How do I figure out what temp to set my water heater?

I have a 50 gallon gas water heater. If I leave the temp on the normal setting, I have to put the shower on almost full hot in order to get a satisfyingly hot shower (especially in the winter when the pipes are cold in the morning) and I suspect my wife goes 100% hot because she likes it even hotter than me.
(pause to wait for all the jokes about my wife liking it hotter than me)

If I turn it on higher, obviously I am able to use a higher ratio of cold to hot water for the shower, albeit with a slightly increased risk of scalding the shit out of myself by accident. But how do I figure out which is more efficient?

My dishwasher heats the water up itself, my washing machine is an HE front-loader but it does not heat the water, and we take 2 showers per day with a low flow shower head (avg 10 - 15 minute shower), with the kids sharing one bath every 2 days.

I have my on demand hot water heater set only as hot as it needs to be without adding any cold. I could never understand heating it up so much that you have to cool it down. Seems like a waste of energy to me. I put the remote bbq thermometer under the flow of water and then go to the heater to adjust the temperature to the level of hot that I want.

It depends on the age of your children for the most part.

If there is a risk of scalding your children, adjust your shower schedule until they are old enough. Water temperatures above 130 degrees is dangerous, above 140 degrees will potentially scald a child in no time.

As a side note, anti-scald shower valves only protect you against scalding due to pressure fluctuations in the pipes, not against actual hot water temperature. If you turn your water heater up too high, even if you have anti-scald faucets you can still scald a small child.

At least here, as a licensed plumber I am not permitted by code to turn your water heater above 120 degrees. I can show YOU how to adjust it, but I can’t legally turn it higher.

First of all, you probably have it set hotter than ‘skin comfortable’ for adequately washing dishes and clothes. Or are you saying you set it an even hotter temp when you want to wash clothes or dishes?

Second of all, I’m curious to know the cost difference (using a simplistic comparison) of a gallon of ‘skin warm’ heated water versus 1/2 gallon of hot water mixed with 1/2 gallon of cold to average it out to ‘skin warm?’

Well, it has to do with the flow rate, really. If I am inthe shower and I need full hot to be comfortable, then any noticeable drop in the hot water pressure (ie someone turning on the dishwasher or washing machine) cuts my flow significantly. If it’s hotter than necessary, I can adjust the amount of cold water flow and get a smaller drop in pressure than if I have to have it on full hot.

As for the kids…right now they don’t take a shower and can’t reach most of the sinks. The bath fixtures, when off, require significant effrt on my wife’s part and mine to turn on, so they can’t turn them on while bathing (and we don’t leave them alone while bathing anyhow).

A thought occurred while reading this thread… initially, I thought that the “set the heater to as hot as you want to in the shower” was a good idea to conserve water and electricity/gas, but the more I think about it, the less of a benefit there is…

That is, if I’m in a house of six, I could easily deplete that hot water reserve fairly quickly, and it would be much easier to have hotter water, mixed with unheated cold water straight from the tap, thereby using less energy…

Maybe? I think my logic might be flawed there.

I think the newer accepted “green” answer to this question is to set the water heater to a lower level (and for so many degrees lower you will get x% savings). Keeping 50 gallons of water at 130F degrees will be cheaper than the same 50gallons at 150F degrees.

As far as saving energy and money is concerned this is going to be the answer.

For most homes I’d bet that for 20 or more of the 24 hours in a day there is little to no flow through the water heater. And for all that time, the water heater has to keep the water at whatever temperature you set. And the lower that temperature, the less energy you use. So setting the temperature at the lowest setting that fulfills your needs is the way to go.

On the other hand, if your water is always in use or you have some kind of tankless on-demand system, and the water is not sitting in the heater losing heat (in other words it gets heated up once and then used) it’s not going to make a huge amount of difference. The higher the temperature the more you lose to the environment through the pipes being exposed to air, but once the pipes are up to temp that probably is a fairly small amount compared to the total usage. But even here, the lower temperature will still use less energy, the difference just won’t be as large.

No, it takes more energy to heat the tank up to the higher temperature and keep it there waiting for everyone to shower. You’d save energy by setting at a lower temp, using all the water for your shower, waiting for the tank to come back up to temperature, let the next person shower, and so on. It’s a pain in the ass (or is that cold on the ass?) but it saves energy.

Barring very unusual circumstances, you’ll use less energy by setting a lower temperature, just like with your furnace.

Some energy-saving, well meaning folks are saying you shouldn’t set the heater any higher than 120-130 degrees F. At first, that seems to be a good idea. However, if you’d like to kill the dust mites and their eggs on your bed sheets, you need 140 degrees. If somebody in your family gets sick, and you’d like to avoid passing the germs around for weeks on dishes and silverware, 120 degrees is not hot enough.

The Second Stone, who has handled litigation involving hot water heater scalding suggests setting it as low as you can possibly tolerate it probably around 110 and that is Fahrenheit. My case involved a drunken mother and a mentally retarded child in a bath in an apartment complex where somebody had access to the water heater and turned it up because the tenants all tried to shower at the same time. You can burn skin and make it melt like butter at temperatures people drink coffee at.

Definitely avoid temperatures where you need to cool the hot water with cold water.

Any time someone has small children in the house, I advise them against turning the temperature up at all. The gain in perceived hot water volume is not worth the trip to the emergency room and the subsequent scarring of your child.