Indoor wood furnace

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all night moe

Minister of Fire
Nov 19, 2015
636
earth
My 4500sq ft farmhouse is somewhat a "disaster." It's been partially remodeled with new sheetrock and insulation, plumbing, and wiring. All this work is, shall we say, subpar by the previous HO. This includes the wood furnace install. The oil furnace has been rendered inoperable with the exception of it's fan for the forced hot air. It is triggered by the fan limit switch in the wood furnace's surrounding air plenum. That's it. No house thermostat to call for heat. The old HO told me they ran the furnace "wide open." The air intake was wired fully open with bailing wire. I disassembled that feature, and operate it like a woodstove. I give it more air when first loaded for a couple minutes. Then I shut down the air intake to a 1/4'' open. The plenum heats up, fan cycles and shuts off, when the off pin of the switch has been reached. I also fixed the smoke bypass inside the furnace. When closed, the smoke exits via bottom of the rear wall.

I would like to establish a thermostat for the heat call. I bought the solenoid assembly for the intake air, but I'm a bit unsure on how everything should be wired up. There is a 24v transformer in the oil furnace.

Even though I want to convert to hydronic heat, I'd be well ahead to get this current system under better controls. In it's current state, I go through a lot of wood. Not to mention, the air system is not adequate. Furnace is in one end of the house with the ducting ending 3/4s of the way to the opposite end. It's never very warm there when temps hit the low 20s. The furthest portion of the house has no heat at all. It was the migrant worker's kitchen, and heated with a wood cook stove. Hydronics makes for the best solution.

Anyone have any links to show me how to correctly wire this?
All help is appreciated.
 
My 4500sq ft farmhouse is somewhat a "disaster." It's been partially remodeled with new sheetrock and insulation, plumbing, and wiring. All this work is, shall we say, subpar by the previous HO. This includes the wood furnace install. The oil furnace has been rendered inoperable with the exception of it's fan for the forced hot air. It is triggered by the fan limit switch in the wood furnace's surrounding air plenum. That's it. No house thermostat to call for heat. The old HO told me they ran the furnace "wide open." The air intake was wired fully open with bailing wire. I disassembled that feature, and operate it like a woodstove. I give it more air when first loaded for a couple minutes. Then I shut down the air intake to a 1/4'' open. The plenum heats up, fan cycles and shuts off, when the off pin of the switch has been reached. I also fixed the smoke bypass inside the furnace. When closed, the smoke exits via bottom of the rear wall.

I would like to establish a thermostat for the heat call. I bought the solenoid assembly for the intake air, but I'm a bit unsure on how everything should be wired up. There is a 24v transformer in the oil furnace.

Even though I want to convert to hydronic heat, I'd be well ahead to get this current system under better controls. In it's current state, I go through a lot of wood. Not to mention, the air system is not adequate. Furnace is in one end of the house with the ducting ending 3/4s of the way to the opposite end. It's never very warm there when temps hit the low 20s. The furthest portion of the house has no heat at all. It was the migrant worker's kitchen, and heated with a wood cook stove. Hydronics makes for the best solution.

Anyone have any links to show me how to correctly wire this?
All help is appreciated.
Do you have 24v supplied to the thermostat you want to use? If so from where?
 
Do you have 24v supplied to the thermostat you want to use? If so from where?
It is still in the oil furnace but the wire for thermostat has been pulled. I also need a new thermostat. The Origional looks to date from the 40s.
 
It is still in the oil furnace but the wire for thermostat has been pulled. I also need a new thermostat. The Origional looks to date from the 40s.
Does the thermostat need to control the hvac blower?

Edit… better question, do you need just a two wire Heat only thermostat
 
No, it does not need to. The solenoid on the air intake does ..... but I wouldn't mind installing a thermostat that could manually control the blower. May use it to move air around in the summer. The ducting stays nice and cool in the off season.
 
So if you want a smart thermostat they need 24v. And you will run a common or use the kits that come with them to add a common 24v. Use the relay (s) to keep the 24v system’s separate. Wood furnace 24v should not ever be tied to a transformer on the oil furnace/blower. If you only have one 24v transformer then relays aren’t needed. Basically keep separate powered systems separate. That’s a simple explanation. If you are you are unsure post more details and pictures and test what has 24 v now. And we might be able to help. I’m a novice just had to help my hvac installers install my ecobee to run a dehumidifier.
 
I'm a novice myself, that's why I'm probing for info. What I do know is, nothing is running on 24volts. The transformer is resting in the oil furnace which, has been silent for almost a decade. This house is wood heat only. I am wanting to use the dormant transformer to operate my solenoid for air intake, (naturally drafted). The blower will kick on once the fan limit switch is in the ''operate zone.''
I was looking at the older round, Honeywell style thermostats. They have a model with the manual fay control as well. No smart thermostat here. In many areas, I prefer simplicity.
 
Thermostats on a wood burning furnaces are worthless. I learned that after having my Caddy for about a month.

Why not just wire up a spring wound timer ? Set the timer for X minutes, it keeps the damper open, when the timer times out it closes the damper. I had the same exact setup on my Caddy. I'm assuming that the damper is ran by an electric motor.

Pictures are worth a thousand words also !
 
Thermostats on a wood burning furnaces are worthless. I learned that after having my Caddy for about a month.

Why not just wire up a spring wound timer ? Set the timer for X minutes, it keeps the damper open, when the timer times out it closes the damper. I had the same exact setup on my Caddy. I'm assuming that the damper is ran by an electric motor.

Pictures are worth a thousand words also !
I am looking to put this old furnace back to normal operation. This includes using the thermostat from the house, that used to control the oil burner, to control the wood furnaces damper solenoid.

wire up a spring wound timer ? Set the timer for X minutes, it keeps the damper open, when the timer times out it closes the damper.
This is what the fan limit switch does now. Now matter how much I stuff the 24x24''x40 plus inch deep firebox, My longest usable burn time is 5-6 hours. A little less when It's really nasty cold out. I end up getting up twice a night to refuel. When I do, I have decent coals but have to tend to it for 20-30 mins. Cuts into my rest horribly.

Instead of burning through the wood in "timed'' temperature cycles, I would like to open the damper only when the house calls for heat.
 
I think if you were to pull up the instructions for the transformer you're using it would be pretty straightforward to see how to do what you want to do. You basically just have the 2 110v connections to power the transformer, 2 wires connected to your thermostat, and 2 24v wires out to the solenoid.

Having a manual draft control on a wood furnace is sketchy IMO. The limited convective airflow through the ducting makes things get stupid hot in a power failure situation.

I had a manual draft on my old furnace. I used a small, normally closed, duct damper as a deadman on that so it closed without power. The manual draft provided my low setting (and my nearly off setting if the power failed or high limit was reached). If I was doing what you are doing, I would add the solenoid to provide additional draft through another draft opening either pulling its air from behind the deadman damper, or with some provision to ensure it would also be closed in the event of power failure.

It would be a good idea to incorporate the high limit in the fan control so that the solenoid cannot have the draft open when the fan control has sensed over temperature. One option would be to have the 110v power going to the transformer run through the fan control high limit switch. That way reaching high limit creates a power failure for the transformer and shuts off the air until things cool down. With the setups I've had, reaching high limit is not routine. High limit is an indication of some major malfunction or the result of a power failure.

I don't understand what you say about the fan switch currently controlling the draft damper. That wouldn't make sense to me, except for what I mentioned above in closing the damper at high limit.

If you want to do more than just call for heat, like run the blower manually from the thermostat, it gets more complicated. More connections, but the transformers I'm familiar with have relays for the 110v blower as well.

My guess is that you're only going to want to add slightly more air when calling for heat. Since you can't turn wood on and off like gas, you want the thermostat to call for more heat in the wee hours when things are cooling off, but ideally never completely satisfy the temp setting so you're not creating a big fire then starving it for air suddenly and creating a bunch of crud. You're right, you probably should try to avoid that cycling if possible.
 
I have heated my home with a wood furnace for 44 years (3 different units)
I have found that a thermostat on a wood furnace is like tits on a bull. Yes they
open and close the draft but a wood fire is not like an oil or gas heat A wood heat
is a more consistent, blower on and off as the plenum heats and cools
also, you can show the heat on a curve as the fire burns from start-up through the
burn to coals and reload time. My new furnace has a reload time of about 6 hours
in normal winter weather. Very cold and windy most likely 4 hours but my home
was built in 1861 of hand squares Cedar logs not exactly air tight.
 
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I have heated my home with a wood furnace for 44 years (3 different units)
I have found that a thermostat on a wood furnace is like tits on a bull. Yes they
open and close the draft but a wood fire is not like an oil or gas heat A wood heat
is a more consistent, blower on and off as the plenum heats and cools
also, you can show the heat on a curve...
Totally agree with you. A wood stove/furnace that is burning at all efficiently is going to produce an output that is curved, not flat, nor stepped as a thermostat attempting to achieve a setpoint might wish. I have a Fireboard on my Kuuma and have years of daily operation curves that look approximately alike regardless of the temperatures and the burn rate setting on the control. About the only difference from "minimum" to "eleven!" setting happens in max temps and the shape of the end of the curve. The control can vary the length of the burn from 12 hours to 6 but isn't going to dictate the exact output at any given time. The Kuuma uses the thermostat to vary the blower speed somewhat, not the burn rate setting, making the thermostat in my house a bulltit. My previous furnace was even less controllable.

I have wanted what I think the OP desires and I think he might achieve a limited amount of success in the way he's going about it. It sure would be nice to have a furnace that could be loaded in the evening when say it's 12 degrees outside and have it ramp up its output at say 4am when the outside temp has fallen to maybe -30 degrees. That's going to take ramping up the air to increase the heat output at a point when the volatiles in the wood have been greatly reduced and the fire is naturally wanting to cool, not get hotter, so the amount of control is going to be limited.
 
It sure would be nice to have a furnace that could be loaded in the evening when say it's 12 degrees outside and have it ramp up its output at say 4am when the outside temp has fallen to maybe -30 degrees. That's going to take ramping up the air to increase the heat output at a point when the volatiles in the wood have been greatly reduced and the fire is naturally wanting to cool, not get hotter, so the amount of control is going to be limited.
Modern downdraft gasifying boilers are darn near capable of turning the fire on/off as needed...but the only forced air wood furnace I can find in that configuration is made overseas, and not readily available here...not sure they are as advanced as the boilers anyways...the brand name escapes me right now...I'll see if I can find it again...EDIT: its the "Angus Orligno 600 Hot Air Blower"
 
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Thank you all for the replies. I'm off to work in a few minute. Sat down with a cup of jo and found recent activity on this thread.
When I get home, I'll post some more about all of this.
Again, thank you.
 
I think if you were to pull up the instructions for the transformer you're using it would be pretty straightforward to see how to do what you want to do. You basically just have the 2 110v connections to power the transformer, 2 wires connected to your thermostat, and 2 24v wires out to the solenoid.

Having a manual draft control on a wood furnace is sketchy IMO. The limited convective airflow through the ducting makes things get stupid hot in a power failure situation.

I had a manual draft on my old furnace. I used a small, normally closed, duct damper as a deadman on that so it closed without power. The manual draft provided my low setting (and my nearly off setting if the power failed or high limit was reached). If I was doing what you are doing, I would add the solenoid to provide additional draft through another draft opening either pulling its air from behind the deadman damper, or with some provision to ensure it would also be closed in the event of power failure.

It would be a good idea to incorporate the high limit in the fan control so that the solenoid cannot have the draft open when the fan control has sensed over temperature. One option would be to have the 110v power going to the transformer run through the fan control high limit switch. That way reaching high limit creates a power failure for the transformer and shuts off the air until things cool down. With the setups I've had, reaching high limit is not routine. High limit is an indication of some major malfunction or the result of a power failure.

I don't understand what you say about the fan switch currently controlling the draft damper. That wouldn't make sense to me, except for what I mentioned above in closing the damper at high limit.

If you want to do more than just call for heat, like run the blower manually from the thermostat, it gets more complicated. More connections, but the transformers I'm familiar with have relays for the 110v blower as well.

My guess is that you're only going to want to add slightly more air when calling for heat. Since you can't turn wood on and off like gas, you want the thermostat to call for more heat in the wee hours when things are cooling off, but ideally never completely satisfy the temp setting so you're not creating a big fire then starving it for air suddenly and creating a bunch of crud. You're right, you probably should try to avoid that cycling if possible.
This furnace is dated 1978. It is the only source of heat. The oil furnace beside it has been removed from service. Only its blower is in use, triggered by the fan limit switch in the hot air plenum surrounding the wood furnace. This same switch, does not control the draft damper. Draft is controlled by me, manually. When I'm starting a fresh fire, or adding wood on a bed of coals, I open the draft door about halfway. After fire is established, I choke down the draft so it sits about a 1/4'' open. This is where I leave it, much like an old wood stove.

The draft control has been catabolized at some point in the furnace's life. I have a replacement solenoid from the manufacture. Since the oil furnace is retired, I'd like to use it's 24v transformer. Disconnecting the control wire, from the transformer to the burner. This wire I would use for the new draft control solenoid. The thermostat from the house has also been put to rest. Its wire to the oil furnace is also missing. I need to run new wire and buy a new thermostat. The wire will be connected to the 24v transformer in the oil furnace. In the event of a power outage, the solenoid will close the draft damper. I am looking to wire this correctly.

I am hoping, the draft control restored to it original functioning status, will help burn less wood. Opening only when the house calls for heat.
 
my home
was built in 1861 of hand squares Cedar logs not exactly air tight
The original part of my house is timber frame, built in 1860. A major sized addition, sits on a crawl space and was built in 1906. A kitchen for the migrant workers, was added in the '20s along with a mudroom. This kitchen sits on it's own separate crawlspace. I am heating this workhorse of a farmhouse with that wood furnace. It's rated for 200k BTU. Of course wood species and dryness plays a huge part in that.
 
Modern downdraft gasifying boilers are darn near capable of turning the fire on/off as needed...but the only forced air wood furnace I can find in that configuration is made overseas, and not readily available here...not sure they are as advanced as the boilers anyways...the brand name escapes me right now...I'll see if I can find it again...EDIT: its the "Angus Orligno 600 Hot Air Blower"
Are you at all familiar with Thermo-control? This furnace exhausts at the rear and 3-4'' off the bottom of the floor. This opening is into a chamber running vertically up the back wall with a bypass at the top. There is also heated air intake at the bottom, just above the exit opening. All natural draft but, when fed good fuel, burns pretty cleanly.
 
Are you at all familiar with Thermo-control? This furnace exhausts at the rear and 3-4'' off the bottom of the floor. This opening is into a chamber running vertically up the back wall with a bypass at the top. There is also heated air intake at the bottom, just above the exit opening. All natural draft but, when fed good fuel, burns pretty cleanly.
Not familiar, no...sounds like it was ahead of it's time.
 
Not familiar, no...sounds like it was ahead of it's time.
Yes indeed it was. There was one member here, some time ago, that had a thread on his. His was a woodstove version. I'm unsure if those models had the same "afterburner,'' although I think they do. I found the thread and read through it a couple years ago. Used Thermo-control in the search menu.
 
The original part of my house is timber frame, built in 1860. A major sized addition, sits on a crawl space and was built in 1906. A kitchen for the migrant workers, was added in the '20s along with a mudroom. This kitchen sits on it's own separate crawlspace. I am heating this workhorse of a farmhouse with that wood furnace. It's rated for 200k BTU. Of course wood species and dryness plays a huge part in that.
How many cords of wood do you burn in year ? 200k BTU's is a serious amount of heat, my house uses about 30 - 50k BTUs depending on the outside temperature and wind. Wind is the big killer for my house and I'd assume most houses. The firebox on it must be massive.

My G4000 ( 68K BTU over an eight hour burn period ) easily keeps up. Heatmasters biggest boiler doesn't even put out 200k ( close ) and it's meant to heat three / four decent size buildings.
 
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How many cords of wood do you burn in year ? 200k BTU's is a serious amount of heat, my house uses about 30 - 50k BTUs depending on the outside temperature and wind. Wind is the big killer for my house and I'd assume most houses. The firebox on it must be massive.
Our first year was about 12-14 cord. We moved in in November with very little wood on premises. That wood was extremely dry though.
I brought home truck loads of chunks and 3' long limb wood up to 6'' in dia. Buddy of mine's tree service waste wood. Soft maple and other garbage, along with uglies of hard woods ..... unsaleable.

Second year, I didn't use the furnace. I used my All Nighter Mid Moe sized stove. I left the doors open throughout the house with fans for circulation. I can no longer run the stove, but it allowed me to catch up on wood supply. I burned about 6=7 cord.

Our third winter was back using the furnace. I had gathered a bus load of 3' long ash rounds all spring. Truck load after truck load, after truck load. Also ended up with black cherry and locust along with some hard maple. I couldn't calculate how much I burned that season. I stacked it all on top of my wood pile. To dry as best as possible without splitting. It got all the West winds and sun all season.

This season I'm trying something different. I split everything to normal size splits, save some larger stuff spit a bit bigger. Even though the firebox is 24x24x almost 48''deep, I'm running it like a large wood stove. On a good bed of coals, I'll throw in 5 or so splits. For night time burn, I'll throw in a chunk or two. Overall, if I was to fill the firebox, it wood burn through at the same rate as with the smaller load. In the same time frame. Regardless, I have to get up once or twice a night depending on outside temps. At least now, I'm consuming less wood.

I'm looking to get a log truck load in soon. I have 7-8 cord split now. Hard to tell for it's in piles. I'll be renting the splitter for the log truck load if I get it. Luckily, it'll be mostly Ash. I'm also throwing together a half cord kiln near the furnace. A vertical one that will be using a run off the duct work. Instead of capping off the legs of cloth stuffed closed runs, from previous HO and his remodeling, I'll reduce one to 4 inches and enter it into the bottom. Kiln will have some vent holes at the top to flow air. Just a little experiment to help get some extremely low MC wood. This furnace behaves the best on it.
 
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Yes this house is drafty. Even though most rooms have new sheetrock and insulation, it has all it's original windows. I have no desire to get replacement windows. Especially with some 33 or so windows. I will be reglazing them all and tightening them up, storms included. I'm also making interior storms from clear 4 mil vinyl on 1x2'' wooden frames. Double sided plastic with weather stripping on the edges. Much easier to pop em in and out as opposed to conventional plastic methods of winterizing. Much more efficient too.

So much to do with this ole farmstead ......