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Heatpumps seem to be most efficient for water / home heat - True?

Posted by gardurnit (My Page) on
Tue, Jan 19, 10 at 2:03

I found something very interesting that I really did not know or realize.
Heat pumps seem to be the most efficient, perhaps more so in value, compared even to solar collectors.
This is hard for me to believe and I know it certainly depends on the final installed costs. See here and
please comment or disprove it.

This site has something that I hope you all will review and comment on. The costs of using methods to heat home water.

Please be aware that every answer is not complete .. ever. There are always new thoughts and developments.

However as of now January 18, 2010 it appears that heat pump is 2.20 or 220% efficient (using heat from the environment).
This could be augmented by using a solar collector to bring more heat to the heat pump. I don't know if this pump uses ground
based heat storage.

For $4000 I should think that 5 sq meters = 4000 watts could supply a lot of hot water to a home. Albeit not at night but with storage heat would be carried over.

Even snow compressed into a large pond in Winter offers some
Minnisota buildings a source of cold water to cool the
buildings in Summer.

What do you think or now know about in regard to the near future of heat pumps for hot water and home heating?

Please do compare what you know to climates from Maine to Texas to Florida to Washington State it would be very helpful.

I'm willing to contribute 1 hour / week on this topic and research it by getting constant news updates about the cheapest ways to get hot water.
I'm building a house from a 1912 Victorian starting point and want to d my best all while saving money and offering an example of 'how to do it."


Follow-Up Postings:

RE: Heatpumps seem to be most efficient for water / home heat - T

Heat pumps have long been one of the most efficient ways to heat or cool a space. Most of the southern US use heatpumps as their primary heating source.

The drawback is that you need a readily available source of relative heat to draw from. In mild climates, the ambient air can work most of the time. In colder climates, you have to go underground to find the heat source. Geothermal systems are just heat pumps with massive installation costs. Lots of people have had this idea, but I don't know of anyone who has made it work in terms of dollars and cents.

RE: Heatpumps seem to be most efficient for water / home heat - T

What I know of these Heat Pump water heaters, is that they are installed into an area which the temp is somewhat controlled. Their suggestion being Garage, Basements, or Attic, so being able to work in somewhat tempered temperature area.

RE: Heatpumps seem to be most efficient for water / home heat - T

Looking at this data, and talking with a co-worker I now believe this PDF data sheet isn't correct. They took cost of installation and life in years and added installation cost over again if it failed under 13 years in which most other technology lived to.

So they show

conventional oil-fired storage

$1400 Installation
$654 Yearly energy cost
8 years of operating life
$11,299 cost over 13 years

Since they added installation cost in at year 9 there cost is higher. I took cost of installation over the 8 years, so I added a faction of installation cost over the period over 13 years. My cost over 13 years


Then we have "Demand gas (no pilot)" if living to 20 years its total cost over 13 years should have been $4446 not their $5008 figure. Solar being the same 20 years of live, it's cost over 13 years should be $6620 vs. their $7072 figure.

Bringing all figures in to a 13 year prioried some interesting facts amerge.

Gas fired hot water ran as the following over the 13 years of installation / energy cost.

Conventional $5394
High Efficiency $5220
Condensing $5170
Tankless $4446

Electric type

Standard $6769
High Eff. $6528
Solar Electric backup $6620

HPHW $4125

In the end Heat Pump Hot Water tank seems to win, but it doesn't stand out like it did before and it's seems more accurate representation of cost.

I do think that to have Hot water all the time, one would need to backup solar with something. So their average monthly cost seems fair to me. Funny in the end with electrical hot water systems it seem everything is about the same cost over 13 years.

RE: Heatpumps seem to be most efficient for water / home heat - T

No doubt solar is not given a fair rap. Where does it get the efficency of 1.2 from? It certainly would depend where you live. I suspect that I get 85% of hot water from solar but it isn't easy to tell since I don't have a meter on the electric backup. But I live in a pretty sunny area and in a cloudier area, those numbers might be right.

The cost estimates also depend greatly on where you live - obviously a kw varies from about 5 cents to 40 cents (top tier in CA) so there is an 8 fold diff in price. NG is a little more constant but varies a decent amount.

Page last updated in 2007.

That being said - in FL, a heat pump HW heater is a great thing and may be cheaper (and more efficient) than solar.

RE: Heatpumps seem to be most efficient for water / home heat - T

Electric heat pump water heater
2.20 EF rating seems fair HP EF and tank heat lose.

$1,660 Installation
$190 Yearly cost
13 Years to life (don't agree but ok)
$4,125 Total after Installation and Yearly cost after the 13 year thing.

Solar with electric back-up
1.20 Seems fair given Electric backup and tank lose.

$4,800 Installation cost
$175 Yearly cost to run / backup
13 years to round to other water heaters
$7,072 They added installation and 13 years of electric, I feel this is wrong as I think they should have done this by the life time.

So mine is

$6620 seems fair.

Solar wins if you only looking at the price to power it over the yearly / monthly price. When you factor in the price to install it then no it doesn't win.

RE: Heatpumps seem to be most efficient for water / home heat - T

Ok - except solar has tax credits that get the install down to about $2000. Also solar should last longer than heat pump.

I don't see the 1.2. If it only supplies 50%, then maybe. But probably most supply more like 80% so the number should be close to 3.0. The heat pump also seems like it would cool the house so in a heating predominant climate - like where 70% of the US is, this heat needs to be given back.... There is no way that this balances the a/c saved - again in 70% of the country.

RE: Heatpumps seem to be most efficient for water / home heat - T

In hot climates like Fl, TX, etc., the hands-down winner is a heat pump with a heat recovery unit using a 80 gallon electric water heater as storage/backup. Since the home is under A/C most of the year, you're getting both free hot water and an increase in your A/C efficiency. You can go back to washing clothes with hot water as the more heat you can shed, the cheaper the A/C runs. Also in hot areas, the A/C runs at night and early morning bettering a Solar water heater's performance since it can't provide hot water then and must rely on it's backup heat...when do you use most of your hot water? All the systems I've been aware of have provided an immediate minimum $50 a month reduction in electric bills upon install. The cost of the HRU is usually <1K (less if you do the mechanical work installing it) and units with 2 coils are available for homes with 2 A/C condensors.

RE: Heatpumps seem to be most efficient for water / home heat - T

gary - Obviously 80 gallons of hot water is still hot in the morning. To say that you would need backup at that time is just wrong. Say at 5pm the tank is up to 140, it will still be 135 in the morning. In S Florida this winter, solar would have easily beat heat pump. Wasn't it 43 in Miami 2 nights ago - not a lot of a/c there while my solar panel was 250 degrees much farther north.

I'm not really disagreeing with your conclusion but don't diss on my solar....

RE: Heatpumps seem to be most efficient for water / home heat - T

You missed the point David...Yes the 80 gallon tank will provide the hot water for your shower in the morning but the incoming cold make up water will cause the backup heat to turn on as there's no solar to provide heat at that time. I'm not 'dissing' solar...just pointing out that in Florida or other hot climates a heat recovery unit is by far the most practical. Cheaper and faster return on investment. Also if you are using the HRU on a heat pump, you're still getting hot water when the heat is on...not quite as efficient but it's still a cheap way to heat water. The system just has to run a little longer. Further north, the equation is not so good for a HRU.

RE: Heatpumps seem to be most efficient for water / home heat - T

Hi Gary,
If the solar system is designed well, there is no need for the backup system to come on at all -- morning, afternoon, or evening. Many people, including me, disconnect the backup system altogether most of the year.


RE: Heatpumps seem to be most efficient for water / home heat - T

Like the Gary to Gary. Obviously I agree with Gary. So I use 10 gallons for a shower, then maybe the water is down to 125. The backup is set at 115....

RE: Heatpumps seem to be most efficient for water / home heat - T

Gary agrees, but I'm not sure what Gary thinks.

RE: Heatpumps seem to be most efficient for water / home heat - T

Next Wednesday we are installing a heatpump hot water heater. My husband and I live beachside in Central Florida and in the 11 years we have lived here, we've never had a freeze. The HWH will be in our toasty garage--insulated to beat blazes and hotter than the hubs. Three cars--if one comes in hot, the garage stays stiffling for 12 hours. Good place, me thinks, for a heatpump HWH. We were able to find a local plumber who has installed two of the Rheem water heaters. He will charge a total of $2100 while Home Depot offered to install it for a total of $2700. Later in the week we will also upgrade our a/c with a Rheem 15 seer. It looks like there will be about $2000 in rebates on the a/c system. Oh how I hope this all works out. I'm really excited about the hot water heater. Strange old lady, I tell you, really, really strange! I don't know anyone else who would be excited about this!

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