Hot water heater too hot for settings

bipbap

Thanks in advance for any advice on this one...

We put in two new 50-gallon gas AO Smith got water heaters in a 6-family building. They are piped so both feed right into one pipe to supply the building.

The issue is they’re set to “hot” which should be 120 degrees but were getting 135 degrees at the faucets and we don’t want anyone to get burned.
I could set them to next lowest setting at “low” but that’s supposed to be 90 degrees and comes out too cool.

I called AO Smith and apparently since these were put in to serve more the one apartment, it killed the warranty and they won’t help even though they’re just 18 months old. I wish someone would have told me that before I got them. She suggested replacing them (!) with a commercial unit but these are just 18 months old and not cheap. Or she gave me names of technicians I can hire which is annoying to spend money on something that new.

Any suggestions?
Thank you in advance for advice!

Paul Pollets

Install a 3 way tempering valve and thermometer that will limit the outlet temp to 120 degrees. This is usually required by code in multi-family buildings.

pecmsg

According to ASHRAE multi family water heaters need to operate at or above 140°.

Raise the temperature and install a mixing valve!

neilc

is that a dial setting?
or a hard choice between the 2 settings?
if it's a dial, dial it down a bit, but not too low.

or,

keep the tanks at 135 / 140 to combat Legionella,
and add a mixing valve (or two, hi / low flow) and mix down to 120 / 115.

This is plumbing 101, you need a better plumber.

bipbap

Setting looks like this... attached.
I don’t think my plumber who installed it knew it was an issue and just did a straight swap from what was there before.
So it needs to be that hot out of the tank to prevent legionella?
Does the mixing valve go right before the faucet or right after it comes out of the tank?
Thanks again- I’m a newbie to this.

pecmsg

If theirs a circulating loop then the loop should be 140°minimum mixing valves at the faucets.
No loop I believe you can have it installed at the tank.

Local JHA has the final say.

bipbap

Here’s a photo of the setup...
And this is installed in NYC if that helps with regard to code/laws.

Is there any reason it should be putting out water this hot if AO Smith says this is the recommended setting and should make water 120 degrees and it’s coming out 135ish?
The rep says this is not a common problem so didn’t have much advice to help me.

ratio

Are both out of cal, or just one? Try turning one off at the gas valve, then closing the outlet valve and see if the temp is still elevated. After that, check the other one the same way. If one were stuck on high/out of calibration, it would drive the whole system high. You might have a better chance with the warranty if you could show that one control is obviously defective.

DZoro

50 gallon water heater will have different water temperatures from the top to the bottom. It will almost be next to impossible to get a 120 degree water temp out of it consistently without a mixing valve. Install the mixing valve and set the water heater to 140 or higher and the mixing valve to 120. That will be your only solution, and yes most commercial applications such as yours will require exactly this set up. For this obvious reason.

the_donut

Dennis said:

50 gallon water heater will have different water temperatures from the top to the bottom. It will almost be next to impossible to get a 120 degree water temp out of it consistently without a mixing valve. Install the mixing valve and set the water heater to 140 or higher and the mixing valve to 120. That will be your only solution, and yes most commercial applications such as yours will require exactly this set up. For this obvious reason.

Heat cold be rising and stratifing.

bipbap

Ok sounds like we need a mixing valve.
And that gets installed right after the water comes out of the hot water tank?

Also just curious, is this a typical hot water setup with two tanks feeding into one line?

Rich_49

bipbap said:

Here’s a photo of the setup...

And this is installed in NYC if that helps with regard to code/laws.



Is there any reason it should be putting out water this hot if AO Smith says this is the recommended setting and should make water 120 degrees and it’s coming out 135ish?

The rep says this is not a common problem so didn’t have much advice to help me.

Common oversight by many . You must understand that the aquastat location is low in the tank and it's reading 120* at that location . The tank stratifies and the higher up in the tank you go the hotter the water . This is the reason that the water heater itself and it's controls cannot be counted on for scald protection . the water heaters are working fine . Install the mixing devices as others have mentioned and please turn the tank temp up to protect against Legionella generation . Nowhere in your heaters is the water hot enough at present for disinfection purposes .

hot_rod

Come up with a total GPM load for the building, I suspect you could have a 20- 30 gpm DHW load under some conditions? So you need a mixer that will be accurate at both low and full flow conditions. Multiple valves or a hi-low.

The industry is moving towards EMV electronic mixing valves for those applications.

They also have anti legionella function to elevate the entire DHW system, as the bacteria lives in the piping also.
Point of use valves will be needed at every fixture when the system goes into anti legionella, high temperature mode.

Some good, current info here. Piping multiple tanks with balance valves is another option for equal draw.

Providing safe DHW is getting more complicated Refer to ASHRAE 188 standard for other options.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_22_na.pdf

bipbap

Ok thanks for the idea.
How do I calculate a GPM load?

hot_rod

There are tables online to estimate DHW loads, and most of the water heater manufacturers have tables for multi family estimating.

Fixture unit count is another way, how many baths in each unit? Any idea on the shower head flow rate, that can change the number a lot. Dishwashers and wash machines in each unit?

Installing a water meter on the cold feed to the tanks would give you some accurate data on consumption.

100 gallons total? It doesn't sound like enough for 6 families? Most single family homes have 40 or 50 gallon tanks.

billtheplmbr3845

I know this is off the original topic but, WHERE ARE THE DRAFT HOODS. Could this be a homeowner job?

bipbap

6 bathrooms total for the building and
2 dishwashers
1 Washing machine
I don’t think it’s ever been an issue of not having enough hot water but the apartments are mostly 1 or 2 people, not big families.
I never considered 100 gallons total could be undersized

JUGHNE

Back to the absence of draft hoods??

Without them, you as an owner are open to possible some severe liability issues, IMO.
The plumber could be named in the wrongful death/tenant illness etc. lawsuit from CO poisoning, also, but he may not be found later down the road.

I recall reading a Forensic report concerning multiple deaths caused by lack of draft hoods, the owner was found to be at fault. FWIW

GBart

Hire a Pro should be the answer, too expensive?? cheaper than a lawsuit.

bipbap

What is a draft hood?
I’ve always used real plumbers, didn’t do the work myself.

bipbap

Is the metal pipe vent at top of each water heater a draft hood?
What’s wrong with the setup in that photo? I thought we had proper venting for them.

Rich_49

No atmospherically vented water heater ever left a factory without one in the box . Why yours are missing or just not installed is beyond me . Why an inspector passed the installation is also beyond comprehension . While you may have paid a plumber a professional's wage to do such a job , I assure you , no plumber installed this , plumbers protect the health of the nation . They do not put people and property at risk . Find a new plumber if this is what our current plumber does regularly
https://www.hotwater.com/lit/bulletin/187010-000.pdf

bipbap

Ok thanks for letting me know.
What exactly is missing from the unit? What does it look like?
I can’t imagine why he wouldn’t have installed it if it came with the water heater.
I googled draft hood and it looks like the metal vent pipe over the top of the unit, but I’m guessing that’s not right.
Please give me some more info, I don’t want any issues of safety.

bipbap

Ok I looked at your pdf. Now I get it.
I have no idea why he didn’t install them if they came with it.
Is there any reason to not install or is it a 5 minute job and he just slacked?

ratio

If I had to guess, I'd say not enough height to get both the draft hood and the reducer (enlarger?) in there. I had a similar issue when I replaced my water heater—not much (but sufficient!) elevation to get the draft hood on the end of the 90, even with a lowboy.

bipbap

Ok so maybe the new hot water heaters were a little taller than the old ones and he didn’t take the time to cut down the vent pipe to fit it in there? Is that a possible (but careless) explanation?

Is the idea that the draft hood allows air to draw in and exhaust to go up, and with the current setup, fresh air cannot get in?

Wellness

@billtheplmbr3845, @Rich & @GBart called this one correctly. I don't know if I'd still be online pondering the finer points of hot water heater installation with potential scalding and heater ventilation issue on my property. I'd be on the phone with a competent plumber, asap.

bipbap

Don’t worry, I already called a company— and also called the other guy to ask why the hell he didn’t install them.

I only ask because I’m curious and want to understand. I learn a ton from this site.

billtheplmbr3845

Keep us informed of the answer, we all think we heard every excuse out there. Can almost guarantee there was no permit or inspection on this. You should also install Co detectors in that area, required in Ma

JUGHNE

The draft hoods would require the horizontal vent pipe above the tanks to be raised about 4". The opening in the chimney might have to be raised up.

bipbap

Ok so you can’t just cut down the vertical vent pipe to fit in the draft hood?

Raising the horizontal pipe gets tricky because it shares a vent with the boiler and that vent runs horizontally out the exterior wall about 8’ through an outside shaftway to a chimney where it then goes vertical.

billtheplmbr3845

If those water heaters were to tall to use the existing chimney connector a new chimney connector could have been installed, or evan better the water heaters could have been power vented models and revented thru the wall independently. I have had to do that in the past when the existing chimney was unable to connect to. Bill

lefty076

Is your water heater a condensing unit where you have pvc going from the top , side, or rear of the water heater ? Because they do not require a drafthood.