Embarrassingly stupid question. What's the best way to set the thermostat on a gas hot water heater (55gal)?

The water coming out of my faucet (hot water only, not dual line faucet that mixes hot / cold) ranges from 115F to 130F. 115 is too cold for the shower - I have turn the shower valve (dual line) to almost full hot to have a comfortably hot shower. And I may be using more hot water than necessary to achieve the desired temp.

But 130F is way too hot - even for dual line in the kitchen, the water is painfully hot. Not safe.

120F is the target temp and what I think is generally recommended. Good for the dishwasher, shower, bath and kitchen. Reasonable hot water use.

The heater thermostat is an analog dial. Hot in one direction, warm in the other. Small tweaks in the dial result in 115-130F. Or high of 120F but then most times it comes out much lower than 115F.

What's the best way to set the thermostat dial such that the hot water is generally 120F whenever I want it; not too cool (don't want it less than 115F) but don't want too hot (maybe 125F at the most; even 125F is pretty hot though).

Or is this a sign that something needs to be replaced? The unit is about 18 years old.... Do I need to drain and re-fill or something (last time was 5-7 years ago - nothing came out but clean water).

Turn the dial to the hot position and try that for a couple days.
If that isn't hot enough, step it up to the next notch and try that for a couple days.
Keep turning it up one step at a time until your eventually happy with the results.

There are no notches or steps in the dial. It just rotates. I found a spot on dial that puts me in the ballpark temp; about 3/4 from warm to hot settings.

But minor tweaks makes the water too hot or too cold. I can’t get it just right.

In my amateur opinion having replaced several hot water heaters, at 18 years your living on borrowed time with that heater. I’d consider pre-emptive replacement before it gives up at a most inconvenient time. That’s close to double the expected service life of 8-12 years.

Yea. I have savings put away for it. Estimate is $3-4k for the heater, install and bring up to code in this crazy state. So trying to squeeze every drop out of this one.

Our water is really clean and soft. No problems with deposits and such like many other areas. And the way we use it, pretty low duty cycle. Same with our furnace and ac. Our appliances have lived well beyond expected life.

Gas control may be bad.

But more likely with a smaller capacity unit, the short cycling from a small dump of hot water, resulting in a fill of cold water that is closest to the thermostatic control causes the heat cycle to overheat the water (as it brings the coler water to correct temp, the hotter water also increases in temp, and you end up with higher temp for a time after that.

The other thing you mentioned is the "swings" in temps. If that is occurring and you are seeing 115-130 and nothing else is changing, the swing is likely from the short cycle.

If it is that you are just unable to "fine tune" and end up too high or too low, that likely goes back to the gas controller.

55 gal. Is that small in this context?

Short cycling: so should i set the dial first thing in the morning based on temp at first use? Or, first thing in the morning, dump some water, say 5 gal, wait for the heater to heat and turn off, then set the temp based on water coming out at that point? It's winter so incoming water is colder so the swings may be more exaggerated?

Gas control; repairable or new heater?

No. 55 is not small, I was referring to the temp swing due to short cycling. It would be more obvious in a larger heater, than a small unit. (I just didn't make it clear that I meant the gas control is more likely the problem in a smaller unit than short cycling.)

If you use a large percentage of heated water from a smaller heater, (than you have), then the inflowing water will create a lower overall temp and the heating time will be fine to bring the temp back up.

With a larger capacity heater (like your 55 gal) the same amount of water used, is a much smaller percentage, and the cold water will trigger the heat cycle, and the larger percentage of still hot water, with a small percent of colder water that enters from the in feed tube, is discharged to the bottom of the tank, and needs to be heated, but the existing hotter water at the top will also be heated to some degree in the process of heating the cold water (where the sensor is).

So, a "short cycle" of smaller use of water will often result in a higher temp from heating as it is a spike, (more heat than actually required for the amount of cold water, because the heating happens faster than convection will mix the larger total volume of all the water, and that results in an overall rise in temp.)

The smaller capacity heater will have a greater amount of cold water to heat, but the time it takes, the convection of the water will mix over the time it takes to heat back up.

And, yes the colder water incoming due to lower supply in winter will also increase that swing.

Set the heater so the swing to the highest, is still the safest and most comfortable (balance).

I live alone, so I have mine set lower, and that minimizes the swing. It is a little cooler than I want, but I never worry about scalding, a problem I did have that "seemed" random, but was a result of short cycling.

Replacing the controls may or may not be possible depending on the unit and/or age (parts availability).
Our local gas company used to provide several services, but last time I used them was back around '94 when I was building houses. But a call to them might get you good information. (an maybe they can do a system checkup)

Thanks!!! I get the rough picture now.

Seriously, the collective SF could write many books on ‘how things work.’ Amazing each time.

Yeah. But how does a Thermos know...?

Mine is digital. I can change it with the press of the button. I too found 110,115 too low, and have it set on 120F. But also in South Florida wherree my house is kept at 74Gg and the water itself on th ecold side isn't super oldcc

Go tankless.

I nudge it up wintertime because PA reservoirs are colder. A little east of B.

quote:

Originally posted by ElToro:
In my amateur opinion having replaced several hot water heaters, at 18 years your living on borrowed time with that heater. I’d consider pre-emptive replacement before it gives up at a most inconvenient time. That’s close to double the expected service life of 8-12 years.

I concur with that assessment. Had a Bradford-White start leaking two months after the warranty expired.

A lot of good responses and yes you are on borrowed time. Although it’s never a good time to spend money it will be cheaper to not have to do it on an emergency basis. Significantly cheaper...

Not knowing your personal situation you should strongly consider a tankless water heater. The better ones like Navian, can be vented with PVC pipes. They will use about 1/3 less gas so it will help recoup the cost.

quote:

The unit is about 18 years old.... Do I need to drain and re-fill or something (last time was 5-7 years ago - nothing came out but clean water).

18 years is pretty old for a gas hot water heater. I think 10-12 years is about average.
It's probably just getting crotchety, maybe a bit senile.

quote:

Yea. I have savings put away for it. Estimate is $3-4k for the heater, install and bring up to code in this crazy state. So trying to squeeze every drop out of this one.

Can't blame you, but that does sound a bit high...
I bought mine at Home Depot for $500-700 or so. Brought it home in the old mini-van we used to have. Had a furnace/ac guy I know hook it up for $200. Under $1K and done.

Thanks all.

I'll reconsider proactive replacement. The estimate is probably ballpark - apparently I can't just remove and replace; there are code changes that need to implement (venting system or whatever).

House is on a slab. I think all the lines are in the slab. Oh, I do have a recirculating line. Is that perhaps contributing to the swings? Causing constant mini-short cycles during winter?

I tweaked the dial last night. This morning, first use was perfect at about 122. I'll measure periodically today to see what the high point might be; adjust down a little if it gets much higher than 122. Tricky part is keep low point above 115.

The thermostat may have some of the scuzzy build up from minerals effecting it's operation. I agree you are long overdue. A new hot water heater may be more efficient too and help offset the cost over time.
Check to see if your gas company offers any help for a more efficient unit.

If you have to replace it, consider a Tankless water heater, since you have Gas already plumbed in to the area and electricity it should be an easy install.

Gas use will be less, you'll have unlimited hot water, if you're in a temperate climate like CA then it should work well.

You might even have some government/utility rebate money for installing an energy star water heater replacement like a tankless or solar water heater unit.

Do you have water heater assisted heating system?

I lived in a apartment that used the water heater as a source. They plumbed them backwards.

the heat exchange dumped the now cold water into the top of the tank, which is where the source for faucets is.

taking a shower, heater kicks on and bam cold shower.

I supposed you could have something like that with a recirc loop, if the pump was going the wrong way.