help with water heat using a wood stove

[Mike]

Hello-Has anyone tried using a interior wood stove to heat water and pipe it
to anther room or building. I am trying to do this and having problems. I
am running a .75 hose (also 1/2 copper) line to a garage and back. total of
300 feet of hose. To heat the water I bought a coil of soft copper 5/8
tubing which I simply put inside the wood stove. I am having problems
getting hot enough temps from the tubing. Max seems to be about 40 degrees
Celsius. I insulated the buried lines with 1 inch of Styrofoam. The return
line and heating line are side by side in the insulation. I simply cut a
groove in strips of 2 inch insulation and trapped the line within two pieces
of the Styrofoam. I have two radiators from a hospital in the garage-each
being about 4 feet long. I have them connected in series. Total amount of
water is about 5 or 6 gallons. Questions:

Am I expecting too much?
Is it too little water to take the heat to the garage?
Should I build a tank and somehow fasten it to the wood stove instead of the
coil of pipe?

Any help would be greatly appreciated as I expected this to work a lot
better. A lot of people around here (Manitoba Canada) heat their entire
farm buildings using outside wood stoves but they have 1.25 buried pipe with
a lot more water.

Thanks
Mike Annetts

 

[Ecnerwal]

getting hot enough temps from the tubing. Max seems to be about 40 degrees
Celsius. I insulated the buried lines with 1 inch of Styrofoam. The return
line and heating line are side by side in the insulation. I simply cut a
groove in strips of 2 inch insulation and trapped the line within two pieces
of the Styrofoam.

Congratulations - you've created a heat exchanger. Hot water from the
hot coil heats cold water coming into the hot coil, and becomes cool by
the time it gets to the far end...

You need to insulate the hot line from the cold line, as well as
insulating both from the ground. You probably also need to use somewhat
larger pipe to get a respectable flow rate over 300 feet. What sort of
pump are you using?

 

[Mike]

Hello

I am using a pump that pumps about 5-10 gallons a minute. I don't know if
there would be enough contact between the two hoses to exchange much heat
but maybe.

Mike

 

[Harry Chickpea]

Am I expecting too much?

Yes. Way too much.

Is it too little water to take the heat to the garage?

Among other things.

Should I build a tank and somehow fasten it to the wood stove instead of the
coil of pipe?

Frankly, you should abandon the idea. A 150' run is too long, 1/2" hose or pipe
is too small, you will have a difficult time getting useful heat out of a stove
using any sort of retrofit, and even if it did work, an unvented coil of hot
copper pipe in your stove could develop a steam pocket that would ruin your
day.

Grab a high school physics book and do some quick calculations. You'll find
the problems are quite apparent.

 

[Ben Simons]

Yes. Way too much. No

Among other things.

Another good idea.

A note to heat exchangers: The larger the exchanging surface, the better.
You took a coil, the best thing you could do since it has a large surface.
But your real problem is the two pipes which aren't insulated from each
other as mentioned already before. Fix this.

Frankly, you should abandon the idea. A 150' run is too long, 1/2" hose
or pipe
is too small, you will have a difficult time getting useful heat out of
a stove

As seen above, the larger surface of the pipe, the better the heat
exchanger -> more losses to mother earth -> colder water in your garage. I
would say, a small pipe is a good idea for a long pipe. A thick insulation
an even better one. Mike, one inch is a minimum, especially over this long
distance. On the other side, a thin pipe has more losses on water pressure
which has to be built up by the pump. If saving electricity is not an
issue for you, the diameter of the pipe is not important, as long as you
get a reasonable amount of water out of the pipe. You can check the losses
caused by the pipe simply by measuring the gallons/minute, one time with
long pipe, and one time without. And if your stove/coil/pump delivers
enough heat just near by the stove (without long pipe) it will also over
the well insulated short pipe.

If you do not want dig in your garden again, an alternative is to install
more heat exchangers (radiators) in your garage. And second (this, you
should do anyway) insulate the garage! I can't say it enough: insulate,
insulate, insulate....

using any sort of retrofit, and even if it did work, an unvented coil of
hot
copper pipe in your stove could develop a steam pocket that would ruin
your
day.

Of course, but as long the pump is running then there is no problem. I
lived two winters in a small hut (3 rooms) with such an installation. It
worked well. Mike, to be safe, install an overpressure safety valve
(correct word in english?) and you can sleep well.

Grab a high school physics book and do some quick calculations. You'll
find
the problems are quite apparent.

please measure the temperatures of the pipes one meter after the stove,
and in the garage. Then it is possible to say more.

 

[[email protected]]

...I am running a .75 hose (also 1/2 copper) line to a garage and back.
total of 300 feet of hose.

....150' one way.

To heat the water I bought a coil of soft copper 5/8 tubing which I simply
put inside the wood stove.

....212 F?

I am having problems getting hot enough temps from the tubing.
Max seems to be about 40 degrees Celsius.

....104 F at the far end?

I insulated the buried lines with 1 inch of Styrofoam. The return line
and heating line are side by side in the insulation.
Oops.

I simply cut a groove in strips of 2 inch insulation and trapped the line
within two pieces of the Styrofoam.

Like this, with a 16" perimeter, and 150x16/12 = 200 ft^2 of outside surface?

4"
----------------------------------
| |
| |
| |
| | 2"
| |
| |
----------------------------------
| | | |
| | pipe pipe |1" |
| | | |
| ------------- | 2"
| 2" |
| |
----------------------------------

I have two radiators from a hospital in the garage-each being about
4 feet long. I have them connected in series.

Big old cast iron jobs?

Total amount of water is about 5 or 6 gallons. Questions:

Am I expecting too much?

Maybe not.

Is it too little water to take the heat to the garage?

The amount of water isn't important, but the flow rate is. You mentioned
5-10 gpm, which sounds more like a guess than a measurement. You might
measure this with a bucket and stopwatch at the stove end. You might lose
(212-50)200ft^2/R5 = 6500 Btu/h to 50 F soil, so more insulation seems
useful, as well as separating supply and return pipes... 5 gpm is 300 gph
or 2400 pounds of water per hour, ie 2400 Btu/h-F, so the water temp might
only drop 6500/2400 = 2.7 F because of the heat loss to the ground.

Should I build a tank and somehow fasten it to the wood stove
instead of the coil of pipe?

Well, hchickpea thinks the coil may blow up, which doesn't sound good, but
it might gather more heat in the fire than outside the fire. Then again,
it might gather carbon or creosote or burn through or undesirably lower the
wood combustion temp. I'd check the flow rate and measure some temps before
changing this. Boiling the water inside the coil would raise the heat transfer
rate. An open tank above might condense steam bubbles and limit explosions.

My woodstove has a flat top, with a vertical steel 55 gallon water drum on
top with several plastic film drum liners inside. The water only gets up to
130 F, with no insulation around the drum, and that takes a few hours...
(130-70)22ft^2x1.5 = 1650 Btu/h. Not much. The drum weighs about 450 pounds,
which helps ensure a good thermal connection between the drum bottom and
the stove top. The drum bottom isn't perfectly flat. The center part dishes
down and touches the stove, but there's an air gap near the rim. Perhaps
I should empty the drum and put a piece of plastic film over the stovetop,
then a 1/2" layer of sandcrete (mixed with ground copper?), then put the
drum back and fill it with water again to try to eliminate the air gap.

I put 150' of high temp garden hose in the drum to preheat cold water for the
electric water heater. You might circulate unpressurized water with no heat
exchanger, and some insulation around the drum.

I've considered replacing the drum with a 2'x2'x2" thick ferrocement pad with
some copper tubing inside, which might make a nice stew-simmering surface,
never much over 212 F, but I worry that the thermal resistance of the stove-
concrete interface and the concrete itself would lower the heat transfer rate
a lot, and making a pad like that isn't easy, and it would still only have
4 ft^2 of surface to transfer heat from the stove.

How would we get heat from a horizontal 55 gallon drumstove with a cylindrical
top surface into water? Could we find a flexible material to make a "water
blanket" to drape over the top surface, or use the top surface as a mold for
a hollow or pipe-lined ferrocement saddle?

Nick

 

[SQLit]

See inside

Hello-Has anyone tried using a interior wood stove to heat water and pipe it
to anther room or building. I am trying to do this and having problems. I
am running a .75 hose (also 1/2 copper) line to a garage and back. total of
300 feet of hose. To heat the water I bought a coil of soft copper 5/8
tubing which I simply put inside the wood stove. I am having problems
getting hot enough temps from the tubing. Max seems to be about 40 degrees
Celsius.

40 degrees is getting there. See what you can do about increasing the 5/8
dia copper exchanger you built would recommend at least 1 inch maybe even
1.5 inch. The copper should be at the top of your stove and near the
exhaust vent. I have seen air exchangers for increasing the out put of a
wood stove, but not water. I wounder if you changed the exhause vent to
guessing 12 inch and coiled more copper pipe inside the pipe to gain more
heat. You would need to be very careful about flue fires because of the
pipes inside of the flue would have a tendenancy to hold soot. My solar pump
only pumps about 4 gallons a minute and does not pump all of the time. Maybe
get your self a solar controler and some thermal couples and let the temp
rise farther before you start pumping. a suggestion.

I insulated the buried lines with 1 inch of Styrofoam. The return

line and heating line are side by side in the insulation. I simply cut a
groove in strips of 2 inch insulation and trapped the line within two pieces
of the Styrofoam. I have two radiators from a hospital in the garage-each
being about 4 feet long. I have them connected in series.

Series, I wonder about that, maybe parallel instead. Hot water into the
first one will start the warming process then the second would be of little
or no use for heating.


Total amount of

water is about 5 or 6 gallons. Questions:

1 inch of Styrofoam is not enough in my opinion. Here in AZ for hot water in
the ground we use 4 inch poly urethane as a minimum. If it is easy to do
then separate the pipes by at least 12 inches and hopefully down deep enough
that they will not freeze. You could have used C-PVC, rated for hot water.
If your radiators are 4 feet long and what 3 feet high they probably hold a
couple of gallons each. Been a long time since I was at grandmas house. I
would bet that you have a lot more radiator volume than you do exchanger
volume. See comment above.

Am I expecting too much?
Is it too little water to take the heat to the garage?
Should I build a tank and somehow fasten it to the wood stove instead of the
coil of pipe?

They tried this on a brittish 1700's house with a stove that was designed
for the purpose. Unless they had a raging fire the hot water was less than
satisfactory. Just what I saw on PBS.

 

[Ecnerwal]

I am using a pump that pumps about 5-10 gallons a minute. I don't know if
there would be enough contact between the two hoses to exchange much heat
but maybe.

This is the rating on the pump, or this is an actual measurered output
WHEN CONNECTED to 300 feet of small-bore pipe/tubing? If you go out and
read a bit more, look into "total dynamic head" - you have a lot of it.
It's the friction loss from pumping a given flow rate through a given
length of a given size of pipe. Your actual TDH is a bit fiddly to
figure since you have a mixture of sizes and lengths of each size, and
we don't know the exact length of each, but for instance, to get 10GPM
through 300 feet of 1/2" pipe, you need 600 feet of head, or 259 PSI at
the output of the pump. For 300 feet of 3/4" pipe at 10GPM, it's 84
feet, or 36 PSI.

Depending on the pump, you could very easily connect a pump rated for 10
gpm and get less than 1 gpm flow in practice. Perhaps very much less.

 

[mike]

If the water is not boiling, you have all the water flow you
need. For a hot fire (to first order approximation), you need
a bigger/better heat exchanger in the fire box to take advantage
of more flow.
Insulating the pair of pipes from the environment is critical.
Insulating them from each other can be important, but as long
as the water is not boiling, you're still getting everything
you put in (less leakage) out the radiator end.
right?
mike



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[daestrom]

Hello-Has anyone tried using a interior wood stove to heat water and pipe it
to anther room or building. I am trying to do this and having problems. I
am running a .75 hose (also 1/2 copper) line to a garage and back. total of
300 feet of hose. To heat the water I bought a coil of soft copper 5/8
tubing which I simply put inside the wood stove. I am having problems
getting hot enough temps from the tubing. Max seems to be about 40 degrees
Celsius. I insulated the buried lines with 1 inch of Styrofoam. The return
line and heating line are side by side in the insulation. I simply cut a
groove in strips of 2 inch insulation and trapped the line within two pieces
of the Styrofoam. I have two radiators from a hospital in the garage-each
being about 4 feet long. I have them connected in series. Total amount of
water is about 5 or 6 gallons. Questions:

Am I expecting too much?
Is it too little water to take the heat to the garage?
Should I build a tank and somehow fasten it to the wood stove instead of the
coil of pipe?

Any help would be greatly appreciated as I expected this to work a lot
better. A lot of people around here (Manitoba Canada) heat their entire
farm buildings using outside wood stoves but they have 1.25 buried pipe with
a lot more water.

The total amount of water is not important unless you're trying to *store*
energy for later use when the fire dies down. What *is* important is the
flow rate, the surface area of your coil, and the heat losses along the way.

Perhaps the first thing you should do is take some measurements. Figure out
just what your flow rate is. Maybe disconnect at the pump suction, direct
the return line into a bucket and have the pump suction take from a second
bucket. Time how long it takes to move a couple of gallons from one bucket,
through the entire loop, and back to the other bucket.

Second, you mentioned 40C. Take four temperatures after the system has been
operating for a while. The stove heat exchanger inlet and outlet, and the
radiator inlet (first radiator) and outlet (last radiator). If the only
temperature readings you can take are by holding a thermometer on the
outside of the pipe/tubing, wrap a towel or something around the
pipe/thermometer and leave it for a few minutes. This way, the thermometer
reads close to the actual temperature, and not just halfway or so between
water temp and air.

With these five numbers, you can find out just what is going on, and from
there we can help you troubleshoot things.

Heat gained/lost in segment ....
Q = gpm * (Tout- Tin) * 480 BTU/hr

If Tout is higher, then Q is positive and you're adding heat (like in the
stove), if Tout is lower, then you're losing heat. For the radiators, this
would be a good thing ;-)

Given that your two runs of pipe/hose are side by side, don't be surprised
if the return line from radiators back to stove show a heat gain. This
would be because the return line is gaining heat from the supply line inside
your grooved insulation. So look carefully at the numbers to see what is
going on.

daestrom

 

[Mike]

Hello everyone

First off thanks for all the replies. An update:

I am getting no heat to the rads in the garage which are 4 feet long and
finned. Each would be about 48 by 2 by 6 with air release valves in them.

I seem to be having air pockets in my coil as I have steam forming. To
prevent "a bad day" I made a makeshift release valve by having a having a
hose teeing off near the coil into a five gallon pail which is about 1/2
full of antifreeze. I figured (maybe incorrectly) that if the hose end was
submerged in the antifreeze it would allow air out but not in. Also I was
thinking that it would draw the antifreeze back into the system as the
antifreeze cooled and lost some volume.
I will pump some water through the system to get a more accurate reading
on the flow rate of the pump.

 

[Nick Pine]

Series, I wonder about that, maybe parallel instead. Hot water into the
first one will start the warming process then the second would be of little
or no use for heating.

Care to explain further?

1 inch of Styrofoam is not enough in my opinion...

Is this a matter of opinion?

If your radiators are 4 feet long and what 3 feet high they probably hold a
couple of gallons each. Been a long time since I was at grandmas house. I
would bet that you have a lot more radiator volume than you do exchanger
volume...

Why would that be important?

Nick

 

[Nick Pine]

I am getting no heat to the rads in the garage which are 4 feet long and
finned. Each would be about 48 by 2 by 6 with air release valves in them.

Fin tubes have about 5 Btu/h-F of water-air conductance per linear foot, so
8' with 170 F water inside and 70 F air outside might provide 4K Btu/h of
garage heat...

Nick

 

[Steve Young]

Hello everyone

First off thanks for all the replies. An update:

I am getting no heat to the rads in the garage which are 4 feet long and
finned. Each would be about 48 by 2 by 6 with air release valves in them.

I seem to be having air pockets in my coil as I have steam forming. To
prevent "a bad day" I made a makeshift release valve by having a having a
hose teeing off near the coil into a five gallon pail which is about 1/2
full of antifreeze. I figured (maybe incorrectly) that if the hose end was
submerged in the antifreeze it would allow air out but not in. Also I was
thinking that it would draw the antifreeze back into the system as the
antifreeze cooled and lost some volume.

I'm glad you stopped for a second to evaluate because you have a hazardous
situation in that you are not able to move the heat out of the stove and the
exchanger is boiling, then your pump is probably losing its prime because of
the steam. Since you have both paths of you piping next to each other, you are
sending your heat back into the stove and causing the exchanger coil to boil
very easily.

What I would do, is temporally move a 30 or 55 gallon drum near your stove and
fill it with water. Work at trying to heat the drum and learn about the
efficiency of your exchanger. Verify you flow volume. You only need several
gallons per minute to move all the heat your stove can produce See how long it
takes to raise the water temp of the drum X degrees. Calculate BTUs from this.
Get a feel for it before you introduce the garage loop. Always install the pump
on the cooler return leg to stove. Less chance to air lock. You should also be
working with a dc pump and battery, in case you have a raging fire and the
power goes out. Also, if you are using one of the lesser expensive circulating
pumps, realize it must be installed vertically so as to better keep its prime.
If it is flat on the floor, you will possible encounter lots of air lock
problems. Slow down and take it step at a time. Put the antifreeze aside for
awhile and use water only to do your testing.

Steve Young

 

[Mike]

Hello again

Again thanks for the help. I removed the pump and pumped water through
about 250 feet of 1/2 garden hose. It only pumped about 20 litres in four
minutes . I might be in trouble. the line I buried is 3/4 hose with the
coil in the stove 5/8 and 1/2 copper fittings for various connections. I
put it through about 15 feet of 3/4 and it really put out but I guess my 1/2
connections will "bottleneck" the flow. The pump is a real bugger to get
primed also. Right now my stove is on the main floor with the pump mounted
horizonticaly on the joists underneath it. I will try the suggestion about
trying to heat a drum of water in the basement first without the garage
loop. does anyone know if you can buy a pressure release valve that opens
up at a low pressure. I was thinking about 15 pounds. A car rad cap would
work but I can't really adapt it to pipe size and I believe that a water
heater pop valve pops at more pressure than this.

Thanks again
Mike

 

[Jim Kovar]

Hello again

Again thanks for the help. I removed the pump and pumped water through
about 250 feet of 1/2 garden hose. It only pumped about 20 litres in four

(snip) does anyone know if you can buy a pressure release valve that
opens

up at a low pressure. I was thinking about 15 pounds. A car rad cap would
work but I can't really adapt it to pipe size and I believe that a water
heater pop valve pops at more pressure than this.

The pressure relief valve on my wood fired boiler opens at 30 lbs, so
I know they are available. If you would like I could describe my system
to you.

Jim Kovar
Vulcan, Mi

 

[Mike]

Hello
Yes, please describe your system. I still can't get this one going without
pressure occurring. I think I must have an airlock but it seems to pump for
awhile and then it will pressure up even though the water SEEMS to be
circulating. I put the pump on the return side of the stove like someone
suggested and the line coming to it seems cool and the line exiting the
stove feels very warm so I am assuming its circulating. This work for
awhile and then all of a sudden I get the pressure. I have a pressure valve
on it and it has gotten up to 25 pounds before I can open a valve and
release . I thought I might have an leak at the fitting but I have pressure
tested it with the line holding 30 lbs overnight with air in it. I am
starting to think this coil idea might be a no-go.
Mike

 

[Jim Kovar]

stove feels very warm so I am assuming its circulating. This work for
awhile and then all of a sudden I get the pressure. I have a pressure valve
on it and it has gotten up to 25 pounds before I can open a valve and
release .

If the water is circulating O.K., it sounds like you may have to
install an expansion tank to take care of the extra volume when the
water is heated.

Jim Kovar
Vulcan, Mi

 

[Steve Young]

Yes, please describe your system. I still can't get this one going without
pressure occurring. I think I must have an airlock but it seems to pump for
awhile and then it will pressure up even though the water SEEMS to be
circulating. I put the pump on the return side of the stove like someone
suggested and the line coming to it seems cool and the line exiting the
stove feels very warm so I am assuming its circulating. This work for
awhile and then all of a sudden I get the pressure. I have a pressure valve
on it and it has gotten up to 25 pounds before I can open a valve and
release . I thought I might have an leak at the fitting but I have pressure
tested it with the line holding 30 lbs overnight with air in it. I am
starting to think this coil idea might be a no-go.

Mike, there is something wrong with your flow/pump. There is absolutely no way
you can boil a 2 gallon per minute flow with your stove, so long as the water is
not steaming hot to start with. I take it, from your comments, you are now
working
from a drum filled with water?

Use hoses to pipe from the drum to the pump, then out of the stove to your drum.
Keep the line from your stove to the drum up out of the water so you can see it
running/pouring into the drum as you test. Before you start anything, prime the
pump through the suction leg. Lift it up out of the water and use a funnel and
pitcher to fill it completely to the top edge. Hold it so that all the air can
come up through the hose. Put you thumb over the end of it and lower it into the
drum of water. Let NO air get into it.

Having the hose laid out so there are no air traps in the piping is also
helpful. Even having the pump at the lowest portion of the piping will make it
easier. The pump really should be vertical to assure priming. These small
circulating pumps can be a booger to get primed and if the are horizontal, they
may loose the prime very easily with just a few small bubbles. Once you have
returned the suction hose to the drum, turn on the pump and watch for a stream
to establish from the return hose. You may need to try priming several times
before you get one to take. Once it does, kick back and watch it for awhile,
measure and time some slugs of it. Once you are confident it is full flow,
start a fire without changing anything on your setup,
just let it keep pumping, with the stream falling into the drum. Start checking
temperatures as you build the fire little larger. I'll bet you'll fire for an
hour before you'll boil a 55 gallon drum of water. I am certain your problem is
circulation.

Steve Young

 

[Dennis Davis]

Hello-Has anyone tried using a interior wood stove to heat water and pipe
it
to anther room or building. I am trying to do this and having problems.
I
am running a .75 hose (also 1/2 copper) line to a garage and back. total
of
300 feet of hose. To heat the water I bought a coil of soft copper 5/8
tubing which I simply put inside the wood stove. I am having problems
getting hot enough temps from the tubing. Max seems to be about 40
degrees
Celsius. I insulated the buried lines with 1 inch of Styrofoam. The
return
line and heating line are side by side in the insulation. I simply cut a
groove in strips of 2 inch insulation and trapped the line within two
pieces
of the Styrofoam. I have two radiators from a hospital in the garage-each
being about 4 feet long. I have them connected in series. Total amount
of
water is about 5 or 6 gallons. Questions:

Am I expecting too much?
Is it too little water to take the heat to the garage?
Should I build a tank and somehow fasten it to the wood stove instead of
the coil of pipe?

Any help would be greatly appreciated as I expected this to work a lot
better. A lot of people around here (Manitoba Canada) heat their entire
farm buildings using outside wood stoves but they have 1.25 buried pipe
with a lot more water.

Thanks
Mike Annetts

A different setup works much better. I built a woodstove thats in the
garage,heat is pumped into the hose in a simular way. I used a 55 gallon
drum for the outside, put a extended 30 drum inside the 55,and used sand in
between the two.the copper coil is in the sand held with spacers so I could
fill sand in without the coil moving. Above this is a second 55 gal drum
with the stack going though it to get more heat from the flue gases before
they go up the chimney. The sand protects the copper pipe from getting
burned through,yet delivers plenty of heat to the coil. Delivers lots of
heat to my garage and heats my house through floor tubing and baseboard
radiators.
On another note,I'm looking for some sources for baseboard heaters, I got
mine thru a H/AC dealer used and cheap, but he isn't selling them anymore
and I need 6 more to finish my basement. The dealer only sells whole hot
water systems so I need a new source,and new would be nicer.