Best energy saving option to replace 2 water heaters ?

thomaskuhnApril 17, 2012


I have read a few "water heater options" post, but everyone seems to have different configurations, so here is mine.

My wife and I live in Orlando, Florida in a 3200 s.f. home. We do not have access to gas, electric only. The house has 2 50 Gal Electric water heaters of average quality, one in the usual spot in the garage (feeds Kitchen, laundry, guest bath, pool bath, bonus room), and a second one that is located in the master bedroom closet (Master sinks, bath, shower) on the opposite side of the house. Taking an inventory of where we use hot water: we use the master bath, sinks, shower and the kitchen sink/dishwasher. We usually never use the hot water in any other part of the house.

I would like to start planning on updating this setup with something more energy efficient. I am always envious of my brother who installed a Rheem Heat pump water heater, and the amount of savings he gets. But in my situation we have two water heaters.

So far my thoughts are to turn off the unit in the garage unless guests come over, replace the unit in the closet with something more efficient. I like the Rheem/GE Heat pump units, but will the noise of it running be annoying? On the plus side it will cool our bathroom/bedroom.

Another option would be to mount it in the attic to have access to more hot air. Could do a tankless in the bathroom, but I am currently leaning away from that as I have not heard the best comments on electric tankless.

This would leave the kitchen sink. What to do there? I would love a tankless here, just to have instant hot water.

Another option is a recirculating main high efficiency tank in the garage? This way we will still get quick hot water all the way in the bathroom.

Any thoughts on the best energy saving approach?

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Just some things for you to know:

Electric tank heaters are ~100% efficient - meaning they turn almost 100% of energy into heated water. There is some standby loss, but that can be minimized through additional insulation. Electric tankless will not improve on that enough to justify the tiny payback.

Heat pump units can be a great choice in hot environments. They will use considerably less energy than a standard heater. They work by removing heat from the surrounding air - so you don't want to use them in a cool environment where you are heating the air (good for your use in Florida!). Access to plenty of warm air is required. Haven't used one myself, but I would expect the same amount of noise as a refrigerator.

If you install in attic (good for lots of hot air), you must consider water leaking. The drip pan will catch some leaks, but not a major leak.

Don't do a high efficiency in garage and circ pump unless you can insulate all of the pipes well. You might consider POU tankless in master bath for instant hot water until main unit in garage can take over.

If you do use circ pump, consider motion detector & aquastat to reduce circulation. The motion detector would turn on the pump when you go in the bathroom, the aquastat would turn it off when the pipes warm up or if they are already warm.

Something else to consider in sunny Florida would be solar. Put the tank in the garage and do a circ pump. Most solar storage tanks have electric resistance heat for backup.
Rheem and others have off-the shelf units - both the storage tank and the collectors. If you can't do the entire thing now, do the tank and add the collector later. BTW: Tax break for that as well!

    Bookmark   April 17, 2012 at 10:49AM
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My climate in South LA is similar enough to yours to say that the HPWH is the most economic way to heat water. You need extensive rebates to make solar DHW a better economic choice, much higher than the federal tax incentives alone. Check local sources to see if there is more help on that end. Do the calculations yourself on the US DOE's web site, the Energy Star web site or look for information at the web site of your local land grant university. Why can't you listen to your brother's HPWH to decide about noise?

Tankless is a very high investment in equipment cost that is difficult to recover.

I have a fuzzy memory that some HPWH have short duct options to move the cool, dry air where you want it if that is not right next to the water heater. I could be wrong about that.

    Bookmark   April 17, 2012 at 12:13PM
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"Tankless is a very high investment in equipment cost that is difficult to recover."

That is true of electric tankless - and I would never recommend it.

It is not true of gas unless new gas service is required.

The OP doesn't have gas an an option - but the above statement would lead people to the wrong conclusion.

Payback in any case will be a function of both the installed cost and the cost of fuel (electricity) as well as future rate increases.

Keep in mind with solar, you don't have to provide 100% of hot water needs. You could even use it as a pre-heater.
A Rheem complete self-contained solar unit is $3200 for the 80 gal model and includes an electric element. A 50 gal Rheem hybrid heat pump water heater is roughly $1300

Here is a link that might be useful: Rheem pasive solar unit

    Bookmark   April 17, 2012 at 2:30PM
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I ran numbers for my house and costs of equipment and fuel. Solar = HPWH with 75% of solar costs coming back from state and feds. Gas instant was much higher than both and higher than gas tank heaters with gas costs about a year ago. Gas costs will probably be going down putting gas instant at a greater disadvantage to gas tanks.

Take-home: With no incentives, HPWH is the clear winner in the hot, humid South LA climate.

    Bookmark   April 17, 2012 at 3:44PM
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I think you've mentioned it before, but where did you go to run those calculations?

    Bookmark   April 17, 2012 at 3:47PM
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Thanks for the great info. You know, I never thought about asking my brother how loud his is or actually listening. I should head over there and check it out.

I can get the GE HP model for If this went into the bathroom closet, what would be the best option for the kitchen sink? Instant? I have 120V for the disposal, but would probably need to 220V to handle the flow.

    Bookmark   April 17, 2012 at 5:14PM
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It is not a plug-in numbers, hit a button and get a result, so a little work needs to be done.

    Bookmark   April 17, 2012 at 7:29PM
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Correction - I could get the GE for Has anyone used a small 4-6 gallon water heater for their kitchen sink? Something like the Botch GL6?

Would 6 gallons of hot water be enough for a kitchen sink?

    Bookmark   April 18, 2012 at 8:46AM
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Dude, I think you have answered your own question.
at $850 you can't beat that.

Regarding "would 6 gal be enough..." I assume that you are saying "would that be enough until the main heater takes over?" The answer is probably. You can do the math on the distance and pipe size between the sink and the main heater. That will tell you for sure.

    Bookmark   April 18, 2012 at 9:01AM
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FYI: I put those formulas into an Excel spreadsheet so that they were more plug-n-chug.

The original estimate for payback on my gas tankless was 5 years vs a standard 40 gal tank heater.(~a $500 difference in installed price - DIY)

The revised payback with lower gas prices is 8 years.

That's okay, but not great - but that's compared to a standard gas tank. I couldn't use a standard gas tank without re-lining my chimney or using a powervent. The powervent was the same cost as the tankless - so it's all savings for me.

All that said, I live in central Indiana where it can get downright cold. Everything in my 100 year old house is gas incl. furnace, water heater, range and dryer. My average gas bill (budget) is $46 - and that's before the mild winter this year and the foam insulation I added on the basement walls and joist pockets. My winter electric bill is $35. I keep things at 68-70 degrees inside.

The continuous hot water is very nice, not having a big tank is great, but not having anxiety attacks over utility bills is wonderful. Of course it's not just the water heater, it's the 92% furnace and insulation and such... I still have the original windows though.

Even with the reduced cost of natural gas, if someone can install a tankless at a reasonable cost (no re-doing the gas service) I would advise that people consider it.

In hot climates, the heat pump water heater sounds like a great option - esp in electric only situations.

    Bookmark   April 18, 2012 at 2:56PM
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I would shut off the garage water heater, and use the 6 gallon as the sole source for hot water at the kitchen sink.

    Bookmark   April 18, 2012 at 6:33PM
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8 years is pretty short with that kind of device. Most people would be longer including pro installation and having the pre-existing ability to just replace a gas water heater. I always (aim to) write that you have to crunch your own numbers to know for sure.

Replacing windows is a tough area. They are often not done correctly by so-called pros and leak more than the original ones. It is also an expensive proposition, if you are not going to buy junk, as you probably already know. Even people that invest heavily in what they think are good windows end up disappointed when they start to fail after a decade or less.

    Bookmark   April 18, 2012 at 7:28PM
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Oh, I have no intention of replacing the windows. The entire neighborhood is on the National Register of Historic Places and the house is a contributing structure. My point is that I have very low gas bills, and the original windows.

In older homes with masonry chimney's the furnace and the water heater were often vented together. When the furnace gets changed out to a 90% and vented through PVC, the naturally aspirated water heater is no longer to code in the flue by itself. You have to either line the chimney with a double walled vent, move to powervent out the sidewall or go electric. That's what my situation was.

I agree, though with what you say about installed costs. The thing is that if installers could get past the "novelty" of the tankless, they are often a breeze to install. I went right through the rim joist with the vent - all 2.5 feet of it. I was able to move the heater closer to the bathroom and it's the size of a small backpack. The worst part was getting the old tank out of the basement.
The new condensing units simplify the flue by using PVC or ABS for a vent.

And when it comes time for a new tankless, wow, that will really be simple! Totally one person, a pair of channel locks and a screwdriver. about as involved as changing a tire.

If you live in warm climates, the entire thing can go outside without a vent kit.

    Bookmark   April 18, 2012 at 9:05PM
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So will a 6 gallon work under a kitchen sink?

    Bookmark   April 20, 2012 at 12:59PM
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Sorry for the side discussion.

The answer is probably - but you can determine the volume of the water between your sink and the water heater and see if 6 gallons will do it.

You will need to know how far it is and the size of the pipe (1/2" or 3/4")

    Bookmark   April 20, 2012 at 1:53PM
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Would the 6 gallon be enough (and i am starting to think it will not)if i turn off the garage water heater? In other words, it would be the only thing providing hot water at the sink.

I am thinking i will need an instant heater under the sink, but running 6ga wire through the walls would not be fun for me, especially because the sink is in a hard to wire peninsula. Perhaps i could hide it in one cabinet next to the wall

    Bookmark   April 21, 2012 at 1:34PM
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Some additional information, just so you know what i currently have (perhaps they are efficient enough... Or junk)

The bathroom water heater is a 40gal rheem "rhreemglas fury" that is listed as using 4775 kW/year. It was manufactured in 2004.

The garage water is an 55 gal A.O. smith promax rated at using 4879 kW/year and mancatured in 2009

    Bookmark   April 21, 2012 at 1:54PM
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A 6 gal heater will not be enough unless it's plumbed in with the main heater. Your dishwasher will empty it.

Your existing water heaters are ~100% efficient, (they have a energy factor of approx .96 without looking them up)

By contrast, the heat pump water heaters have an energy factor of 2.0 - meaning one would cost you about half of what you are paying for hot water now.

My suggestion would be to install a small electric tank in the bathroom (10 gal or so), and hook it in series with the garage heat pump water heater.

A good alternative - if it works for you - is to install a heat pump heater in the attic to serve the bathroom, since that's really where the bulk of the hot water use probably is.

    Bookmark   April 23, 2012 at 8:09AM
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I just plumbed in the GE heat pump in the bathroom. IT is a little noisy, but since it is in the closet, you can not hear it too bad. We still have the other water heater n the main part of the house. SO you are saying I should remove the garage unit, move the GE into the garage. Run a new hot line to the master batch, and run it to a small 10 gallon water heater?

    Bookmark   April 26, 2012 at 8:55AM
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