Tankless Electric vs Hybrid

[Brian Gix]

A couple years ago I had a new electrical panel installed that has 6 blank slots, and no space saving "peanut" breakers... the world is my oyster

I did that work to support minisplits and a Rheem Hybrid electric water heater, which I have now been using for about 2.5 years. I maintain it, so it will probably still last me another 10 years, but I wonder if anyone knows how to compare efficiency numbers between *tankless* electric and hybrid electric. My wife and I are now empty nesters (again after many fits and starts) and so we can probably get by with an 11KW system rated at 2.68 Gpm.

I know this is all inductive heating... no heat pump efficiency. But because it doesn't need to keep (our current 60 gallon capacity) water hot even when we don't need it, I wonder if tankless would actually use less electricity in the long run.

Anybody know?

[Jonlin, Duane]

Heat pump wins, hands-down. See explanation in the link below.  For Western WA, get a HPWH sized such that supplementary "hybrid" heat is never needed, to maintain heat pump efficiency year-round.

Tankless Water Heaters vs. Heat Pump Water Heaters (monkeywrenchplumbers.com)

	Duane Jonlin, FAIA Energy Code and Energy Conservation Advisor City of Seattle Department of Construction and Inspections P.O. Box 34019, Seattle, WA 98124-4019 P: 206.233.2781 |  duane.jonlin@seattle.gov Facebook I X I Blog
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Subject: Tankless Electric vs Hybrid

 

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[Galen Ward]

Tankless is going to be close to 100% efficiency. A little heat is lost to the room.

The heat pump is 250-350% efficient when running on heat pump mode. If you can, turn it on permanent heat pump mode so it never goes into inductive mode (my 80 gallon tank has yet to run out for our family of 4). 

Heat loss from your tank isn’t going to be high enough - you aren’t functionally heating every gallon of water from tap temp to 120 2.5-3.5 times before using it, which would be break even. 

Galen 

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[Tom Balderston]

good  comparison,  but two points.    Where did he get that heat pump  water heaters cost $9000-13000?      Perhaps that is his price for puting one in?       Mine cost  $1200 but i put it in myself.      Assuming the electrical service ok as is,   i'd be curious for feedback on the group  on what a water heater change out costs.

Also,  to be fair,    tankless gas water heaters use a less expensive fuel per  btu,     so   they dont cost 3x as much to operate.   Heat pump  water heaters are cheaper to operate than  tankless gas,  but the savings is more like 20%.    The fact that the climate impact is much bigger   makes them a  great idea. 

tom 

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Tom Balderston
BALDERSTON ASSOCIATES
11208 1st Ave NW
Seattle WA, 98177

[Galen Ward]

He asked about an electric on demand hot water heater. Same fuel as the heat pump. Also I’ve heard on demand electric is not highly reliable. 

You are correct: Gas on demand is much cheaper on a BTU basis. 

Galen

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[Jonlin, Duane]

Yes, gas is cheaper per BTU, but the heat pump water heater has three times the efficiency, so the energy costs are a wash.

	Duane Jonlin, FAIA Energy Code and Energy Conservation Advisor City of Seattle Department of Construction and Inspections P.O. Box 34019, Seattle, WA 98124-4019 P: 206.233.2781 |  duane.jonlin@seattle.gov Facebook I X I Blog
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From: Galen Ward <gale...@gmail.com>
Sent: Wednesday, July 3, 2024 5:19 PM
To: Tom Balderston <ecod...@gmail.com>
Cc: Jonlin, Duane <Duane....@seattle.gov>; Brian Gix <bria...@gmail.com>; Western Washington Home Electrification <seattle-home-e...@googlegroups.com>
Subject: Re: Tankless Electric vs Hybrid

 

[Brian Gix]

This is the answer I was looking for — Electric for Electric… Gas is a non-starter for me.

I am still very tempted by the fact that Electric tankless seems to be *very* inexpensive to maintain, lasts twice as long, disposal creates much less waste, and takes almost zero space… so I am not ready to take it off the table.

But I also bow to the laws of physics: harvesting heat from the surroundings means less strict conversion of adding heat calories to the water from the room instead of an inductive coil. However, that means the winter, that heat needs to replaced (although perhaps thru  a heat exchanger with the outdoors).

—Brian

[Jonlin, Duane]

remember that almost no mechanical equipment goes to the landfill, at least in Western WA - the steel, copper, and aluminum in them is too valuable for scrap dealers.

	Duane Jonlin, FAIA Energy Code and Energy Conservation Advisor City of Seattle Department of Construction and Inspections P.O. Box 34019, Seattle, WA 98124-4019 P: 206.233.2781 |  duane.jonlin@seattle.gov Facebook I X I Blog
	Helping people build a safe, livable, and inclusive Seattle.

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From: Brian Gix <bria...@gmail.com>
Sent: Wednesday, July 3, 2024 5:27 PM
To: Galen Ward <gale...@gmail.com>
Cc: Jonlin, Duane <Duane....@seattle.gov>; Tom Balderston <ecod...@gmail.com>; Western Washington Home Electrification <seattle-home-e...@googlegroups.com>
Subject: Re: Tankless Electric vs Hybrid

 

[Thad Curtz]

On Jul 3, 2024, at 5:27 PM, Brian Gix <bria...@gmail.com> wrote:

But I also bow to the laws of physics: harvesting heat from the surroundings means less strict conversion of adding heat calories to the water from the room instead of an inductive coil. However, that means the winter, that heat needs to replaced (although perhaps thru  a heat exchanger with the outdoors).

You can duct the intake and the output (at least on my Rheem, and I think on pretty much all the other brands.) The Rheem allows up to 50 feet of flex duct, if I remember correctly. A few people do fancy stuff, like piping the cold exhaust into their hot attic in the summertime, etc., but if you’re concerned about getting the heat from inside the building envelope you may well be able to use outside air, depending on where the water heater is in your house…

Best wishes,

Thad Curtz

[Jonlin, Duane]

Here's another way to look at it, which I first heard from Sean Armstrong of Redwood Energy:

• Heat pump water heaters are amazingly efficient at room temperature - they might have a COP as high as 5.0.
• If your heat pump is exhausting cooled air to the outdoors, remember that an equivalent amount of cold outside air will have to infiltrate around your door sills or whatever to replace it.
• Heat pumps for space heating are optimized for best efficiency boosting your indoor air back up to comfortable temperatures.

So, you can use your space heating heat pump to keep indoor temperatures comfortable, and the HPWH to periodically move some of that energy into your water heater, with both pieces of equipment running at their most efficient levels.

DJ

	Duane Jonlin, FAIA Energy Code and Energy Conservation Advisor City of Seattle Department of Construction and Inspections P.O. Box 34019, Seattle, WA 98124-4019 P: 206.233.2781 |  duane.jonlin@seattle.gov Facebook I X I Blog
	Helping people build a safe, livable, and inclusive Seattle.

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To: Brian Gix <bria...@gmail.com>
Cc: Galen Ward <gale...@gmail.com>; Jonlin, Duane <Duane....@seattle.gov>; Tom Balderston <ecod...@gmail.com>; Western Washington Home Electrification <seattle-home-e...@googlegroups.com>
Subject: Re: Tankless Electric vs Hybrid

 

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[Thad Curtz]

On Wed, Jul 3 2024 at 5:08 PM, Tom Balderston <ecod...@gmail.com> wrote: 

good  comparison,  but two points.    Where did he get that heat pump  water heaters cost $9000-13000?      Perhaps that is his price for puting one in?       Mine cost  $1200 but i put it in myself.      Assuming the electrical service ok as is,   i'd be curious for feedback on the group  on what a water heater change out costs.

Replacing my aging gas water heater with a 50 gal Rheem Performance Platinum heat pump one - 

The heater itself - $1,125 at Home Depot (including a $750 rebate from PSE - bumped up temporarily from $500 at the very end of 2023)

New 30 amp circuit (which I had done in advance while the electrician was here for something else - $329

Parts and permit for a shutoff switch and a new receptacle for a condensate pump, which I installed myself - $170

Installation by Home Depot’s plumber - Roughly $2,600, including $239 for the pump itself.

(I was going to install it myself, but my helper kept cancelling; I wasn't brave enough to try to get it down the stairs into my basement by myself; and I finally gave up and hired the plumber. I went with Home Depot’s because I figured they’d be experienced, and that if I did have any trouble with the water heater Home Depot might be better about the warranty if they’d installed it.  

Best wishes,

Thad Curtz

[Izaak Koller]

I think you are going to be in the noise as far as efficiency difference for a small household with minimal water use.  Yes, on-demand is probably a bit more efficient for small demand applications, but that comes with quite a few caveats.  If you have the Rheem app set up and can turn off the tank when unoccupied, you may get near tankless performance.  

The bigger issue is reliability and solvency of the company for any of the new electric tankless.  I certainly would not believe that they are less expensive to maintain or last longer.  I have been tracking these products for the past few years and they are terribly unreliable due to the very high heat density of the resistance heating elements and the tendency to flash boil and accumulate mineral deposits on the element sheath.  This leads to overheating along with other failure modes that often can turn into flooding issues. Also the very high current switching seems to cause electrical control problems. Read the reviews for pretty much all of them and more than 50% seem to be nightmare scenarios with floods and fires far more common than acceptable.  I was excited by the engineering sales pitch of Heatworks not using metal elements when they came out to address these issues, yet they also had just as many problems with catastrophic failures.  

I do see that A O Smith now has a product along with some of the other bigger players and would only consider one from a reputable brand that has stayed in the industry for 20+ years and it is critical that you have a good mineral-free water supply.

The most efficient choice is often to use the product for its useful life and that is what I would recommend.  There should be much better options in 3-5 years.  

-Izaak

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