Worth Switching to Tankless?

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bfr57

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Been doing a ton of research on tankless vs tank heaters. Let me describe our current setup and then I'll pose my question. We have an electric 50 gal tank (almost 20 y.o.) that's starting to seep so I know I'm on borrowed time; if we were to switch systems, now is the time. I have a timer on it that runs 5-6 hours a day; we do most of our hot water use in the evenings. Plus, living in southern AZ, the water gets heated naturally in summer time with garage temps seeing 110. We don't have NG but have plenty of space to bring in a 250 gal LP tank. I could get the LP within 15' of a tankless heater. I can do the installation myself and would install tankless in the garage where the existing tank is, so plumbing would be minimal. We have really hard water here, but do run a softener.

So, my question is this: Is all of this really worth it running an electric heater only 5-6 hours a day? That's what I can't find in my research. When the 2 systems are compared, it's with the electric running fulltime; no timer. My simple mind says no.....
 

Dana

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Running even the old electric on a timer has miniscule savings, unless you have time-of-use rate structures to take advantage of. The standby losses of a plain old electric tank are tiny, especially in a 100F+ garage. There is effectively zero savings to be had using an electric tankless (and considerable up front expense for the fat wiring and large breaker.)

For the installed cost of a 20kw tankless you could probably install a heat pump/hybrid water heater, which would use less than 1/3 the amount of electricity of a plain old tank, maybe even less than 1/4. In almost all cases a heat pump water heater can use the same wiring & breaker as your plain old tank. It would need something to manage the water condensation it produces- either a floor drain or a condensate pump like those used with air conditioners. They're usually a bit taller than a traditional 50 gallon tank, but that's not a problem in most garage installations. These are now mature products, much quieter and far more reliable than those of a decade or more ago.
 

WorthFlorida

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Below shows my electric usage for most of Oct. The first week of Oct no one was occupying the home. The electric company, Orlando Utilities Commission (OUC) started this monthly email report a few months ago. It is interesting that with smart meters usage, the usage is sampled every hour and by particular power draws, it is summarized which appliance is being used. For example, most electric WH's uses a 4500 watt heating element at 240 volts, less wattage at lower voltages. When the electric usage jumps or drops by about 4500 watts, it's easy to summarize that it is the water heater. I cannot find any information on the OUC website about how these reports are generated but at one time I did read about it.

The $120 range is about the lowest power bill I get. Looking at the other few summaries, water heating is below $15 a month for a three month period. The household is just the wife and I, retired. A 2475 sqft 2 story home with a typical 50 gal standard electric WH installed when the home was new in 2007 in Central Florida. As Dana stated the savings using a timer is hardly measurable. For several years the home was not occupied but about every other weekend. At that time I would switch off the WH at the breaker panel.

Tankless electrics are hardly worth the cost since heat pump WH have really been greatly improved on. An electric tankless needs upgrade wiring if your breaker panel can handle the extra load and you'll not be saving in energy cost. Most of hot water heat lost is from the plumbing system. Pipes running through walls and floor is where most of the energy lost occurs regardless of what type of WH you install.

Screen Shot 2021-12-16 at 6.38.26 PM.jpg
 

Reach4

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It would need something to manage the water condensation it produces- either a floor drain or a condensate pump like those used with air conditioners.
The plants like that condensate water. I was thinking a hole through the garage wall; you would have to be concerned with freezing blocking that path.
 
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bfr57

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Running even the old electric on a timer has miniscule savings, unless you have time-of-use rate structures to take advantage of. The standby losses of a plain old electric tank are tiny, especially in a 100F+ garage. There is effectively zero savings to be had using an electric tankless (and considerable up front expense for the fat wiring and large breaker.)

For the installed cost of a 20kw tankless you could probably install a heat pump/hybrid water heater, which would use less than 1/3 the amount of electricity of a plain old tank, maybe even less than 1/4. In almost all cases a heat pump water heater can use the same wiring & breaker as your plain old tank. It would need something to manage the water condensation it produces- either a floor drain or a condensate pump like those used with air conditioners. They're usually a bit taller than a traditional 50 gallon tank, but that's not a problem in most garage installations. These are now mature products, much quieter and far more reliable than those of a decade or more ago.


Thanks for the input. Yes, we are on a TOU and have solar. So when the solar is over-producing (power back to grid) is when I have the WH timed to come on, so basically power is free as long as sun is out! Think I'll just stick with another electric tank unit.
 

John Gayewski

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No a tankless water heater isn't worth "it". You'r hard water will have it mucked up and useless in 5 years. If you want to really save money keep doing what your doing.

Hybrids do save energy. The up front cost is high. It only pays for itself after 10 years or so. Then you'll need to be lucky enough to have a hybrid unit last that long to pay itself off, but then pretty soon (likely) you'll need another hybrid unit.

If the price for hybrids gets much closer to a regular tank style heater they would be great.
 

Dana

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Thanks for the input. Yes, we are on a TOU and have solar. So when the solar is over-producing (power back to grid) is when I have the WH timed to come on, so basically power is free as long as sun is out! Think I'll just stick with another electric tank unit.

The "free" power isn't really free- it's just already paid for in the sunk cost of the solar. The levelized unsubsidized cost of the lifecycle output energy of typical rooftop residential solar varies (a LOT) by location and installation particulars, but in most instances is still well above fixed rate retail power. With state & federal subsidies it's usually at or less than residential retail, but not below most off-peak rates. It's only "free" if it's power that would otherwise be exported to the grid at $0 remuneration from the utility, or curtailed for lack of load.

If the utility isn't paying you for any exports it's of course better to dump it as heat into the tank. It's possible to intelligently control the resistance element of a wi-fi enabled hybrid heat pump water heater to use it at a a power dump, in much the same way as you would a plain old tank. Most tanks can handle storage temps up to 175-180F, even though the heat pump on the hybrid water heater would never be able to take it there on it's own.

An even better power dump for otherwise unremunerated PV output would be an electric vehicle battery charger (or a home battery pack, which is also useful as power backup during /after hurricane damage to the grid.) But this is a much broader topic than mere water heater options.

A heat pump water heater is still likely to a financially better choice than a plain old tank despite the upcharge, but how the utility treats your solar exports (of course) plays into how much better it would be.
 

jadnashua

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One thing to consider is that the heat pump/hybrid WH will pull heat from your garage, effectively acting as an air conditioner, so you get the benefit of cooling it. But, if you run it on a timer, and it had cooled off a bunch (may not happen in a hot garage with the insulation much), if the water was too cool, it would engage the resistance heater to heat the water faster. Under more normal conditions, it would use the heat pump.
 

WorthFlorida

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Add up the money over your lifetime. What you'll spend on three or four tankless, vs tanks which last longer. You'll spend about 7 times as much money. That's not efficient.

Costs and efficiencies are not the same. The cost to produce hot water is associated with efficiency. Total costs for higher efficiency usually cost more than a lower efficient rated water heaters. Checking HD site for prices, tank water heaters are generally less costly than tankless. Price of tankless have dropped quite a lot but usually priced somewhat higher than tank units. Hybrid water heaters are now cost two times or more of a standard tank model for 2-3 times higher efficient rating.

A good generally write up on water heater from the EPA web site.
 

John Gayewski

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The efficiency claimed by the manufacturers aren't reproducible in real life. The heat lost by the exhaust on a tankless adds up to a alot. It goes right up out of the stack the warm condensate that comes running out of them is wasted heat. If you read these articles they will say "CAN" save up to (fill in the blank) energy. But they really don't. They waste like everything else, they just cost an arm and a leg. By all means keep buying them. It's great for plumbers to be out changing your piping and all of the service calls and descaling. Efficiency it does equal.
 
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