Will adding a mixing valve increase the available hot water?

fred9

I'm a homeowner who did NOT do any research (other than deciding to not go tankless) on DHW when we converted from oil to Natural gas. You all were very helpful with the furnace specs.
For 23 years we have had 3 or 4 Boch 32e's that met our needs. But the new gas 50 gallon gas one is not providing the wife enough hot water for her LONG showers and then no hot water for me shower until after 30 -45 minutes.

I now realize the Gas 50 gallon by State has much lower specs than the Bock 32e.

First hour rating - Boch 170 vs State at 90 gallons.
Recovery 90 degree rise - Boch 114 vs State 44.7
I have also just learned that oil produces much higher BTU's.

Our plumber is recommending installing a "mixing valve". We have the water temperature turned up as high as it will go. And after seeing how different the specs are I'm thinking I need one with better specs and/or 75 gallon tank. That is, I doubt the mixing valve will help very much.

Am I wrong or should we give the mixing valve a try?
Thanks,

Canucker

The mixing valve will help no matter what you end up with, i would get it installed. Low flow shower heads will help, if you don't already have them. That's the low hanging fruit before you need to think of upsizing

JUGHNE

If you have the WH t-stat as high as it goes, then your shower valve is being used as the mixing valve.
Have you measured the water temp delivered to the shower right after the fire shuts off in the WH?
That temp should be way beyond what you would usually want to see in your shower. (I'm pretty old school, so maybe modern WH T-stats will not let you burn yourself.....I don't know).

The mixing valve at the WH tank usually gives you more available hot water capacity as the tank would run well above what the valve would deliver. Perhaps 140-150 in the tank and 120 sent to the shower. But if WH already is maxed out then maybe there is no answer with what you have.

Go for the low flow shower heads, it will give you more air than water but the illusion works. The comfort received is more the time spent in the shower than the water used. (Yes, I am married, pushing 40 years).

JasonLandry

I agree with Canucker, set water heater aquastat to 160* and mixing valve for a 125* output, virtually increased your volume.

JUGHNE

Yes, that is the solution.....but WH is maxed already.

JUGHNE

The simplest solution:
The husband showers first.
After a quick time of adjustment, he will know how short his shower should be.

JUGHNE

Ah.....how big is the shower???

SWEI

fred9 said:

I have also just learned that oil produces much higher BTU's.

Oil does not produce more BTU's per se. The burner on that 32e was firing at roughly three times the rate used in a typical residential gas tank-type heater. If the wife wants 45 minute showers, I'd give serious consideration to a gas tankless. How hard is your water?

fred9

WOW, thanks for all the quick and VARIED replies.

JUGHNE, I used to always take the first shower, but now when I do that the yelling from the bathroom wakes me up!! :-))

I will look closer at each reply tomorrow, but, as of now, I agree with HATTERASGUY because that's what I've been thinking.

BobC

Are you sure there isn't something wrong with the water heater thermostat? How long can you hold you hand under the hot water faucet. I keep my tank at about 140 and I can't use just hot water, it has to be mixed with cold in the shower and the sink.

Bob

Larry Weingarten

Hello: There really isn't much to add here, but I do think it would be interesting to know just what the flow from the current showerhead is. If you replaced it with a 1.5 gpm head, what would that do to the length of time you could stay in the shower? Even if you have a standard 2.5 gpm head now, this would add about 2/3s to the length of your showers before cooling.

Additionally, smaller water heaters tend to develop odor problems less than bigger tanks because water in the tank is turned over faster.

Yours, Larry

Fred

How long of a shower does she take? Does she start the water 10 or 15 minutes before she actually gets into the shower and does she let it run for 5 or 10 minutes after she get out to dry off? I have a 50 gallon tank as well and I can't imagine not having enough hot water for at least three people to take a reasonable length shower. What is the water heater thermostat set at? I agree with @BobC, either the thermostat is set way low or there may be a problem with the thermostat.

JUGHNE

I would check the actual max temp of the water. This does not sound right.....your t-stat may be defective or just maybe too overprotective by design.

4Johnpipe

I don't have the actual calculation in front of me. The mixing valve will increase the amount of of hot water delivered by roughly 25 to 30%. When you store the tank water high at 150 and set the mix at 120. You are effectively mixing 1/4 to 1/3 of a gallon of cold water to each gallon of hot water leaving the mixing valve. Installing 1.5 GPM shower heads is also a good idea. If I get time I will post the calculation here.
The process behind this is to get the water heater firing before the tank temp drops below the mixing valve set point. Most tanks are pre set to roughly 10 to 15 degree temp drop before firing.

fred9

Hot water temp is 168 degrees using a meat thermometer in a glass in the basement sink. The thermostat works cuz we started with it at "medium" and after I moved it to max I had to move the handle closer to Cold during my shower. My problem is my wife's long showers. As I tried to show in my initial post, this new gas heater does not have the same rating or recovery as the previous Boch. And even with the Boch she said it would get cold and then heat back up. I'm now realizing that's because the Boch had a quicker recovery rate. Right?

hot_rod

Lochinvar has a nice DHW calculator at their Toolbox tab.http://www.lochinvaru.us/pages/toolbox.html

Remember high operating temperatures will shorten the life of the water heater. High temperatures precipitate minerals at a higher rate.

When you use thermostatic mixers, use isolation valves and unions to allow service. The mixer will require more frequent descaling at elevated temperatures, unless you soften your water.

Thermostatic mixers may be the most abused valve in our industry. They get returned to us for warranty on a weekly basis, looking like this. Pretty sure they did not leave the factory like that!


Consider a solar pre-heat tank. Properly sized and installed it should provide 40- 50% of your DHW loads.

Zman

Don't be distracted by the published recovery rates.There are really only 2 factors to be considered when comparing DHW systems. BTU output of the appliance and storage capacity. The output will dictate the systems ability to maintain temperature at a given rate over a long period of time and the storage capacity will dictate the ability of the system to deal with surges of higher demand.
In your case, you seem to have long demands and not enough output to keep up with them. The old system had about 2-3 times the BTU output as the new one.
The only time adding a mixing valve will help is when you want to add "effective storage" by running the tank at a temp which is potentially unsafe for scalding. It will have no benefit with a problem like yours where you have a long sustained flow in excess of your output.
You might try sneaking flow reducing devices in the shower head and see if you get complaints.
I have a similar setup with low flow shower heads and never run out of water.

JUGHNE

If you have the floor space, gas pipe sizing and chimney capacity, then perhaps a second NG WH tank in series with this one may be the most practical solution.

You would not need the temp/mix valve then.

Gordy

Agree with others. Adding a mix valve does nothing for extending usage. The tank temp is maxed out, and you are manually mixing at the point of use.

The only options are cutting the gpm at the point of use, shortening of use time, or adding more storage.

I found it hard to run out of HW with a 40, and 3 women plus me at max tank temp. 36k burner. However I installed 1.5 gpm heads at the shower.

I find the highsierra 1.5 gpm shower heads the right mix of water diffusion, and pressure.

Gordy

Tanks in parallel if an extra water heater is going to be utilized. Close attention to detail for exact piping lengths need be utilized.

Gordy

One other thought is if your HW supply piping has long runs a recirculating system can help with extending usage a little. Running the shower waiting for it to get hot wastes water, and blends down the tank before you even start showering

Gordy

If you let the shower run for 2 min. With a 2.5 gpm head you have just dumped 5 gal of 55-60 degree water in the tank.

fred9

Wife is in shower about an hour but does turn it off at times to "conserve". She's not open to a low flow shower head but the Symmons Temptrol valve does have a graduated handle. That is we don't have it on "full blast".
I have emailed my plumber with a comparison, including BTU's, of the former Boch32e, the current 50 gallon and three 75 gallon tanks by State. I also said "Maybe a second heater is series is an option, but you know I'm not an expert."

I will update you after I talk with him.
Thanks again for all your help.

SWEI

fred9 said:

Hot water temp is 168 degrees using a meat thermometer in a glass in the basement sink.

Be very careful with that water.

Gordy

Cook lobster from the tap all most.

Gordy

Hatterasguy said:

Gordy said:

One other thought is if your HW supply piping has long runs a recirculating system can help with extending usage a little. Running the shower waiting for it to get hot wastes water, and blends down the tank before you even start showering

By the time you purchase and install the recirc system, you're 1/2 way to the second WH. I think the OP would rather have 50 additional than another 5.

Agree, however having near instant hot water at point of use has conservation bennies. Especially if piping runs are long. More so water conservation.

Gordy

http://www.hotwater.com/lit/bulletin/bulletin64.pdf

In case your plumber does not understand the difference, and pros/cons of parallel, and series piping of water heaters.

JUGHNE

I mentioned the series connection because of the simplicity of plumbing. If you go for the parallel set up as Hatter mentioned then be certain you get a plumber who understands the importance of the exact piping required. It is not rocket surgery, just common sense.

FWIW: Just a note of changing times; about 25 years ago while doing a new house for a dairy farm family with 7 children, yes 7, count them. They said their old 40 gal NG just would not cut it for them. So for the new house we made the big step up to a 50 gal tank (was a non stock item for my supplier at the time)......the family said that the 50 made it for them most of the time....also "chore time" was twice a day and after milking many cows everyone involved (4-5) would shower.
I will say that at that time a 40 gal had maybe a 39,000 burner.
The 50 had more, not sure, maybe 48,000? There was later a mandated attempt at energy savings by installing smaller burners on new tanks. Also WH thermostats now have a lower (safer) max high temp adjustment.....I believe.

JUGHNE

I think that for electric WH there are 160 degree max T-stats available......labeled for Dairy Barn use.....also work for small time commercial dishwasher water heating.

4Johnpipe

@Hatterasguy you are incorrect in your statement about mixing valves. Example if you have a hot water demand of 1 GPM and the mixing valve at the heater is mixing 1/3 gallon of cold water with every 1 gallon of delivered hot water to deliver a lower temp than the tank stored temp you are effectively changing the flow through the tank. The result is more standby hot water.

4Johnpipe

Yes it does we have hundreds in service. We know what flow does correct? The mixing valve slows the flow of hot water leaving the tank. Thus the cold water entering the tank is slowed. The result is more available hot water.

Gordy

If the mix valve is set to 120, and the point of use is mixed down to say 100. It would be the same affect as no mixing valve, and mixing down at point of use to 100. All the mix valve is doing is limiting the highest possible temperature to reach the point of use. The difference would be the shower valve mixer would be turned more to hot with a mixing valve than it would be with out.

4Johnpipe

There is a difference between a TMV and a point of use valve at the shower. Example...no TMV at water heater. Set temp of heater to 150. Run shower head at 120. Keep adjusting handle to maintain 120 while filling a container. Repeat test set shower valve to 120 and leave it without adjusting handle in a separate container. Time how long it is before temp at shower goes cooler then shut off. Then go back and measure both containers. The one with that was adjusted through the test (as with a TMV) will have 30% more water collected in the container.
Ask me how I know this...

JUGHNE

fred9;
Just out of curiosity, how far is the WH from the shower?
Is the WH in the basement and shower on 1st or 2nd floor?
Is the basement ceiling from WH to shower finished?

RJMCTAFO

I have added a good quality tempering valve to underperforming water heaters many times and have had almost nothing but success. Thermal expansion tank+ TV + water heater set to 145* is always the first attempt to rectify a tank that was too small. Only once did the customer have us upsize storage.

4Johnpipe

@Hatterasguy the container was the bathtub (marked water level with tape). The variables are the cause of the result however it is not erroneous. The result is anticipated and desired. Yes the flow rates are different. What we need to account for are the flow mixture rates. When a TMV is installed at the WH. The valve will look to mix cold into the outgoing hot. To do this it closes the outgoing hot side to allow more cold to mix. This changes the flow mixture rates. The water heater cannot fill more than it lets out. Having higher store temp allows the heater to fire before the outlet set temp of the TMV...I think this calculation is in a folder on or next to my desk. I will post it as soon as I get home and have a minute.

hot_rod

4Johnpipe said:

@Hatterasguy the container was the bathtub (marked water level with tape). The variables are the cause of the result however it is not erroneous. The result is anticipated and desired. Yes the flow rates are different. What we need to account for are the flow mixture rates. When a TMV is installed at the WH. The valve will look to mix cold into the outgoing hot. To do this it closes the outgoing hot side to allow more cold to mix. This changes the flow mixture rates. The water heater cannot fill more than it lets out. Having higher store temp allows the heater to fire before the outlet set temp of the TMV...I think this calculation is in a folder on or next to my desk. I will post it as soon as I get home and have a minute.

John, is the listed TMV a code required device in your area, if the tank is set above 120F?

4Johnpipe

@hot rod Yes. The water heater cannot be the sole control for hot water. For some strange reason our code the NSPC has been augmented by the state of NJ only to define hot water as between 120 and 140. It's crazy and I can't believe there have not been more law suits. Other model codes seem to stop short which is smart by saying anything over 110 is hot and scald protection would be required.
Tankless is not included in the control portion as they are flow related instantaneous devices.
@Hatterasguy not exactly. The TMV limits hot water delivery where as throttling the shower valve "adds" more cold water. Yes flow restricted shower heads help overall but they do not put a limit to the hot water deliver they simply scale the results down by limiting the outlet at the point of use.

Gordy

RJMCTAFO said:

I have added a good quality tempering valve to underperforming water heaters many times and have had almost nothing but success. Thermal expansion tank+ TV + water heater set to 145* is always the first attempt to rectify a tank that was too small. Only once did the customer have us upsize storage.

The reason is because the tank temp was increased. The result would have been the same with no TV added. The TV is just doing the tempering at the tank. Instead of manually by the user at the point of use.

The only difference is the user with a TV installed uses less cold water to reach desired use temp because the temperature from the tank is already mixed down once before it hits the faucet.

With no TV the user would use more cold water to get same desired temp at point of use. Because it has not been stepped down in temperature by a TV.

I'm in no way saying a TV should not be used with high temp DHW tanks. The argument is that when the tank temp is already maxed out adding a TV that did not exist does not increase hot water storage. It does provide safety however from scalding.

SWEI

Gordy said:

The only difference is the user with a TV installed uses less cold water to reach desired use temp because the temperature from the tank is already mixed down once before it hits the faucet.

With no TV the user would use more cold water to get same desired temp at point of use. Because it has not been stepped down in temperature by a TV.

This is the only substantive performance (as in quantity) difference between mixing at the tank and mixing at the POU.

Temperature-controlled shower valves are wonderful, but they have even more fiddly bits inside them with the potential to lime up.

4Johnpipe

@Hatterasguy I should have said "reduce" not throttle. You have to add or adjust more cold water at the shower to reduce the temp to 120 or lower. The amount of hot water leaving the tank is unchanged without a TMV.