Tankless water heaters are terrible....

[SSedan]

I am going to say this as someone who picked up a Richmond Hybrid water heater yesterday which is I believe the same as the Rheem linked above.

I would take the operating costs with a whole shaker of salt not just grain of you live in a cold climate without waste heat to use I heating the water.

Don't get me wrong I am confident it will save me money vs. my 24yo electric which claimed $408 a year to run back when electricity was $.08xx a kwh and now it is about $.14 here. Since I am using Fujitsu heat pumps to heat our home near Green Bay I am on the ragged edge once it gets cold and if it stays below -15f long I already have to turn on some of the old electric baseboard.
I expect the ambient heat pumps will supply enough to let me run this as a heat pump water heater maybe 9 months of the year. It will put extra load on them a few months and will likely be switched to resistance electric December thru February. I am going to save money but I am also not going to see costs anywhere near as low as the label.

 

[bxr140]

I’m not sure this is really feasible.

Just seeing whether it’s on or off wouldn’t be enough since you wouldn’t be able to tell how much LP it was using while it was on.

Hmm...fair point. Was hoping there'd be a bit of law-of-averages going on, but you're probably right that the swings in effective duty cycle are too big. So maybe a flow meter is a better option? Seems like LP use would be pretty proportional to total volume of water moved through the unit...?

Or maybe I just don't worry about it and I make a HWHP my next project.

 

[Watts_Up]

Can someone clarify how the water get heat, if there is no resistance?

Note: Beside the provided white pages (see below) I found a reference in Google Books for: " Ohmic Heating "

from the book " Food Engineering - Volume III " (page 37)​

HeatWorks.com

The breakthrough Ohmic Array Technology at the heart of the MODEL 3 Water Heater
is the most advanced method for heating water in the world.

Our technology is the first to use a proprietary algorithm coupled with a unique electrode geometry
to deliver a precise, adaptable electrical current to any conductive liquid.​

Water itself is an electrical conductor.

Instead of having elements that get really hot and then transfer the heat to the water,
we actually pass electrical currents through the water itself.

Using graphite electrodes and electronic controls, we increase the energy state of the water molecules,
so they move faster. The faster they move, the more kinetic energy they have.

This causes the molecules to begin to bounce off each other; that kinetic energy turns into heat.
Through direct energy transfer,
your water is heated instantly, within (+/-) 1 degree Fahrenheit of the temperature set point.​

 

[brkaus]

My Navien gas tankless heater has smart recirc which also reduces the time for hot water to come out. Shower is always hot in less than 5 seconds. Insulating all the hot water pipes during construction also helps.

This reminds me... when we moved into our house ~20 years ago... it has 2 40gal propane heaters in series plus a recirculation pump that completed the loop including both tank heaters. In addition the hot water pipes in the slab do not appear to be insulated AND there was no on/off pins in the recirculation timer. Always on.

We have central propane that the builder was taking a % profit on propane sales through a complicated lease plant the gas company for the huge tank that is in the middle of the neighborhood.

We had ~$200 gas bills every month and the builder was being rewarded for the inefficient design.

 

[brucet999]

I think most of the losses are not from the tank, but in the piping.

Piping heat losses would not count, since they are the same for tankless as for tank WH. The reductions in heat losses for tankless vs. tank type are mostly seen where the house stands vacant for extended time, since the tankless is not trying to keep 40 gallons of water hot.

 

[miimura]

This reminds me... when we moved into our house ~20 years ago... it has 2 40gal propane heaters in series plus a recirculation pump that completed the loop including both tank heaters. In addition the hot water pipes in the slab do not appear to be insulated AND there was no on/off pins in the recirculation timer. Always on.

We have central propane that the builder was taking a % profit on propane sales through a complicated lease plant the gas company for the huge tank that is in the middle of the neighborhood.

We had ~$200 gas bills every month and the builder was being rewarded for the inefficient design.

Wow. Just wow. Sounds like you have always on radiant slab heating. None of my water pipes are in the slab, just sewage pipes. That sounds like quite the racket for neighborhood LPG.

 

[SageBrush]

Piping heat losses would not count, since they are the same for tankless as for tank WH. The reductions in heat losses for tankless vs. tank type are mostly seen where the house stands vacant for extended time, since the tankless is not trying to keep 40 gallons of water hot.

Some tankless supply only one faucet. It is a fashion in some circles to have 'instant hot water' and that is one way they do it. They also benefit from markedly reduced pipe runs that do not waste hot water between uses.

 

[nwdiver]

Can someone clarify how the water get heat, if there is no resistance?

Note: Beside the provided white pages (see below) I found a reference in Google Books for: " Ohmic Heating "

from the book " Food Engineering - Volume III " (page 37)​

HeatWorks.com

The breakthrough Ohmic Array Technology at the heart of the MODEL 3 Water Heater
is the most advanced method for heating water in the world.

Our technology is the first to use a proprietary algorithm coupled with a unique electrode geometry
to deliver a precise, adaptable electrical current to any conductive liquid.​

Water itself is an electrical conductor.

Instead of having elements that get really hot and then transfer the heat to the water,
we actually pass electrical currents through the water itself.

Using graphite electrodes and electronic controls, we increase the energy state of the water molecules,
so they move faster. The faster they move, the more kinetic energy they have.

This causes the molecules to begin to bounce off each other; that kinetic energy turns into heat.
Through direct energy transfer,
your water is heated instantly, within (+/-) 1 degree Fahrenheit of the temperature set point.​

???? Conservation of energy.... not just a good idea... it's the law.

If you want to add a watt of heat to water you need a watt of energy. If you're not using a heat pump or thermo-couple the best you can achieve is 1w. You can't add >1w of heat with 1w of electricity unless you're pumping the heat from somewhere else....

But thank you for highlighting why I hate tankless so much. They take advantage of general ignorance about physics to sell crap. '99% efficient'... wow... that sounds really good... until you realize that even a modest heat pump uses ~70% less energy than a '99% efficient' tankless.

 

[SageBrush]

???? Conservation of energy.... not just a good idea... it's the law.

If you want to add a watt of heat to water you need a watt of energy. If you're not using a heat pump or thermo-couple the best you can achieve is 1w. You can't add >1w of heat with 1w of electricity unless you're pumping the heat from somewhere else....

The US screwed up so badly when it did not adopt the joule as a unit of common measure.

Anyway ... I've often thought that part of the reason why heat pumps appeal to techno-nerds like us is that on first blush they appear to transcend the conservation of energy law. Put in one joule, get 4 out --- it is magic ! To this day, I do not really grok why the work of compression is less than the heat transferred.

 

[brucet999]

I'd like to install a tankless electric water heater for my property but none of the options I've found are outdoors. They all recommend being installed indoors. Does anyone know any that are allowed outdoor or the reason why? I'm not interested in gas nor traditional tanks.

Closest reason I found were due to freezing temperatures but I don't remember ever getting those here in Southern California.

My existing gas tank water heater is already outside near my electrical panel (but not too close) so I'd like to use the same location. I'm not sure where to put it if I were to choose an indoor location. It'd look weird in my living room/kitchen, our closets are too small, our garage is becoming an ADU, and I'd like to avoid bathrooms/bedrooms.

I've been eye'ing this Rheem unit for a while:
https://smile.amazon.com/dp/B01MS9DVEE/ref=cm_sw_r_other_apa_i_oW-8Eb4FR5288

Before you install a tankless, know that you will have to flush it twice a year with white vinegar, using a sump pump to recirculate 2gal of vinegar out of a bucket, through the system and back to the bucket for about 1/2 hour. Be sure you get it plumbed with isolation valves and hose-bib connections for the flushing pump hoses.

Colorado river water is so hard that the heat exchanger tubes of gas tankless and the heating elements of electric tankless get coated with minerals that reduce efficiency of the electric heating elements and clog the heat exchanger tubes of gas units. Rinnai actually voids warranty in hard water areas.

 

[brucet999]

Some tankless supply only one faucet. It is a fashion in some circles to have 'instant hot water' and that is one way they do it. They also benefit from markedly reduced pipe runs that do not waste hot water between uses.

But that is not what OP is doing.

 

[nwdiver]

The US screwed up so badly when it did not adopt the joule as a unit of common measure.

Anyway ... I've often thought that part of the reason why heat pumps appeal to techno-nerds like us is that on first blush they appear to transcend the conservation of energy law. Put in one joule, get 4 out --- it is magic ! To this day, I do not really grok why the work of compression is less than the heat transferred.

If that breaks your brain you'll love adsorption chillers. Wasn't my job in the Navy so I don't have a full understanding of them except that we used steam to keep our berthing cool....

 

[SageBrush]

If that breaks your brain you'll love adsorption chillers.

Actually, as soon as I read "crappy COP" ** in your link my dizziness resolved.

** slight leeway in quotation

 

[mongo]

Put in one joule, get 4 out --- it is magic ! To this day, I do not really grok why the work of compression is less than the heat transferred.

Hope I got this right...

Short version:
Before the evaporator (on a heat pump), the refrigerant output of the system is colder than input, that heat plus compressor work is transfered to the desired object.

Long version:
The compressor raises the gas pressure and temperature. Then the refrigerant loses heat to the water and changes to a liquid (due to the higher pressure). So you get the phase change heat of condensation (evaporation) along with gas temp drop.
Post expansion valve, the low pressure liquid is colder than ambient (the starting temperature) and that is where the extra energy came from. The refrigerant is then boiled to regain the heat of evaporation.

 

[Pkmmte]

The '24' in RTEX-24 is 24kW. Do you understand how much power that is? The peak demand my entire house had this month was 5kW. Better hope you're never exposed to demand fees... those usually run ~$10/kW so your hot showers could cost $240 per month excluding the cost of energy. Can't repeat it enough.... Tankless water heaters are terrible. It's also responsible for tripping one of the solar inverters I installed. Instantaneous ~24kW load creates a pretty good voltage dip inverters don't like. Tankless water heaters are terrible

My peak demand is usually around 14kW, but I've never seen a charge from my utility provider for it. I'm with LADWP here in SoCal and closest thing I see on my bill is an "access charge" or something like that for always going into Tier 3.

I googled it and I found a page describing demand charges like you've described from LADWP, but only for commercial buildings. I'm honestly not sure if that's a thing for residential with my utility. I'm willing to reconsider my tankless purchase if that's the case.

 

[nwdiver]

My peak demand is usually around 14kW, but I've never seen a charge from my utility provider for it. I'm with LADWP here in SoCal and closest thing I see on my bill is an "access charge" or something like that for always going into Tier 3.

I googled it and I found a page describing demand charges like you've described from LADWP, but only for commercial buildings. I'm honestly not sure if that's a thing for residential with my utility. I'm willing to reconsider my tankless purchase if that's the case.

It's not common for residential service yet but Utilities are seeking a way to recover lost revenue from solar generation and demand charges are one option they're looking into.

Massachusetts approves new demand charge for Eversource's net metering customers

But simply from an energy perspective a HPWH is so much better than tankless using ~70% less energy. Then there's also the ability to use cheap off-peak energy. I know the new Rheem water heaters can be programmed to preferentially heat during certain hours and only use energy outside that time frame if tank temperature dips too low.

 

[SSedan]

I just double checked and Richmond water heaters are made by Rheem.
Bet it is a way to sell to Menards and Home Depot at the same time without making price shopping so easy.

I bought the Richmond as all the specs are the same, the online control the water leak sensor etc. But Menards has an 11% rebate bringing the 50gallon to $1067 after rebate. Rebate is merchandise credit check but $130 is easy to spend at Menards later.

 

[nwdiver]

I just double checked and Richmond water heaters are made by Rheem.
Bet it is a way to sell to Menards and Home Depot at the same time without making price shopping so easy.

I bought the Richmond as all the specs are the same, the online control the water leak sensor etc. But Menards has an 11% rebate bringing the 50gallon to $1067 after rebate. Rebate is merchandise credit check but $130 is easy to spend at Menards later.

Yeah that looks like a pretty good deal. There is a new generation that's slightly more efficient but IMO the increased cost is probably not worth it.

 

[SSedan]

That is sitting in my garage waiting for me to install. Unfortunately I did the middle aged male thing and injured myself, then continued on making it much worse. Probably September before I get no it installed.

 

[abasile]

For our cool mountain climate, I'm interested in Sanden's heat pump water heaters because they work in low temperatures and do not require resistive heating coils. They use an outdoor compressor, just like an HVAC heat pump, and the tank is kept in a protected or indoor space. It would be nice to buy something like this when our gas-fueled water heater is ready to be replaced.

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