[net.consumers] Heat pump/water heater energy conservation

donn@neurad.UUCP (Donn S. Fishbein) (12/11/85)

Having recently moved, and for the first time having to pay energy bills
directly, I have several questions about the most efficient use of an
electric heat pump and electric hot water heater.

First, the manual for my heat pump recommends setting one temperature and
making no further adjustments.  Is it more economical to set back the
temperature at night, and during the day when no one is home, or to leave
the temperature adjustment alone?  Is there something unique to heat pump
technology in this regard?

Assuming that temperature set-back is economical, I have noticed that nearly
all of the automatic thermostats available specifically say "NOT FOR HEAT
PUMPS".  After diagramming the existing thermostat and one automatic
thermostat (Magic-Stat 3000), the major problem seems to be that the heat pump
contains two thermostatic switches; one for the heat pump compressor, and one
for the aux. heating coils.  The heating coils are activated if one changes
the temperature set point abruptly eg. from 55 F to 68 F.  Does this occur
simply to decrease the time it takes to achieve the new temperature,
or is the heat pump incapable alone of affecting the change?  Is it more
economical to allow the heat pump to operate alone?  (NOTE: I have not seen a
situation yet where the heat pump alone could not maintain a temperature,
but I realize that if it is too cold outside the coils will be needed. )
Is there a solution to this problem of automatic thermostats being unable to
control an essentially two-stage system?

Finally, with regards to the hot water heater, is it advisable to install a
timer so that it only runs when people are likely to be home.
In other words, is the energy needed to reheat the water more or less
than that required to maintain the water temperature for a prolonged period of
no hot water use. My hot water usage is quite modest, yet I think this
appliance is quite an energy hog.

I realize that I have posed many questions, but I would appreciate hearing
from those with experience in these areas who can answer any or all of these
questions.  Thank-you


-- 
Donn S. Fishbein, MD  (N3DNT)   (301)496-6801
..!{harpo,allegra,decvax,ihnp4}!seismo!neurad!donn

ark@alice.UucP (Andrew Koenig) (12/13/85)

Well, I can talk about water heaters anyway:

> Finally, with regards to the hot water heater, is it advisable to install a
> timer so that it only runs when people are likely to be home.
> In other words, is the energy needed to reheat the water more or less
> than that required to maintain the water temperature for a prolonged period of
> no hot water use. My hot water usage is quite modest, yet I think this
> appliance is quite an energy hog.

Electric heaters are essentially 100% efficient.  In other words, all
the electrical energy you buy goes into heating the water.  Once the
water is heated, some of that energy leaks away -- through the walls
of the tank, through the pipes, and so on.

Given that you do not change your hot water usage, the ways to
reduce your electric hot water bills are:

	1. reduce the amount of energy that leaks away.

	2. reduce the energy rate you pay.

It may be possible to use a timer to achieve #2 -- some electric companies
vary their charges depending on time of day.

But what about #1?  Well, the amount of energy leakage is proportional
to the temperature difference between the water heater and the
surrounding air, multiplied by a constant that measures the efficiency
of the insulating barrier between air and water.  Thus, if you
lower the average temperature of the water, you lower your energy
loss.

In other words, to reduce energy leakage, you can (a) lower the temperature
of your hot water, or (b) improve the insulation on the tank.  Doing
both together, of course, works better still.

Since energy loss per unit time is linear in the temperature difference,
reducing the water temperature only while no one is home is indeed
a win compared with keeping it hot all the time.

Another possibility is to do what I did -- scrap the electric water
heater entirely and replace it by an oil- or gas-fired heater.  Buying
energy in the form of electricity is much more expensive than buying
it as oil or gas.

ajs@hpfcla.UUCP (12/13/85)

> ...the manual for my heat pump recommends setting one temperature and
> making no further adjustments.
> ...the major problem seems to be that the heat pump
> contains two thermostatic switches; one for the heat pump compressor,
> and one for the aux. heating coils.

You nailed it.  The problem is, you never want to run the aux heat if
you can help it, but any sudden change greater than the preset delta
(about two degrees) will do it.  There's nothing wrong with a smooth (or
small-step) transition; I often fake this manually.  Just so the heat
pump does all the work, not the aux heat, and you never restart the
compressor within a couple of minutes of it turning off (it takes time
to equalize some pressures which stress it if quickly restarted).

I suspect the reason you can't (easily) buy a heat-pump set-back
thermostat is that it's tough to make a cheap (mechanical) one which is
also sufficiently flexible (programmable).  An electronic solution would
be better, but probably hard to make cheap and portable (will it work
with YOUR heat pump?  what's the time to ROI?).

Related note:  When the weather is continuously cold enough that the
heat pump is inefficient or turns itself off, expect the house to
average "delta" degrees cooler, as the aux heat does all the real work
but has a set-point "delta" degrees lower.

Sigh, it's an AI problem...

Alan Silverstein

cb@hlwpc.UUCP (Carl Blesch) (12/13/85)

> Another possibility is to do what I did -- scrap the electric water
> heater entirely and replace it by an oil- or gas-fired heater.  Buying
> energy in the form of electricity is much more expensive than buying
> it as oil or gas.

Along these lines, the PBS television show "This Old House" recently
demonstrated a tankless gas water heater.  Water is heated only as used
by this gizmo -- apparently the incoming water goes thru enough length
of coiled tubing to pick up all the kilocalories it needs to become hot.
On the show, the heater kicked in as soon as the homeowner turned on
the hot water faucet, and shut off as soon as he shut it off.
This avoids wasting energy on maintaining the thermal mass of a 40 gal
water heater.  I'd like to investigate these further, as my water heater
is getting old.

Carl Blesch

ccrse@ucdavis.UUCP (0058) (12/13/85)

>                                 ....Is it more economical to set back the
> temperature at night, and during the day when no one is home, or to leave
> the temperature adjustment alone?  Is there something unique to heat pump
> technology in this regard?....
> 
> Finally, with regards to the hot water heater, is it advisable to install a
> timer so that it only runs when people are likely to be home.
> In other words, is the energy needed to reheat the water more or less
> than that required to maintain the water temperature for a prolonged period of
> no hot water use. My hot water usage is quite modest, yet I think this
> appliance is quite an energy hog.

If I remember correctly from when my father installed his heat pump, the
explanation runs something like this:

Heat pumps modify the air temperature only very slightly, i.e. the difference
between the inlet and outlet temperatures may be only a few degrees.  They
are able to maintain a given temperature quite efficiently by moving rather
large volumes of air through the system, but for this reason will require a VERY
long time to make significant changes in air temperature.  (For this same
reason, it is not unusual to find that the system will run almost continuously
under extreme temperature conditions, whether hot or cold.)  When large changes
are required, it is more desireable from the viewpoints of both efficiency
and speed to use resistance electric heat to make the change, then let the
heat pump take over to maintain it.  While the resistance unit may be more
faster and more efficient at making larger temperature changes, though, it
is still no where near as efficient as just letting the heat pump maintain
a given setting.  This is why you are counseled to 'set it and forget it'.

As regards your second question, unless you are gone a great deal, I suspect
you would be better off to leave the water heater on continuously.  Considering
how long an electric water heater can take to come up to temperature, you pro-
bably would only have it off a very few hours each day.  While this *might* save
you a small amount of energy, the additional stress on the heater from the
heating and cooling might cause it to wear out prematurely, thus costing you
as much or more in the long run.

avolio@decuac.UUCP (Frederick M. Avolio) (12/14/85)

In article <237@neurad.UUCP>, donn@neurad.UUCP (Donn S. Fishbein) writes:
> First, the manual for my heat pump recommends setting one temperature and
> making no further adjustments.  Is it more economical to set back the

Here's how a heat pump (kind of) works.  It uses the compressor to produce
(extract really) heat.  If the temperature in the room and the temperature
you want is more than 4 (settable) degrees, it kicks in the heating
coils (furnace) to get the house up to the desired range and then maintains
it with the compressor.  If the temperature ever drops below 4 degrees
under the set temperature, again the coils are used.  And most have an
override button in case the compressor isn't working.

In most cases, it is cheaper to have the compressor maintain the
temperature than to employ the heat coils every morning to bring the house
up to temperature.  The only case in which it wouldn't be is if you -- by
hand -- raised the thermostat a few degrees at a time so that that coils
were never employed.

But, if you are usually home (and awake) only a few hours a day, it may be
better tpo set it down.  The only time we turn it down is when we are going
to be gone a day or more.

> or is the heat pump incapable alone of affecting the change?  Is it more

It is not very effective in raising the entire house temperature a great
amount.

> Finally, with regards to the hot water heater, is it advisable to install a
> timer so that it only runs when people are likely to be home.

You might take out teh heater and install an instant hot coil unit. That's
not really what they are called, but something like that.  If the tank is
insultated well, you might do well to put a timer on the thermostat on it.
For most people, the energy needed to reheat the whole tank is much greater
than that required to maintain it.  Water holds the heat pretty well in
an insultated tank.
-- 
Fred @ DEC Ultrix Applications Center    {decvax,seismo,cbosgd}!decuac!avolio

blarson@oberon.UUCP (Bob Larson) (12/15/85)

In article <237@neurad.UUCP> donn@neurad.UUCP (Donn S. Fishbein) writes:
>Is it more economical to set back the
>temperature at night, and during the day when no one is home, or to leave
>the temperature adjustment alone?  Is there something unique to heat pump
>technology in this regard?

(I am assuming the heating case, most things also apply to cooling with
oposite temperature directions.)  In many cases it is more economical 
to set the temperature down at night, but not all.  Heat pumps heat most
eficently when it is warm outside.  However, when there is a large
temperature change to be made, or the heat pump alone cannot handle the
heating, electrical heating elements will also be used.  (Lower efeicency.)
Avoid a large setback at night or else raise the temperature gradually.
Since the heat pump heats most efiecently durring the day, a day setback
may not be a good idea.  (It probably isn't a good idea to set the
thermostat up at night when cooling.)

Changing thermostat settings should not be done often.  Compressors in heat
pumps and air conditioners cannot restart immediatly after shutting off.  (5
minutes is ususally recomended.)  Better systems have special timers to 
protect users from this mistake, cheaper ones tend to use circut breakers 
for this, (often auto reset type) but occasionaly the circut breaker won't 
act fast enogh to save the compressor.

>I have noticed that nearly all of the automatic thermostats available 
>specifically say "NOT FOR HEAT PUMPS".
I recomend following such advice unless you realy know what you are getting
into.  The warentee won't cover specificly prohibited use, and it is possible
to damage the heat pump.

>the major problem seems to be that the heat pump
>contains two thermostatic switches; one for the heat pump compressor, and one
>for the aux. heating coils.
Some contain more than this.  Changeover (heat to cool) and several stages of
additonal heating are sometimes used.

>The heating coils are activated if one changes
>the temperature set point abruptly eg. from 55 F to 68 F.  Does this occur
>simply to decrease the time it takes to achieve the new temperature,
>or is the heat pump incapable alone of affecting the change?
Mostly to decrease the time.

>Is it more economical to allow the heat pump to operate alone?
In most cases, yes.  Heat pumps are most eficent at higher outdoor
temperatures.  Below a certain outdoor temperature, the auxilery heaters are
more efficent.  (Usually in the 0-20 F range, depending on many factors.
(humidity, heat pump design, air circulation around heat pump, etc.)

>Is there a solution to this problem of automatic thermostats being unable to
>control an essentially two-stage system?
There are automatic thermostats for heat pumps.  It's mostly a matter of the
mass produced thermostats only fit the most common case.  (After all, it
might cost a couple of dollers more to put in the extra parts to handle a
heat pump.)

Improving the air circulation around the outdoor side of a heat pump or air
conditioner is an often overlooked way to improve their efficency.
Placement also makes a big difference, a warm in winter cool in summer
location is prefered.

>Finally, with regards to the hot water heater, is it advisable to install a
>timer so that it only runs when people are likely to be home.
>In other words, is the energy needed to reheat the water more or less
>than that required to maintain the water temperature for a prolonged period of
>no hot water use. My hot water usage is quite modest, yet I think this
>appliance is quite an energy hog.
It depends on the length of your "prolonged period".  For less than a day at
a time, it probably isn't worth the bother.



-- 
Bob Larson
Arpa: Blarson@Usc-Ecl.Arpa
Uucp: ihnp4!sdcrdcf!oberon!blarson
__________________________________
Unix: An operating system similar to Os-9, but with less functionality
and special features designed to soak up excess memory, disk space and
CPU time on large, expencive computers.
-- Os-9/68000 operating system users manual

johnt@tekecs.UUCP (John Theus) (12/19/85)

>In article <237@neurad.UUCP>, donn@neurad.UUCP (Donn S. Fishbein) writes:
>
>(extract really) heat.  If the temperature in the room and the temperature
>you want is more than 4 (settable) degrees, it kicks in the heating
>coils (furnace) to get the house up to the desired range and then maintains
>it with the compressor.  If the temperature ever drops below 4 degrees
>under the set temperature, again the coils are used.  And most have an

We're in the process of building a new house, and have done some research
on heat pumps.  What is said above is typically true, but there are better
solutions.  Heat pump thermostats are available that make to easy and
economical to set back the temperature.  The processor in the thermostat
runs an algorithm that minimizes the use of the resistive heating elements.

If you want the temperature raised to normal from the night time set back
at 8 am, then the thermostat starts running the compressor early enough
before 8 am so that the normal house temperature is reached at 8.  The
resistive coils are never used to raise the temperature, even though the
temperature delta is greater than 4 degrees.

For hot water heating, the most efficient heater is a heat pump hot water
heater.  These units are available as either retrofits to existing electric
heaters, or as a monolithic tank and heat pump.   The heat pump water heater
extracts energy from the air in the vicinity of the tank.  Usually a large
closet has sufficient air volume.

While a normal electric hot water heater is 100% efficient in converting
electricity to heat, a heat pump hot water heater is about 300% efficient.
The main drawback with these units is their cost, they usually run in the
range of $800 to $1200.

John Theus		tektronix!tekecs!johnt
Graphics Workstations
Tektronix, Inc.

daemon@houligan.UUCP (12/20/85)

In article <637@hlwpc.UUCP>, cb@hlwpc.UUCP (Carl Blesch) writes:
> > Another possibility is to do what I did -- scrap the electric water
> > heater entirely and replace it by an oil- or gas-fired heater.
> Along these lines, the PBS television show "This Old House" recently
> demonstrated a tankless gas water heater.  Water is heated only as used
> by this gizmo -- apparently the incoming water goes thru enough length
> of coiled tubing to pick up all the kilocalories it needs to become hot.
> On the show, the heater kicked in as soon as the homeowner turned on
> the hot water faucet, and shut off as soon as he shut it off.

I have seen this idea in practical use in 3 different countries.
	1.  Australia.  Visiting several of my relatives <undisclosed number>
	    years ago, they (each house) had a "box" (in the electrical wiring
	    sense) about the size of a "lawn sprinkler" timer, high up in the
	    wall inside the house, opposite the main feed into the house (for
	    short wire losses, I would guess).  Since this "box" was somewhat
	    old, it would buzz rather loudly when activated, but worked great.
	    The idea was: suck HEAVILY on the 220V input and heat that water
	    FAST as it went through.  A flow-sensing switch turns on the
	    heating element once you get enough flow to carry away the heat
	    (so it won't boil itself away if you just turn on a trickle).
	2.  Brazil.  Yes, I have led a weird life.  These would probably NEVER
	    get UL or CSA approval, but they sure worked great!  Take an
	    ordinary electric kettle.  Reshape it a little to make it look
	    like a tupperware cylinder for holding a cake.  Add a pipe in, and
	    punch lots of little holes in the bottom (and close the spout, of
	    course).  Now, a flow-sensor switch turns on the heater, and
	    PRESTO, you have a hot shower with only 1 valve (slower water =
	    more time to heat it up = hotter water, faster = colder), and no
	    need for large hot water tanks.  Our house had only a 15 litre
	    tank (about 10 gals) and it was enough for dishes (what else
	    besides shower/bath and dishes do you need hot for?).  Laundry was
	    just tough cookies, since all houses (that could afford to have
	    machines) were pre-piped for cold only.
	3.  Grenada.  Yes, same place, but much earlier.  Same idea as (1),
	    but substitute natural gas for electric.  Didn't work out as well,
	    but mostly because the unit in the borrowed house was underpowered.
	    To get a strong blast from the shower head was too much for the
	    poor thing.  Came out rather cold.

--tgi

	while (--tgi)	/* my mind continues to decay */
		;	/* even though I do nothing.. */    

{brl-bmd,ccvaxa,pur-ee,sun}!csd-gould!midas!tgi (Craig Strickland @ Gould)
305/587-2900 x5014  CompuServe: 76545,1007   Source: BDQ615   MCIMail: 272-3350

(echo ".ft B"; echo ".ps 999"; echo "$disclaimer") | troff -t	# :-)

chad@anasazi.UUCP (Chad R. Larson) (12/20/85)

Re: Your hot water heater--
Why would anyone want to heat hot water?

I installed a MagicStat setback controller on my heat pump.  The problem
is that furnaces generally control the blower motor with a separate
thermostatic switch in the plenum.  This means when the wall
thermostat "calls for" heat it only closes the control loop that turns
on the burner.  Some time later the blower kicks in as the plenum
heats.  Heat pumps have a separate control loop to run the blower
directly, for what I surmise are two reasons: 1) The heat is available
immediatly  2) They almost always double as air-conditioners with
different speed blowers.  Anyway- the thermostats that say not for
heat pumps usually mean they are not equipped to deal with the extra
wires to run blowers etc.  In the case of the MagicStat I used there
was on the printed circuit board a trace to cut and jumper to install
that fixed it right up.  I don't know why they didn't document it
unless product liability/support worried them.

On the water heater, timers are commercially available for exactly
what you suggested.  They will help you if your pattern of usage is
such that you don't use hot water for long periods of time each day.
(Everyone gets up and showers/shaves/etc., then goes to work--wash
cloths & cook in evening, then go to bed.)  In that case the timer is
set to turn off the electricity thru the day and during sleeping
hours.  The recovery time on modern heaters makes this operationally
feasable.  If you use hot water throughout the day it doesn't do you
any good.

ray@othervax.UUCP (Raymond D. Dunn) (12/23/85)

In article <5885@tekecs.UUCP> johnt@tekecs.UUCP (John Theus) writes:
>
>For hot water heating, the most efficient heater is a heat pump hot water
>heater..
>Usually a large closet has sufficient air volume [as a heat source for
> the pump]
>
>While a normal electric hot water heater is 100% efficient in converting
>electricity to heat, a heat pump hot water heater is about 300% efficient.

When you are NOT heating the house this is true, however when the
house is being heated, you are essentially using the heat generated
by your house heater to heat the water.  This two stage process must
be less efficient than a direct water heater.

Ray Dunn.  ..philabs!micomvax!othervax!ray

chad@anasazi.UUCP (Chad R. Larson) (12/31/85)

In article <637@hlwpc.UUCP>, cb@hlwpc.UUCP (Carl Blesch) writes:
> Along these lines, the PBS television show "This Old House" recently
> demonstrated a tankless gas water heater.  Water is heated only as used
> by this gizmo -- apparently the incoming water goes thru enough length
> of coiled tubing to pick up all the kilocalories it needs to become hot.
> On the show, the heater kicked in as soon as the homeowner turned on
> the hot water faucet, and shut off as soon as he shut it off.

I have also seen these described (I think in Consumer Reports).
They are rated in delta-t (what temperature rise do you want?) and
have a thermal switch that cycles the electric power when a given exit
temperature is reached.

My question is:  Does anyone know where I can get one in the good old
U.S. of A.?  My wife tells me they were very common in Brazil and
Honduras where she grew up, but the plumbing supply companies around
here look at you very strangely when you try to describe one.  They
seem like a natural here in Phoenix to supplement my solar heater on
cloudy days.
>I have seen this idea in practical use in 3 different countries.
>	1.  Australia.  Visiting several of my relatives <undisclosed number>
>	    years ago, they (each house) had a "box" (in the electrical wiring
>	    sense) about the size of a "lawn sprinkler" timer, high up in the
>	    wall inside the house, opposite the main feed into the house (for
>	    short wire losses, I would guess).  Since this "box" was somewhat
>	    old, it would buzz rather loudly when activated, but worked great.
>	    The idea was: suck HEAVILY on the 220V input and heat that water
>	    FAST as it went through.  A flow-sensing switch turns on the
>	    heating element once you get enough flow to carry away the heat
>	    (so it won't boil itself away if you just turn on a trickle).
>	2.  Brazil.  Yes, I have led a weird life.  These would probably NEVER
>	    get UL or CSA approval, but they sure worked great!  Take an
>	    ordinary electric kettle.  Reshape it a little to make it look
>	    like a tupperware cylinder for holding a cake.  Add a pipe in, and
>	    punch lots of little holes in the bottom (and close the spout, of
>	    course).  Now, a flow-sensor switch turns on the heater, and
>	    PRESTO, you have a hot shower with only 1 valve (slower water =
>	    more time to heat it up = hotter water, faster = colder), and no
>	    need for large hot water tanks.  Our house had only a 15 litre
>	    tank (about 10 gals) and it was enough for dishes (what else
>	    besides shower/bath and dishes do you need hot for?).  Laundry was
>	    just tough cookies, since all houses (that could afford to have
>	    machines) were pre-piped for cold only.
>	3.  Grenada.  Yes, same place, but much earlier.  Same idea as (1),
>	    but substitute natural gas for electric.  Didn't work out as well,
>	    but mostly because the unit in the borrowed house was underpowered.
>	    To get a strong blast from the shower head was too much for the
>	    poor thing.  Came out rather cold.
>
>--tgi
>
>	while (--tgi)	/* my mind continues to decay */
>		;	/* even though I do nothing.. */    
>
>{brl-bmd,ccvaxa,pur-ee,sun}!csd-gould!midas!tgi (Craig Strickland @ Gould)
>305/587-2900 x5014  CompuServe: 76545,1007   Source: BDQ615   MCIMail: 272-3350
>
>(echo ".ft B"; echo ".ps 999"; echo "$disclaimer") | troff -t	# :-)

jak@whuxlm.UUCP (Keegan Joan) (01/03/86)

> In article <637@hlwpc.UUCP>, cb@hlwpc.UUCP (Carl Blesch) writes:
> > Along these lines, the PBS television show "This Old House" recently
> > demonstrated a tankless gas water heater.  Water is heated only as used
> > by this gizmo -- apparently the incoming water goes thru enough length
> > of coiled tubing to pick up all the kilocalories it needs to become hot.
> > On the show, the heater kicked in as soon as the homeowner turned on
> > the hot water faucet, and shut off as soon as he shut it off.
> 
> I have also seen these described (I think in Consumer Reports).
> They are rated in delta-t (what temperature rise do you want?) and
> have a thermal switch that cycles the electric power when a given exit
> temperature is reached.
> 
> My question is:  Does anyone know where I can get one in the good old
> U.S. of A.?  My wife tells me they were very common in Brazil and
> Honduras where she grew up, but the plumbing supply companies around
> here look at you very strangely when you try to describe one.  They
> seem like a natural here in Phoenix to supplement my solar heater on
> cloudy days.

We have a wood stove catalog that shows a version of this kind of
water heater.  I will try to remember to bring in the details.
As I remember, though, the rate of flow was very low - i.e., it
doesn't heat the water very quickly.  We thought this might be a problem,
although I guess it's a way to restrict your water usage as well.

Joan Keegan
AT&T (Bell Laboratories)

cb@hlwpc.UUCP (Carl Blesch) (01/03/86)

> In article <637@hlwpc.UUCP>, cb@hlwpc.UUCP (Carl Blesch) writes:
> > Along these lines, the PBS television show "This Old House" recently
> > demonstrated a tankless gas water heater.  Water is heated only as used
> > by this gizmo -- apparently the incoming water goes thru enough length
> > of coiled tubing to pick up all the kilocalories it needs to become hot.
> > On the show, the heater kicked in as soon as the homeowner turned on
> > the hot water faucet, and shut off as soon as he shut it off.
> 
> I have also seen these described (I think in Consumer Reports).

Yes, I just got my Consumer Reports, and there was a review of these
devices.  All were gas-fired (some could be used with LP gas -- either
a slightly different model or a conversion kit).

Consumer Reports wasn't too high on them . . . said that loss from the
tank of a regular water heater wasn't all that great, and that the
temperature rise from the tankless units might not get cold winter
water hot enough.  They all delivered a sixty degree F rise, but if
water coming from your well or underground supply system is 45 degrees F
in wintertime, your hot water would be only 105 F -- far too low for
some uses, like dishwashing.  Tank heaters, however, always deliver
water at the temperature you set them for.  Also, the tankless ones
couldn't keep up with multiple demands -- a shower and a washing machine
drawing water simultaneously, for example.

Carl Blesch

wcs@ho95e.UUCP (Bill.Stewart.4K435.x0705) (01/03/86)

In article <459@anasazi.UUCP> chad@anasazi.UUCP (Chad R. Larson) writes:
>In article <637@hlwpc.UUCP>, cb@hlwpc.UUCP (Carl Blesch) writes:
>> Along these lines, the PBS television show "This Old House" recently
>> demonstrated a tankless gas water heater.  Water is heated only as used
>> by this gizmo -- apparently the incoming water goes thru enough length
>> of coiled tubing to pick up all the kilocalories it needs to become hot.
>> On the show, the heater kicked in as soon as the homeowner turned on
>> the hot water faucet, and shut off as soon as he shut it off.
>
>I have also seen these described (I think in Consumer Reports).
The January 1986 Consumer Reports rated tankless gas water heaters.
>
>My question is:  Does anyone know where I can get one in the good old
>U.S. of A.?  My wife tells me they were very common in Brazil and
>Honduras where she grew up, but the plumbing supply companies around
>here look at you very strangely when you try to describe one.  They
>seem like a natural here in Phoenix to supplement my solar heater on
>cloudy days.

They come in different sizes; small ones for a single hot-water tap,
medium for campers, etc., and large ones for houses.  Consumer Reports
rated only the large gas ones (they consider the electric ones too
wimply for typical American usage.)   They're expensive; they rated a
$400 model which produced 2.8 gal/minute at 60 degrees temperature
rise, and several $600-700 models which produced 3.1 gal/min.
They come in natural-gas and LP-gas models.  As a supplement to solar
heat, you can probably get by with one of the smaller ones; a heater
that's inadequate with 50-degree incoming water may do all you need
with 90-degree water.  You might check out stores that sell RVs and
mobile homes.
-- 
# Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs