For anybody in TVA's electricity networks (mostly: Tennessee): they offer an annual promotion to single-family homeowners only to purchase an $1800 AO heatpump waterheater for only $250.
Maths: 85% discount on fancy new waterheater, which also dehumidifies and cools your house (passive result of heatpump).
TVA usually offers this promotion between Thanksgiving and NYE. You can order online from HomeDepot, or walk into a local store [0]. This ends up costing LESS than a new traditional resistive-type heater.
[0] either method: they DO verify SFH (by more than just ZIP code) -- duplexes and contractors not authorized/allowed
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My own $250.00 "TVA homeowner special" (as a licensed electrician):
<https://i.imgur.com/4wCez9u.jpeg> this specific design draws from both bath and bedroom [dual 6" inlets], exhausts into kitchen [single 8" outlet] | utility closet is only 5ft x 4ft (~20sqft)
Don't forget to use a pressure regulator, expansion tank (coldside, only), & (preferably) a sediment filter. Whatever you do: do NOT use a water softener before the tank.
Interestingly, TVA/EPB/Lowes [7] never asked for our swaps (I threw all four oldtanks away).
[7] not Home Depot; AOSmith -eligible, not Rheem (can no longer edit abovepost)
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Didn't know about the gas disqualifier... or the great URL/reference (thanks)!
For future TVA homeowner installers: the website seems to indicate that you MUST use an approved contractor for the rebate — at least December 2025, in EPB/Chatt, this was not required: just had to go to Hixson Lowes and have them look up address and then paid (w/ delivery, not in-stock).
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Less than a decade ago, I helped install a 38kW [•] tankless/instaHot heater (¡¡¡ that's three 240v40a two-pole circuitbreakers !!!) into a beautiful new home. Homeowner is actively doing his part not maintaining the unit in eventual hopes of justify purchasing a new heatpump waterheater.
Godspeed.
[•] I think technically it's 28kW -rated (there's a consumer-installed limit, w/o boilermaker license), but the circuits support more w/o 80% derating applied
> I think technically it's 28kW -rated (there's a consumer-installed limit, w/o boilermaker license), but the circuits support more w/o 80% derating applied
A tankless water heater is not considered a continuous load so there’s no need to apply the 80% rule.
A 60A 2P breaker will have a trip curve that results in a thermal trip for just under 100% of rated current in around 2-3 hours. The fast acting part of the trip curve is magnetic, longer duration trips are thermal.
The trip curve on page 25 of the pdf applies to Square D QO plug-in (residential breakers are usually plug-in, commercial are bolted on) 2-pole breakers rated 120/240V from 45A-60A. Find the 1 (times rated current) at the bottom and follow it up the chart until it intersects with the black area of the trip curve, that is approximately when the breaker will trip at 100% of its rated ampacity. Look at the left hand side to see the time in seconds that it will trip in.
It’s hard to see exactly where it intersects, but it’s somewhere between 7000-10000 seconds, or 2-3 hours.
So, you need to apply the 80% rule to continuous loads because breaker trip curves are adjusted so the thermal overload trips in 3 or fewer hours at 100% of rated ampacity. If you look at .8 times rated load, the line never intersects the trip curve.
Here’s a manual for an A.O. Smith tankless water heater:
On page 10, the 4 element, 7kW per element unit draws 58.33A per 60A breaker, 7000/240 = 29.167A, two elements a piece for 58.33A per 60A breaker.
It’s lot cheaper to wire up a 28kW electric heater if you have 480V three-phase, it’s only 28000/480/1.732 = 33.68A, all you need is a 35A 3P breaker, three #10s and a #10 ground.
240V single phase needs two 60A 2P breakers, four #6s and two #10 grounds, or if it was a single-point connection, one 125A 2P breaker, two #1/0s and a #6 ground.
The 28kW limit is from the Boilermakers Union, not ours [IBEW] =P
As much as I hate AFCI breakers, I do love a well-designed "stupid" heat-response timeout that's in compliance with the NEC. You're correct that residential waterheaters are not "continuous loads" – had slipped my mind.
I used a tankless/instahot heater (and helped install a few hundred in the early 2010s) and am so much happier with my hybrid/heatpump tank-type (it is so much cheaper to operate, requiring a relatively minimal upkeep of: an annual drainage).
Plus: there are no "miminum flow" requirements/bullshit, which results in some tempermental dishwashing among the water-conscientious (sp?).
> The 28kW limit is from the Boilermakers Union, not ours [IBEW] =P
Ahh gotcha, they must’ve pushed for some good ol trade protectionism after electric boilers came out and high-power tankless water heaters are within their wheelhouse or something like that. I wouldn’t consider it a pressure vessel but I don’t blame them for scooping up the work, lol. I’m not in the union myself, but I do manage IBEW electricians and know enough to be dangerous ;)
> As much as I hate AFCI breakers, I do love a well-designed "stupid" heat-response timeout that's in compliance with the NEC. You're correct that residential waterheaters are not "continuous loads" – had slipped my mind.
I believe electric tank style water heaters under a certain size are considered continuous loads, but tankless are not.
> I used a tankless/instahot heater (and helped install a few hundred in the early 2010s) and am so much happier with my hybrid/heatpump tank-type (it is so much cheaper to operate, requiring a relatively minimal upkeep of: an annual drainage).
Plus: there are no "miminum flow" requirements/bullshit, which results in some tempermental dishwashing among the water-conscientious (sp?).
Heat pump water heaters seem amazing, 25% of the power usage of a resistive heater, and especially for $250!
I wasn’t aware of minimum flow requirements for tankless heaters, I suppose it’s necessary to prevent overheating/steam or something? I mostly see tankless water heaters as part of emergency eyewash station installations, most commercial buildings around here either use boiler water for domestic hot water heating or have point-of-use tank water heaters near sinks/bathrooms.
>IBEW electricians and know enough to be dangerous
You definitely sound just like us =P
>minimum flow [for tankless]
Yes, my brother has a kitchen pretty far from his tankless and if you don't have a disrespectful (i.e. anti-environmentalist) flow going, it's going to get cold and then stay that way for quite a while. It is aggravating, even as an occassional guest in his house – the whole damn line has to heat back up, again!.
> . It is aggravating, even as an occassional guest in his house – the whole damn line has to heat back up, again!.
For point sources located far away from the heater, you are supposed to install a return loop. Modern tankless have a tiny (1-3 gallon) superheated tank and recirculation pump designed specifically for this use-case.
You can pry my continuous water heaters from my cold dead hands. What is much more annoying is running out of hot water when you have a peak guest load in your house right before an evening event and everyone is taking showers at the same time after a day out.
Since I use very little hot water otherwise, it pencils out for the environment too! The few times a guest is in a far guestroom and needs to use a small point of use hot water source, the few extra gallons of use to wait for it to kick in is a rounding error.
The two tankless heaters I have installed in my place are by far the single best upgrade I did since buying the house. I often comment on how much better my quality of life is with them vs. before they were installed.
I would never use a water heater with a tank ever again unless forced to. Other than air conditioning it is basically one of the top luxuries I work to provide for myself. My wife can take a bath, 3 other guests can shower all at the same time along with two loads of laundry and a dishwasher cycle going. No worries and no waiting around for an hour for hot water to regenerate. Since it's designed for peak loads and only spins up the second unit on-demand, it's much better in terms of energy use than a boiler designed to support those types of loads it sees 2 or 3 times a year at most.
If I were re-designing my system today I might do a heat pump water heater in-line with a continuous water heater, and the continuous only fires up once the tank runs empty.
In your personal usage preferance (tankless), the only reason you would consider using a tank again is if you wanted a reasonably-efficient backup generator/offgrid/standby (or the free dehumidification/energy savings).
I've used both and from an environmentalist living in a humid subtrop. rainforest, the hybrid tank (heatpump) makes most sense. Thankfully, they also have heating elements (and can run both heat sources, simultaneously).
I have a heat pump hot water heater, and it's been awesome. It's ROI has definitely improved with all the energy price spikes. It's located in my garage (I live in Florida) so there's no shortage of hot air for it to use.
Same — I maintain four (one RHEEM and three AO's).
The AO is a much cleaner/simpler/nicer install. The Rheem stupidly requires duct adapters (for small-space, <700sqft "closet" installations). AO won't last as long, but at $250 who cares?!
This reduces electric infrastructure demand, which is why it's subsidized. Presumably, this saves money (duh) for the company (duh) and possibly the customers (presumable duh). Presumably people who care about the planet understand this.
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Running a single heatpump waterheater is the equivalent of not driving your car, annually, according to TVA (in carbon footprint).
I'm running four [two households, ten people]. What's your question?
> This reduces electric infrastructure demand, which is why it's subsidized. Presumably, this saves money
Short term gain, long term pain. The story of our entire electrical infrastructure the past couple generations. Why invest in capital infrastructure like generation or transmission capacity when you can simply reduce peak demand via stuff like this.
Eventually you run out of cheap tricks and need to actually build things. We are roughly at that inflection point now - brought forward maybe half a decade or so by datacenter demand.
We had it really damn good the past 30-40 years due to investments in all area of the grid our grandparents and great grandparents paid for. Then we decided it was cheaper to let a lot of that stuff age out and deteriorate vs. replacing it via efficiency gains and de-industrialization. We reap what we sow. It was obvious electrical demand was going to increase at some point, and we have run out of the cheap parlor tricks of the past couple decades while we let everything else decay around us.
It's been incredibly frustrating to watch since I was a teenager 30 years ago and figured out why electric companies would pay someone to use less power against the obvious incentives. It's so they didn't have to do their jobs - just sit on capital equipment others paid for and collect rent.
TVA delivers among the least expensive power in the country. This is largely due to substantial nuclear and hydro, albeit with coal and gas-peakers to fill in gaps.
We also have a huge pump-storage facility, and are (foolishly, IMHO) pursuing a second pump facility in Alabama (instead, we should pursue battery electric storage at sub-stations). The currect structure can sink an entire nuclear facility (or deliver, relatively instantaneously by grid standards).
µicronuclear is the next big buzzword in TVA – which I think is smart but question-inducing (e.g. consider the multi-billion dollar Bellafonte facility, which has never generated a single kWH – and has largely been scrapped to lowest-bidding salvagers). I love nuclear energy, but TVA doesn't have the best track-record (despite substantial generation from current facilities).
My personal suggestion for a unified electric america would be to have Texas join the federal grids (i.e. accept national regulation) so that their massive wind and solar can then slosh around the entire continent (similar to how PNW buys most of California's main daytime generator: solar; then offset dips with their own massive hydro). As they operate now, they refuse federal regulation (so don't have any substantial cross-border connections). See: ERCOT (Texas Grid Operator, ideal crony capitalist market IMHO), particularly how they regulate/price MWHs.
Corrosion will destroy the tank's fittings/liner. Quickly.
So quickly, in fact, that it is mentioned multiple times in the installation manual to not do lots of things (no salt-fed softeners in bold/red/all-the-things).
While this may be true (have no knowledge | how does it work w/o salts?), the OEM will immediately void your warranty if you use any sort of homeowner water softener, per both Rheem and AOS installation manuals.
I have both; mine are warranted "platinum|10yrs" — why chance it?
water softeners in general are pretty bad. they're not great for your health, they're terrible for your soil. and the benefits to pipes and appliances are marginal at best. i completely shut down my water softener.
> the benefits to pipes and appliances are marginal at best
It probably depends on how hard your tap water is. My tap water is really hard. because it all comes from a river fed via glacial runoff in the mountains, so a water softener makes a huge difference, to the point where the water even feels different in the shower. But if your water source is naturally softer, then I can see that it would make less of a difference.
Absolutely. Not just because of the heat, but because large parts of Tennessee are subtropical rainforest (~60+" annual rainfall) so dehumidification is absolutely essential. Why not get free dehumidification from heating water?
Installing an air-exchanging heatpump OUTSIDE?!? is absolutely a massive waste of energy in such a climate (and many more).
>isn't noise an issue?
All four of mine are installed in 20sqft utility closets, using insulated ducting to top-wall registers (also, insulated). For my first install, only, I used a solid metal 90° to pierce the wall/inlet (this one is loudest, basically as if the wall weren't there).
Granted, there is definitely a "louder" side (the inlet-sides), but not by much. None of my utility closets are insulated (from surrounding draw rooms), and the entire unit isn't loud enough to justify more than just a layer of sheetrock on both side of the wall/partition.
If this was installed in a garage, it would definitely be known-to-be-on, but not aggressively-so (if you have a workbench outside, e.g.). I don't know the decibel rating, but it's about the same loudness as a stand-alone dehumidifier (same wattage/concept, actually), without walls.
Should you desire the quietest install, insulate the wall (between studs) and use dual 6" insulated ducting, with switchbacks, for both inlet and outlet (that's a lot of hardware). In such an unnecessary installation, it would be whisper-quiet.
I recently had mine installed indoors and regret it.
It's not so much the noise, it's the vibration. The damn thing reverberates through the whole house. In some areas it's quiet, in other areas there's a very disruptive hum.
The worst part though? It has an app which is infuriatingly shit. None of it makes sense, and much of it is silently locked down without informing the user (get used to "Oops! Try again!" messages).
There is no way to shut it up during sleeping hours. I cannot believe there is no option to do so. If I had kids trying to sleep here, I would demand a refund for this reason alone. It is marketed as a super quiet heat pump for indoor installation.
The firmware is cooked. Sometimes the compressor just stays on... I've left it for 36hrs+ and it never turns off. I have to power cycle it.
Fortunately there is an option in the app to use the backup electric heater instead of the heat pump. I'm willing to just use it as a poor electric heater at this point. But... It's broken. It just silently doesn't take effect. Literally as I'm typing this, the room is vibrating due to the compressor while the app reports the electric heater is off.
I've never used a Steibel Eltron tank heater (but have owned their tankless), but neither the AOSmith nor Rheem require an app to use. Both can be placed into "Electric Only" mode via front control buttons == no noise.
The Rheem specifically has a time-of-use relay/powerbox, so you can put a timer onto it which will interrupt ALL heating with a rotary dial/timer. This is entirely mechanical, without computer/app.
Sounds like your unit is cooked (36 hours continues heatpump is very bad for the pump).
An electric tankless water heater uses around four times more energy than a heat pump water heater.
Natural gas water heaters don’t use electricity.
That’s why the utility is offering rebates on them and not tankless (or tank) electric water heaters. The rebates are incentives to reduce peak electrical demand, which a tankless electric water heater does not do.
The reason the electric utility offers this huge rebate is because they are attempting to reduce their peaking load delivery — a tankless instahot peaks exponentially more than a resistive-heater.
Maths: 85% discount on fancy new waterheater, which also dehumidifies and cools your house (passive result of heatpump).
TVA usually offers this promotion between Thanksgiving and NYE. You can order online from HomeDepot, or walk into a local store [0]. This ends up costing LESS than a new traditional resistive-type heater.
[0] either method: they DO verify SFH (by more than just ZIP code) -- duplexes and contractors not authorized/allowed
----
My own $250.00 "TVA homeowner special" (as a licensed electrician):
<https://i.imgur.com/4wCez9u.jpeg> this specific design draws from both bath and bedroom [dual 6" inlets], exhausts into kitchen [single 8" outlet] | utility closet is only 5ft x 4ft (~20sqft)
Don't forget to use a pressure regulator, expansion tank (coldside, only), & (preferably) a sediment filter. Whatever you do: do NOT use a water softener before the tank.