Hot water tank power saving?

[wwat]

Beaumeri,

Yes there is savings to be had. Actually I have found this to one of the biggest saving on my pursuit of lower energy bills. On the 12th Nov the hot water heater was on 24 hours, usually I have it on only during off peak hours. You can see it came in at over 20 KWH. Just make sure the temperature doesn't drop below 130 deg which is the safe minimum temperature for a hot water tank.

Regards, Wayne

 

[apostolakisl]

Your water heater should have a wattage rating plate on it, so you don't need a current clamp for ballpark numbers. So really you just need to know how long it is on. I use a 240VAC relay with the coil connected to a heater element and the relay contacts to my Elk zone. IIRC, it took about 30-45 minutes to heat up my 50 gallon electric tank when I installed it last year. The big variable is the temperature differential, which is how hot you want your output compared to how cold your input is. Our Florida water supply is relatively warm and our Florida garages are fairly warm, so we usually don't spent a lot of energy on hot water.

I live in Texas. I used to have a natural gas house. The hot water tank was in the garage. In the summer, the water input is at least 80 and the garage is usually well into the 90's (which is where the tank is). My summer time gas bill would be about $5.00 in gas and $7.00 connection fee. In the summer, the only thing using gas was the hot water tank.

I had no way to know what the winter time use was since the furnace was also gas. The total bill in Jan for gas might be $250 in that house.

 

[ano]

You've all spoken about the savings of doing this, but not about the added costs. Yes, you will save electricity, because I have done this for several years. But the savings didn't cover the costs. So what costs? A new hot water heater every two years. Every time you let the water cool and then heat again, the tank will contract and expand, and this, over time will cause leaks that will require a new water heater. Mine had a 15-year warranty, and it was replaced twice for free, but I did have to pay labor costs. I couldn't figure out why these top-of-the-line water heaters were going out in less than two years, always failing with leaks, then it dawned on my, it was the thermal cycling. They just aren't designed for that. So I say, don't do it. Sure, if you are going away for a week or more, turn down the temp to save power, but otherwise, you'll be sorry. I keep the power on now, and the third one has been running 5 years and no problem.

 

[wwat]

ano,

You should not let the water cool down so much. It should not be allowed to cool lower than 130 degees. I've been doing this for some time now and have not experienced the
problem you described. Yes there is some initial outlay but most things you do to save energy dollars are a long term investment, just like LED's for example.

 

[apostolakisl]

I don't doubt Ano's contention about the expansion/contraction cycle being an issue. Of course, this same thing happens when you use a lot of hot water quickly and the tank starts to fill with lots of cold water.

ano,

You should not let the water cool down so much. It should not be allowed to cool lower than 130 degees. I've been doing this for some time now and have not experienced the
problem you described. Yes there is some initial outlay but most things you do to save energy dollars are a long term investment, just like LED's for example.

wwat, how hot do you normally keep your tank? Seems like cooling to 130 would not be much cooler than full temp.


I still contend that the real way to save is to use a heat pump water heater. You can get 3 times the hot water out of the same amount of electricity.

 

[firstone]

I don't doubt Ano's contention about the expansion/contraction cycle being an issue. Of course, this same thing happens when you use a lot of hot water quickly and the tank starts to fill with lots of cold water.




wwat, how hot do you normally keep your tank? Seems like cooling to 130 would not be much cooler than full temp.


I still contend that the real way to save is to use a heat pump water heater. You can get 3 times the hot water out of the same amount of electricity.

I'm curious about this too. I've had my water set to 135, and I thought it was very hot. I'd think normally you'd have it in 120 - 125 range. Does the heater run at much higher temp than the water coming out of it or something like that?

 

[wwat]

wwat, how hot do you normally keep your tank? Seems like cooling to 130 would not be much cooler than full temp.

I think its set for approx 140 or 145. Most of the savings are had because of the higher electricity prices during certain hours of the day. Generally I only run the HWH during off-peak times, I have also programmed an override switch in ISY for the odd time we need it.

I'm curious about this too. I've had my water set to 135, and I thought it was very hot. I'd think normally you'd have it in 120 - 125 range. Does the heater run at much higher temp than the water coming out of it or something like that?

I have mine set for approx 145 so when the HWH is off during on-peak electricity times it has enough temperature to drop and still stay above 130 (there are times when this wont happen) generally it works out.
So basically I am storing cheap electricity in the form of hot water. The reason that you should keep the temp above 130 is to help prevent bacteria from growing in the system i.e Legionella.


Regards, Wayne.

 

[apostolakisl]

My on-demand system maxes out at 120. You can jimmy with it to go higher, but I believe it is actually code on them to max out at 120. Since they don't store hot water you don't have the issue of bacterial growth. It's a safety thing at 120, it's pretty hard to get anything more than a little pink and tender at 120. Eventually you'd actually injur yourself, but it would take some effort.

The deal with needing hotter water with a tank system is that with 140 deg water you use a lot less of it to get 105 or so at the faucet (mixed with cold) so the tank lasts a lot longer. The tank systems rely on intermittant use and the heat storage since the btu's they are capable of can not keep up with real time use.

I can definitely see where timing your tank heating cycle could really help if you have peak demand penalties. Sounds like you live in the great electrical rip-off state of California!

 

[firstone]

The deal with needing hotter water with a tank system is that with 140 deg water you use a lot less of it to get 105 or so at the faucet (mixed with cold) so the tank lasts a lot longer. The tank systems rely on intermittant use and the heat storage since the btu's they are capable of can not keep up with real time use.

Yeah, that's the reason I've had it at 135. Even then my 40 gal tank would run out with a few successive showers. Never knew about 130 minimum temp. I think it was at 120 when I bought the house. I can't really imagine safely using the unit if you keep it at 140 - 145. As it is I burned myself a bit at 135. Not such a big deal but a little painful.

And one of the reasons I've switched to tankless models is the quick way to adjust temperature. I can just use 105 for shower, 110-115 for bath and 130-135 for shaving. My unit goes to 145 with remote (and can be adjusted to 185 internally).

 

[wwat]

A little more info http://en.wikipedia.org/wiki/Water_heating , scroll right to the bottom under section 'Water heater safety'.

 

[jharrell]

My gas hot water tank has a tempering valve on the output that can be adjusted and mixes some cold water with the hot water allowing higher tank temperatures but lower temperatures at the faucet. This helps prevent the bacteria risks while also prevent scalding risks. They also have the side effect of extending the capacity of the tank since less tank water is used to achieve final output temp water.

I bet a lot of you have one on your tank, they are a relatively common thing to install, it looks like a shutoff valve with a connection to both the cold and hot sides of the tank, usually very close to the tank. You have to adjust the this valve in unison with changing the tank thermostat to achieve a desired output temp.

They are also a relatively cheap addition to an existing tank, I think is the one installed on mine actually: http://www.amazon.com/Watts-Consumer-Markets-Tempering-Valve/dp/B000KKKH9E

 

[firstone]

Thanks guys, a lot of useful information here. Somehow people who preach "good ol' tank heaters" and bashing tankless do not mention any of the potential health issues and such. I still think going tankless was the best decision I've made even though it costs me double.

 

[apostolakisl]

Thanks guys, a lot of useful information here. Somehow people who preach "good ol' tank heaters" and bashing tankless do not mention any of the potential health issues and such. I still think going tankless was the best decision I've made even though it costs me double.

I don't really look at tankless as a way to save energy. I look at them as a way to have your hot water heater disappear into essentially zero space, a way to have a hot water heater that is almost certainly to never leak, a way to have hot water flow that never runs out, and a way to have a hot water heater that I will probably never need to replace.

Tank style hot water heaters end up leaking, they just always do. Unless you just schedule to replace it every 5 years. It is far and away the most likely reason to have to replace one. I have personally had multiple hot water tanks that leaked and needed replacing. They have always been 5 to 10 years old. None of them ever damaged anything becuase they were either in the basement or garage. But if you can't put a heater in one of those places, you are setting yourself up for disaster. I know two people in the last 3 months who had significant damage becuase of that. So, a tankless may cost twice as much, but I think it will pay off both dollar terms and in reduced headaches. Plus, the bonus of no space used up and endless flow.

 

[Kevin L]

Tank style hot water heaters end up leaking, they just always do. Unless you just schedule to replace it every 5 years. It is far and away the most likely reason to have to replace one. I have personally had multiple hot water tanks that leaked and needed replacing. They have always been 5 to 10 years old. None of them ever damaged anything becuase they were either in the basement or garage. But if you can't put a heater in one of those places, you are setting yourself up for disaster. I know two people in the last 3 months who had significant damage becuase of that. So, a tankless may cost twice as much, but I think it will pay off both dollar terms and in reduced headaches. Plus, the bonus of no space used up and endless flow.

For the most part, Lou, that's true. As an insurance agent for 34 years, I've seen plenty of claims for water damage from leaking hot water heaters.

When I designed and built my home a few years ago, I had considered tankless water heaters. Mostly, I didn't want to run out of hot water if multiple showers were running at the same time. I settled on a tank water heater from Marathon. For starters, Marathon removed my concern about leaking:

Residential Warranty YOUR MARATHON TANK IS WARRANTED NOT TO LEAK FOR AS LONG AS YOU OWN YOUR HOME*�
Marathon offers this no-leak promise because of its superior, non-metallic PermaGuard tank construction - a seamless blow molded polybutylene tank with a filament wound fiberglass outer tank for maximum strength. Superior performance, high-efficiency, and low operating cost�for a lifetime*!

Second, they do not use a metal tank, so no rust or need for an anode. The tank is encased in foam, so heat loss is minimal. My 105 gal tank was installed in 2007 and still looks and performs like new. Here's some information about Marathon heaters:

The Marathon electric water heater offers these advantages:

• Technologically advanced design is clearly differentiated from short lived steel water heaters.
• It's the most durable water heater made, with a warranty to match
• Envirofoam™ insulation is completely free of CFC and HCFC ozone depleting gases. Marathon leads the way in environmental friendly manufacturing, design and operation.
• Tank comes complete with a factory installed vacuum relief valve, ¾" brass tee and ¾" brass nipple for easy, professional installations.
• Replaceable brass drain valve
• All wiring run in conduit for easy control wiring
• Seamless blow molded polybutene tank with no anode rod required for a corrosion free life
• High temperature, commercial-grade diptubes for greater durability
• The filament wound fiberglass outer tank is designed to be more flexible and withstand more pressure than conventional tanks
• Our unique high temperature dip tube is offset from the concave bottom, creating a "whirlpool effect" which helps prevent sediment build-up
• Every tank includes 4' of pipe insulation for even greater savings.
• For complete specifications of all models, click here: Specifications

See the Marathon Tour for an informational video.

With the insulation, and the fact it's in my garage in Southwest Florida, heat loss is very low, so I've never bothered turning off the heater to save energy.

Kevin

 

[apostolakisl]

Looks like one hell of a tank. In south Fl you probably have 70 plus degree cold water so I imagine between that and 105 gallons, you should never ever run out of hot water. That monster tank must have cost a fair amount, though. I assume it put you back about the same or more than a tankless?

The higher btu tankless heaters will easily run multiple showers at the same time when your cold water isn't that cold. If I lived up north, I probably would not do a tankless.

The only thing I don't like about tankless in my house is the fact that you really can't do a recirc pump.