DIY Outdoor Furnace

Comments from Visitors . . .

                               February 08, 2003
                               hot rod (
                               Subject: Sounds Rube Goldburg-ish to me!

                               But.. Typically all the components would match. For instance the amount of heat
                               emitter area should match, somewhat, to the amount of boiler output.

                               I'd worry that those radiators "glued" to the boiler, would adversly effect the
                               boilers ability to heat them :) Will these be inside or outside the fire box?
[["Clamped" - outside]]

                               Inside the firebox may cause a serious creasote producer. Outside, I wonder
                               about the thermal transfer and condensation issues.

                               All that aside, do it safely, install adequate pressure relief valves sized for the
                               potential output of this beast, move the women and children to a safe location,
                               and up your insurance coverage :)

                               Although I would be embarassed to tell you about some of my "Rube" projects.
                               Play safe and consider the energy bottled up in that devise. A little steam, out of
                               control, is a lot like a stick of dynamite.

                               hot rod 


                               February 08, 2003
                               John Lenhart (

                               I agree with hot rod. You might become the only guy on the block with a
                               backyard rust-maker.Just kidding!  Good luck


              February 10, 2003
                         K.Field  Easton, Pa.

                         My only suggestion would be to use propylene glycol anti-freeze instead of ethylene glycol.
                         It is made for heating systems and is compatible with the circulators and valves used in
                         hydronic heating. I'm not sure that you will get the output you want from the radiators
                         because of their design. If you look at how they work in a heating system, the inlet and
                         outlet is usually on the bottom and the heat goes toward the top. When you circulate water
                         through them, it may go in one end and out the other without a good blend of water. I
                         could be wrong but wanted you to be aware of the possibility.
 - - -
I was not aware of the special anti-freeze. I will research it.
I assumed that the water pump lubricant in automobile anti-freeze
 would benefit the circulators and valves.
I appreciate your reply.

                         Feb. 11, 2003
                         Greg H.

                         I too have a wood fired boiler on my mind as a daydream project I would like to do

                         The way you propose to build yours will not work very well.

                         These wood fired boilers are normally made with an open water tank above the fire with a
                         loose fitting lid.
                         The circ pump draws water from the bottom of this tank and the return dumps into the top.

                         Closed, presssurized wood fired boilers are not permitted where I am, for the main reason
                         that the fire is hard to turn off in the event of a temperature/pressure problem.

                         Automotive anti-freeze is not permitted as well because of it's toxic nature. Leaks are a
                         safety and enviromnmental hazzard.
                         The correct heating fluid as KField suggested is propylene glycol. It is an inhibited grade of
                         a fluid that is used for human consumption by the food industry.
                         You probably have some food in your cupboard or fridge with this stuff in it.
                        One trade name for this product is Dowfrost.
                         Another anti-freeze that can be used is ethyl alcohol based.
                         It is the alcohol that those fools put a substance in to make you sick if you drink it.
                         A trade name for one is Loopanol.

                         The alcohol based one is quite a bit cheaper but the glycol doesn't evaporate as quick in an
                         open tank.

Duncan W.
Feb. 11, 2003

You have a Grundfos model UPS 15-42F three speed circulator.

Typically, there's screw-in or push-in terminals for the line voltage and neutral supply
voltages and ground.

The capacitor is usually connected to leads in a sealed molded rubber block, at least in
the newer ones. Can't remember the 1986 models. It's an AC capacitor, not polarized, but
needs to be connected correctly to the motor windings.

The large screw on the end is to access the end of the motor rotor shaft. It could spray
you with water if removed while the pump is under pressure, but most likely would dribble.

Patrick O'Rourke
Feb. 11, 2003

I like your idea, however you will lose so much heat to the elements that I
would be willing to bet the heat transfer from the wood box to radiators
will be negligible. That said, why don't you construct some sort of
enclosure which would minimize heat loss? You could go one of 2 routes,
masonry or metal. If you've got access to some heavy gauge sheet/bench
metal and a welder, you could go that route. If not, build a block
enclosure in which you would house the stove/radiator combo. Or better yet,
do both, but insulate the hell out of it to minimize your heat loss to
outside air.

Greg H.
Feb. 12, 2003
It would be good to know where you live and the temperatures you experience.
 Also, what size and types of buildings do you want to heat.

 Another thing you will have to deal with when attempting to run a pressurized system using system heat to pressurize it.  If the system is running at a high fire and the bladder tank takes all it can handle the pressure relief will discharge some of the antifreeze. When the system cools off it will be short of liquid and will require refilling and bleeding each time this happens.
- - -

From your website:
"An in-line thermostat will run a combustion blower."

You cannot use a "combustion blower on a wood stove.  A blower is what a blacksmith would use to melt steel, which is what would happen to your stove if you tried this. What you need is a motorized damper connected to the draft vent to control the fire.

What your trying to do sounds like a fun project and I don't want to discourage you,
but you  will go to a lot of trouble to do this with less than stellar results.

I can tell you more if you want to hear it.
 - - -

                         Tell me more;
                         my imagination needs the exercise.

                         Like sex; a combustion blower must be used in moderation, or it can kill a guy. But a little
                         may be a good thing. If I put a steel tube under the fire and blow in it with my mouth, the flame will benefit with
                         no harm caused. If I go crazy and put a 100 horsepower turbine on the tube, the furnace will last 15 minutes.
                         But there is a happy medium that will improve overall temperature control and performance.

                         I have a blower taken from a wood burner.
                         It has an adjustable baffle on it to control the amount of combustion air.

                         My shop is 12 X 14. My greenhouse is 9 X 12. Hot tub 8 X 8.
                         I'm in central Pennsylvania.
                         "Fun project" - YES; I enjoy this sort of challenge immensely :)

- - -
Tell me about the motorized damper
The expansion tank is a good idea; I may have to add a second tank.

Greg H.
Feb. 12,2003

                        I have to say that your project is a little out in left field.
                         You must keep an open mind and research what information you are given to ensure it's

                         This would take forever to debate the suggestions I give you, and unfortunatly I don't have
                         the time to do this.
                         Use my suggestions as a seed for further research.

                         I will repeat that it would be unwise to put a blower of any kind or strength on a wood
                         burning appliance that wasn't designed for it.
                         You will burn out the firebox and use up your wood too quick.
                         Attaching the radiators to the firebox will result in poor heat transfer to the water, again
                         resulting in inefficient use of the wood.

                         If you are handy at welding build yourself a steel tank that goes across the top and down
                         the sides of the firebox, in the shape of an upside down U. Build a lid that comes off to
                         clean out the tank.
                         Attach a fitting to both sides at the bottom of the U for the feed to the pump and dump the
                         water back in about halfway up the side of the tank.
                         All you need then would be a pump and nothing else.
                         There are many commercially prduced wood boilers around here and this is how they are

                         If you've made up your mind to proceed with this project I would be most interested in
                         hearing of your progress and results.
                         - - -
                         Your design would be more efficient than mine, and I have two welders. But I don't have the
                         steel plate, and I do have the radiators.

                         I have been toying with the idea of using cast iron baseboard on the top of the furnace,
                         since the back is flat and would give me better heat transfer. I'd be inclined to put it in the
                         firebox, but it would get sooted up and less efficient over time, plus it would take up room
                         that I want for burning wood.

Feb. 13, 2003
                       At $30 per foot, cast iron baseboard is probably not a good choice either. I'm sure you have
                         a welding shop not too far away who could fab something for a couple hundred dollars and
                         that would be cheaper than buying cast iron BB. I'm in Easton and I'd be happy to put
                         something together for you if you can come and get it. I don't have a lot of surplus steel
                         plate but I can get it easily. I could use a good project anyway.

I have access to  about 20 feet of baseboard free gratis.
But I'm wondering if I could get the holes threaded
where the connecting sleeves go.
A 3/4" pipe thread would be great.

                         Feb. 14, 2003

                         Those openings are for the push nipples used to join sections of baseboard together so
                         there is a possibility that the size would work for 3/4 pipe threads. If I get a chance tonight,
                         I'll mike one up and see if is close enough to do that. I still think you should sell the
                         baseboard for $20/foot and use the money for a better plan.

You'll be jealous when I get a contract to supply these to the Army to heat Hummers        : )

                        Ed Imeduc
                        Feb. 14, 2003

                        Dont know if it helps. But on the old hand fired furnaces we started useing the first tstats
                         inside the homes. It worked with a two arm motor that would do a 180d turn. One arm went
                         by small chain down to a draft door on the ash pit clean out. The other arm and small chain
                         went to the so called check damper that was put on the smoke pipe. So if the tstat called
                         for heat this would open the draft door and close the check damper. When it had enought
                         heat it would close the draft door and open the check damper on the smoke pipe.So if you
                         use a immersion aquastat on this set up for the fire would use the pumps for the control of
                         tthe heat in the building. Like Greg said You dont need a blower at all for the fire to go up
                         or down ED

Feb 15, 2003

                         What ever you build...don't make it the sole means of heating the three buildings. You
                         appear not to be too concerned with leakage/spillage most likely you have a large property.
                         Alot of people don't get concerned till the EPA finds the contamination in someones
                         waterwell came from your yard. (it can travel for miles)They'll come down on you with both
                         feet, and worse than a pitbull. The fines will cost you everything you own.. My company wont
                         use anything but the food grade stuff, it eliminates liability. It sounds like to me you have
                         alot of radiators that need a good use. Have you thought of just trying to use them as a
                         passive solar collector for heat/hotwater. Cast iron has alot of thermal mass to store heat
                         in. I'm no expert on solar but it's free energy.

Feb 15, 2003

You could use ram air then to boost the fire. You would be able to see them coming for
miles with the wood smoke billowing into the air.
Could even be adapted for use in the H3.


Feb. 17, 2003

I've attached 4 pics of the wiring on the circulators that I have.  After
looking at your web page, your's is the same as my older one, w/ the 3 speed
switch (fastest with switch turn to the most clockwise position).

The capacitor connets to positions 4 and 8 (right most connection location).
Your unattached wire needs to connect there.

I'm not sure about using the cast iron raditors clamped to the firebox to
heat the water.  You might consider using coils of copper instead and/or a
manifold of iron pipes inside the firebox.

Also, depending on your distance, you may need multiple circulators.  I am
adding another heating zone to my furnace this summer (when I can drain the
water and have a few weeks to work on it).  I am planning on redoing it
using 2 or 3 circulators.  I've determined that when I have multiple zones
call for heat concurrently, I don't think I'm getting enought water flow -
as determine by the temperature differentail of the water leaving the boiler
versus the return water line.  In some cases it is 25 to 30 degrees.

Good luck.
John Scott


Thanks a LOT!
It Works !!

On mine, there are no internal connections to pins 2 and 3,
so I'm not sure what the jumper is for.

Thanks again,


Feb. 23, 2003

Looking good,
but I wish you would stop calling the boiler a furnace.   lol

Jeff Clark

Well Jeff,

I always thought a "boiler" had a water jacket;
a double wall with water in between.
Mine does not; it only has a meager coil on the firebox wall.
It is meant to heat the surrounding air by radiating heat.
Maybe the coils were meant to heat a remote room.

I'd call it a hybrid, but then the local Amish farmers
would think I'm talking about burning corn, and ask where the hopper is,
and then the plumbers would think the hopper is a commode,
and the the local Moonshiners would wonder why I'm wasting all that good corn,
and the Revenuers would want to look at my copper pipes . . .

Woe is me; what to do, what to do ...

Nevin   : )

Feb 24, 2003
Jeff Clark

I was thinking you might be better off usin fintube for the heat exchange
rather that the radiators you were strapping on. The heat transfer may be
better that way. But I am not positive?

I gave that some thought;
I have 1- 8' length with backer.
I'll try the cast iron first.

I also thought of using 1/2" copper lines
zig-zagged back and forth on the furnace top.
Then pour concrete on them for a heat sink.

I don't know how the copper might get along with the chemiclas in concrete.


Feb 26, 2003
Corran Vincent

Just a couple of comments,
1) It is doubtful that the vehicle radiators will take much pressure as
the radiator caps are usually rated at only 9 or 15 psi .
So I would make sure the safety valve you use is only rated at about 15
psi too.Otherwise you run the risk of blowing the headers of the rads,.
 15 psi will push the water in the system to a distance of 15 x 2.3 =
34.5 ft above the boiler, Note this static head NOT circulating head,
  this has NOTHING to do with the circulation of the water.

Note you will have to drop the pressure in the pressure tank otherwise the tank won't
take any expansion until the pressure gets to about 15psi which is what
most tanks are set to. ie if the bladder is at 15psi it wont move over
to allow the expansion of the water until the system pressure gets to
15psi  so on firing up pressure gets to 15psi very quick then starts
blowing off your safety valve. Then when cold you will have to top up
the pressure again which means the system is getting the water changed
all the time which will cause corrision.

Another way is to use a feed tank mounted above the level of the highest
point in the system plus a bit. The tank should only fill to a point
cold where the total expansion can be taken in the system without the
water reaching the overflow when hot. To protect the pump incase of a
leak fit a low pressure switch which will shut the pump off if the water
level falls too low, You could also put an alarm on it too raise the
alarm to warn you as well.

It is a good idea to have an exhaust from the boiler going above the water level, perhaps bending over back into the tank, The pipe feeding water to the system should be connected to the boiler on the discharge side of the pump.(otherwise the pump will push the water up the exhaust and empty the system or into the tank if the exhaust is over the tank). In your very cold climate I guess you have to put the tank inside somewere say in the
ceiling. Make sure you put an overflow tray under it.

2) The cast iron radiators really need to be able to 'see' the fire not
just clamped on the outside of the heat exchanger.

3) The underground pipe system is good just make sure it is water tight
especially were it come up out of the ground and where one pipe joins the

I  have been in the heating trade now since 1964 and have a trade cert
in HVAC, I live in NZ that paradise in the south pacific just to the
east of Australia.
Years ago I fitted little coal fired boilers in homes and used a infloor
convector heater with a car type core in it and found that using a
pressure tank caused the blow, These were just a square box
hanging from the floor with a core with a fan under it blowing the air
into room the cold return air flowed down into the box on the 3" gap on
each side of the core.

Hope this helps
If I can help any more send me an email.

Hello Corran Vincent,

You are a gold mine of information.
I greatly appreciate the insight,
and the invitiation to pick your brain.

I will post your message on my web site.
Others may like to ask you questions.
Do you mind if I post your e-mail address?

Health and Happiness,
Nevin Hawlman

Feb 28, 2003
Corran Vincent

Hi, Nevin,
I've just read the responses and would comment further,
1) As Patrick says the heat transfer rate with the CI rad bolted to the
outside will not be great which is why I said it would be better for the
rads to 'see' the fire ie be on the inside of the firebox. If you use
finned tube you will probably find the fins clog up with gunk very
quick.What would be better is to use a plain copper pipe (which has higher
transfer rate than CI ) and make up some grid header to fit inside the
firebox. Make it removable so once a year you could remove and clean. You
may have to make in 3 pieces 1 on each side and one at the rear.

2) A small fan can be used to blow the fire connected to a thermostat. say
a 4" with a 25 watt motor  (1/16-1/10 hp) However remember a wood fire is
not sudden death, So always leave the pump running otherwise you can get a
boil up, once the fan stops the fire will keep on putting out heat for
quite a while after the fan shuts off which you need to get rid of
otherwise you get overshot. Actually a good scheme is to use storage like a
big cylinder so that the excess heat is used up heating the larger mass of
water which would even out the hi & lows of the temperature. Bit like
having a great big capacitor.
3) The higher the pressure in the system the higher the temperature can go
before a boil up occurs however the pressure in the system is limited by
the weakest link which will be the vehicle radiators. I would agree with
Greg about using a feed tank mount it up in the roof space some were. use
3/4" as the smallest feed pipe down from the tank and for the exhaust going
up. An open exhaust is good safety measure to prevent a buildup of excess
pressure in the system. You probably need to take the exhaust out though
the roof  which could cause a problem if it ices up, But make sure the
exhaust exits though the roof well above the feed tank so the exhaust will
not have water in it to freeze, In your cold climate good idea to insulate
the pipe also.

4) Radiators are best piped the European way. Flow in the top and return
out the bottom the other end what we call TBOE (Top Bottom Opposite ends)
They can be BBOE (Bottom Bottom Opposite ends) and they will work too the
heat rise to the top of the rad as it comes in the flow and then as the
water cools (because it has given up heat to the room) 'falls to the bottom
of the rad at the other end to discharge though the return. In the boiler
you must take the water out the top of the CI rads as you must not airlock
them ie as you have shown them in your diagram.

5) If you give me the size of the CI rads in the boiler I will try and give
you some idea of the output of the Boiler.

6) the system should work bearing in mind the comments made, To mininise
cresote only burn wellseasoned dry wood. Nothing that still has the birds
in it.

Cheers hope this of help.
Corran V


I'm not the first to get this DIY Outdoor Wood Burner idea:

"If at first you don't succeed...":

Mar 02, 2003

"I wanted to give you my humble opinion about some concerns that may or may not make themselves evident in your system.  I must tell you that this has been learned by experience as well! My first boiler was something I had spent months trying to figure out.  Getting advice from a few sources (innovators anonymous), my first go was with a modified barrel boiler design that had a 3-tier zig-zag coil, that I built, installed inside the top third of the barrel - form fitting, of course.  Two longer extensions on the coil served as supply and return lines to the coil and with some mounting rings welded to the extensions, mounted through holes on the back (bottom of the barrel) of the barrel boiler.

These I hooked up through flow-checks and relief valves directly into my new oil boiler inside the house using PEX tubing and constantly circulated with a TACO 005 circulator.  The PEX was rated at 100 psi at 180 degrees and 80psi at 200 degrees, so I determined that this was a safe operating environment.  Also, since the PEX was so expensive, I hated to cut it any shorter than half of the total length of 300 feet.  So I have a tube pair at 180' to go from the wood burner, 45' to the house and about another 35'-40' around the ceiling of my basement to my oil boiler and coiled the rest up and hung it there - all insulated to reduce heat loss.  Oh, I also had a forced air blower into the base of the burner.

The barrel assem bly was then mounted in a metal building and insulation wrapped arount the barrel itself.  This worked ok except it burned a full wood load in about 2 hours and took too long to recover heating after a loading.  I then discovered that the blower manifold I fabricated did wonders for burning PEA coal ( I did say my oil burner was new!) and started tinkering with that.

Then one day at work, I receive a call from home from my dear sweet wife saying that the system is blowing steam enough to blow the doors open on the metal building.  After having her pull the plug on it, she said it exploded!  "Um.", I said, "Go put the fire out with the hose and I'll look at it when I get home."  She kept saying the tubing was dancing like a serpent!

What I found was that the boiler superheated, started producing steam, and when the steam bubble hit the circulator, circulation stopped and just amplified the problem so much that the PEX found it's weakest point and blew out there - about a 10" section was blown wide open!  Fortunately, the break was inside the PVC conduit underground and some water drained into my basement and no one and nothing was hurt except for my pride.  This all took place between Feb and April of 2000.  The following season, I added a 20gal. open-vented resevoir in the building and plumbed in some bypasses and a heat exchanger to make a zero-pressure system.

I burned the remainder of the 6 tons of coal I had from the previous year fixing things like the bypass circulator and the blower manifold.  That still took too long to recover after loadings and a wood loading still burned up like crazy!  That's when I decided to go bigger and better.  My plan was to put a 55 gallon barrel in a 275 gal. oil tank thinking that that would take care of the recovery time and remove the coil from inside my firebox.

I was poking at things on the web when I stumbled onto a person's web site where I could buy plans for a wood boiler with a 300 gallon water jacket reservoir.  I did so and the pictures are the result of that purchase with some modifications of my own.  Now, I cannot share the plans to the boiler due to copyright infringements, but I can tell you that I bought the plans and I would be happy to share my modifications and suggestions on what I would do differently had I to build it again.

That said, let me voice my concerns of what I saw, and you can decide what you want to do with them. First, need I say more about the pressurized system?  You don't necessarily need the exchanger unless you need to heat another system which is a pressurized system or if your boiler is at a lower elevation from your heating requirements.

Secondly, as you discovered, those old cast-iron radiators are hard to come by.  I had two broken ones that I took out of my basement left from the prior owners because the system was inadequately protected against freezing (the house was vacant for a few years).  I about fell over when the installer of my oil boiler told me the price of one was (a 3' x 6-core was about $800 - used!).  You could instead use steel pipe and elbows (something I learned from my first attempt) and strap them to the wood burner.  Most hardware stores will cut to length and thread pipes if you like that route (Lowes did it for free).

The other idea would be to use a continuous copper coil.  I'd stay away from solder joints there just in case of a "melt-down". I wonder how a bus or truck radiator would work here. You should also consider insulating your return line in you transfer conduit as well.  This will increase efficiency and protect the conduit PVC.  I have no idea what my "melt-down" did to the PVC, but I was still able to remove and reinstall (cut to length this time) the PEX with the polystyrene sleeves on them, so maybe the protection issue isn't so important. . .

The radiator exchangers were quite impressive and I'll bet they will put out the heat.  You'll be able to grow tropical plants in there in the middle of winter!  I also can't help you on the 3-speed circulator.  I never heard of such a critter, but from what I saw in your picture, it looks like you got it figured out. I've been planning a garage and workshop project that I'm definitely going to incorporate in-floor heating in the concrete floor.  This presents other challenges since this water can only run a max. of 80 degrees and my boiler runs 200, but I'm looking forward to it.  I've always said that there is nothing like laying on cold concrete in a garage on a winter day with your feet sticking out from under a car, except when there isn't any concrete or garage.  My wife also wants me to run under-floor heating in the kitchen and  living room of our house and planned addition, so I should be pretty busy this year."

Visit Curts page

Mar 02, 2003
Corran Vincent

Well done I see you have tested the system I'm a bit suprised the
vehicle rads took the pressure but that they did is great you must have
really solid rads headers over there. Did you do a drop rest on the
system ? and hold it for say a hour.

I recently did an unground pipe run in an trench 35metres long  in a
product called Flexalon, tested for over 2 hours before the engineer
came (then he hardly looked at it) and when we came in the next day it
was still holding at the same pressure 400kpa (almost 60psi) for over 24

That underground pipe of your is quite good if you silfos the joints it
should last well just make sure it has room to expand in length as
copper has a hi expansion rate.

Oh yes I saw a comment about copper pipe in concrete before, The lime in
the concrete can cause a problem so mostly if we lay copper in concrete
we usually wrap with Denso tape (Petroleum tape, greasy stuff) Years ago
it was laid in concrete for infloor radiant heating  but there were
problems with the expansion and contraction breaking the joints where
they had been softened by silfosing or bending at corners plus the lime
in the concrete.

I'm also a reg gasfitter too and we sometimes lay copper under the
concrete for gas line but even then wrap with Denso and well test it too.
Well so far you doing well  keep it up.

- - - - - -

Ps I would make the rubber hose on to the vehicle rads as short as
possible just enough hose to get on to the rad and enought to get onto
the reducer which should be almost hard up to the rad connection. If you
have lots of overheats you will probably find the hose will get a
shortened life but store the excess hose you've cut off for later use.


Mar 03, 2003
Corran Vincent

Probably better to keep the pump running continuously and control the room (building) temp by a stat which switched the fans on the vehicle rads If you shut the pump off there is more likely hood of a over temp by the boiler.
What is the rating on the pump? probably uses (as I don't know the amperage) something like 100watts a hr therefore at 10c/hr = 1c/hr or 10 hrs = 10cents. You could also wire all thermostats so when they are all satisfied the boiler fan (damper) shuts down regardless of whether the boiler is up to temp, This could cause a bit of a lag when heat is required but you can't have it always.

Just went back to have a look at your pump; almost looks too big but then I don't know total loading etc, usually try to get a 20 deg temp diff over the flow and return although that subject to factors too. try it on low speed to start with. One of the problems with very small pumps they have little guts to starts as they have such little power that after a year or so especially after
laying idle over summer sometimes you have to give them a thump on the end to shake the rotor to dislodge a slight bit of sediment stopping it from starting. you shouldn't have any problems to start with but keep this in mind for the years to come. Once you get them going its better to keep them going
rather than stop/start.

1 Btu = 1lb of water raised 1 deg F.
Therfore 40 galls x 10 x say 60 to 180 = 400 x 120 = 48000 Btus =14 kws  the heat given out to the room will depend on the uninsulated area of the cylinder. usually at 180 deg F 1 square foot emits approx 180-200 btus to a room at 70 f . Oh yes I'm working on Imperial Galls too not sure about US galls which I think is about 85 % of an Imp galls too.

We use Pex pipe over here too but I never mentioned it as 1) you already had the copper pipe in 2) I certainly wouldn't have recomended it any way as if you get a boilerup the pex would be getting a bit iffy anyway.

Say If you want real cheap heating have you thought of waste oil most
garages would be glad to get rid of it and an oil burner would be more
atuomatic with less work in stoking than a wood burner, Mind you  you
get heated twice with wood the first time chopping it up and then
burning it oh yes don't forget the ash disposal which is ok for the
garden But NOT coal ash.
As I said before a copper pipe grid would be easier to make and give
better results than the CI Rads provide you keep the coil full of water
you'll have no problem with the joins.
Yes would be good idea to insulate the return actually didn't think that
you weren't going to only thought the insulation was off for the pic.
I watching this with great interest.

Page 2-
The thought stuck me that perhaps you need to work out:

1) The total heat required on an average every hour. Note there are
several web sites which have heat loss calculators which you could use
to determin the heat input required.

2) The is a site ( which will
give some uses full information on the burning of wood and how to
minimise creosote formation in the flue and heater Also give the heat
output of the various woods you have over there.

3) The calculated output of the boiler you have.

4) For 100,000 btus at 20 deg temp drop you will need to pump 1.4 galls per min at 100 deg delta t ( ie 170deg mean water to 70 deg room temp) you can prorata  the input into your building from that and then  you should have have some idea of how much water you need to pump. With the pump you should have got a performance sheet. (Note Imperial Galls not US galls).

Then you will have some idea of how much wood you will need to burn each
hour to mantain the temperature you want, The thing I don't like about
wood is the overnight requirements getting out of bed to a cold house
and then having to get the fire going to get warm is not my idea of a
joke,  Can you get enough wood in the firebox to maintain an over night
burn ?.

Would not like to see you work day and night all summer just to get
enough wood to keep you going all winter.

Q, Are you going to have a lo water temp stat which will ensure the fans
on the vehicle rads don't come on until you have some temperature in the
heating water so there is not cold air circulated if the boiler goes cold ?

I haven't fired it up yet, but it does have a large fire box.
I'll add this stat later if it proves necessary.

Thanks again,

My "Spread" with all the free firewood I can burn