Hot water tank power saving?

[apostolakisl]

Sounds like fun. I wanted to do geo-therm but it just didn't make sense where I live. Primarily I am in a cooling environment (Texas) and the ground here just isn't that much better of a heat sink as compared to air. For the 2 or 3 months that we heat the house, it would work awesome. But for $80k installation versus $25k for a seer 19 air exchange heat pump, it just didn't make sense. Our electric rates here are fairly reasonable at 10 to 12 cents. The poor guys in CA are getting hit with 40 cents or more, probably it would work out there.

 

[tmbrown97]

so just to throw this out there... I have a 60 gallon gas heater - house is 6 years old... a few weeks ago I had new gas lines installed (for a fire pit - talk about a true energy waster!) - so gas got turned off about 10:00AM. That night, the kids got a bath; the next morning my wife took a shower... we did some laundry and a load of dishes... it wasn't until the following evening that I noticed that the water wasn't really getting warm and remembered I still needed to go light the pilot.

That tank apparently doesn't lose too much heat if it took us that long to notice it was off...

 

[apostolakisl]

so just to throw this out there... I have a 60 gallon gas heater - house is 6 years old... a few weeks ago I had new gas lines installed (for a fire pit - talk about a true energy waster!) - so gas got turned off about 10:00AM. That night, the kids got a bath; the next morning my wife took a shower... we did some laundry and a load of dishes... it wasn't until the following evening that I noticed that the water wasn't really getting warm and remembered I still needed to go light the pilot.

That tank apparently doesn't lose too much heat if it took us that long to notice it was off...

That is becuase of the specific heat of water is very high.
It takes 4.2 joules to heat 1 cc of water 1 degree celcius.
It takes .0013 joules to heat 1 cc of air 1 degree celcius.

4.2/.0013 = 3230

So to lower cubic foot of water one degree, you would raise 3230 cubic feet of air one degree. That is why it takes so long to boil a pot of water and why it takes so long for a 120 degree hot water heater to cool off.

 

[fwd03]

If really want to save energy, there is a tankless water heater, like this:
http://www.buyplumbing.net/R94LSING-Rinnai-Tankless-Indoor-Water-Heater-9.4-Gpm-Natural-Gas.html

 

[apostolakisl]

If really want to save energy, there is a tankless water heater, like this:
http://www.buyplumbing.net/R94LSING-Rinnai-Tankless-Indoor-Water-Heater-9.4-Gpm-Natural-Gas.html

Frankly, I don't really think the tankless jobs make a ton of economic sense in the pure sense of savings on fuel consumption. They are substantially more expensive so the payoff is pretty long if you consider only that.

I do love them for 3 reasons.
1) They take zero space. I have two of them mounted in the stud space on the outside of the house. This truly equals zero otherwise usable space consumed.

2) They are easier to locate near the usage spot. (This probably saves more energy then the other factors, especially when you consider the other option of doing a recirc pump, especially when you spend most of the year with AC on and you don't want to dump all that heat into the house)

3) They way outlast tank heaters. And, more importantly, when they fail, it is almost never becuase they bust a leak. I can't tell you how many people I know who have had substantial expense related to leaking hot water tanks.

 

[tmbrown97]

To Lou's points... I want one because of #1 - to get that corner of my garage back!

And #3 - they can fail catastrophically if not installed correctly, and if you get a cheaper unit. I guess they need to have auxillary heaters in them to compensate for cold air coming through the flu - and I think someone I know was putting a battery backup on his for extra protection - I need to ask again.

Also - they really need to be hooked up right - they create a lot of heat in a hurry, so any problems with the exhaust can cause real problems.

 

[apostolakisl]

I think it would be safe to say that anything that uses electricity, water, and/or natural gas needs to be hooked up properly or very bad things can happen.

Regarding the freezing issues, I agree that tankless are bad options in cold places. Primarily becuase you are dealing with very cold water, 35 degrees or less in the winter up north. That requires at the very very minumum a 75 degree rise and that requires a very big heater if you want any meaningful gpm's. In reality, you probably need more like an 85 degree rise. The expense of such a big heater probably out weighs the benefits.

Plus, you can't mount them outside, so you have added costs of plumbing the vent lines, which are pricey. Plus there is that remote chance of a freeze up with a long power failure on a cold day. However, just trickling a faucet will prevent the freeze-up, but you have to be home and actually think about it.

 

[szoostrom]

I found the attached post on another site when trying to answer this same question. The author estimates about $0.24 savings when he turns off his 80 gal hot water heater for an 8.5 day vacation. He also provides a basis and math to back it up.

http://www.leaningpinesoftware.com/hot_water_heater_vacation.shtml

He also poses some questions about whether or not it's worth the effort for so little savings. Each individual would have to answer that for themselves.

 

[apostolakisl]

I found the attached post on another site when trying to answer this same question. The author estimates about $0.24 savings when he turns off his 80 gal hot water heater for an 8.5 day vacation. He also provides a basis and math to back it up.

http://www.leaningpi..._vacation.shtml

He also poses some questions about whether or not it's worth the effort for so little savings. Each individual would have to answer that for themselves.

I agree, the main way to save money is to use the most cost effective fuel. Electrical resistance is pretty much your most expensive option. If the OP puts his geothermal heat pump in, that will heat the water way more efficiently in the winter and for free in the summer.

This website says it all. http://www.smunet.net/electricvsgasheat.asp

Geothermal heat pump is 350% more efficient than resistance. Air source is a respectible 250%. Now there is a real savings on the electrical bill!

 

[LCARS]

jrnkempa's link above is pretty convincing that the savings would not be that much, but I think I'd like to prove this for myself using my own real world variables. I have a (huge) 80 gallon tank that I don't use at all for 4.5 straight days every week. I have a kill-a-watt that I can stick on there and try it both ways: 1) Leave it on for 4.5 days 2) Leave it off for 4.5 days and heat it back up. It'll take me two weeks to report back my findings, but I'm quite curious now.

In order to get accurate power consumption results, I guess when I test the second way I'll have to keep an eye on the kill-a-watt to see when the power consumption dips down to know when the heater is all done heating. I don't honestly know how long that will take to heat the water back up from scratch.

 

[znelbok]

They are some results I would like to see.

Please do this test and report back.

Mick

 

[apostolakisl]

I would be curious to see what the water temps are at different times.

 

[tmbrown97]

Your heater should be hardwired 240V - what kill-a-watt do you have that can measure that?

It seemed like my gas heater took about 45 mins to get full-hot again after I fixed the pilot... not sure how long electric would take - I'd imagine like a good 2 hours minimum.

With everything you're doing to this weekend home, maybe it's time for an Elk or something for true automation! Then you can fire up your phone or even send the house a text message when you're on your way and have it prepare for your arrival!

 

[LCARS]

Work2Play, you had better intuition than I did. There's no way I'll be able to put my kill-a-watt on there, first it does appear to be 240v, second it's hardwired. It could probably be measured with a current clamp instead, but I don't have one of those.

 

[WayneW]

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.