Logic of using a 30 gallon electric vs 9 KW tankless hot water heater.


A 9 KW tankless HWH manufacturer claims that it is sufficient for a whole house at up to 3 GPM.
A 30 gal short tank HWH is about 30" tall and many are mounted over a clothes dryer on a shelf.
That got me to thinking:
Size - not too important if hung.
Power - both 9 KW.
Instant hot water: - Tank water is preheated. The tankless requires 0.5 GPM to begin heating.
Cost - Conventional HWH is cheaper.
Longevity - Tankless is supposed to last twice as long.
Replacement elements - Conventional elements about $15 at Home Depot, etc. Tankless elements are not standard and cost more.
Recovery - With 9 KW of heating available in both units they may be equal. (You must use up all the 30 gallons before additional HW is needed.)
Upgrading: Conventional elements are available in 5, 5.5, and 6 KW sizes. Therefore a 12 KW 30 gallon is doable and it would heat faster.
Efficiency: Tankless is slightly more efficient.
Location - I am in Florida where the input temperature is 70*F.
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Biggest deal is the upfront cost. 30 gal tank heater is usually a DIY job. Installer gets all the money you would save over life of the tankless. You probably have hard water too living in FL, not good for the tankless.
Jimmie
Jimmie
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a 9000w tankless of 3 gpm might wash your hands with the unit under the sink, maybe you could use it for a shower if it was behind the shower wall but its not whole house. What temp rise does it give at 3 gpm, and is it 70f supply in winter on the coldest week. Having the unit maybe 30 ft away you might loose 5-10 f after the water travels a distance. A real whole house but single use electric consumes a massive amount of electricity and usualy needs a panlel upgrade, look at some real name brands like Boch, Takagi, and see what their specs are. There is a good reason people stay with electric tanks, mainly they can consume as much as your whole house and require a new service and panel. I have a gas tankless and you have to do alot of homework to be sure it will work before spending any money, you know the tank works and its reliable, many cheap tankless are not long term reliable.
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You should ask yourself, with company mergers and bankruptcies, will your tank-less water heater company be around for the next umpteen years? So do you feel LUCKY?
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On 6/5/2010 7:30 PM, BoyntonStu wrote:

If you go tankless, go with one that runs on gas unless it's new construction and extra electrical work needed won't be as expensive as a retrofit. My friend and me installed a Bosch tankless that uses NG for fuel and the water heater had a little water wheel electrical generator that supplied power to the electronic ignition for the burners. It was a slick system that worked very well.
TDD
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One thing I did not see mentioned is that if the power goes out, the tank can be heated by an average 5 kw generator. The tankless can not be heated. NOt sure how the power outages are in your part of Florida. Where I am at the power has been taken out for a week or more due to ice storms. I have been lucky and only have it out for about 2 days sofar at any one time.
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Ralph Mowery wrote:

Not to mention even without a generator you still have enough hot water for a shower or two, or three.
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The tankless output is at a rated voltage probably 240, Your voltage may be only 220 and go lower during high demand, so take their published specs with great suspicion. The only way to know is buy one and hook up garden hoses to test output and test it at the same length run of what you have to measure temp drop from a long run, I think its to small a unit. and how cold is incomming water in winter, that colder water could ruin everything you paid for. Mine is a 117000 Btu Ng unit, a comparable electric might consume 40,000 watts
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snip
Yet another option :
http://www.geappliances.com/heat-pump-hot-water-heater /
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TheHack wrote:

Forgets to mention that you are cooling the space around the water heater. In Florida that is probably good. In Minnesota in the winter you are also supplying heat from space heating to heat the water. Cost per year figures may be bogus.
--
bud--

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And in a natural or man-made disaster, the water in the tank gives you a sizable drinking water resevoir.
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thing.
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If you dont research it before you purchase it yes, likely you will be left cold and mad. My 2 happiest days with my 117000 btu Ng Bosch are when I get my 9.60 $ gas bill, and when I pay my 9.60$ gas bill, my incomming is near 37f at -20f outside and my shower is hot without the Bosch on high.
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