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Control electric water heater or use tankless for best efficiency?

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  • dumplingseggplant
    replied
    Tankless Water Heater can be great and you can enjoy constant supply of hot water.

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  • centerisland
    replied
    Energy source (gas versus electricity) should be distinct from the tank / tankless approach. Yes, the cost of a BTU to heat water may be different between these two sources in different markets, but the cost of upgrading your gas or electric service to support a water heater might overwhelm that.

    We have a Rinnai gas heater, which the previous owners installed in an exterior wall of the garage to replace an electric water heater located in the furnace room (where there was also gas service for the furnace). But the Rinnai consumes an astonishing 199K BTUs / 199 CFH, which is greater than the rated gas flow through 3/4" pipe!

    Our current gas bill is $18.75 for a summer month when it's unlikely that the furnace came on (we have been using some air conditioning though!). But that includes a $10.29 "basic charge" for the connection. The actual usage is $7.29, and that's for hot water for 3 long showers per day, dishwasher every other day, and a few loads of laundry. Honestly, our cost of heating water is so low that it's not even a consideration.

    What is a consideration, though, is that the run from the garage to the kitchen is rather long - maybe 25' longer than from the furnace room - so I added a 2.5 gal Bosch heater under the kitchen sink (and the electricity for that is not included in the calculations in the above paragraph). And we are remodeling the master bath that is located above the garage, so I had a plumber home run new supply lines from there to the Rinnai to shorten the distance. I'm sure that will lessen the amount of water run in that bathroom in order to get hot water - and that's a double savings because our sewer cost is based on water consumed.

    While I appreciate the low operating cost of the Rinnai, I'm also quite happy that the water heater is effectively outside the house. I've had a water heater fail and leak inside a home and it wasn't a great experience - and as far as I know, water heaters are still not considered leak-proof.

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  • collegeboyslive
    replied
    i have had both in places i lived, Tankless is the way to go simply you NEVER have to worry about running out of hot water oe with a tank and HS, worrying about needing an unexpected bath or shower at an odd hour, plus the energy savings. ( Sorry, there are a few things that even HS cant improve on )

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  • Extreme-Z
    replied
    Originally posted by AshaiRey View Post
    I use a solarboiler for this. In the summer it switches off at about 11:00 AM because the 110 liter boiler reach its maximum temperature of 95 degrees Celcius. And in the winter, freezing cold (-15) out side but with a sunny day the boiler still reach about 55 degrees Celcius
    A local buddy has a solar water heater he put in about 4 or 5 years ago. Initial install cost was around $4000 but there were several federal and maybe even state rebates back then. I think he said his total out of pocket cost was about $2000. That is definitely a good option I think if one has a larger family and plans to stay in the home for many years. Me, if my water heating bill portion goes to under $10 a month it would take a long time to pay for it!

    Originally posted by Rupp View Post
    Wow. I guess we are blessed to have gas available. Our gas bill in the summer months which is for hot water only for our family of 4 is only $20 a month. I'm guessing it would be less but that's the gas company's minimum charge now. Winter time is a different story. We have a 50 gallon water heater located in the garage and it could have been laid out to be much more efficient. Our bathroom is on the exact opposite side of the house and it takes forever to get hot water to our shower/bath. We run the dishwasher nightly, 4-6 showers a day and laundry several times a week. I even have a water hose attached to the water heater so I have warm water to use in the fall and winter months to was the cars. If you have gas available that would seem to be a better option.
    I think you are definitely correct, Rupp, if one has a lot of water usage like you. A bud at work uses gas in his home for cooking and water heating. He has an tankless gas whole house water heater that he paid a little over $1000 for years ago. He told me last night he uses right a tank a year (100 gal) which is about $400 to fill. He has a family and does use his stove/oven but I don't know the breakdown. Still, both together are only around $33 a month which is less than just an electric 40 gallon water heater.

    As for your problem with it taking so long for the water to get hot, I'm not sure of your water piping layout but look into adding a natural circulation recirc line. You might be able to do that fairly inexpensively depending on your piping layout.

    Originally posted by misraels View Post
    I'm with Rupp on this one, the best answer is really switching to gas if you have that as an option. I was surprised when i saw the original post stating $70 per month...but in looking up some charts on water heater costs per month along with comparisons over their expected lifetimes, gas is definitely much more efficient, and uses very little power and can run off generator when needed (ours is electric igniter)
    I think you're right if you use a lot of hot water. For me though, it is still looking like this little tankless heater is the best option in my case. With an initial cost of around $250 to heat my water for less than $10 a month (and probably closer to $5), it is going to be hard to beat that.

    I also did some testing at my dads tonight with this $179 unit. With only the hot water on, I can't keep my fingers in the stream for more than a second and it flows at 2gpm (I forgot to check the setting on the heater but I think it is a little over 1/2 way up on the dial). If I mix in some cold water and adjust to slightly hotter than what I take a shower at, I get a little over 3gpm. Adjusting to where I normally takes showers should be around 3.5gpm. With a 2.5 gpm shower head, I can turn down the power even more which should put me at around $5 a month for showers and then less than buck for running my dish washer

    I've got a couple power metering devices on the way. I'll install them on both my 40gal water heater and tankless and continue to run my 40gal heater for a week or so to get some data. Should be interesting to see if the real world ends up matching what it is calculating out to be. The Energy Guide on my existing water heater indicates at $.14 kw/hr it estimates $794 a year and I pay $.147 a kw/hr above 1000kw/hrs. The estimate is based on likely more hot water use than I do. But, the water heater is 24 years old and I've probably flushed it once and I'm sure there is some buildup on the elements so it probably offsets.

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  • misraels
    replied
    I'm with Rupp on this one, the best answer is really switching to gas if you have that as an option. I was surprised when i saw the original post stating $70 per month...but in looking up some charts on water heater costs per month along with comparisons over their expected lifetimes, gas is definitely much more efficient, and uses very little power and can run off generator when needed (ours is electric igniter)

    Leave a comment:


  • Rupp
    replied
    Wow. I guess we are blessed to have gas available. Our gas bill in the summer months which is for hot water only for our family of 4 is only $20 a month. I'm guessing it would be less but that's the gas company's minimum charge now. Winter time is a different story. We have a 50 gallon water heater located in the garage and it could have been laid out to be much more efficient. Our bathroom is on the exact opposite side of the house and it takes forever to get hot water to our shower/bath. We run the dishwasher nightly, 4-6 showers a day and laundry several times a week. I even have a water hose attached to the water heater so I have warm water to use in the fall and winter months to was the cars. If you have gas available that would seem to be a better option.

    Leave a comment:


  • AshaiRey
    replied
    I use a solarboiler for this. In the summer it switches off at about 11:00 AM because the 110 liter boiler reach its maximum temperature of 95 degrees Celcius. And in the winter, freezing cold (-15) out side but with a sunny day the boiler still reach about 55 degrees Celcius

    Leave a comment:


  • Extreme-Z
    replied
    Originally posted by mrhappy View Post
    Does the heater have it's own internal thermostat? This is a power chart for my heater last night when the heater was actually turned on in HS for three hours (at 2AM) but it only took an hour for the water to heat and it to turn itself off, looks like it had another quick turn on at close to 5AM also. Just saying monitoring the time something is on might not be that accurate if it does have an internal stat and you are much better off monitoring the usage. I use the Current Cost Meter but there are loads of different of methods.
    Yes, the water heater has its own internal thermostat. However, it is a simple thermostat and only turns the heating element on or off. I think there is a control board that operates the upper and lower heating elements differently but it is still an on/off function so monitoring the time a constant wattage element is on should still get me pretty close. But, I'm not doing that... I have the kw meter on the way to do the monitoring more accurately

    Originally posted by Rotech View Post
    Here where I live, ( Florida) I use a Elk 9200 relay box connected to a zwave plugin device to control my water heater. It works like this, I use BLradar to monitor the home to see if we are home. If there movement within the area of family room, kitchen, living room HS keeps the water heater in on position. If we retire to our rooms let's say, and we are there for more then 30 min. ( retired for the day or just reading a book) HS shuts off water heater until it see any movement within the mention rooms.

    When we leave home and the alarm is set, it also shut off the heater. Doesn't make sense if your not home and the water heater is heating water. When we come back the reverse happen, heater turns on. I have been out for weeks and I return I still have hot water. I have seen reduction in my bill since this was installed. Just to mention my water heater has a internal thermometer which also shut it self when water reaches it's temp.
    That is very interesting and thanks much for the info/ideas. I think the way I shower is much different than you though. LOL Since I shower immediately when I get up, my house would be idle for many hours and then, within 5 minutes, I'd want hot water. I think your method would work great if you showered before bed but for me I shower right when I wake up. I could still use HS to control the hot water heater but might be better for me to use BLGData plugin to see when I go to work because I shower either at 4am or 4pm depending on if I'm working day shift or night shift. But then I have my days off where I shower when I get up... but depending on how I feel sometimes I get up at 6am and sometimes if I can't get to sleep until 6am I get up early afternoon. ARGH! hahahaha Being a shift worker makes things complex. hahaha

    Originally posted by S-F View Post
    Yeah, for the low installation cost and infrequent use the on demand unit might make sense. If you ever end up using more water though it would be a good idea to get a heat pump DHW heater. They can usually be had for the cost of installation after rebates.
    I'll keep that in mind for sure. Right now, since the cost is so cheap, I'm going to give the Rheem RTE13 a try I think

    I'll keep you guys updated on what I find. I'm going to install the kw meter and use my regular 40 gallon unit for like a week and see what I get. I'm then going to install the tankless with another kw meter and see what it does after the same amount of time. I'll try to be fair and do the same exact thing for the week for each one. Should be interesting!

    Thanks much again for the help and recommendations!

    Leave a comment:


  • S-F
    replied
    Yeah, for the low installation cost and infrequent use the on demand unit might make sense. If you ever end up using more water though it would be a good idea to get a heat pump DHW heater. They can usually be had for the cost of installation after rebates.

    Leave a comment:


  • Rotech
    replied
    Here where I live, ( Florida) I use a Elk 9200 relay box connected to a zwave plugin device to control my water heater. It works like this, I use BLradar to monitor the home to see if we are home. If there movement within the area of family room, kitchen, living room HS keeps the water heater in on position. If we retire to our rooms let's say, and we are there for more then 30 min. ( retired for the day or just reading a book) HS shuts off water heater until it see any movement within the mention rooms.

    When we leave home and the alarm is set, it also shut off the heater. Doesn't make sense if your not home and the water heater is heating water. When we come back the reverse happen, heater turns on. I have been out for weeks and I return I still have hot water. I have seen reduction in my bill since this was installed. Just to mention my water heater has a internal thermometer which also shut it self when water reaches it's temp.

    Leave a comment:


  • mrhappy
    replied
    Does the heater have it's own internal thermostat? This is a power chart for my heater last night when the heater was actually turned on in HS for three hours (at 2AM) but it only took an hour for the water to heat and it to turn itself off, looks like it had another quick turn on at close to 5AM also. Just saying monitoring the time something is on might not be that accurate if it does have an internal stat and you are much better off monitoring the usage. I use the Current Cost Meter but there are loads of different of methods.
    Last edited by mrhappy; January 20, 2015, 10:14 AM.

    Leave a comment:


  • Extreme-Z
    replied
    Was searching through different options for monitoring power usage on my existing water heater and was going to try hooking up an hour meter to each element. Total cost would be about $25 and with some math and some assumptions of the ratings of the heating elements I could get pretty close. Not 100% ideal but cheap

    I then ran across maybe using a regular refurbished type house meter connected to just the water heater as I have a mount somewhere I'm pretty sure. Kinda a pain to hookup though.

    Finally, I ran across a gizmo that would very accurately measure usage over time for $20! I found a number of places on the web which indicated this works for either 50Hz or 60Hz and a lot of good reviews on it here in the USA so am going to give this a try. I'll keep it hooked up for a week or so and will report back my findings.

    Leave a comment:


  • Extreme-Z
    replied
    Slow night shift so was checking out some posts here and have been reading about the Brultech GreenEye Monitor. That's a nice setup... a little overkill and a bit expensive for just checking out the water heater though. LOL

    Leave a comment:


  • Extreme-Z
    replied
    Thanks much for the suggestions and ideas, guys!

    S-F, did you take into account the unit I was looking at was only $179 and I can install it myself? I know many of the units are around $500 up to $2000 with high installation costs as well but, for whatever reason, it seems Rheem has chosen to hugely discount this model to its distributors which has made it a very popular model with a decent amount of time under its belt so it is a proven unit.

    I did figure that my showers alone would cost me no more than $10 a month at $0.147 kw/hr. That assumes the heater at full power with no cold water which is way conservative since I live in FL and it seems a lot of people who have this model set it about 1/2 way up. Since my ground water is 72 degrees and we don't really have much of a winter here I can probably keep mine operating at 1/2 power most the year so I'm probably looking at around $5 a month for showers then throw in the dishwasher that I run maybe twice a month and it seems like it wouldn't be on much at all. I just remembered too that I think the settings I use on my clothes washer is cold for all cycles... one cycle might be "warm" but it is a newer He machine and I don't think, the way I do clothes, it uses much hot water at all.

    The only real way for me to do a fair comparison for my exact situation is to somehow monitor for like a week how much my 40 gallon electric heater is costing. I do have several Kill-A-Watts that are good for 15amps 120v. Has anybody ever wired up two of these suckers to measure each leg of a 240v setup??? Hmmm??? LOL

    S-F, I'm only familiar with the Rheem RTE 13 installed in my dad's shop but I can tell you the water gets hot in like a second or so... not much of a delay at all. It is mounted under the sink and when I was checking it out it seems like the only delay was the water that was left in the line? I don't know... but it got hot pretty damn quick to the point I couldn't keep my hand under it anymore! hahaha

    My current water heater still works and the options you mention look to be fairly expensive. It also seems like the more people you have using hot water all day long a tankless would be less ideal... not more... at least in my case because the little $179 unit wouldn't work and I'd need the $1000+ one. Heck, if I were to take a shower someplace else for the day my electricity cost for heating my water that day would be ZERO Actually, just thinking about it in my head, it would seem like a tankless heater would always be more efficient whether you had one person or a hundred since, in my case, with them both use resistance heating then they both should take the same amount of energy to heat up my ground water to give me 105 degree water for 10 minutes at the faucet. The difference being the tankless only uses energy when water is demanded but my 40 gallon unit keeps the water hot all day long.

    Hmm? Any ideas on a not too terribly expensive way to accurately check the energy usage of my current water heater whether it be able to be used with Homeseer or not? I kinda like the idea of hacking a couple kill-a-watts but I've never heard of it being done before and there might be a reason for that. LOL

    Leave a comment:


  • S-F
    replied
    I deal with these kinds of issues on a daily basis. I work in domestic energy efficiency. Generally unless you have more than 5-6 occupants using hot water all day long an on demand unit doesn't make financial sense (takes a ton of juice to heat the water up quickly) and takes longer to get hot water to you when you want it (they ALL have a startup lag. Every single on demand DHW heater ever made). For electricity the most cost effective option outside of a ground source heat pump is a regular heat pump hot water heater. The one made by GE is cost effective and very quiet but the Steibel Eltron is the most efficient by far. Plus you get the added benefit of some dehumidification if you keep it in your basement or you live in a cooling dominated climate.

    Leave a comment:

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