More Recycled Refrigerator Solar Water Heater Designs

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Drawing shows details of passive solar water heating system recently developed by MOTHER.
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Diagram of a recycled refrigerator solar water heater design from MOTHER's staff.

More recycled refrigerator solar water heater designs offered by MOTHER’s capable staff.

More Recycled Refrigerator Solar Water Heater Designs

When Miles K. Free III sent us an article telling how he’d
recycled an old refrigerator into part of a solar water
heating system (see “Recycle a Refrigerator Into a Solar
Water Heater”, pages 108-109, MOTHER NO. 48) . . . he
didn’t know that MOTHER’s researchers had already been
working on the same idea for some time.

Whereas Miles began his project by thinking about how easy
it’d be to convert a refrigerator into an insulated storage
cabinet for a tank of solar-heated water, however, MOTHER’s
research staff sorta approached their conversion project
“the other end to”.

It all began with an old junked Hotpoint refrigerator that
a couple of MOTHER’s people were taking apart with the idea
of using its compressor as a small solar-powered steam
engine or something of that nature. Almost immediately,
though, the experimenters were speculating about the heat
exchange coils on the back of the reefer’s cabinet.

“Hey, that looks an awful lot like the serpentine tubing
which goes inside a flat-plate solar collector.”

“Yeah, except that the diameter of this stuff — it
looks like it’s about a quarter inch — is so much
smaller than the diameter of the tubing — about a half
inch — generally used in a collector.”

“Yeah . . . but I betcha this exchanger will work in a
flat-plate. It may not work as efficiently as a
heat exchanger custom-made of bigger tubing, but I think
it’ll still work. And if it does . . . heck, the price is
surely right.”

So our intrepid adventurers forgot all about their steam
engine project and began looking for an insulated collector
box to mount their prefabbed heat exchanger in. Just then
their eyes fell on the old Hotpoint’s front door.

“Hot dog. Look at this. All we’ve got to do is take the
plastic liner out of this door and the exchanger will fit
right in. We’ve already got two-thirds of our whole
flatplate collector built for us . . . and we haven’t even
picked up a hammer yet.”

What the boys were crowing about was the fact that whoever
had originally designed that trusty old Hotpoint …
couldn’t have done a better job of making the fridge easy
to recycle into a flatplate solar collector. On the one
hand, the reefer’s heat exchanger — a nearly flat sheet
of steel with a serpentine length of tubing already welded
to it looked (except for the fact that its tubing was
small) just one heck of a lot like the heat exchangers in
some very expensive solar collectors. And on the other, the
fridge’s door — which was really a shallow steel box
that was already well insulated — made as nearly an
Ideal flat-plate collector box as if it had actually been
planned for that end use.

So the boys pulled the liner out of the Hotpoint’s door and
replaced it with the heat exchanger. Then a couple of holes
were drilled through one end of the door and a couple of
pieces of scrap copper tubing (also scavenged from the
refrigerator) were used to extend the exchanger’s coils
through the insulated wall. (It was exceptionally easy to
slip the recycled 3/8-inch tubing right over the ends of
the 1/4-inch plumbing and solder the “splice” into a
watertight junction.)

Next, six holes were drilled through both the exchanger
plate and the “back” of the collector box (actually,
through the main body of the old refrigerator door) and the
two were fastened together with stove bolts. Some odd
pieces of cardboard were then used to cover the insulation
that was still exposed around the “rim” of the exchanger
(this was done purely for appearances), and the heat
exchanger and its surrounding paperboard trim were all
painted flat black.

Finally, two pieces of glass were cut to fit as a “top” for
the collector box. The panes were mounted just under the
old door’s rubber gasket (how’s that for having just what
you want just where you want it?) and seated in place on a
bead of silicone caulking.

MOTHER’s crew of merry experimenters then hooked their new
collector to a small pump and circulated a strong detergent
solution through the flatplate’s plumbing to flush out any
residue Freon. After that, they connected the
collector/pump to a barrel of water, aimed the solar panel
at the sun, and turned the pump on. Sure enough! The
circulating water immediately began picking up Btu’s as it
passed through the collector . . . and a thermometer soon
showed that those calories of heat were, indeed, being
transferred to and stored in the drum of water.

An Important Point: Please note
that — due to the small cross section and serpentine
pattern of the tubing in the old Hotpoint’s heat
exchanger — this flatplate collector was not suitable
for use in a “passive” thermosiphoning water heating
system. (See the interview with David Wright in MOTHER NO.
47 for an explanation of a passive solar heating system’s
operation.) However, merely by hooking a small pump to the
flatplate and pumping water through the collector (and a
great many “real solar panels” are set up to work
exactly this way), MOTHER’s
collector was made to work just fine.

Another Solar Water Heater Design Innovation

So far, so good. But our researchers hadn’t even gotten
started. As long as they already had the makings of an
exceptionally low-cost active solar water heating system on
their hands, they figured they might as well go ahead and
do the job up right. With antifreeze (so sub-zero
temperatures wouldn’t bust their solar panel or the
plumbing attached to it) circulating from the recycled
collector to an insulated exchanger tank . . . and a separate
set of waterlines (cold in and hot out) leading from that
exchanger tank to somebody’s home.

The only real problem with that idea, of course, is that
exchanger tanks are expensive ($170 and up) and hard to
locate. Which is why MOTHER’s deucedly clever inventors
didn’t even bother trying to find a ready-made exchanger
tank to buy.

Instead, they went down to the warehouse/workshop of the
local natural gas utility (United Cities Gas) and asked for
one of the “worn-out” gas-fired water heaters that such
companies frequently sell as scrap. And the folks at UCG
were nice enough to lay such a tank on MOTHER’s men for

Now one of the nice things about the “worn-out” water
heater tanks which the various gas companies around this
continent discard . . . is the fact that a good many of those
tanks aren’t really worn out at all. They’re merely
defective. The containers leak water all right, but not
necessarily because they’ve rusted through. And if you
remove the sheet metal “wrapper” and fiberglass insulation
from the basic tank itself . . . you’ll very often find that
the container is only leaking from one small pinhole on a
single seam which was never welded quite right when the
container was put together in the first place. Such a hole
is very easy to “patch” with just a tiny spot weld.

Another very nice thing about these discarded gas-fired
water heater tanks is the exhaust stack that extends right
through each one of the drums, from its bottom all the way
up to its top. This stack was originally designed to
transfer heat from a gas flame (burning inside the stack)
to the water in the surrounding tank. It’s very obvious,
then, that if you plumb one of these heater tanks up and
run solar-heated hot antifreeze through its stack …
you’ll stand a very good chance of transferring large
quantities of heat from the central pipeful of circulating
antifreeze to the water surrounding it.

Which is just what our boys had in mind. And which is just
what they did. The conversion was made by welding one
two-inch pipe coupling into the top of the water heater
tank’s exhaust stack and another into the stack’s bottom. A
two-inch- to- three- quarter- inch reducing bushing was
then screwed into each of the couplings and standard 3/4 inch
copper tubing and fittings attached to the bushings.
Presto! A $170 exchanger tank was ours for slightly over
$5.00 In hardware and a couple of hours of our time.

At this point we could have put the original meager
insulation and sheet metal wrapper back on the exchanger
tank . . . but we wanted something much better. So we built a
plywood box big enough to give the tank a good six inches
of clearance all around when set down inside the wooden box
… and completely filled the space surrounding the drum
with MOTHER’s good ole homemade cellulose insulation (see
“How to Make and Install Your Own Insulation”, pages
120-121, MOTHER NO. 48).

The super-insulated exchanger tank was then carted over to
the home of Butch and Larry Goodwin (two of MOTHER’s
helpers) and plumbed up with copper tubing to the Hotpoint
refrigerator door collector, a second collector built from
a Coldspot refrigerator door and heat exchanger, a Grundfos
pump, a Hawthorne controller, and the waterlines for the
Goodwin’s house.

And what happens now is the controller constantly monitors
the tempera. ture of the antifreeze in the collectors and
the water in the exchanger tank. And whenever the first is
at least 3 degrees Fahrenheit warmer than the second, it turns on the
pump and circulates the hotter antifreeze from the
collectors through the exchanger tank’s central stack
(where the hot fluid gives up some of its heat to the
surrounding water) and back again. The controller also runs
the pump at a slower speed when the collectors are only
slightly warmer than the storage tank . . . but at high speed
when the sun is really blazing and there’s a great deal of
trapped heat in the collectors to transfer to the exchanger

An ordinary paint can with a plumbing connector soldered to
its bottom serves as both an expansion tank and a filter
spout on the “closed loop” of circulating antifreeze. The
system is filled with a 50/50 solution of water and
propylene glycol . . . and propylene glycol (which is used to
winterize the plumbing fixtures in motor homes and camping
trailers) was chosen because it’s non-toxic and will not
contaminate the Goodwin’s household water supply if the
stack inside the system’s exchanger tank ever develops a

The total cost of this solar water heating system (which
now heats most of the water used by a family of four) was
$173.04 . . . and we’ll put the rig up against manufactured
units costing anywhere from $500 to $1,500.

Another Solar Water Heater Design

Nobody could have called us quitters if we’d stopped this
particular set of experiments right there. But once we’d
gotten that far with an active solar water heater scrounged
up largely from recycled refrigerators and other salvaged
parts . . . well, we’d begun asking ourselves why we couldn’t
cobble together a passive system from mostly the same kind
of materials.

So MOTHER’s Little Elves selected a relatively tall General
Electric fridge from her large stock of old freezers and
refrigerators (see sidebar) and removed its compressor,
heat exchanger coils, motor, and other hardware. Then they
stripped out all the unit’s shelves and racks . . . even its
lining and insulation (the insulation was carefully set
aside for later use). The lining — but not the
insulation — was also taken out of the reefer’s door.

The resulting empty case was then turned on its side and a
salvaged, stripped-down, 40-gallon, electric water heater
tank was mounted inside the box on wooden supports. (In
addition to being stripped, the tank was further modified
by the addition of a fitting welded into its original base
and the plugging of an “extra” opening on its other end.)

Next an “absorber plate” — much like the scavenged heat
exchanger panels used in the refrigerator door flat-plate
collectors already described in this article . . . except
with parallel runs of 1/2-inch copper tubing instead of a
serpentine run of 1/4-inch tubing for the circulating fluid
to flow through — was put together.

The absorber consists of six parallel lengths of 1/2-inch
hard copper pipe spaced 3 3/4 inch apart and connected across
their ends with standard plumbing T’s and elbows (see
illustration). This manifold was then soldered onto the
flattened and trimmed (so it would just fit inside the
refrigerator door in place of the removed lining) sheet of
steel that had once been wrapped around the insulation on
the salvaged water heater tank. Note, too, that the
manifold was mounted on the sheet of metal with one end
slightly higher than the other. This was done on purpose so
that any bubbles which might ever form in the tubes
willinstead of forming an “air lock” — automatically
rise up and flow out of the manifold into the water storage
tank above.

The absorber plate — manifold and all — was then
painted flat black and mounted inside the insulated
refrigerator door. The manifold was connected to the
storage tank with two flexible hoses and a double strip of
Masonite was added to the door to [1] hold the hoses in
place and [2] form one edge of the mounting for the glazing
that was installed next. Just as in the refrigerator door
flat-plates already described, this glazing consisted of
two pieces of glass cut to fit, mounted under the door’s
rubber gasket on three sides (and on the double strip of
Masonite on the other) and scaled in place with silicone

The whole unit was next mounted on the sunny south wall of
MOTHER’s research shop and its storage
tank was plumbed up with two connections: a cold “in” line
from the city water main and a hot “out” line running into
the workshop. After all the connections were checked for
leaks, mucho insulation (both the fiberglass batting that
had originally been removed from the case and as much
“extra” homemade cellulose as could be packed in) was
stuffed around the storage tank, and the refrigerator case
was closed off with a panel of waterproof Masonite.

You’ll notice that this sheet of Masonite has aluminum foil
glued to its front (to reflect a little more solar fall
down onto the collector panel). If you look closely at the
opened solar water heating system, you’ll also see that the
two hoses running from the collector panel to the insulated
storage tank pass through elongated slots in the sheet of
Masonite fastened over that tank. These slots allow the
hoses to ” fold up” inside the insulated cavity, thereby
making it possible for the flat-plate collector door to be
swung up and closed at night and on overcast days. This [1]
protects the unit from freezing up during subzero weather,
[2] protects the critical parts of the system from vandals
at night, and [3] makes it possible to heat a tank of water
with solar radiation on a bright, sunny day . . . and then
save and use that hot water as desired throughout as much
as a following week of overcast, cold weather.

Pretty clever, these experimenters of ours! And this whole
passive solar water heating and storage system -which
supplies 100% of a three-to-four-man shop’s hot water
needs — only cost us $41.97 out-of-pocket. Show us a
commercially manufactured unit with anywhere near the same
performance for anything less than $1,000 . . . and we’ll
give you a free blistering-hot hand wash on any winter’s
day of your choice.

A Small Discovery

While working on this recycled refrigerator project,
MOTHER’s researchers stumbled onto an idea that could well
be developed into a profitable home business by hundreds of
readers scattered across the country.

What happened was — in an effort to assemble a large
collection of old refrigerators, freezers, and water tanks
to experiment with — we ran a small classified ad in
the local very small daily newspaper. The ad read: “Will
haul away discarded refrigerators and hot water tanks” . .
. and the response was overwhelming.

Within two days (well within two days) we were
qualifying our telephone calls (is (“What kind of
refrigerator’? What shape is it in?”). In short, if our
experiences are any indication, a lot of people at
any given time in any given community across the United
States and Canada are anxious to have someone haul away old
refrigerators, freezers, and water heaters.

We found that quite interesting. But the really
amazing part of the whole deal was the fact that
six out of the first eleven refrigerators we picked up were still in working order . . . or began running as soon as we replaced the appliance’s temperature control switch. Or, to put it another way: With just
a little tinkering, over half of all the fridges we picked
up could have been sold at a handsome profit as “good used
refrigerators in operating condition”.

Aha! Suddenly it became apparent to us why so many small
towns across the country always seem able to support at
least one “used furniture dealer” who specializes in old
kitchen ranges and refrigerators . . . and who always seems
to do as well or better than the “real” merchants downtown.
This guy may look as if he’s dealin’ in junk . . .
but he’s really handling solid gold!

Very quickly, then: [1] A very small and very inexpensive
classified ad can very quickly put more used refrigerators,
freezers water heaters, etc., at your fingertips than
you’ll know what to do with. [2] A number of people will
even offer to pay you to haul the units away. [3] Over half
of those appliances — if our experience is any
indication — still work beautifully or can be put back
in running order with hardly any output of labor or cash.
[4] There’s always a market for good used major appliances.
[5] The real clunkers will still cover your overhead when
carted to a junk dealer and sold as scrap. [6] Or, better
yet, convert those clunkers into solar water heaters and
sell ’em that way! Any way you look at it, there’s a good
solid net $10,000- or $15,000-a-year business here on
hardly any initial investment at all.

One Further Point on Recycled Refrigerator’s: Experiments have shown us that other brands of refrigerators and freezers seldom
convert into solar collectors as easily as our original
Hotpoint. But that’s not as bad as it sounds. In most
cases, it takes only a small amount of trimming and
reshaping to make things fit together the way you want
them. And, at worst, an insulated wooden box can be
fabricated around really odd-sized-and-shaped exchanger
coils to make a flat-plate collector . . . but there’s so
many “good” old refrigerators around that it’s just easier
to look a little further and find one that’s already
“custom designed” for conversion into a solar panel.

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