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.

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ethansinjin 2 hours ago | parent | next [-]

Important caveat:

> You must swap out an old electric unit; switching from gas to electric doesn't qualify.[0]

That’s a bummer; totally would have done this otherwise

[0] https://www.hotwater.com/water-heater-rebates/tva-heat-pump-...

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ProllyInfamous 2 hours ago | parent [-]

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

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quickthrowman an hour ago | parent [-]

> 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.

Here’s a link to a Square D breaker guide: https://ressupply.com/documents/square_d/QO_and_QOB_Circuit_...

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:

> https://assets.hotwater.com/damroot/Original/1000/100306523....

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.

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ProllyInfamous an hour ago | parent [-]

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?).

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quickthrowman 29 minutes ago | parent [-]

> 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.

	▲	ProllyInfamous 19 minutes ago \| parent [-]
		>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!.

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GenerWork 4 hours ago | parent | prev | next [-]

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.

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ProllyInfamous an hour ago | parent | next [-]

>>Florida>> "no shortage of hot air"

hot HUMID air – which heatpumps love!

Draw your inlet from [at least one] humid bathroom source, if you can. Always use insulated ducting to lessen local condensation.

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I always smile knowing that using hot water doesn't cost any more than cold, at least when the AC would otherwise be cooling (offset).

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ProllyInfamous 4 hours ago | parent | prev [-]

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?!

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fsckboy 2 hours ago | parent [-]

>at $250

after subsidy

>who cares?!

fellow taxpayers, fellow ratepayers, people who care about the planet, etc. etc.

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ProllyInfamous 2 hours ago | parent [-]

>fellow ratepayers

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?

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edit/tone (educatable moments): <https://www.hotwater.com/water-heater-rebates/tva-heat-pump-...>

	▲	phil21 14 minutes ago \| parent \| next [-]
		> 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.
	▲	laurencerowe 37 minutes ago \| parent \| prev [-]
		> Running a single heatpump waterheater is the equivalent of not driving your car, annually, according to TVA (in carbon footprint). This seems a lot but for utilities which still have coal plants it seems accurate if the reduced demand allows them to close the coal plant down. A typical car emits 4.6 tonnes CO2 per year. https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-t... Heat pump saves around 3,760 kWh per year. https://www.energystar.gov/products/heat_pump_water_heaters/... Coal emits 1.02 tonne CO2/MWh = 3.8 tonnes CO2 per year savings from the heat pump. Natural gas emits 0.44 tonne CO2/MWh = 1.65 tonne CO2. https://www.eia.gov/todayinenergy/detail.php?id=48296 That's a pretty substantial saving which will kick in when the next administration reverses Trump's absurd orders to keep existing coal plants open.

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gucci-on-fleek 3 hours ago | parent | prev | next [-]

> Whatever you do: do NOT use a water softener before the tank.

I'm curious why not? I can't immediately think of a reason why that would be bad, but I admittedly know hardly anything about plumbing.

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ProllyInfamous 3 hours ago | parent [-]

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).

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andy99 an hour ago | parent | next [-]

Curious about this because I thought the entire point of a water softener was to prevent damage to appliances due to mineral buildup. I’ve never heard before that the salt is bad for any appliance.

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tass 2 hours ago | parent | prev [-]

Possibly obvious point, water softeners add salt to the water.

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rstupek 2 hours ago | parent | next [-]

Not all water softeners add salt to the water. nuvoh2o sells a water softener that does not use salt.

	▲	ProllyInfamous an hour ago \| parent [-]
		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?

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ProllyInfamous 2 hours ago | parent | prev [-]

Correct. This is the reason.

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dzhiurgis an hour ago | parent | prev [-]

> which also dehumidifies and cools your house (passive result of heatpump).

Wait do you install these indoors? I get it's pretty hot in Tennessee, but still got some winters? Also isn't noise an issue?

In most of Australia these are installed outdoors. Pool heaters is another one where one could harvest indoor heat.

	▲	ProllyInfamous an hour ago \| parent [-]
		>Wait do you install these indoors? 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.