# This is how I have my outside wood furnace system (with photos)



## moonwolf

I hope some of you might get something out of this. 
It's a description and pictorial of the Outside Wood Furnace I use to heat a house (1450 sq. ft.), the hot water. I don't show the brances that valve off into the barn and a nearby greenhouse that I could heat also. 










This is the outside unit that I load wood into about 2 x/day. It's a Classic brand model with a 400 gallon insulated water jacket around the firebox that hold 4' lenght logs. The water lines go in an underground trench that was lined with styrofoam and go slightly uphill too the house. The hot line and cold return line enters at near floor level in the basement which makes for a very low 'lift' that the inside basement pump can handle to distribute the 170 F degree water heated by wood outside. 










Distance from the house line entry to the furnace outside is about 150 ft. This essentially keeps smoke and grime away from the house, and wood is stored down there. The extra water lines to the barn are dug in about 50' away, but not used yet.










This shows the entry of the lines at the basement floor. The bright orange marks the hot water line, and the other is the retun line which circulates back to the furnace water jacket for a continuous flow. The pump is shown that is a 1/12 hp. standard called 'little red' that is recommended for this installation. The switch is shown on the wall for the pump. 

closeup of pump below:




















The cold water line that is pumped back about 4' high goes through a concrete wall. Behind the wall is the room where the hot water tank and water conditioning stuff is. The hot water line is a foot above floor level that enters the hot water heat exchanger.










The fat copper tube is the 'jacket' for the hot water that circulated from the line entering below that is pumped from the furnace. The regular 1/2" copper plumbing within that jacket flows from within the hot water tank and gets circulated to get 'heat exchange' through the pipes and fully heats the water.....very hot water!
you can see the return line at the top going back through the wall as was shown from the other side in the photo above. That line now enters the furnace heat exchanger in the plenum:


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## moonwolf

(continuation of above post)



















closeup of that heat exchanger unit installed within the plenum above the fan force of the oil furnace. The option here is that if wood isn't being burned, the oil funace automatically kicks in with a separate thermostat set at the temp to heat. The wood thermostat is also separate. Either can be shut off, depending on needs and usage of which fuel. 










The extra bit I did when a new addition was put on, was to install under floor heating of part of the basement with water flowing lines from the hot wood furnace burning outside (boiler). This shows the line brancing down to that under the concrete and to the left is a valve to shut off floor heat, or turn it on. It's manual now, but could be manipulated with an automatic valve I haven't bothered with yet. The floor heat is substantial that radiates upwards to keep the upstairs floor warmer, and especially it's below the sunroom and kitchen/living area makes it nice and toasty for feet and saves a bunch of power with not kicking in the squirrel fan on the furnace as much. Only on really below zero days does the furnace fan kick in. 










This is the baseement floor area covering the cirulating tubing from the flow of heated water and gives themal heating to the space. In the basement it usually gets above 80 degrees that transmitts to keeping the above floor in the range of about 70F with no extra use of power from the furnace fan. 

That's it. It gets to 40 below in this zone. Most years I would burn from December to about end of March, using anywhere from 12 to 15 cords of green unsplit poplar mixed with dense dry ash wood. No hot water expense when burning wood either. The small greenhouse has 3 small baseboard heat exchange units directly connected to 3/4" copper piping that has a valve to open and bring in boiler water with an extra small pump. It is used only during April/May when new transplants are in the greenhouse and nights get below freezing that helps.


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## Ross

Great pics! Some questions, is the tap off the plenum coil near the top to bleed off air? I'm curious if there's any throttling valves being used and where in the system you put them.


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## moonwolf

Ross, 
yes, that is basically a bleed off valve above the heat exchange unit on the return line. If also facilitates filling when opening it to allow the upward flow on the hot line. I guess that is what a bleed off valve is for, right? 
I don't have any throttling valves in the system as such. There is also the valve at the bottom of the hot line just before it goes in the hot water heat exchanger. I forgot to mention. It's more of a drain cock if the system ever needed draining, or I can shut off the pump and valve it off there, open the 'drain cock' and it will drain the plenum heat exchanger. The system is all operated from the movement with the flow of that little red pump which uses very little power. In case of a power failure, that is the only unit would need powering from a generator, and leaving a crack open in the door of the furnace outside since the damper would be closed. Have to watch for overheating in that particular case if it was for hours on end.


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## Ramblin Wreck

I'm envious MW. That's a great looking system. I use a wood stove to heat the farm house, with two propane fired furnaces for backup. The stove is very effective, even on our colder days; however, it doesn't do hot water. You also have to take care to avoid a mess in the house, but I've developed a technique for minimizing that...and keep a Dustbuster close at hand for when I fail. One advantage the stove has is that it minimizes the amount of fuel used. It is very "stingy" with wood, especially once the fire is hot and the catalytic converter is engaged. The converter does have a life expectancy less than the stove itself, so there will be some maintenance required in the future. Asthetically, I like watching the fire through the glass door, and it's sure nice to back up to a hot stove on a cold day.

In the barn I plan to build, I'm going to install a wood cookstove to be used for Winter heat, Summer canning, and basic cooking/baking when there is a need/desire for it. 

Since my brother has a band saw mill, I have access to free wood, well almost free. I do lend a hand helping with some of his orders, but that's more fun than work.


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## moonwolf

Ramblin Wreck said:


> I'm envious MW. That's a great looking system. I use a wood stove to heat the farm house, with two propane fired furnaces for backup. The stove is very effective, even on our colder days; however, it doesn't do hot water. You also have to take care to avoid a mess in the house, but I've developed a technique for minimizing that...and keep a Dustbuster close at hand for when I fail. One advantage the stove has is that it minimizes the amount of fuel used. It is very "stingy" with wood, especially once the fire is hot and the catalytic converter is engaged. The converter does have a life expectancy less than the stove itself, so there will be some maintenance required in the future. Asthetically, I like watching the fire through the glass door, and it's sure nice to back up to a hot stove on a cold day.
> 
> In the barn I plan to build, I'm going to install a wood cookstove to be used for Winter heat, Summer canning, and basic cooking/baking when there is a need/desire for it.
> 
> Since my brother has a band saw mill, I have access to free wood, well almost free. I do lend a hand helping with some of his orders, but that's more fun than work.



sounds good, RW. 

One thing eventually I would like in the house is a fireplace or wood stove chimney. Probably a fireplace, since that heat system is already in operation from the outside furnace. So, I'll only need a little bit of wood into the house for aesthetics I'd prefer from a fireplace than a woodstove. 
I'm not sure the direction I'll take with that, except a spot is picked out for future fireplace location. :shrug: I guess I like a lot of options, including the back up oil when needed. Also, loading the furnace outside gives me a reason to get outdoors at 30 below in the middle of the night. I mean we northerners gotta stay tough, ya know!


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## Ross

I'm doing the same sort of thing except I am assembling an air handler from parts. I've got a globe valve just before the coil so I can adjust the flow through and get the delta T I want or adjust it up or down if it's not working out. I am concerned about going over a delta T of 20 degrees without a bypass to the return to temper the water going to the boiler. Hard to get an answer as to the suseptibility of thermal shock to the boiler. I'm still undecided if I'm going to have a supply return line system like yours or a header loop, pulling off circuits with "T"'s. I also have to prioritize one circuit over another, which I'm thinking can be done with a 24v AC thermostat (so it closes the circuit on a rising temp) to open the zone 2 valve. Set it slightly below the prioritized zone so it won't open the zone 2 valve until it's warm enough in zone 1 (or thinking in reverse closes the zone 2 valve until zone 1 is warmed) Nessicarily complicated, as only zone 2 has back up heat! There's probably a controller built to do this I just haven't looked for it yet.


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## moonwolf

Ross said:


> I'm doing the same sort of thing except I am assembling an air handler from parts. I've got a globe valve just before the coil so I can adjust the flow through and get the delta T I want or adjust it up or down if it's not working out. I am concerned about going over a delta T of 20 degrees without a bypass to the return to temper the water going to the boiler. Hard to get an answer as to the suseptibility of thermal shock to the boiler. I'm still undecided if I'm going to have a supply return line system like yours or a header loop, pulling off circuits with "T"'s. I also have to prioritize one circuit over another, which I'm thinking can be done with a 24v AC thermostat (so it closes the circuit on a rising temp) to open the zone 2 valve. Set it slightly below the prioritized zone so it won't open the zone 2 valve until it's warm enough in zone 1 (or thinking in reverse closes the zone 2 valve until zone 1 is warmed) Nessicarily complicated, as only zone 2 has back up heat! There's probably a controller built to do this I just haven't looked for it yet.


I'm not sure I follow what your system is like, compared to mine (not surprising, since I'm really fairly simple minded  ). I'm thinking zone valve for where you want to control off/on flow through any part of your system. My floor heat has a manual shut off. Talking with the electrician, he said a zone valve installation for that would cost about $200. For now, I have that one valve above that feeds down to the floor that I open very slightly to reduce flow, thus reduce the heat somewhat in that floor. It really needs seperate thermostatic control if I didn't want to monkey with it manually, but I just go down and shut it on warmer days. 

As for the greenhouse temperature control. I simply installed a baseboard heater thermostat to the small pump. When it reaches a certain temperature, the circulating pump stops, than comes back on when the thermostat senses it cooling again. Since that line was flat and close to the furnace, a very minimal ciruclating pump works that is also cheaper.


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## Beeman

Is it water that circulates to the wood furnace and back or a different fluid? I have forced hot air heat now and don't really like it. I always liked circulated hot water, wouldn't this system work well with circulated water? Is that what you have in your greenhouse?


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## moonwolf

Beeman said:


> Is it water that circulates to the wood furnace and back or a different fluid? I have forced hot air heat now and don't really like it. I always liked circulated hot water, wouldn't this system work well with circulated water? Is that what you have in your greenhouse?


yes, it's water that flows through the lines, both in the house furnace and through the greenhouse baseboard heat exchangers. 
Antifreeze mix could be added in case of any concern the furnace might freeze up if it was idle, which *could* happen in this climate.


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## Ross

The scary part is the plan I have is the simplified version! I really can't do this manually it has to work off thermostats with electircally operated valves. My parents will live in the attached apartment to my house (1000 Sq ft and called zone 1) and my house (1900 sq ft and zone 2) will use heat from one line of the furnace and another building has line 2 to heat about 1500 sqft. The boiler is rated for 8000 sqft. All will use fan coils except there may be a few convectors in the mix too. At some point there will be an oil fired boiler as back up and maybe a solar collector to do spring and fall?? We'll see.


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## moonwolf

Ross, 
I think I asked that question to the plumber once about heating other spaces and I thought about 'lifting' up the wall in the basement to another trench for the garage (which doesn't exist anymore). I was told simply to put another small cirulating pump for that and than I guess maybe that pump could be thermostatically controlled to come on and off with heat demand? does that make any sense? :shrug: 

Of course, I could be WAY off in trying to understand what exactly you are trying to achieve. My 400 gal. boiler should heat close to 8000 sq ft.. One needs to only maintain that the water temp stay around 170F, which would require more filling of the firebox and burn more wood obviously. eh?


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## Ross

I think 400 gallons is supposed to heat 12,000 sqft, but results may vary and I was cautioned to be conservative with the sales claims. You have a pretty good understandign of what I'm doing except as i am only heating zone one OR zone two I only need one pump. The other buildign is zone 3 but not on the same plumbing so not really important unless the boiler can't keep up and then (A) I'm dissed because I'm well within the boiler's limits and (B) I shut zone 3 down manually as it has oil heat too. The 24v zone valves I'm using are three ways so there is a small bypass built in. For zone one I plumb that back into the supply so there's always some hot water to the zone 1 coil (66% less when the zone 1 valve is closed) zone two's bypass really does bypass to the return line to temper the return water to prevent thermal shock to the boiler (which may or may not be an issue) If there's one thing I've learned about outdoor wood boilers is the installers (and builders?) don't know much about hydronics! At least around here they don't seem to exude much confidence. One company (which will remain annon) shows a DHW exchanger plumbed into the temp and pressure releif valve port on a water heater and the T+P valve moved out of the tank into a "T" with the exchanger!! Well that ain't to the plumbing code anywhere I expect, certainly not in Ontario. You don't mess with the installed T+P except to test it and replace it.


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## lisa in ozarks

and may i say your system looks grand,,,, good work moonwolf, i like your outside to, it looks rugid beautiful,


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## john stone

Hi
Do you think i could run my hot water from my Mahonny outdoor stove directly through my hot water radiators?

Thanks John Stone...................did anyone ever try this? great job Moon!!


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## mike554

Yes you can run your radiators off your outdoor stove. We have hot water baseboard heat in our house. Right now I'm using my 50gal propane water heater to heat with and plan to install a outdoor wood boiler.


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## Ross

I'm not familiar with your outdoor boiler, and I don't have enough info about your existing system of hot water radiators you're asking about. If those radiators are hooked up to a pressurized system then maybe a direct hook up won't work. Most outdoor boilers are open pressure systems. The other issue is lots of rads are cast iron meant for closed systems, where the oxygen becomes depleted to zero over time. They will rust out over time when used with an open system. You may need a plate exchanger to transfer the heat from the outdoor boiler to the indoor pressurized system.


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