heat shields on a freestanding stove vs output

[brider]

How much do side/back heatshields affect the heat output of a freestanding wood stove?

One of the stoves I'm looking at is the Napoleon 1100P, and it has what looks like insanely close installation clearances, due no doubt to the integral heat shields (that channel cold air around the firebox and out the front louvers; a clever design, I think) on the sides.

Is this likely to inhibit the tranfer of the firebox heat to the room?

 

[begreen]

There will be less radiant heat, but good convection, especially with the blower going. Several stoves are designed this way and work fine.

 

[fossil]

To the extent that I understand it, the purpose of the heat shields is to limit, to the degree they can, the radiant energy that would otherwise go directly into the adjacent materials, and thus they allow for the reduced stove clearances. The heat shields do nothing to decrease the amount of heat the stove is producing. They provide channels for vertical convection, so air between the stove & shields gets warm and rises, and thus carrying away, through natural convection, heat that would otherwise be radiating directly out. As the air between the stove and the shield warms, it becomes less dense, and it rises. Relatively cool air enters from the bottom to replace the warm departing air. The shields will remain a bit cooler than the stove walls. The heat from the stove will get into the room, what you do with it after that, in terms of blower kits, ceiling fans, or whatever, is up to you. I'm sure experts will amend/correct what I've just said here. Rick

 

[Thomask9590]

What are your thoughts about cutting a vent directly bellow the stove to pull air up from the basement. Especialy if you have a blower system like the Napoleon 1400PL that brings make up air in from the bottom and sends it into the fire box?

 

[begreen]

What would the goal of that be TGun?

 

[fossil]

...Especialy if you have a blower system like the Napoleon 1400PL that brings make up air in from the bottom and sends it into the fire box?

Your blower kit doesn't send any air from anywhere into the firebox...it circulates air around the outside of the firebox, providing forced convection to more effectively move the heat from the stove out into the room. All the combustion air passing through the firebox does so through its own natural convection path. If you're referring to an OAK (Outside Air Kit), that's more than just a hole in the floor, it's an installed continuous pathway for air from outside the living space to the combustion air intake of the stove, and, to my knowledge, none of them include any kind of blower. Rick

 

[Thomask9590]

This air flow image of the Napoleon stove is what pushed me into purchasing it. Now, I have not fired this thing up yet and I have not climbed inside it so I am not speaking with any suporting data. I was just brainstorming on what might help maximize by burn efficiency, so I figured if I could increase cool air into the stove I would increase my heating efficiency. Maybe I'm all wet but I figured I would ask.

 

[begreen]

Like Fossil noted, there's a difference between combustion air and convection air. This isn't really shown in the diagram. There is a place on the back to connect a 4" outside air kit if desired. But generally if you want to supply fresh combustion air to the stove it is done with a sealed pipe. Otherwise there could be a bunch of cold air coming into the house when the fire is out or in the late coaling stage.

 

[Thomask9590]

Maybe I should have included this in my picture above. After looking the stove over and reading the manual %-P , I found that there is a channel above the air damper that feeds right into the combustion chamber. Here is the explanation below. Also, click on the picture to get a little better resolution.




12. Cool room air is circulated around the firebox, heated and returned to the room.
13.The single lever burn control regulates primary and secondary air establishing a perfect mix and a clean burn.

 

[fossil]

Number 12 is what your blower's doing for you...what BeGreen referred to as convection air. Number 13 is your combustion air, natural convection from the room, through the firebox, then up the pipe & out. Number 13 is where you have the option of that air coming directly from the room where the stove's sitting or, by installing an Outside Air Kit, in which case it's ducted to the stove from outside the space. In neither case is there a blower invloved in providing cumbustion air. If there were, you wouldn't have a stove, you'd have a forge and you could make horsehoes or something with it. :bug: Rick

 

[webbie]

Technically, if you move too much air across the stove exterior, you are cooling the firebox walls and quenching combustion......to a small degree.

Introducing cold air into the combustion chamber has the same effect - that is why designers have tried for years to preheat combustion air.

In most cases, modifications will not help much - because if they would, the engineers at the factory would have done them already.

 

[brider]

TGun:

I'm curious about your 1400, I'm looking at the 1100, and I started a separate thread to see who's used one.

The Napoleon models are sure better priced, I'm hoping it's because of the steel firebox, and not any other get-what-you-pay-for issues.

 

[Thomask9590]

Brider,
My Family sold Jotel wood stoves for years and we burned a #118 and a #4 on a regular basis. Great stoves, we would get that #118 so hot you could see through it. :ahhh: My father pushed me away from both Jotel and Vermont Casting due to increasing quality issue with no reduction is price. He was very imprested by the engineering and the price on the Napoleon. I have not put a fire in this yet but I'm optimistic. I have been in manufacturing all my life, one of the variables that helps keep your cost down is standardized product that help reduce SKU counts. I noticed that Napoleon gives you very few options in the way of luxuries and several options in the way of functionality. I feel they keep their cost down by not making the product "SEXY" but by making the product versatile. That and they are made in Canada where our dollar is week and shipping is easy.

 

[rob bennett]

Not to get too off the mark, but the canadian dollar is not exactly weak right now. That last time I drove up and bought my used vista insert I ended up spending more money with the exchange rate. That was a few months ago, but even now I wouldn't call it a weak dollar. You should see how many canadians are shopping in the states the last few months. Its been pretty good for the border towns.

 

[begreen]

TGun, I would like to know more about what your father perceived as increasing quality issues with Jotuls. I have seen some issues in some VC stoves, but the Jotul stoves I have owned in the past several years have been first rate in quality. Their joint seals, latch mechanism, and enamel finish have been nicely improved on our old Jotul.

 

[Thomask9590]

You have to keep in mind that my father sold these stoves in the 70's and he is not a fan of the glass front stoves that Jotel has gone to. He is getting his data from some long time and old time Jotel owners. His basic comment was that you just don't get the same stove for the price anymore. He did elude to some door sealing issues and some cast issues but his biggest gripe was the price.

 

[begreen]

OK, this sounds more like a "they don't build 'em like they used to" issue more than a quality issue. Having owned both old and new I think Jotul has made some good improvements over the years. Personally I like seeing the fire. And burning cleaner is a good thing for us all.

 

[Thomask9590]

I love the stove but this year I just could'nt swing the price. I did read that the Jotul F 400 stove had some quality issues with the white enamal.

 

[stoveguy2esw]

To the extent that I understand it, the purpose of the heat shields is to limit, to the degree they can, the radiant energy that would otherwise go directly into the adjacent materials, and thus they allow for the reduced stove clearances. The heat shields do nothing to decrease the amount of heat the stove is producing. They provide channels for vertical convection, so air between the stove & shields gets warm and rises, and thus carrying away, through natural convection, heat that would otherwise be radiating directly out. As the air between the stove and the shield warms, it becomes less dense, and it rises. Relatively cool air enters from the bottom to replace the warm departing air. The shields will remain a bit cooler than the stove walls. The heat from the stove will get into the room, what you do with it after that, in terms of blower kits, ceiling fans, or whatever, is up to you. I'm sure experts will amend/correct what I've just said here. Rick

Fossil, the explanation is PERFECT. very well done , all a passive heat shield does is create a "mini chimney effect" this as rick stated allows heated air to rise and draw cooler air in at the same time , this literally changes the direction of the generated heat from horizontal to vertical. some stoves are designed to allow assistance from a blower to move this air through and deflect it out into the room , our 12, 13 and 30 series do just that(as im sure a large percentage of others do as well). as for reduced combustion efficiency , its infintesimal literally not perceptible.
though with forced air , the degree of temperature in each cubic inch of air will not be as high , the volume of warmer but not blazing hot, air makes up the difference

think of it this way; the movement of air created by this updraft is similar to a very low powered blower i mean really low powered , but the air will be very hot , im going to use numbers which reflect this easily but may not be indicative of actual numbers you would see (making the math easy) and assists in building a convection current to move the heat around the dwelling more readily.ok, 75F room temp starting this out. say the air flowing from the heat shield from natural convection (updraft) is moving at 10 cfm, but is heated to 450F. , adding a blower that runs at 50 cfm, moves 5 times the air, but the temperature of that air might be say 150F which is a third of the air temp you had without the blower. its still going to move heated air that is twice the start temp around the dwelling , so you arent losing anything really. and in reality in most circumstances you actually gain as the faster heat is spread the more broad the heated area will become radient heat will travel only as far as the natural convection built by heat rising and cooler air decending will carry it, forcing heat away expands the range.

guess i got off topic a bit but i hate to dump it. remember also that the numbers i came up with are not backed by data so much as to make it easier to do the math in my head. hope it makes sense to ya.