Hearthstone Mansfield 8013 - Auto temperature control

[5U4]

A neighbor has an old Vermont Castings with a control system, very simple, a bi-metallic spring controlling a flapper that regulates the amount of air that enters the stove. The spring monitors the temperature of the casting at the back of the stove.

A system to automatically control the burn rate and limit the maximum stovetop temperature would be a nice addition to the Mansfield. The question is how to implement such a system as far as where physically to sense the temperature and how to actually control it?

Where to start, any thoughts?

 

[Todd]

I would rather have a Blaze King thermostat on my stove.

 

[stoveliker]

But I think that is more or less the same?

I'd put it near the flue exit.

 

[5U4]

Sensing on the casting at the flue exit seems right, the question is how to control burn rate with a low force bi-metallic spring? The blaze king nicely integrated the control at the flue exit and the spring attached to the control plate; this is ideal requiring very little force to rotate the plate. The Vermont casting mounted the spring on the back casting with a chain going down to operate a small plate covering the air inlet; this system also requires very little force to operate. On the Mansfield there is no convenient location to put a plate to control the inlet air flow.

Looking at the air inlet location on the Mansfield it may be possible to add an inlet air control plate however would require the installation of the outside air kit, the kit would have to be modified to incorporate the control plate.

One concern is how the air control system works on this stove. There are two air paths, one to the primary air and one to the secondary that may or may not both be controlled by the control lever. When observing the operation it appears the control lever only adjusts the air flow to the primary air, and the secondary air flow rate is fixed. I can't prove this but suspect it. If this is true, and the fact that both air paths have a common inlet at the bottom of the stove, adding the outside air kit with a plate to control the air flow would interfere with the intended operation and causing the burn process to degrade.

Any thoughts or information on exactly how the air circuits are controlled in the Mansfield?

 

[stoveliker]

Secondary air often is not controlled. It is regulated by the strength of the draft in the flue, which increases when it gets warmer (hotter fire).

I am not sure a thermostatic controlled primary air makes a lot of sense when there is uncontrollable secondary air.

I think decreasing primary air can actually increase heat output (at least in some range). A thermostat wouldn't work well then.

 

[John Lehet]

I think decreasing primary air can actually increase heat output (at least in some range). A thermostat wouldn't work well then.

That was definitely the case with my old Jotul 3 CB. If it was cold and the draft was strong, the hottest fire was just off of fully shut down. Definitely non linear.

 

[stoveliker]

Yes. Even worse, the sign of the result (more or less heat) changes with the cutting of the air in some range.

 

[Highbeam]

I’ve read the Amish like to use wood furnaces but without electricity so they attach an off the shelf thermostat contraption to open and close the air intake that uses a bimetallic coil. The device exists.

Controlling the primary air only with a thermostat is just like adjusting the intake control manually so you have the same level of control as normal. A valve over the OAK is a very reasonable place to begin experimenting with this concept.

 

[stoveliker]

Except that it will act opposite to what you may want; the stove getting hotter, it decreasing the primary air, leading (due to secondary air system) to an even hotter stove .. and this at the range where the primary air is almost closed.

It will act the other way when the air is almost open, I think.

Due to this, I think a coil thermostat is unsuitable for a stove that (also) has secondary air.

 

[begreen]

A neighbor has an old Vermont Castings with a control system, very simple, a bi-metallic spring controlling a flapper that regulates the amount of air that enters the stove. The spring monitors the temperature of the casting at the back of the stove.

A system to automatically control the burn rate and limit the maximum stovetop temperature would be a nice addition to the Mansfield. The question is how to implement such a system as far as where physically to sense the temperature and how to actually control it?

Where to start, any thoughts?

VC stoves have always had thermostatic air control. Some of the older Hearthstone's had thermostatic regulation too. It probably would be possible to rig up something on the outside air control. For some stoves, a servo driven thermostatic control has been employed. There was a cool thread on this several years ago.

Thread 'Wood stove automation using the Raspberry Pi'

Jan 2, 2018

Happy New Year!

It has been a couple of years since I started working on my wood stove automation project. Its based on Python and currently runs on a Raspberry Pi3 Model B. I got quite far but until now I never documented any part of what I did. Took me about a week to take pictures and write up just the first phase. I don't think Ill ever be done so I'll just post this before I get lost in trying to make the doc perfect. Yes, it needs more pictures that I should be able to add soon. Feel free to use any part of this project for your own builds. I have learned a lot about...

• MisterFixIT
• automation raspberry pi
• Replies: 55
• Forum: The Hearth Room - Wood Stoves and Fireplaces

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