Honeywell short cycle on Super Jack

[Sulakd]

I moved into a house that has a Super Jack connected to a propane furnace. I set the Super Jack thermostat higher than the propane furnace to use the wood burner. But the wood burner turns on the fan for only about 30 seconds at a time. I took the cover off the honeywell limit switch and set the "on" to about 200 and the "off" at 100. That switch still rotates so fast that when the fan kicks on, the heating cycle lasts for only 30 seconds. That means it kicks on every few minutes. Is that normal?
Thanks!

 

[begreen]

Is 200º a high limit to cut off air or is that the fan on temp? If it is the latter, that is way too high. The fan on setting should be more like 130º.

 

[brenndatomu]

200 is too high...130 is low though...150 to 170 is more common on those old school furnaces.
Do you know what speed the blower is wired to? I would probably use low...that will give you the most run time. The wire colors should be on the blower motor, or in the owners manual...if you don't have it, one can be downloaded from Yukon's website. Cycling can be an issue on wood furnaces sometimes...you could always call Yukon too...

 

[brenndatomu]

You could install a filter with a higher MERV # on it too...that would limit the air flow a bit...slow the cycling down some...

 

[Sulakd]

Is 200º a high limit to cut off air or is that the fan on temp? If it is the latter, that is way too high. The fan on setting should be more like 130º.

200 is the fan on setting now. I set it higher just trying to get as much range as possible between the on and off temps. When it was set lower, the fan-on cycle was about 10 seconds. Not really enough to even push heat all the way through the ducts.

 

[Sulakd]

200 is too high...130 is low though...150 to 170 is more common on those old school furnaces.
Do you know what speed the blower is wired to? I would probably use low...that will give you the most run time. The wire colors should be on the blower motor, or in the owners manual...if you don't have it, one can be downloaded from Yukon's website. Cycling can be an issue on wood furnaces sometimes...you could always call Yukon too...

What's the disadvantage with having it kick on at a high temp? I'll see if I can get the blower to a lower speed somehow. That makes sense, thanks. There's a second fan in front that's always running too. I might take it off. I think it pushes air into the firebox, but the box already has a spinner on the front to let air in.

 

[Sulakd]

I also noticed that the carpet and walls by the ducts all have black soot. I assume it's from smoke from the wood burner. Is that normal, or does it mean there's a leak somewhere that shouldn't be there? I've had natural gas, propane, fuel oil, and geothermal. This is my first wood-burning furnace. I've called furnace companies, but no one has been familiar with a wood-burner add-on setup like this.

 

[begreen]

What's the disadvantage with having it kick on at a high temp? I'll see if I can get the blower to a lower speed somehow. That makes sense, thanks. There's a second fan in front that's always running too. I might take it off. I think it pushes air into the firebox, but the box already has a spinner on the front to let air in.

brenndatomu is correct. 130º is a bit low. I had to dust off some old manuals to check. Supply clearances from combustibles are determined on a design temperature range. 200º is too high The normal operating temperature for the supply when the blower speed is set correctly is about 80-90º over return temp or 150-160º for 70º return air temp.

The soot issue is unknown, is the wood furnace return air being pulled from the basement? Has the heat exchanger been inspected for any signs of decay? If it is in good condition and the return air is sealed and being pulled from the main central furnace return, then it could be the previous owner had some smokey startups and refills.

 

[brenndatomu]

What's the disadvantage with having it kick on at a high temp? I'll see if I can get the blower to a lower speed somehow. That makes sense, thanks. There's a second fan in front that's always running too. I might take it off. I think it pushes air into the firebox, but the box already has a spinner on the front to let air in.

As was already mentioned...clearance to combustibles was calculated with running lower temps...wood pyrolosis can start at 180*. Plus you are losing efficiency...cooler air running across the heat exchanger will pick up more heat from the exhaust gasses than hotter air does...and the biggest issue is it will run the duct blower much less at that high temp...so much less heat to the house.
The forced air blower (combustion fan) doesn't have to be run...or you can just use it to build the fire right after you load, then shut it off...just use the swinging flapper to control the burn rate. I had a Big Jack (same as SJ, just without the extra secondary heat exchanger) some years back, and I learned to hate that combustion blower! Using it is very inefficient, can blast through a load of wood in 2 hours if left on!
That spinner on the door is secondary air...the air going in through the combustion fan is your primary air, and that is what should be used to control the burn rate more so.
I had some tricks I learned about running the Jack line furnaces...can't remember them now, its been while since I had it! I will have to look it up...I believe I posted it here somewhere once or twice...

 

[brenndatomu]

I also noticed that the carpet and walls by the ducts all have black soot. I assume it's from smoke from the wood burner. Is that normal, or does it mean there's a leak somewhere that shouldn't be there? I've had natural gas, propane, fuel oil, and geothermal. This is my first wood-burning furnace. I've called furnace companies, but no one has been familiar with a wood-burner add-on setup like this.

There could be a leak...the furnace and stove pipe need to be inspected to be sure its OK. Make sure the secondary heat exchanger cleanout door is installed correctly too.
It could be all from a smoky start up though.
If you can find a local stove shop that sells wood or coal furnaces, they should be willing to look at it...there are very few Yukon dealers in the states...and Yukon can't sell new units here anymore because that haven't passed the EPA's latest emissions requirements.

 

[brenndatomu]

Here is one place where I described the mods that I did to my BJ that helped clean up the burn and make it run more efficiently too...

I started a chimney fire

I had been keeping an eye on my chimney and knew it was time to clean it. My furnace will smolder when it gets to the temperature that it is set to so I have to clean it often. I was waiting for a day when I had some time and was not too cold. It was 27 this morning but would be in the 50s in...

www.hearth.com

 

[Sulakd]

Here is one place where I described the mods that I did to my BJ that helped clean up the burn and make it run more efficiently too...

I started a chimney fire

I had been keeping an eye on my chimney and knew it was time to clean it. My furnace will smolder when it gets to the temperature that it is set to so I have to clean it often. I was waiting for a day when I had some time and was not too cold. It was 27 this morning but would be in the 50s in...

www.hearth.com

Thanks for all the info above. I'll check out your link. I'll probably run it for the winter and see if the soot reappears on the walls and carpet. I haven't opened that panel yet for the heat exchanger. I'll have to read up because I don't know anything about these furnaces. Since the Honeywell limit switch controls the fan, I don't know why it even has a wall thermostat.

 

[brenndatomu]

Since the Honeywell limit switch controls the fan, I don't know why it even has a wall thermostat.

The tstat controls when the "magic" combustion blower runs...I say "magic" because when it runs, your wood disappears!
Its supposed to build the fire hot to satisfy the tstat sooner...but like I said earlier...I didn't let it run except when building the fire after loading...I wired in a switch so I could kick it on while I was standing there...