Will installing a timer box on my electric water heater really save me any money on electricity?
Here are the details:
2 people in the house taking 2-3 showers per day at odd hours. Tank is electric and 50 gallons. I have a switch in-line now as it was required by code when I built the house so installing a timer box would be easy…just the cost of the box and my time.
But would it really amount to anything or would the onoff cycling of the element in the tank cause more damage than benefit?
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Replies
Interesting question. If you don't get a definitive answer, you could get one of those KWH meters (it would need to work on 240V), and gather the data yourself.
Please let us know what you find.
Thanks,
Scott.
Probably not much. If you only used hot water at one time once a day you might save a little, but even then I doubt it.
A reasonable modern WH has lots of insulation and the heat loss is not that much it will still be hot 12 to 24 hours later. And whatever loss there is will have to be made up with it is turned back on.
You probably have to go to once every 48 hours to start to get savings.
William the Geezer, the sequel to Billy the Kid - Shoe
Yeah, I shut it off if we are out of town for more than one day but was always just curious if it switching onoff two or three times a day would help out any?
Hmmm?
No.I heard a prodfessor who specializes in testing things like this. He sets up systems with thermocouples and ways of measuring all sorts of test scenaarios.You need to be off for three days before it makes a diffference, because a well insulated WH will maintain good temp when not in use for a day anyhow. Then there is the cost to bring ccold water back up to seting temperature vs btus it takes to simply maintain temp over a given time.So his omnlusion was that anyone who manually shuts off when leaving for a number of days does well, but turning n/off over a 24 hour cycle does themselves no good - no harm either, but no good gained
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Piffin,
Thats what I wondered is if the "recovery time" of it being on and heating would negate the potential savings of being offnot heating. Seems like if it went onoff two or three times a day it might even cost more to run to reheat the water.
Mike
Maybe the hot lick would be to put the timer on the lower element (the large demand part of the water heater) and only set it to be on around your peak demand times.
Most people I know never miss a lower element until the kids come to visit. How long does it take to use 50 gallons of hot water with 3 GPM shower heads, using a mix of cold water? Usually a shower will be fine with the 10 gallons or so around the top element.
It's simpler to just turn down the bottom thermostat 5-10 degrees.
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How long does it take to use 50 gallons of hot water with 3 GPM shower heads, using a mix of cold water?
Well if my calcs are correct, about 18 minutes if you assume a 115 degF shower (which is my standard for this calc). While shower temp can vary a LOT depending on the person/weather/etc, I think 115 is a reasonable value to use. At 110, it's 20 minutes. 110 deg shower isn't really that warm IMO.
But you are in violation of the max 2.5 gpm flow rate allowed. :) Personally I'd go for e.g. the Jet Stream 1.5 gpm shower head ... particularly if I had a couple of daughters from heck that loved to take showers. It wouldn't discourage them, but then I'd save on the hot water and water ... I'd shut OFF the water to discourage them. :)
A recent concern which has arisen about water heaters (and esp elec) is whether temps which are too low will allow legionella bacteria to grow in the tank.
I've found 2 studies, one says no difference if temps are below 140, another found differences, but tested elec water heaters on private wells only.
My own view is that if the lower temps encourage/allow such growth, any system with a central heater is likely to have lower temps in the distribution pipes and thus would also "encourage" /allow such growth.
To CMA, in my inspection reports I recommend against using the "vacation setting" or, when returning, set the temp very high temporarily and flush the hot water pipes with extra hot water for awhile
BTW, the legionella bacteria problem is said to an issue when respirated mainly.- such as in showers or humidifiers (if fed from the hot water line.)
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I've researched this a bit about legionella and domestic hot water systems. Historically legionella have the potential to proliferate in e.g. cooling towers. I think the combination of air, temperature, and water are the key factors. I think that there is also a time factor that must be present. Legionella is acquired by breathing in the microbes.
From what I understand, typical domestic hot water and water storage systems are not really good places for legionella to survive. The question comes up about e.g. taking showers. I don't think that a shower provides enough sustained environment for legionella to survive. We would likely have all kinds of design/construction requirements if domestic hot water systems readily supported legionella.
That being said, I'm no expert in legionella and you should do your own research on this topic to satisfy any specific questions or concerns. What I've gotten is that legionella survive in some fairly specific environments that simply do not coincide with common domestic hot water systems - residential or commercial. While the environments are similar, they aren't enough to really even come close to supporting legionella ... or as I said, we would have a lot of additional codes requirements to ensure the health of users. But do your own research ... see what you get out of it.
Interesting...never thought of that. Although our m,unicpal water supply has such high chlorine levels, I wonder if it would ever be an issue?
But still food for thought!
Had a timer on the WH when the poco had a time of day rate structure, WH only on during low rate times. Saved 4-5 bucks a month or so all due to rate structure. Do have a separate kw-hr meter on the WH. Also have a box on the WH with R-19 insulation.
Used to turn off the WH when gone for a week or so, the meter said (from power used when it was left ON) that saved about 8 cents per day, hardly worth the trouble.
Insulating a WH much more cost effective than a timer.
Maybe a bit of backpeddling here ...
I've been doing more reading ... but not done. My research is saying legionella can exist in 'water storage' systems (pipes and/or tanks). Legionella is only transferred via breathing it in is what I understand. It is not infectious (i.e. I can't infect you if I have it).
But it exists in some of the most common systems we encounter on a daily basis as you implied. There is a key here as to why it isn't more commonly a problem. I'm not sure what that is, yet.
It is a major concern for cooling towers (e.g. large commercial cooling systems) and that is why they require specific maintenance using chemical treatments ... also why ventilation air intakes are not placed near cooling towers.
So why isn't e.g. the common shower an issue? I don't know ... I'll be out for a week or so, but maybe someone might shed some additional light on this topic for us all. I thought I'd satisfied my curiosity in my past research, but maybe I either forgot (CRS in my old age) or didn't fully understand ... either could be likely. This can be interesting stuff.
Edited 10/7/2009 9:14 am ET by Clewless1
the common shower is used regularly so legionella concentrations should be low.typical problems are things like guest baths where legs stay "dead" for long times, vacation homes that aren't drained, stuff like that.water heaters may promote growth, but my suspicion is that the average household turns over the water in the tank often enough to avoid excessive concentrations of the bacteria... since any hot water use in the house goes through the tank.however, that isn't a "failsafe". it would seem entirely possible if you went on vacation for a week and came back that a water heater at optimal growth temps could now pose a risk.. especially if one of the first things you do when you get home is take a shower.In europe, some water heaters have timers that elevate their temperature to bug-killin' temps at least weekly, and I think some are even daily. Until we get nifty units like that, I spec 140 as a storage temp in a water heater to sidestep the entire issue. of course that requires a tempering valve in line, and it still leaves the legs as possible growth habitats.-------------------------------------
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There is also pressure to take into consideration. I understand that at over 20PSI or so bacteria don't do as well.
I wouldn't think that they would be all that sensitive to pressure.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
that's a new one on me.-------------------------------------
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It was in one of our utility handouts.
That's what I thought, too, but the information I'm getting on line indicates pretty short periods of development given the right conditions (hours and days, not weeks and months). I'm getting a lot of talk out of my research and not much hard evidence of the realities of where and when and how. My research refers frequently to the temperature at which it thrives and that it could be in any domestic water system.
It does confirm that commercial cooling towers are common 'hang outs', but implies that the average domestic hot water system could be as well ... many readers would run away in a panic after reading the implications of some of this. It's leaving me confused now ... just when I had thought I understood it enough to not worry about it, now I need to know more and the research isn't telling me why the common shower or ... better yet, evaporative coolers, don't readily support it's growth (they are common where I live).
The Center for Desease Control (CDC) talks a lot about it, but not much about the sources and why certain sources (like cooling towers) support it while the average shower routinely does not.
Frequent use at various times would tell me ... no ... not really worth it. I wouldn't do it for myself or recommend it to my clients. YES you do save the energy lost through the tank as it sits waiting for the next use, but if that next use is frequent ... not really worth it.
Oh ... and the energy loss through the tank is relatively tiny compared to the energy you use in heated hot water. I've calculated it a number of times. Better to e.g. install a low flow shower head (1.5 gpm), better dishwasher, and/or clotheswasher.
Edited 10/6/2009 7:16 pm ET by Clewless1
What the others said. The standby losses from a good quality electric water heater are minimal, so the unit has to be off for days at a time to make much difference.
I had the power company do an energy audit years ago. I had a timer and they recommended I disconnect it as it would use more energy than it saved.
One thing to consider is, where is the HW heater located, and where are you located? If the HW heater is within the heated space of your building, and you are in a heating climate, any heat lost by the HW heater to the ambient air simply reduces the heat load of your heating system.
So the 'savings' can sometimes be a lot less than people will calculate, if those factors aren't taken into consideration.