Safety Heat Dumps On Wood furnaces

[laynes69]

I see that there are only a couple manufacturers out there that make these. I know its a simple concept, but effective? I'm interested in hearing about how they work, for my wood furnace can and will produce high heat quickly. This is something that if will work I would be interested in. I have the option on my wood furnace to add an electric backup, or an oil or gas backup so I have a door that can be removed at the base of the unit. I would remove this to help gravity feed the home in case of a power outage, but like said I am interested in the plenum heat dumps and how effective they are. With my old wood furnace I had a few scares, due to me not being able to open anything on the furnace. This would be some insurance if we weren't home. The new one will be setup differently.

 

[CrappieKeith]

Typically in our furnaces we have a fan & limit switch which operates the blower. The fan side of the switch cycles the blower as the heat builds to 150 degrees and off at 125 degrees. If it ever got too hot(250 degrees) then the fan would be told to blow non stop and the limit side of the switch kills the power to whatever is making the heat.

A heat dump uses a fuse-able link(lead) to hold the spring loaded door shut.
If it gets to 265 degrees ,the lead melts and the spring pulls open a large flap to let the heat escape into the room.
The heat dump is mounted in the hot air plenum.
If your ducting does not make a downward turn you'll be able to use gravity heat assuming all of your ducting is made of metal which is what the heating code calls for with the correct clearances within 6 feet from your furnace.
After your hot air run makes a 90 degree turn ,your clearances disappear.

A heat dump really only needs to be installed if you have downward turns in your ducting.

 

[laynes69]

Theres a limit control on the furnace, and when the high is reached, the servo will close the draft door and the blower will continue to run. The ductwork is all sheetmetal due to there being a woodfurnace on there prior. Plus I tore out and reducted the whole home. My main run is 16 feet long before it goes into a 90 then from there a few more feet then into the second story into the attic. All clearances are to be followed according to the furnaces spec. I thought the heat dump would help in case of an outage, but like said I can remove the panel down below the firebox and set it up as gravity. Once installed and knowing how it operates, I may consider a heat dump. Also the rear of the furnace has an access door just like any gas furnace, which can be removed and the filters be removed to assist in gravity feed. I couldn't get gravity heat in the old furnace without removing 10000 screws. Plus it was setup in series. Worked fine, but had to watch it during an outage.