joints (potential leaks) there are less on this config than there would be on a pyramydic parallel piping, which equates to a worthwhile savings of materials, labor and risk exposure.

ME

hot_rod

ChrisJ said:

Only experience I had with mixing valves was one going bad. It was removed and replaced with another one which ended up just getting scrapped for unrelated reasons.

I also recall several sources, including professionals telling me mixing valves are known for failing often. Since that was my only experience with one, I tend to believe them of course.


If it is true, that they are known for failing then the cost of them is certainly not very appealing.

While it is certainly possible to have a manufacturing defect, by far most DHW thermostatic valves fail due to water quality.

Under the hood it is a fairly simple device, a spool, few O-rings, spring and wax cartridge. The wax "pill" is similar to that of a TRV.

Mineral content in the water causes the valve to bind or stick..The hotter the water supplied by the tank, the more mineral precipitation. If you run the DHW tank at 160 and hotter, expect frequent maintenance of the valve, and a shorter life expectancy of the tank. Softening the water will help.

In some cases the valves need to be de-limed every few months.

One property I know of in Florida maintains around 18,000 mixing valves! Full time crews are constantly maintaining, and cleaning those valves.

We warranty most every failed valve even when it i

s obvious that it has been over-heated at installation, or plugged solid with lime.

Hydronic applications are less prone to problems, but crappy fluid conditions will still take a toll on valves in sealed, hydronic systems.