IS vs 30-NCH Help Needed

[windthrown]

So sounds like wood stoves followed along with cat usage around the same time as cars.

Yes, same time, same technology. Platinum coating to convert bad stuff into harmless stuff in the air.

Sad to say the concept is lost on me as well. Wouldn't the heated air passing out of the firebox actually have more energy since it's hotter? Always thought heat to be a form of energy.

Heat is a form of energy, or entropy (unusable energy), as it becomes in this case. The reason that using stove heated air to feed your firebox is less efficient is because of the energy lost to heat the inside air with the stove to begin with. Its better to heat cold air once in the firebox and extract and radiate that heat into your house. One cycle, where the energy from burning the wood is reduced by the efficiency of the stove one time. If you use stove heated air to feed the firebox, you are using energy (house heat) that has been reduced by the stove's efficiency losses once, and then reducing the results again by the same efficiency. In other words, you cycle the heat twice through your stove by not using an OAK and lose heat to the stove's efficiency losses. The end result is more heat going up the flue w/o an OAK. Here in this area at least most stove dealers understand this concept and preach it when selling stoves.

This is my ignorant newbie wood burner thought process on a OAK. I think it's almost like the reason for a fan on an insert. At least with my particular insert, the fan has nothing to do with actually blowing out heated air. It's just there to circulate hopefully cooler air around the insert to cool off the stove. Ideally most of the heat will get the hell out of the stove through the ceramic front. The fan helps keep the stoves outer perimeter cooler so it can absorb more heat which will then get the hell through glass front. Soooo, an OAK is sending in really cold air from outside vs semi-cooled inside air.

Well after typing all that I realized I'm making no sense. I don't feel like deleting it though lol. Back to spreadsheets I go.

More than noobs debate this topic, and it has been raging for many many years on many a wood forum on the web. Actually the fans in inserts do circulate the hot air into the house. If you are cooling the firebox around an insert, the heat energy is being driven someplace else. The reason for a fan in an insert is not to cool the fireplace so it can absorb more heat, the reason is to distribute the heat into the house by forced air convection, wherever the fan is ducted to.

There are three forms of heat transfer: radiation, convection, and conduction. Heat conduction is heat moving through something solid like metal, heat one end and the other gets hot. That is how a steel stove transfers heat to the outside of the firebox from the inside. Once on the outside, the energy is radiated away from the steel. Radiation energy flows in all directions, and does not need a medium to carry it. It is low level electromagnetic energy and will travel through space. It will also travel through air, and that is what you feel when you put your hands in front of a fire. Finally there is heat convection. Convection is what drives the stove in the first place. Cold air enters the firebox, and once heated, the hot air rises up the flue. This is because hot air is less dense than cold air. It is called natural convection because there is no fan or other force driving the air. Add a fan and you have forced convection. You are moving air over a hot surface and extracting heat energy from the stove surface into the air, and moving it around the house. This results in ambient heat in the house. W/o a fan, wood stoves radiate heat and there is some natural convection around the surface of the stove, but it is small. Add a fan and you greatly increase the convection heating of the stove, and greatly increase its efficiency to heat your home.

Clear as mud?

 

[Ambull01]

Heat is a form of energy, or entropy (unusable energy), as it becomes in this case. The reason that using stove heated air to feed your firebox is less efficient is because of the energy lost to heat the inside air with the stove to begin with. Its better to heat cold air once in the firebox and extract and radiate that heat into your house. One cycle, where the energy from burning the wood is reduced by the efficiency of the stove one time. If you use stove heated air to feed the firebox, you are using energy (house heat) that has been reduced by the stove's efficiency losses once, and then reducing the results again by the same efficiency. In other words, you cycle the heat twice through your stove by not using an OAK and lose heat to the stove's efficiency losses. The end result is more heat going up the flue w/o an OAK. Here in this area at least most stove dealers understand this concept and preach it when selling stoves.

I don't get this whole paragraph lol. Damn I feel dumb right now

I would think you would WANT to re-heat the same air in your house since it will be warmer than the air outside. So less heat from the firebox would be needed to re-heat said air which would equate to a warmer house. I need to visit the library and read about this stuff. Spend too much time reading classic novels and articles about economics.

More than noobs debate this topic, and it has been raging for many many years on many a wood forum on the web. Actually the fans in inserts do circulate the hot air into the house. If you are cooling the firebox around an insert, the heat energy is being driven someplace else. The reason for a fan in an insert is not to cool the fireplace so it can absorb more heat, the reason is to distribute the heat into the house by forced air convection, wherever the fan is ducted to.

There are three forms of heat transfer: radiation, convection, and conduction. Heat conduction is heat moving through something solid like metal, heat one end and the other gets hot. That is how a steel stove transfers heat to the outside of the firebox from the inside. Once on the outside, the energy is radiated away from the steel. Radiation energy flows in all directions, and does not need a medium to carry it. It is low level electromagnetic energy and will travel through space. It will also travel through air, and that is what you feel when you put your hands in front of a fire. Finally there is heat convection. Convection is what drives the stove in the first place. Cold air enters the firebox, and once heated, the hot air rises up the flue. This is because hot air is less dense than cold air. It is called natural convection because there is no fan or other force driving the air. Add a fan and you have forced convection. You are moving air over a hot surface and extracting heat energy from the stove surface into the air, and moving it around the house. This results in ambient heat in the house. W/o a fan, wood stoves radiate heat and there is some natural convection around the surface of the stove, but it is small. Add a fan and you greatly increase the convection heating of the stove, and greatly increase its efficiency to heat your home.

Clear as mud?

How the hell do you know all this?

On another note, you know anything about those heat powered fans? I mentioned somewhere on this site about my plan to cut out the transoms above my doorways in several rooms downstairs. I would like to stick in a box fan sized air mover into the open transom with possibly a decorative grate of some sort to fill out the extra space. I know they make those little fans that you attach to the side of doorways but I want MORE air than that. I would also prefer something that will operate without the need for electricity and be really quiet. Any thoughts?

 

[windthrown]

This stuff is not simple, and I have 2 college/university degrees in engineering. We had to take lots of survey course in thermodynamics, heat transfer, statics, dynamics, physics, chemistry, math, more math and then even more math, electronics, computer design, etc. etc. I was also an engineer for about 20 years. Still am, technically as I do consulting work now and then. I am mostly retired from engineering though, and I delve in arbor and chainsaw stuff for fun and profit, as well as firewood, property and timber management here. I also did a lot of energy installation stuff when I was in college: solar heating, insulation, house wiring, etc. for a contractor I used to be roommates with. I have also designed several heating systems using boilers, wood stoves, inserts, and masonry over the years in the houses I have owned and rented.

Fans require energy to move air around. I am not really an HVAC guy, that is another type of engineering. If you want something from nothing you are not going to get it. Well, except for natural convection. That is free. In order for that to work you need a second story house and the warm air will raise naturally. But in a single story house the air is not going to move laterally without some help. For heat powered fans to be effective they need a lot of heat energy, like on a wood stove top. I use an electric box fan at the side of my wood stove in the living room of my house, and that is enough to move the air around and heat the entire 1300 sq ft house. I leave all the doors open here though. If I wanted to close the doors here and circulate the heat, I could add a downdraft duct to the furnace ducting in the house and add a blower of some type, which the previous owners here tried and failed at with the old stove. I could also add fans at the top of the doorway but they would need to be battery operated, or hardwired or plugged in. Quiet fans are not so common. Vent type bathroom fans are always noisy. My kitchen stove downdraft fan is noisy. My 30NC fan is really noisy. The box fan is pretty quiet, and effective in my case here.

 

[Erik B]

Some on this site have mentioned OAK. What is it?

 

[TheLazyBFarm]

Outdoor Air Kit. It's basically a tube that allows the stove air to come from outside the living area/home. Most stoves have the capability to add it now since some areas (e.g. WA) require it, or a gov't agency requires it (HUD) or it's required in a mobile home by the manufacturer (e.g. Englander, although that may be due to some gov't requirement also, don't know).

 

[Erik B]

@TheLazyBFarm Thanks for the explanation. Good to learn something new every day.

 

[zogger]

Some on this site have mentioned OAK. What is it?

Outside air kit. Plumbed air from outside someplace direct to the heater.

 

[Oldman47]

The heat driven fan is easy. A thermocouple creates a voltage by the 2 metals involved having different potentials. Most often it is used to drive an instrument, a thermometer. If you create a larger junction than a typical thermocouple you have the ability to have enough current to actually drive a small motor. That is what they are doing. Some of the heat from the stove is converted to electrical energy and it drives the fan.
Something to understand about radiant heat vs convection: Radiant heat is a very poor way to transfer energy because it relies on EM radiation to make it happen. Without an enormous temperature difference between the radiating object and the heated object, you just can't detect it happening. Worse yet, it only heats objects. The air around those objects stays cool. Convection directly heats the air in the room as it passes by so it is far more effective in a heating situation than trying to warm each item in a room and hoping the air warms a bit. The reason a shielded stove works better to heat a house compared to a naked stove is that convection air currents are set up inside that shielding and can carry the heat around the house. The radiant heat of an unshielded stove feels great when you are standing next to it but it really does not heat the air much because it is dominated by the radiant heating mode.

 

[betterbuilt]

Sorry to the OP if this is getting side tracked.

Lots of good info. I'm still trying to grasp why a shielded stove can heat better then an unshielded stove. To understand that I'd have to know the difference between the 2. I'm thinking a shielded stove is a mass heater of some sort. If that's it then it's starting to make sense. That would explain why my friends rocket stove seems to heat his house so well.

I'm still also wondering about the OAK. I've never seen this or even heard of it. It does make some sense. Any pictures or drawing?

Windthrown: You said earlier that some designs of Masonry heaters work and others don't. Could you point me in the direction where I would find the difference between the two.

 

[Oldman47]

What I called a shielded stove is one designed to run close to combustibles. It often has a metal shield on it an inch or two from the firebox that allows room air to keep the outside cooler. That gap becomes a convection passage and heats room air directly while keeping the outer surface cooler. End result is warm air flowing into your room from the top of the shield area. Because the air flow is guided by the shield it is more effective moving the heated air than a simple exposed hot surface.

 

[betterbuilt]

That makes sense. Thanks

 

[Ambull01]

This is where I learned about OAKs: http://woodheat.org/outdoor-air-supplies.html

 

[Ambull01]

That site seems to loathe OAKs though lol. If it's easy to install/hook up I may try one and compare it to a non-OAK setup.

 

[betterbuilt]

That site seems to loathe OAKs though lol. If it's easy to install/hook up I may try one and compare it to a non-OAK setup.

I see there is a lot of debate on the subject. I'm not seeing any concrete evidence one way or another. I would say each individual installation would have it's own results. So many variables.

 

[Ambull01]

This stuff is not simple, and I have 2 college/university degrees in engineering. We had to take lots of survey course in thermodynamics, heat transfer, statics, dynamics, physics, chemistry, math, more math and then even more math, electronics, computer design, etc. etc. I was also an engineer for about 20 years. Still am, technically as I do consulting work now and then. I am mostly retired from engineering though, and I delve in arbor and chainsaw stuff for fun and profit, as well as firewood, property and timber management here. I also did a lot of energy installation stuff when I was in college: solar heating, insulation, house wiring, etc. for a contractor I used to be roommates with. I have also designed several heating systems using boilers, wood stoves, inserts, and masonry over the years in the houses I have owned and rented.

Fans require energy to move air around. I am not really an HVAC guy, that is another type of engineering. If you want something from nothing you are not going to get it. Well, except for natural convection. That is free. In order for that to work you need a second story house and the warm air will raise naturally. But in a single story house the air is not going to move laterally without some help. For heat powered fans to be effective they need a lot of heat energy, like on a wood stove top. I use an electric box fan at the side of my wood stove in the living room of my house, and that is enough to move the air around and heat the entire 1300 sq ft house. I leave all the doors open here though. If I wanted to close the doors here and circulate the heat, I could add a downdraft duct to the furnace ducting in the house and add a blower of some type, which the previous owners here tried and failed at with the old stove. I could also add fans at the top of the doorway but they would need to be battery operated, or hardwired or plugged in. Quiet fans are not so common. Vent type bathroom fans are always noisy. My kitchen stove downdraft fan is noisy. My 30NC fan is really noisy. The box fan is pretty quiet, and effective in my case here.

Yeah getting heat up to my second story isn't an issue. My issue is getting the heat from my stove room which is in an outer wing of the house pass the hallway/entrance way to another room across from the stove room and through that room to dining room/kitchen.

I've seen the wood stove heat powered fans. Those look pretty cool. I just saw a hand heat powered fan yesterday but I can't seem to find it again. I'm guessing the heat powered transom fan is a non option. I was hoping to power the transom fan from the naturally rising heat kicked off from the wood stove. I figure there's a bunch of heat just sitting up at ceiling level that's virtually wasted so I hoped that would be enough to get some fan blades moving and push the heat pass the entrance hallway and through the other transom. Hope that makes sense because I kind of confused myself writing that.

The heat driven fan is easy. A thermocouple creates a voltage by the 2 metals involved having different potentials. Most often it is used to drive an instrument, a thermometer. If you create a larger junction than a typical thermocouple you have the ability to have enough current to actually drive a small motor. That is what they are doing. Some of the heat from the stove is converted to electrical energy and it drives the fan.
Something to understand about radiant heat vs convection: Radiant heat is a very poor way to transfer energy because it relies on EM radiation to make it happen. Without an enormous temperature difference between the radiating object and the heated object, you just can't detect it happening. Worse yet, it only heats objects. The air around those objects stays cool. Convection directly heats the air in the room as it passes by so it is far more effective in a heating situation than trying to warm each item in a room and hoping the air warms a bit. The reason a shielded stove works better to heat a house compared to a naked stove is that convection air currents are set up inside that shielding and can carry the heat around the house. The radiant heat of an unshielded stove feels great when you are standing next to it but it really does not heat the air much because it is dominated by the radiant heating mode.

Your first paragraph totally lost me.

So wait a minute, you're saying splurging for the optional stove heat shields will result in greater heat efficiency? How does a simple heat shield set up "convection air currents" and "carry the heat around the house"? Doesn't the heated air have to rise first then make it's way around the house?

Edit: Wait, I think I figured out what you're saying. The heat shield sets up the convection current because it almost funnels the heat up instead of the heat slowly rising. Faster heat rise results in a faster air current. Is that right or am I totally off base?

Sorry to the OP if this is getting side tracked.

Lots of good info. I'm still trying to grasp why a shielded stove can heat better then an unshielded stove. To understand that I'd have to know the difference between the 2. I'm thinking a shielded stove is a mass heater of some sort. If that's it then it's starting to make sense. That would explain why my friends rocket stove seems to heat his house so well.

I'm still also wondering about the OAK. I've never seen this or even heard of it. It does make some sense. Any pictures or drawing?

Windthrown: You said earlier that some designs of Masonry heaters work and others don't. Could you point me in the direction where I would find the difference between the two.

This is the second time I've heard about a rocket stove. I'm going to look it up now lol.

What I called a shielded stove is one designed to run close to combustibles. It often has a metal shield on it an inch or two from the firebox that allows room air to keep the outside cooler. That gap becomes a convection passage and heats room air directly while keeping the outer surface cooler. End result is warm air flowing into your room from the top of the shield area. Because the air flow is guided by the shield it is more effective moving the heated air than a simple exposed hot surface.

So I'm not saying I think you're full of it or anything but I don't understand this lol. Keep in mind I've already mentioned I'm an ignorant dude when it comes to this stuff.

With that in mind, I don't see how adding a "shield" will increase efficiency! Wouldn't less air be warmed by the shields vs a non-shielded stove? I would think you want the most air heated as possible. That's precisely why I want my future wood stove be a free standing model vs insert and I want it to be outside the chimney's firebox. If heat shields are more effective than why don't manufacturers place them on every single stove vice offer them as an option? The only thing that makes sense to my ignorant ass is if you're saying the heat shield guides the heated air directly up so less heat is loss while rising so more heat is available for the rest of the house. The stove room is usually the warmest room in the house since that's where the heat is generated. Although that still brings up the issue of heating less air because of the heat shield.

Edit: If my above edit is correct then disregard this post lol. If my first edit is wrong then I'm still confused.

 

[Ambull01]

I see there is a lot of debate on the subject. I'm not seeing any concrete evidence one way or another. I would say each individual installation would have it's own results. So many variables.

Yes sir. I'm usually a variable lover but there's far too many with burning wood lol.

 

[betterbuilt]

With that in mind, I don't see how adding a "shield" will increase efficiency!

I think he's trying to say it's easier to transfer the heat using the shield to naturally convect. I think it's all over my head. I think you could use an electric baseboard heater as an example. They have the metal cover over it to wash the colder air over the element creating air movement.

 

[betterbuilt]

This is the second time I've heard about a rocket stove. I'm going to look it up now lol.

To explain how clean and efficient its burn for the first couple years he had it venting through the side of his house flush with the board and batton. At the exit it would be around 80 degrees. I think the only issues he's had is ash settles out in the ducting, so you need clean out to get to it. It seriously makes me so jealous when he talks about having to get his face cord in for the winter. I'd be 20+years ahead if that was the case.

 

[Ambull01]

I think he's trying to say it's easier to transfer the heat using the shield to naturally convect. I think it's all over my head. I think you could use an electric baseboard heater as an example. They have the metal cover over it to wash the colder air over the element creating air movement.

Wouldn't that be conduction heat? The heating coils sends heat up through natural convection to heat up the metal plate for conduction. The heat from the metal plate then sends heat up again through natural convection and radiates that heat. As you can tell I totally made that up lol.

 

[betterbuilt]

Wouldn't that be conduction heat? The heating coils sends heat up through natural convection to heat up the metal plate for conduction. The heat from the metal plate then sends heat up again through natural convection and radiates that heat. As you can tell I totally made that up lol.

Yeah this is how the OAK thing came about. I read it on the internet it must be true. LOL