Where does the heat go?

[karri0n]

Many stove have rear heat shields to reduce the Clearance to combustibles. These stoves also often have a blower available that moves the air between the heat shield and the stove into the room. However, if you don't have a blower attachment, where is the heat going? I can put my hand on the rear heat shield of the stove when the stove is running at 600. Is this hot air simply going back into the stove through the OAK port? (when an OAK is not connected)


My stove sits in an old masonry fireplace, so CTC is not an issue. Without the blower, I'm considering removing the heat shield to either get some more heat into the room or to radiate more heat into the masonry thermal mass behind the stove.


Any Isle Royale owners run their stove without the rear heat shield?

 

[BrowningBAR]

Many stove have rear heat shields to reduce the Clearance to combustibles. These stoves also often have a blower available that moves the air between the heat shield and the stove into the room. However, if you don't have a blower attachment, where is the heat going? I can put my hand on the rear heat shield of the stove when the stove is running at 600. Is this hot air simply going back into the stove through the OAK port? (when an OAK is not connected)


My stove sits in an old masonry fireplace, so CTC is not an issue. Without the blower, I'm considering removing the heat shield to either get some more heat into the room or to radiate more heat into the masonry thermal mass behind the stove.


Any Isle Royale owners run their stove without the rear heat shield?

I have a heat shield on the Intrepid and I am amazed how cool the shield is when touched. Either Bart or BeGreen mentioned the heat is deflected upwards.

 

[karri0n]

Simple physics shows that there is no way the extra heat is going "nowhere", I'm just at a loss for where it could be going.

"Upward" is certainly not where I want it going. My blockoff plate is less than optimally sealed or insulated(probably a home job my landlord did himself). The blower for this stove is a pretty penny.

 

[begreen]

That should help. Heat can get trapped into the damper chamber above the stove and dissipate into the masonry. This is especially true with exterior chimneys which suck out heat like a sponge. Try lowering the block off plate to the lintel level. Seal and insulate it well. A blower would also make a world of difference for this type of installation.

With wet wood, the performance must be pretty dismal, but take heart, there's a lot of room for dramatic improvement by addressing these issues.

 

[karri0n]

Actually, that's an old signature. I have good wood right now. I'm lucky that this is a central chimney rather than an exterior, so heat going into the masonry (BELOW the blockoff plate) isn't necessarily a bad thing. My bricks stay warm for several hours after the stove is calmed down, and this puts some heat back into the room. I just may try lowering the blockoff plate, though. That sounds like a pretty good idea.

 

[Adios Pantalones]

My guess- the air between stove and shield heats up and rises. More cool air is drawn in from below. The shield is continuously cooled by natural air convection/rising- it's a little chimney.

I've made a bunch of shields from flashing for wooden beams under my kiln shed- the beams are not really even warm after a 40 hour firing.

 

[Jags]

The air rises my man.

 

[Adios Pantalones]

You're not as dumb as I look

 

[Jags]

You're not as dumb as I look

WHEW! Thats a relief.

 

[JonOfSunderland]

Simply put, stove heatshields ONLY reflect radiation back to the stove. The more detailed explanation is:

There are three types of heat transfer: conduction, convection, and radiation.

Conduction is the transfer of heat through a material. Heat conducts from one side of 1/4" thick steel to the other. Some materials conduct heat faster than others. This is why baseboard CONVECTORS (they're not really radiators) are finned with aluminum and not soapstone)
Convection is the transfer of heat from the surface of a material via a fluid (air/water). Air blowing over a surface convects heat away from it. Hot air rises. Therefore, hot surfaces will generate what is know as natural convection when the air next to them heats up and rises away, pulling in cooler air, and the cycle repeats.
Radiation is straight transfer of heat from one object to another via electromagnetic waves without the assistance of a convecting fluid. Radiation is the instant heat you feel when you step out from shade into the sun. It is also the blast you feel when you open the fire door of your stove. Dark objects emit radiation better than light colored objects.

Stove heatshields reflect radiation back to the stove. They prevent that radiation from ever reaching an adjacent wall/object. They remain cool because they are designed to be mounted with a space between them and the stove where natural convection takes place. Hot air in the space rises away and pulls in cooler air. Usually they are painted black, which is actually a bad idea because black objects soak up radiation worse than light colored objects. Ideally, stove heatshields would be white or bear metal. Same idea with automotive exhaust manifolds and exhaust systems with the thin heat shields above/around them. Same idea with double wall stove pipe.

 

[BrotherBart]

The heat rises and pulls convection air through the heat shield and it goes out the top. I have the side heat shields on my 30-NC in the fireplace and when the stove is cranking you can hold a BIC lighter over the top opening of the shield and the air coming out will blow out the flame.