Wood consumption of a free standing stove vs. insert

[Hogwildz]

I didn't want to totally hijack another thread, so I am starting a new one.

[quote author="brooktrout" date="1199608693"]Hogz is trying to say, correctly so, IMHO, the freestander will give more radiant heat than the insert, thus allowing the operator to use less fuel.[/quote]
I understand and agree to that in some degree. But load a Summit stove & a Summit insert, with same amount of wood. They are going to "consume" the same amount in same amount of time. Then at reload, same thing. A stove burns no cleaner or longer than an insert, so from a consumption point, there is no difference. Now on the other hand, the insert with a blower, I feel is going to blow and spread hot air faster & further than a stove without a blower. Now if the same stove has a blower, now yes, its going to heat the area faster & warmer through the blower & radiated heat. But still not consume wood any more or less than an insert. Coals are coals, when they are down its time to reload. If your burning 24/7 whether stove or insert, the freestander is going to need to be reloaded same time the insert will. The only difference I will concede to is if the free standing stove has a blower on it, then there is a difference. But it will still consume the same amount of wood in the same amount of time. The only difference may be the temperature of the area being heated. If the point is that a stove with blower will heat more than an insert with blower & especially without. Yes I totally agree. But if the point is consumption, I see no difference. That 3cf firebox is going to consume the same amount of wood in the same time whether stove or insert.
Now here is something to ponder......
If an insert which is more or less semi enclosed on 5 sides and loosing less heat on those sides, therefore theoretically the firebox not cooling as fast or losing heat to the room as fast. Will it burn any more efficient or better yet keep a firebox temp hotter longer due to this lack of heat loss? Ok give the top side on say mine up cause its got a blower blowing heat off the top.
I am not saying this is a fact, I am just wondering if anyone has given this thought? Is a stove while yes radiating more heat, but is it burning cooler? or using more energy to keep the firebox hot as its losing more heat from all 6 sides? or at least 5. I think its a good question and interesting question, and would like to see others opinions on this.

 

[brooktrout]

Giving this some thought- I am by no means experienced in the general area of wood heat, only a few weeks in. And certainly not an expert in thermodynamics. But, I think an insert would lose quite a bit of heat to the walls surrounding it. Some may be radiated back into the room, but, especially when the fireplace is located on an exterior wall with an exterior chimney, much is lost. So, in order to maintain a constant desired room temp, the insert probably needs more fuel than a stove. But then there's the blower question. Does it make up for the heat loss? Not sure... My Buckstove has a triple wall construction, blower with cold air intake on both outter sides and warm air exits on the top, bottom, and both inner sides. I haven't gotten a chance to put the surround up yet, so I can reach around and feel the stove- the sides are barely warm, but the top is hot, mostly near the stack. So compared to a freestander, the only heat I lose is from the top and stack. Tough call... Great question, Hogz.

 

[Todd]

Sure, they will burn the same, but the heat output efficiency is a little different, so theoretically, if you had a summit insert and a summit freestander in the same type of room, you should get better heat output with the freestander and would either have a hotter room or you could load less wood to keep the same temp as the insert. I'm sure there are all kinds of variables that could play into this like blowers, or whether it's an inside or outside chimney and the difference is probably so small you wouldn't notice it.

 

[webbie]

Speaking in generalizations, an insert in a masonry exterior fireplace would, IMHO, be quite a bit less efficient than a freestanding stove with some exposed stovepipe.

Obviously each situation is different - north side, south side, climate, amount of the masonry that is exterior, insert type, current weather and more....

BUT, I have little doubt that a realistic AFUE type efficiency test in northern climes would show efficiencies that are quite a bit lower than some that are advertised.

 

[Hogwildz]

Good answers. I appreciate the input from you gentlemen.
Oh and btw web, I agree. The numbers most the manufacturers post should be a crime. Even car manufacturers have to put a realistic number to fuel economy.
Most post between x amount of mpg and x amount of mpg. Somewhere in between is a basis to start at at least. I wonder why stove manufacturers are not held more accountable for the numbers they post in their web sites & brochures.

 

[TMonter]

I wonder why stove manufacturers are not held more accountable for the numbers they post in their web sites & brochures.

Because there is no industry standard for reporting such figures. There does seem to be an industry push to move towards standardization however.

 

[struggle]

Speaking in generalizations, an insert in a masonry exterior fireplace would, IMHO, be quite a bit less efficient than a freestanding stove with some exposed stovepipe.

Our house is set up with a masonary upstairs fireplace located on an exterior wall and while it can easily bring the house temp up to the 90s if one wants it consumes I figure twice the wood the soapstone in the basement uses. It also requires frequent fillings.

I have no idea how the insert stoves are to handle for heat output but would think if it is on an exterior wall a good deal of heat goes out the the back of it that does not get recovered as it heat the area around it before it can blow warm air out as it would just be pulling cold air off the surounding areas of the insert.

 

[Kilted]

So are you talking about a fireplace insert that was designed as an insert or just a free standing woodstove stuck into a fireplace opening?

I have had TWO fireplace inserts that were designed as inserts a pre-EPA insert and my current EPA insert. The one major difference the designed as insert woodstove has is it is a box-in-a-box design. There is the inner box which is the combustion chamber-air space-outer box. This is where the forced air from the blower picks up the heat from the outer walls of the combustion chamber. I also do not understand concerns about the lose of heat to the FP masonary. That has not been a problem the outer skin only gets to the temperature of the air in the air channel.

Is this the way freestanding stoves are constructed? I would think a woodstove designed as an insert would actually put out more heat than an equavalent free standing stove with no forced air circulation.

Is there a difference in the construction between the Summit free stand and the Summit insert? I went to the website and my guess is it looks like two different stoves, even if they share a common design.

Are not burn times related to the temperature in the combustion chamber? Having a blower running would seem to me to lower the temperature of the firebox and affect burn time. Of course I can not prove any of this and it is just my opinion.

-- Brandy

 

[daleeper]

Good answers. I appreciate the input from you gentlemen.
Oh and btw web, I agree. The numbers most the manufacturers post should be a crime. Even car manufacturers have to put a realistic number to fuel economy.

Come on, who has purchased a vehicle that came anywhere near the numbers posted on that sheet? Use the numbers relative to different models, and they are somewhat useful in knowing which vehicle will be more efficient than the other, but none will actually do what the number says.

Back to stoves. I have no experience with an insert, so cannot comment from experience, but it would seem to me that a freestanding stove would have the opportunity to radiate into the room better, but the insert, if surrounded by a good storage mass, would be able to hold the heat more steady, for a longer period of time. Can't see why btu output would be any different if operated the same, but would be distributed differently.

 

[JimWalshin845]

I think it has already been stated, but exposing a cube with a lot more easily circulated air will make a better heat exchanger and you are not heating up the back of a masonry firebox where quite a bit of the heat is lost.

Another feature of a free standing is the fact that you can push air across the top of the stove to move air towards an adjoining room, much less effective with an insert.

The last item is stove pipe. Mine is 8” exhaust, so for every foot of run I am exposing another 150sq/in of hot pipe, that’s pretty significant.

So we may be burning the same amount of wood, but the free standing should get more BTUs from it.

 

[brooktrout]

Come on, who has purchased a vehicle that came anywhere near the numbers posted on that sheet? Use the numbers relative to different models, and they are somewhat useful in knowing which vehicle will be more efficient than the other, but none will actually do what the number says

.

I know we've gotten off topic a bit, but my new Toyota Yaris states it gets 34mpg city and 41 highway. I live in a rural area with lots of hilly driving. Average has been 36. On a recent wknd trip to NJ, it got 42. That's with reg. gas. If anyone is looking for a small fuel efficient car, I highly reccomend it. Sedan version, that is. The hatchback is sinfully ugly, IMO. Plus, it's a Toyota.

 

[bokehman]

when the fireplace is located on an exterior wall with an exterior chimney, much is lost.

The outer skin of insert doesn't get that hot; most of the heat is collected by the airflow.

car manufacturers have to put a realistic number to fuel economy.

Apples for oranges. A wood burner is just an iron box whereas a car is a complete system. With a wood burner the user controls how and what is burned and how much air the fire gets; With a car the manufacturer is in control of the fuel system and the combustion environment.

The last item is stove pipe. Mine is 8” exhaust, so for every foot of run I am exposing another 150sq/in of hot pipe, that’s pretty significant.

How did you work that out? Should be 302sq" or 2.1sq' per foot. But not everyone has the stovepipe exposed. On the other hand, in my install for example, I have an insert and at ceiling level there is an 8" square opening with forced ventilation that feeds air warmed by the back of the insert and the stovepipe into the room.

One point no one has mentioned so far is whether a stove is more efficient because there is no forced airflow continually cooling it down.

 

[hilly]

I've had some interesting experiences with my insert in the two seasons I've been burning although my set-up may not be like most. My insert is in an interior brick fireplace that has a brick chimney running up the middle of my house. Last season I didn't have a fan for it and it heated quite well but after my reading here I paid my $200 and got a blower for it. Surprisingly, it hasn't made as much difference as I would have suspected although it lets me regulate the temperature upstairs a bit better.

As Hog says, the heat given off by five splits will be the same in an insert as a freestanding, it's just where that heat goes. I'm lucky, because any heat I lose out the back and off the top of my insert goes into the brick to be reradiated later but I imagine if your fireplace is on an outside wall a bunch of heat is lost to the great outdoors.

 

[JimWalshin845]

Oooops - used the radius rather than the diameter. So double that area.

 

[webbie]

I wonder why stove manufacturers are not held more accountable for the numbers they post in their web sites & brochures.

Because there is no industry standard for reporting such figures. There does seem to be an industry push to move towards standardization however.

Hey, T, where did you see the "push".

The docs I have seen say that manufacturers have no good reason to report proper specs, nor to improve the quality of the stoves as to how well they hold up (in efficiency) over the years. That is from the Omni and Epa reports.

I don't think you will soon see the type of real standard or test as with the Energuide (Canada) efficiency standards, because it might take the wind out of the "sales" of certain products. Folks do their "savings" calculations based on high efficiencies (pellet, clean wood), and if they had to enter 50% instead of 70% or more, some sales might be lost.

I would guess that the only real solution is for an independent test lab....or a VERY forward thinking manufacturer to start testing and publishing real results. It would shake things up, that's for sure! Just look at those 80+ % gas stoves that come in at 60% when tested by Energuide!

 

[webbie]

One point no one has mentioned so far is whether a stove is more efficient because there is no forced airflow continually cooling it down.

This has been well documented by testing labs - in our particular case starting with Jay Sheltons lab in the early 80's. Same goes for outside air. Anything that cools the other walls of a stove will, to some degree' quench the fire. That is a big problem with stove design....if you go all the way toward one end, some VC's being an example (highly insulated fireboxes), then you end up with glowing flue collars - too much heat and not enough exchange. It is one reason why a gasification boiler is an almost perfect solution - burn the wood as hot as possible in one chamber and then use tubes surrounded by water to exchange the heat from the hot (but clean) exhaust gases.

This also speaks to the benefits of cat stoves- but making the gases burn at lower temps, you avoid some of the potential problems and can keep the heat exchanged contained.

 

[iceman]

ok how about this if someone takes off the shroud then how much heat will naturally convect/ radiate into the room ?
if so (if it does make a diff) unless you like the look we should consider insulating the outer box which in theory would keep the insert warmer, stop losing heat to walls and we would consume less wood or consume the same with longer burn times so to speak (the insert will continue to give heat longer)

 

[Martin Strand III]

Just my opinion on this:

If you have a wood burning metal insert and a similar stove made by the same Mfg with essentially the same firebox size made with the same materials and you load them both with the same fuel charge, the winner and the one I'd opt for will be the one with the greatest weight (read total mass) since thermal mass (metal and ceramic bricks), all else the same, would be the "best" heater.

Aye,
Marty

Grandma used to say, "It's not my pants that make my a** look big. It's my a** that makes my a** look big."

 

[Todd]

Well a few hours ago I started up my cold soapstone stove and was sitting here feeling the radiant heat from the 5' of exposed single wall pipe while the stove was still cool. I'm thinking there is quite a bit of heat radiating from that pipe. If my stove was installed into a fireplace, I would not be feeling any heat til the stove comes up to temp. So that tells me there is some extra efficiency just from the pipe. More efficiency means less wood.

 

[Bill]

One point no one has mentioned so far is whether a stove is more efficient because there is no forced airflow continually cooling it down.

This has been well documented by testing labs - in our particular case starting with Jay Sheltons lab in the early 80's. Same goes for outside air. Anything that cools the other walls of a stove will, to some degree' quench the fire. That is a big problem with stove design....if you go all the way toward one end, some VC's being an example (highly insulated fireboxes), then you end up with glowing flue collars - too much heat and not enough exchange. It is one reason why a gasification boiler is an almost perfect solution - burn the wood as hot as possible in one chamber and then use tubes surrounded by water to exchange the heat from the hot (but clean) exhaust gases.

This also speaks to the benefits of cat stoves- but making the gases burn at lower temps, you avoid some of the potential problems and can keep the heat exchanged contained.

So do I understand this correct, would a blower than reduce the temperature of the fire, and reduce efficiency, and do blowers create any additional heat, or just move the heat?

 

[Gunner]

IM(uneducated)O..... all splits being equal, a freestanding stove will put more heat into the room than an identical insert.

Burn time will be the same, but more heat per load will end up in the house with a freestander.

Exception may be an insert not on an exterior wall.

 

[webbie]

"Everything I need to know about woodheat, I learned from John Gulland."

C'mon, Gunner, you must have learned something from the folks here!.....Just one teensy thing?

 

[Chettt]

Blowers do little more than move dust and noise. A freestanding stove is better in every way.