
Heat Pump Water Heaters - branko_d
https://www.energy.gov/energysaver/water-heating/heat-pump-water-heaters
======
nickdevore
I've had mine for about a year. I put it in my garage which previously, would
reach easily 100F + in the summer. This past summer, on the hottest day, it
got to about 90 in the garage. When the water heater was running, it easily
kept the garage below 90. I purchased the hybrid version which can use
straight electricity when the heat pump won't cut it. This serves to also keep
the garage cooler for the second fridge I have in the garage.

I was previously on propane to heat my water, which was costing between $50 -
$60 a month. During the summer, my electricity bill only went up $12 a month.
During the coldest part of winter, it was at about $30 a month more. But, I
pay considerably less for electricity in the winter than in the summer.

Just for reference, I purchased the Rheem 65 gal 10 year warranty from Home
Depot when it was on sale. This has definitely been one of the best purchases

~~~
nkurz
I replaced our older electric water heater with the 50 gallon version of this
last month: [https://www.homedepot.com/p/Rheem-Performance-
Platinum-50-Ga...](https://www.homedepot.com/p/Rheem-Performance-
Platinum-50-Gal-10-Year-Hybrid-High-Efficiency-Electric-Tank-Water-Heater-
XE50T10HD50U0/300620237). The heater was about $1200, the rebate from the
state of Vermont was about $800. I did the install myself with about $100 of
parts.

Positives: As far as I can tell so far, the savings in electric usage should
pay back within 2-3 years. It has a 10 year warranty, which should keep it
working for a while. If the compressor fails, there is an electric element as
backup. The device itself seems solid and well built.

Negatives: Even though it's in the basement, it's louder than I'd like ---
about like an window air conditioner. Getting it down the narrow basement
stairs (and getting the old heater out) was hard. Reheat is fairly slow if you
keep it on the highest efficiency "heat pump only" setting. I've yet to get
the phone app working to control it from upstairs. The basement is quite cool
(especially in winter) so I'm worried it won't be maximally efficient. It
produces a small amount of condensate water, which requires a drain of some
sort.

Overall, I'm hoping it will be a win. It produces enough hot water for our
2-person needs, and seems like it should be more efficient than what it
replaced. If you are considering one, it's worth thinking about the cooling
effect that it will have on the room that it is in. If you already run an air
conditioner, this is a win. If you are heating, this is a loss. We heat with
wood in the winter (which is inexpensive if you cut your own) and don't have
any other summer air conditioner, so for us this aspect is fairly neutral.

~~~
AnthonyMouse
> We heat with wood in the winter

You should stop doing this. The impact on air quality is very bad and is
disproportionately bad for the people nearest the source (i.e. you).

[https://www.lung.org/clean-air/at-home/indoor-air-
pollutants...](https://www.lung.org/clean-air/at-home/indoor-air-
pollutants/residential-wood-burning)

[https://www.epa.gov/burnwise/wood-smoke-and-your-
health](https://www.epa.gov/burnwise/wood-smoke-and-your-health)

~~~
wldlyinaccurate
I'm not disagreeing that wood burners have a negative effect on air quality,
but there are plenty of valid reasons to burn wood for heating. Not having
access to a stable uninterrupted electricity supply is one reason. Cost is
another reason. A good cast iron wood stove can be quite efficient and will
continue to put out heat long after the wood has finished burning.

Yes, we should all aim to pollute less. But we should not attach stigma to
things that for many people is their only choice of heating, transport, etc.

~~~
AnthonyMouse
> Not having access to a stable uninterrupted electricity supply is one
> reason.

Non-electric heating systems use relatively little electricity, to the point
that a small inexpensive solar panel and battery would suffice. Some don't
require any. Also, this criteria doesn't apply to the vast majority of
locations which do have access to the power grid.

> Cost is another reason.

Cost is generally regarded as an invalid reason for pollution. Surely it costs
less to dump industrial waste in the river as well.

Also, how much money is your health worth to you?

> A good cast iron wood stove can be quite efficient and will continue to put
> out heat long after the wood has finished burning.

This kind of system is less efficient than modern heating systems designed for
fuel efficiency, which run only when they're needed and only to the extent
they're needed. Storing heat in metal rather than burning fuel as needed means
burning more fuel at the start and less later, which means a greater
temperature variation and more fuel required to maintain the same minimum
temperature, which exacerbates the level of pollution being generated.

> But we should not attach stigma to things that for many people is their only
> choice of heating, transport, etc.

We should attach a stigma to things that have negative externalities, because
they have negative externalities. If some people can't afford it then give
them money instead of overlooking the harm they cause.

~~~
gambiting
>>Cost is generally regarded as an invalid reason for pollution. Surely it
costs less to dump industrial waste in the river as well.

You know, I'm feeling idealistic like this quite often, but then the reality
hits hard sometimes. In Poland where I'm from apparently 35% of residential
properties still use coal for heating in 2020, which to my modern
sensibilities is insane, but then I speak to some of my family living outside
of the cities and the reality is:

1) there is no mainline gas supply, so gas is not really an option, unless you
want to pay a lot of money to have an external tank installed at your
property(look at point 3)

2) electricity is _far_ too expensive to use for heating, every back of a
napkin calculation shows that it would simply eat your entire salary to heat
using electricity in colder months. Electricity in Poland is both hugely
expensive and almost entirely from fossil fuels, we produce most of our
electricity from coal power plants(and building more of them!). I can keep
telling people that "surely their health is more important than money" but it
would literally by a question of "heat or food for the month" if they used
electric heaters.

3) there are some "eco" options like converting your boiler to eco-pellets,
but even with EU grants, realistically, it's still like 2-3 months worth of
salary to fit a new boiler for a lot of people. Simply not an option.

4) coal is very very cheap. You can buy supply that will last you entire
winter for about ~400USD, maybe less if you're willing to burn poorer quality
coal(which theoretically shouldn't be burnt anymore but yeah good luck
enforcing it).

>>If some people can't afford it then give them money instead

Again, that's cool as an idea, that's just not how it works in reality.

------
alliao
I like the idea but I can't find a brand that I'd trust in this day and age.
Whiteware goods used to last 20yrs, or people expected them to. Nowadays 5yrs
warranty seems to be the timeline they're expecting people to accept.

Heatpump water heater will save energy, but more parts to break. I'm sure it
can be engineered to be reliable, just not sure by whom...

~~~
TaylorAlexander
I know this is not a concept people are used to, but I’m really in to the idea
of open source appliances. In that case there’d be one centralized (and
forkable) project where skilled engineers from around the world could design a
suitable machine. I’d love to see companies pop up to manufacture those
designs the same way 3D printer companies have done.

~~~
lotsofpulp
How does liability work for open source appliances? That’s the first thing
that comes to mind when doing business in the US, especially with a product
that can cause carbon monoxide poisoning or fires.

~~~
kube-system
You'll probably have a tough time even installing it legally under many
building codes.

~~~
TaylorAlexander
I don’t see why an open source design manufactured by a competent manufacturer
would be any different from a proprietary design. It would need to pass
certifications and the regulator may require a version freeze, but it seems
like it could be done.

There’s also countries all over the world who don’t have these regulations,
and would appreciate good quality plans for useful appliances.

------
agent86
When my water heater last needed replacing I went and got a Propane Condensing
Gas Tank water heater[1]. It was a bit expensive up front, but at 96%
efficiency I thought I would make up the difference on gas while enjoying the
performance. It is pretty wild - we lost power for days once in the winter
cold, and it brought the water back up to temperature in under 10 minutes.
Even empty it can basically keep up and heat like a tankless unit would.

It has a little LCD panel where you can check the stats of the unit, so I just
took a look. We've had the heater on for 3430 days, it has cycled 15,584
times, and run the burner for 57 days. It has basically run about 1.5% of the
time it has been on.

In the future I'd consider going the heat pump route if I can get solar, but
given the topology and how my house is positioned it doesn't look like I'm a
great candidate for it :-(.

[1] [https://www.hotwater.com/water-heaters/residential/high-
effi...](https://www.hotwater.com/water-heaters/residential/high-efficiency-
gas-tank/)

~~~
teruakohatu
I had not heard of Condensing Gas Tank water heaters before. They are very
clever. Gas water heaters are very popular here in New Zealand. Do you know
how much more efficient the Condensing Gas Tank water heater is over regular
gas?

If I understand it correctly, the difference is that the condensing system
pre-heats the cold water with the exhaust gas from the burner.

[https://www.hotwatercylinders.nz/images/source/Bosch_26eco_C...](https://www.hotwatercylinders.nz/images/source/Bosch_26eco_Condensing.jpg)

Did you compare costs of a regular gas heater vs. condensing?

~~~
elric
Best case, a condensing heater uses 20% less gas than a conventional one. But
there are some caveats...in order to condense the exhaust fumes, the returning
water has to be cold enough. Low temperature radiators or underfloor heating
are best for that. If you have huge, old, cast iron radiators that get super
hot and stay hot for a long time, there probably won't be much condensing
going on.

Basically any time you see white smoking coming out the flue, it's not
condensing.

------
gregmac
Why aren't there integrated systems for heating/cooling? (Or maybe this exists
and I just don't know the proper terms to search for)

We have multiple cooling devices: air conditioning (dumping heat outside) and
refrigerators (dumping heat inside). Then we have multiple separate heating
devices: furnaces and hot water tanks that burn electricity or gas to generate
heat.

I've always thought it would be more efficient if these units were all
connected with some kind of coolant loop, and a heat pump / control unit that
could route heat/cooling to where it's needed.

I did find a similar system for connecting air conditioning to heat a swimming
pool (instead of outside condenser unit), which is pretty neat, but I'm
thinking bigger. If you're going to dump excess heat anyway, might as well use
it to heat water, at least.

~~~
chris_va
Lot's of small reasons.

You don't want to transport heat a far distance (thermal loss becomes too
high), so keeping the vent for the refrigerator integrated into the unit is
generally better than shipping it off outside.

CoP is the lift you get from a heat pump given a specific delta-T. The smaller
the delta-T (like an air conditioning unit's 90F->70F), the more efficient you
can make it. If you group a bunch of components together with different target
temperatures, you'd either effectively have 2 lines (so 2 systems), or run the
system at the lowest temperature you care about. 2 systems is what you have
today, and 1 system with high delta-T would have a much worse CoP.

And other reasons...

~~~
evjim
Also refrigerant has a very high carbon cost and installing piping on site
between all of these appliances would require more refrigerant to fill those
pipes and a higher potential for leaks.

------
lsllc
If you have a geothermal heat pump, you can install a "desuperheater" [0] to
recover the excess heat for hot water during the shoulder seasons. It doesn't
work so well during the winter, so you need "backup" heat such as an electric
element, or a more traditional fossil fuel hw heater (and you might also want
one of these as a backup for the geothermal loop depending on where you live).

[0]
[http://www.geojerry.com/desuperheater.html](http://www.geojerry.com/desuperheater.html)
(sorry, couldn't find a better site)

~~~
q084yn39cptyth
We have geothermal HVAC. When we moved in we had that water heating setup, but
then changed the water heater (natural gas tank). When we did, we asked about
hooking up the desuperheater again and were told the energy savings weren't
worth it on newer water heating units because of the efficiency. This is
coming from a well respected company in the area that specializes in
geothermal and heat pumps, and generally has bent over backwards to suggest
improvements to all sorts of things in other ways (I also am pretty sure they
installed the original system).

Not sure if they were right or wrong, but my experience with a lots of these
heating and cooling things is that the real world efficiencies are often
different from theoretical values.

~~~
bluGill
Geothermal water heating just barely works out in general because efficiency
drops with higher temperature differentials. If you would accept you water at
noticeably below body temperature it would be great (though I suspect this is
ideal for bacteria growth) efficiency. If you want your water as warm as the
minimum recommended temperature by efficiency experts you are already in
questionable efficiency range. If you go hotter it gets worse.

~~~
makomk
Yeah, reducing the temperature on water heaters is a great way of causing
Legionnaire's disease.

------
m463
Years ago, I was convinced that solar hot water heaters were ridiculously
efficient and paid for themselves in just a few years.

Since that time, I've come to think that solar PV + an electric water heater
is probably a better answer - easier to install, very little relative
maintenance.

Now I wonder how solar PV + a heat pump water heater compares (especially if
it doubles as a cooler for a surrounding room).

~~~
grecy
In certain parts of the world (tons of Australia, parts of Africa) literally
every single building has a solar hot water heater.

They are fantastic in hot climates, and should be littering the roofs in CA,
AZ, TX, etc.

~~~
autonoshitbox
Americans are afraid of the "third-world look" of solar water heaters they
know from vacations in Europe

~~~
grahamburger
I don't think this is true? Also for what it's worth I've spent time on the
roofs of a lot of apartment buildings in the bay area and seen many solar
water heaters. Newer buildings and homes tend to just have solar panels if
anything, though.

------
magoon
My electric bill has gone down over 30% per month after getting one of these.
Replaced a super old electric unit. Many states have rebates that an installer
can have applied when getting the part from the supplier. For me this cut the
whole cost in half. It paid for itself in less than a year. And now my
basement is dry and cool in the summer without running a dehumidifier.

You might ask, if these are so great then why aren’t people yelling it from
the hilltops? They are, but nobody’s listening.

~~~
koolba
How’s it compare to a tankless gas heater?

~~~
stevehawk
Tankless heaters seem like the biggest over promise household tech I can
recall in the last decade or two. I have not found over that I would even come
close to breaking even on when replacing either of the water heaters in my
house.

~~~
ed_balls
Tankless heaters heaters are great if you live in a small flat or don't use it
extensively (living alone, half of the time taking the shower at the gym).

Currently, in my flat there is only district heating which is way cheaper
(lower cost, no maintenance). It's really great, should be the default in high
density areas.

------
mrb
It would be neat to combine a heat pump (water heater or general heater) so
that the outdoor coil (cooling down the air) is put to good use instead of
being wasted cold. For example the cold coil could be cooling down a fridge or
freezer.

I'm not sure how feasible it would be in practice. There is an advantage in
having appliances that are independently serviceable and replaceable. But then
again one heat pump system cooling the fridge and heating up water is simpler
and less likely to break than two separate systems (one for the fridge, one
for the water heater.) Price-wise, however, the labor costs of installing one
physically larger integrated system are probably high than the labor costs of
installing 2 smaller systems. So many tradeoffs...

~~~
torpfactory
The big issue is timing: hot water, fridge use, and home heating would need to
be well synchronized to take advantage of this. I.e. you don't necessarily
want to make your fridge colder just because you happen to be heating water.
The fridge and temperature is set so your lettuce doesn't freeze and your
hamburger says solid. Your water heater turns on because you took a shower.
You would need to store the thermal energy (a block of ice, perhaps), but this
adds complexity and cost.

~~~
TaylorAlexander
If the link was optional, so they could either share heat movement or discard
waste heat, then there’d be plenty of room for an algorithm to sort it out.

~~~
mrfusion
Maybe you can pipe all your heat and cold to central locations and have some
kind of heat broker. There’s also a lot of heat in your attic.

~~~
ikiris
perhaps maybe in a large tank of a thermally dense fluid.

------
rossjudson
I visited a house years back that captured back hot water heat from the shower
drain. Hot water going down the drain went through a pipe wrapped with a
spiral pattern of other pipe (and fresh water from the hot water tank
circulated through there). Don't know how efficient it was, but it was pretty
cool to see as a working system.

~~~
theluketaylor
Here in Canada recovering heat from the drain can be used as part of energy
efficiency code requirements in new builds.

They can recover quite a bit of heat, around 50% depending in inlet and outlet
temperatures. Pretty good for a fully passive technology that has no
maintenance or moving parts.

It does require a lot of copper, so the parts are about $1000 but it's a
really easy install.

~~~
frosted-flakes
Those things are neat. I always wondered why they were wrapped around vertical
pipes rather than horizontal, because intuitively it seems like horizontal
would be better, but that's not the case. I looked it up and it's because
falling water in a vertical pipe will cling to the pipe wall, while in a
horizontal pipe it will just sit in the bottom. It's obvious in hindsight, but
I've never thought about the physics of water in a vertical drain pipe.

~~~
twic
I've seen a design which exploits this by having the waste pipe flare out
enormously - imagine two squat cones joined at their circular faces. You get
loads of surface area for heat exchange, with slower flow across it, and no
chance of blockage.

------
astawertwe
This is a big deal. When I moved into my current apartment, the thermostat had
two settings, "Heat" and "EM Heat". I didn't know what they meant, or what the
difference was, and I never bothered to ask. But then one month by mistake I
set the thermostat to "EM Heat" instead of "Heat". And I got a $300 electric
bill instead of my usual $80. "Heat" means heat pump, and "EM Heat" means
emergency heat, which means direct heating, which as the article explains
requires several times more energy. I won't forget that again.

~~~
rathel
Yay for another descriptively named controls on an appliance. What did people
designing this think? I know it's probably in the manual. But there are people
from whom you can't expect reading the instructions - not because of "fuck the
manual" attitude - like guests who live only temporarily.

Would a more descriptive label save them $0.01 on ink or what?

------
henrikberggren
Heat pumps are really amazing and can be used both for cooling and heating
with the same hardware. If it wasn't for natural gas they would make sense for
many American homes

[https://medium.com/hackernoon/the-magic-of-heat-pumps-
fd2721...](https://medium.com/hackernoon/the-magic-of-heat-pumps-fd2721a00586)

~~~
quickthrower2
It might solve some of the solar demand problem. Heat water up during the day
when the sun is out, and then store that in an insulated tank.

Have both bath water and central heating run off that.

~~~
JshWright
That's already a thing, they just skip the intermediate steps and run the
water through black pipes in a sunny spot.

~~~
quickthrower2
Black pipes are great, it would make some interesting calculations to compare:

Pipes vs. PV taking heat pump characteristics into account, whose efficiency
depends on climate. Installation costs, maintenance costs. The Pipes compete
for real estate space against the PV, so if pipes are more efficient, does it
off set the lost electricity (that would be more expensive, but cheaper than
from the grid, but only when it's sunny and you can use the appliances at that
time, unless you have a battery which is more capex, so does the
interest/repayments on that cost get offset by using electric 24/7). Etc. Etc.

It might need some ML to figure out the best solution. And by ML I mean linear
regression.

------
reyoz
I put in a Sanden heat pump to replace an old electric gravity water heater
1.5 years ago. Based on power meter data it uses 30% of the energy of the old
system on average. This is probably understated as hot water consumption has
gone up as the new system and new pipes increased pressure and flow. I say on
average as there is seasonality to the energy consumption. I live in a
temperate climate, no snow.

We run it at night to take advantage of cheaper separately metered electricity
rates ('controlled load'), it could be run even more efficiently during the
day, but at higher cost. This and replacing the old gas ducted heating with
reverse cycle air conditioning has allowed us to stop using gas, saving the
fixed $~30/month service charge. Eventually the additional of solar will
further increase our use of renewables.

------
WaitWaitWha
I do not understand why anyone uses water tanks at all. The tankless or
demand-type water heaters tend to be more energy efficient, take significantly
smaller space, less parts, and have been in use successfully since the 19th
century. Am I missing something?

~~~
erik_seaberg
Apparently tankless water heaters draw something crazy like thirty kilowatts,
which is more than the rest of your appliances _combined_ and probably
requires a landlord to agree to rewiring. Maybe if you have a natural gas
supply it's more practical.

This is also why it's rare to fast charge an EV at home—that can top _fifty_
kilowatts.

~~~
magicalhippo
If you need 10 liters/min of hot water, got an intake temperature of 10C and
want to heat it to 40C (hot shower, my gf loves them), it takes about 21kW[1].

If you use a water-saving shower head that only uses 5 liters/min that cuts in
half, but still quite a lot of peak energy.

Now you might argue that you only use it for a wee bit while you shower. And
that is true. However here in Norway they will soon introduce a peak demand
pricing element on the electricity bill, which means you'd likely end up
paying a lot for that instant heating.

In contrast, showers are typically taken in the morning, so the water heater
tank could get nice and hot during the night when electricity prices are low,
and then kept off during the day.

[1]: [https://bloglocation.com/art/water-heating-calculator-for-
ti...](https://bloglocation.com/art/water-heating-calculator-for-time-energy-
power) (Water Heating Power Calculator)

------
duxup
My concern with these is always the noise. The compressor on there has to be
fairly noisy.

~~~
esaym
There's a compressor too on your fridge you know...

~~~
duxup
It's pretty annoying too, and so does my air conditioner...the range of noise
seems quite wide.

~~~
willvarfar
Mine hums like a fridge. Luckily, its straightforward and normal for the heat-
pump to be outside or in a garage or basement, so the sound isn't in the
living space. Its like: who would want a window-mounted air-con when they
could have one of those white boxes up on the roof where nobody hears them
instead?

------
JackPoach
Heat pumps are nothing new. They are not wide spread for a reason. It's weird
how old ideas get a new life over and over again. My pet peeve is that these
ideas are presented in an overly simplistic way that simply aren't true. "Did
you know that you can get free electricity by simply installing solar panels
on your roof?" Or "Cut your utility bill 50% by harnessing the power of wind".
We know about heat pumps for 100 years. There's a reason why most heaters use
gas or electricity - it's cheaper and more simple in installation. There are a
lot of enthusiasts who can do things well with their own hands, including
sourcing materials, so it's really cheap and simple FOR THOSE FOLKS. But for
regular folks these things tend to cost more even for totally proven and
technically viable technologies - solar, heat pumps, passive house, water
harvesting, etc.

------
TopHand
I live in one of the most continuously windy parts of the nation (US state of
WY). In the winter time, the heater, a ground source heat pump struggles most
when the wind is blowing. I've often wondered if a hybrid heat pump system
could be built that drives the compressor and circulation system directly from
the mechanical action of a wind turbine rather than first converting the wind
energy to electricity, then goes back to drawing from the mains when the wind
is still. My thought process is that you would lose energy by first converting
to electricity, then converting electricity to mechanical motion. If someone
out there likes this idea, and wants to pursue it, I hereby release it to
public domain.

~~~
ptspin
Here is some information on this concept.
[https://solar.lowtechmagazine.com/2019/02/heat-your-house-
wi...](https://solar.lowtechmagazine.com/2019/02/heat-your-house-with-a-water-
brake-windmill.html)

------
jagger27
Could you use one of these to cool your house and heat your outdoor pool?

~~~
willvarfar
My pump heats my outdoors pool in summer and the house in winter.

Its more usual to have a small heat-pump just for the pool, though. These are
surprisingly cheap, considering the premium on all pool parts generally. I
mean, a pool roof made of plastic costs 3x or 4x more.

------
teruakohatu
These are relatively common here in New Zealand, but the upfront cost is high
and there is more maintenance than a insulted electric water heater.
Retrofitting one will never pay itself off so they only go into new homes.

Most homes in NZ use electric water heaters with gas becoming more and more
popular. Gas is only used for heating tap/shower water and cooking, not for
heating the home.

~~~
Max_aaa
Considering that hot water does not need to be heated right away, solar water
heating (Direct or via photo-electric) with an electric hot water cylinder as
a backup for overcast days would result in more reliable and more long lasting
system.

~~~
teruakohatu
Some people have them here, but it is not that popular. Most of the country
has a mild climate and so you would still need an electric heater to keep the
tempreture constantly high enough to kill legionnaires bacteria (over 60
degrees celcius).

I think over the lifetime of the system money saved in electricity would not
be offset much due to installation. Most of the country is run off hydro so
not much environmental benefits either.

~~~
robocat
> Most of the country is run off hydro so not much environmental benefits
> either.

Actually, the majority of marginal units of electricity come from gas. That
means that every extra kWh you use comes from gas, and every kWh you save
reduces gas usage. There are few times when the lakes are full and your
marginal unit would come from hydro.

The easy way to think of it is that all the hydro is already used up by other
people, so your electricity usage comes from gas.

Hopefully NZ gets some large solar generation, since NZ can “store“ it in
lakes by reducing lake outflows during the day (I think).

~~~
teruakohatu
I get what you are saying but that is not quite how it works. The marginal
price may be determined by gas, but my electricity in the south island is
mostly hydro.

Right now as I write this comment, the grid in the south island is being
powered by hydro and wind. Less power is currently being exported north than
is being generated right now by gas up North. So if I turn on a heater, it
does not mean that an extra couple of kw of gas is being turned on in
Auckland.

Right now the total power accross the country is 84% renewable. So worst case
if I use a heater it is 16% not renewable.

In any case, electric water heaters in nz are ripple controlled and only heat
at the lowest demand. So any electric water is using as much hydro as
possible.

~~~
robocat
> So worst case if I use a heater it is 16% not renewable.

As a choice as an individual: The heater is off. You turn it on. The extra
demand you _added_ usually comes 100% from gas generation.

> In any case, electric water heaters in nz are ripple controlled and only
> heat at the lowest demand. So any electric water is using as much hydro as
> possible.

Our lakes are like batteries. If you choose to take an extra long hot shower
powered by hydro at the moment, but 3 months later the lakes get low (because
there is not enough rainfall) then extra gas generation is used 3 months later
which matches 100% of your extra power usage due to your hot shower choice.

Reducing your power usage works similarly, in that you save gas generation.

As an individual, your choices 100% affect how much gas is used, because we
are assuming others make no change. This is the key to thinking about marginal
usage. Marginal economics are critical to understand when running a business
too, since it is similarly confusing (and we all naturally make simple
mistakes when thinking about it).

There are times when your extra usage comes only from hydro, but it is usually
not simple to know at the point when you are adding power usage. Reducing
power usage can only ever help, so different.

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milofeynman
I want to pump this cool air into a server closet with an outtake but I'm sure
there are problems with that... Anyone tried?

~~~
frosted-flakes
It would probably be more efficient to pump the warm air from the server
closet into the water heater room.

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alkonaut
Isn't this just a normal water heater?

Apart from the very simplest models that you might install in a small cabin or
separate building (direct-electric or maybe gas powered) isn't this is what
you'd normally install in a new house for the last 30 years or so?

~~~
rini17
No, normal heater heats water directly using supplied energy, while heat pump
works like fridge or AC in reverse - it pumps ambient heat to the water using
smaller amount of energy.

Perhaps in some locations they install it in new houses as a standard, but I
doubt it, it is more expensive.

~~~
alkonaut
I guess it depends on where you live. In Northern Europe it's been the default
for a very long time, but so has triple glazing and a foot of insulation etc
(For obvious reasons). Heating is a large part of living costs and a 30%
efficiency increase pays off in no time not least because the hot water is
used for space heating as well as for household water.

For that reason you'd expect the same to apply for parts of northern USA and
Canada.

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dirtyid
[https://www.youtube.com/watch?v=omivdhxdGv0](https://www.youtube.com/watch?v=omivdhxdGv0)

Matt Risinger has some approachable videos to building technology for those
interested.

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bkovacev
I moved into an apartment that has a Gree Versati Pump, and it's super neat
because I can control it via modbus and raspberry pi. Electricity bill
decreased tremendously when I moved.

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xfitm3
In hot climates you can also recover heat rejected from your A/C compressor,
circulate water into a tank, and get a bunch of hot water for free.

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hinkley
Some jurisdictions have a rebate program in effect for these. You should look
at whether your utilities company has any information on the subject.

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ars
For even better efficiency use an Absorption Heat Pump, powered by natural
gas.

But they are hard to find.

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mlindner
These make no sense if there's natural gas available. Natural gas is dirt
cheap (heck recently it's being given away for free in many places because
it's a waste product from oil extraction).

~~~
hyperbovine
Not true at all. My basement is a muggy swamp in the summer. I have to run a
dehumidifier 24/7 else everything molds. This water heater does that as a side
effect. Plus, some of us enjoy owning things that are energy efficient, and
are willing to pay for it. Enjoy your global warming.

~~~
teruakohatu
Is your gas burner inside the house?

Here in NZ I have only ever seen them installed externally.

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expensivepool
We use a heat pump to heat our 15,000 gal pool in FL - we keep the temp at 94°
basically year-round, minus a few weeks, and it costs only ~$150-300/mo,
depending on outside temp.

~~~
senectus1
holy hell. thats more cost than our whole house of two adults and two (just)
pre-teen kids every month... JUST for the pool. in fact thats more than our
bill every two months (AU$400 every two months), and that's our new place
which has some 80's design issues that i need to resolve. our bill should be
nearly half that.

~~~
jamiek88
You've never seen energy used until you live in the American South for a bit.

$400/month for a/c and pool in summer isn't unusual and power is cheap too,
$0.10 - $0.15 kw/h.

It's jaw dropping.

