Hot water Heater Question????

[69boss9]

On a gas water heater , does it use less gas to run it at a low temp. setting ( I would think it would use more HOT water in a bath tub ), or to run the heater at a high setting ( and use less HOT water in the same tub and more cold)

 

[Knipper]

Obviously the lower the temp setting on the water heater the less gas you will use to heat it. The trick to finding the right setting is determining how much hot water you need before you run out.

This is how I find the best setting. Turn down the thermostat about 5° (on my heater, half a notch). If no one complains, turn it down again, until you do get complaints (hopefully it will be you in the shower and not a half-shampooed wife). When you rach that threshold turn it back up 5°. Future tweaking may be necessary but thats a good baseline.

 

[LocoCoco]

^ That's a good way to do it. I've never really thought about the temp of my water but if I could turn it down a bit and save a few bucks and have no change in quality of life then I'm game.

Except I disagree about the half-shampooed wife. In my house it would be pretty funny, well, to me.



LC.

 

[HoosierBuddy]

The advantage of a lower temperature setting is you'll have less standby loss from the hot water tank to the surrounding space and PROBABLY less heat loss in the hot water pipes, as heat loss is going to be proportional to the temperature differential. (I say "probably" because the heat loss in the pipes will also depend upon fluid velocity...and that brings in a lot of tricky issues related to laminar vs. turbulent flow that make my head hurt to even think about.)

Anyway, if you could neglect the standby loss (which you can't really...because it is significant), and assume no lost heat in the pipes, it would be the same cost to take the shower at a given temperature regardless of the water heater setting, as it takes the same amount of heat to raise the tank's temperature by 1 degree...regardless of the temperature it started at (until it reaches its boiling point).

None of that is really helpful. The "turn it down a notch until they complain" trick is probably the way to go. Beware of the fact that you need more hot water in the winter because the incoming cold water is colder. You also need A LOT more hot water once your kids hit about 14...but that's a whole 'nother thread.

Phil

 

[green.bubbly]

That is actually a interesting question to which I do not have an answer.

When you take a shower or bath, you must mix hot and cold water to get the temperature you want. Lets say for example that when the hot water is set at 120, you need a mix of 50% cold water and 50% hot water. So during your five minute shower, you use 10 gallons of hot water and 10 gallons of cold water.

But what happens when you lower your heater to 110 degrees? Now instead of a 50/50 mix, you must adjust the flow to 70% hot and 30% cold. Now instead of using only ten gallons of water, you are using 14 gallons hot and 6 gallons cold.

So even though you would see an energy savings by only heating the water to 110, you must now heat an extra 4 gallons for the same quality shower.

So the question is, is it cheaper to heat 10 gallons to 120 or 14 gallons to 110?

 

[Falcon67]

Wee keep ours at 140F. That sterilizes things for the grandbaby and keeps the showers hot. We have single turn shower valves that let you set the max hot temp to help prevent scalding. The water heater does not run that much and recovers quick. My wife likes long showers. Also, in the winter the water towers lower the cold water temp in the lines. If your hot water isn't hot enough, you'll find out on a cold morning and it'll be not happy time LOL. I think the savings will be minimal from 120 to 140 with a good quality heater.

 

[jvitez]

The lower the temp difference between room air temp and the water heater set temp the lower the RATE of heat loss. Remember velocity vs acceleration in science class? It's always more efficient to set a water heater as low as possible. Using more cool water than less hot water is no difference when the heater has to heat up the cold water that entered it, but during standby is where losses are less.

That being said, Legionella bacteria thrive is lukewarm temps, so 140F or higher is better in this case. You can run out of water is the temp is low and the tank is smaller than you need, as a tank can only provide ~70% of it's volume before starting to cool off significantly, so a 40 gal water heater has only 28 gal of usable hot water.

A cooler tank temp will also reduce the rate of galvanic corrosion, prolonging the life of a glass lined steel tank.

The real answer is a Marathon electric tank (polybutylene, so never rusts, and no galvanic corrosion so no need for an anode rod), or a tankless water heater, or a stainless steel highly insulated tank. Actually, the real answer is solar hot water. It gives so much a bit of heat loss doesn't matter.

I have a Marathon tank set at 130F.

 

[deathbound]

Tankless water heater, digital setting, endless hot water, no pilot light, no tank to keep water heated. May not answer your question, but only uses gas/water on demand. Pros & cons with these.

 

[Robert Haas]

Uhm, why would you heat Hot water?