I have a conventional wood boiler, older Logwood boiler that works great except for sometimes the flue temp races out of control (over 1000F deg) and I fear a chimney fire. This is expecially true when the boiler water jacket is cold and im just firing it up say in the morning. It takes the bi-metal draft door controller too long to start moving to keep the flue temp in a safe range.
So after seeing what another member did with his wood furnace controller I decided to do a similiar thing. Rob H on this site was willing to help and provided me the assistance and guidence to make it work.
The draft control on my boiler is a mechanical bi-metal device and works off of the water jacket temperature and controls a draft door on the bottom of the wood boiler. What I did was add a electronic temperature monitor/controller and a motorize draft door controller. The electronic temp unit has a sensor in the flue pipe.
Normally the chain goes directly from the bi-metal control arm to the draft door and as the water temp in the boiler jacket changes it pulles the door up and down.
Now I took and routed that chain through a pully that is connected to an arm that is connected to the motorized draft controler. see pic:
This is the PID controller (electronic temp monitor/controller) The top number is the current temp of the flue, the second lower number is the temperature that the motor will move to the fully closed position.
So as the temperature of the flue stack increases beyond what is a SAFE temp (It starts moving at 550F deg) the controller sends a signal to the motor and tells it to start closing, as it closes it moves the arm toward the left closer to the boiler. as it does it takes out the slack of the chain and lowers the door. As the temp gests back to/under 550 the motor will open back up.
In this last picture the temperature was high and the motor moved to the close position taking the slack out of the chain and closing the door lowering the flue stack temp. As it got back under 550d it opened it back up allowing the bi-metal controller to open and close the door as it normally would
So when the motor is in the OPEN position (top picture) the bi-metal controller regulates the temp of the boiler by the temp of the water jacket, the normal operation.
IF the bi-metal controller lets the flue temp get too high, then the electronic controller kicks in and moves teh arm to take the slack out of the chain. Between the two the boiler runs in a safe stack temp, usually 500ish. Now I dont have to baby sit the boiler in the morning before leaving for work and I dont have to worry if the kids add wood as this device will keep the flue temp safe.
Again many thanks to Rob H.
~ Phil
So after seeing what another member did with his wood furnace controller I decided to do a similiar thing. Rob H on this site was willing to help and provided me the assistance and guidence to make it work.
The draft control on my boiler is a mechanical bi-metal device and works off of the water jacket temperature and controls a draft door on the bottom of the wood boiler. What I did was add a electronic temperature monitor/controller and a motorize draft door controller. The electronic temp unit has a sensor in the flue pipe.
Normally the chain goes directly from the bi-metal control arm to the draft door and as the water temp in the boiler jacket changes it pulles the door up and down.
Now I took and routed that chain through a pully that is connected to an arm that is connected to the motorized draft controler. see pic:
This is the PID controller (electronic temp monitor/controller) The top number is the current temp of the flue, the second lower number is the temperature that the motor will move to the fully closed position.
So as the temperature of the flue stack increases beyond what is a SAFE temp (It starts moving at 550F deg) the controller sends a signal to the motor and tells it to start closing, as it closes it moves the arm toward the left closer to the boiler. as it does it takes out the slack of the chain and lowers the door. As the temp gests back to/under 550 the motor will open back up.
In this last picture the temperature was high and the motor moved to the close position taking the slack out of the chain and closing the door lowering the flue stack temp. As it got back under 550d it opened it back up allowing the bi-metal controller to open and close the door as it normally would
So when the motor is in the OPEN position (top picture) the bi-metal controller regulates the temp of the boiler by the temp of the water jacket, the normal operation.
IF the bi-metal controller lets the flue temp get too high, then the electronic controller kicks in and moves teh arm to take the slack out of the chain. Between the two the boiler runs in a safe stack temp, usually 500ish. Now I dont have to baby sit the boiler in the morning before leaving for work and I dont have to worry if the kids add wood as this device will keep the flue temp safe.
Again many thanks to Rob H.
~ Phil