Do stove fan's make a stove more efficient, or does it just help spread the heat around.

[lsucet]

Wouldn't that be 0% efficient?

I bet SuperJ had no inkling that his original question would cause so much controversy!

If 0% make you feel better then it is

 

[Highbeam]

If 0% make you feel better then it is

Really.

I'm at the "whatever dude" point with this jackoff.

 

[bholler]

Wouldn't that be 0% efficient?

I bet SuperJ had no inkling that his original question would cause so much controversy!

Well no the input and output are equal so it is 100%

 

[bholler]

Really.

I'm at the "whatever dude" point with this jackoff.

He is right about the fan thing though. By extracting more heat off of the stove and putting it in the room you are increasing one part of efficency. But you are also right in some situations because it could potentially reduce the efficency of the birn by lowering firebox temps

 

[WoodyIsGoody]

Really.

I'm at the "whatever dude" point with this jackoff.

Can you try to remain civil here?

That's not appropriate here. It's a discussion about heating efficiency, not some kind of dong waving contest!

 

[bholler]

But honestly the differences in efficency either way are typically not that great. It all depends what works best in each situation. People put way to much emphasis on the efficency numbers anyway

 

[lsucet]

Really.

I'm at the "whatever dude" point with this jackoff.

Just let it be. At the end we all want to help the OP but he should be more confused now.

 

[WoodyIsGoody]

By extracting more heat off of the stove and putting it in the room you are increasing one part of efficency. But you are also right in some situations because it could potentially reduce the efficency of the birn by lowering firebox temps

Yes, and I think that's what's going on with Highbeam's setup when he says it makes heat better with the fans off. A stronger drafting flue could solve that. BK's have an uncanny ability to burn super low and slow and this is not the time to use fans to try to scavenge every last bit of it.

If you study the design of the BK stoves you will notice the fan kit mostly removes heat from the top of the stove and the stove collar. Of course it's unavoidable that this will slightly lower temperature in the lower firebox but the designers did a good job of minimizing that.

 

[WoodyIsGoody]

But honestly the differences in efficency either way are typically not that great. It all depends what works best in each situation. People put way to much emphasis on the efficency numbers anyway

Right, the numbers vary widely anyway in the real world, there is no one "efficiency" number when you're burning different species, different sized splits and have the stove attached to different flues with different drafts.

What I care about is heating my home without burning all the wood up. And the fans help considerably with that, particularly noticeable when heating up a cold structure at higher burn levels. Last week I had 560 degree air blowing out of the blower vent! I was pretty impressed!

 

[WoodyIsGoody]

Well no the input and output are equal so it is 100%

Yes, but if no work is being done, there is no efficiency number...zero heat, no efficiency.

 

[Highbeam]

Yes, and I think that's what's going on with Highbeam's setup when he says it makes heat better with the fans off. A stronger drafting flue could solve that. BK's have an uncanny ability to burn super low and slow and this is not the time to use fans to try to scavenge every last bit of it.

If you study the design of the BK stoves you will notice the fan kit mostly removes heat from the top of the stove and the stove collar. Of course it's unavoidable that this will slightly lower temperature in the lower firebox but the designers did a good job of minimizing that.

My fans absolutely increase the stove output as well as the wood consumption at any particular thermostat setting. Real experience. I do not believe that they increase efficiency by any significant amount. Efficiency as total heat delivered per lb of fuel burned.

I get one vote.

 

[yooper08]

Well no the input and output are equal so it is 100%

Add a fan, it'll lower the efficiency.

End of thread.

 

[lsucet]

At the end, this is all good. It goes back to the point that same stove at different locations and installs perform different. What makes us not to agree at some points because our different own experience.

The only thing we have in common is that we all love our stoves regardless brand and technology used plus we all stay warm. What I don't know now is if I should use the fan or not this winter.

 

[SuperJ]

I bet SuperJ had no inkling that his original question would cause so much controversy!

I think I'm following the discussion alright... I'm just sitting back, eating popcorn, watching the discussion. It's nice to see a vigorous discussion on something.

I've decided to hold off on the fans for now, mostly cause I blew the budget going for the BK Ashford 30. Easy enough to add them later if necessary.

 

[lsucet]

I am sure you will like it with fans or not. When you can or if need them don't hesitate. It will be a good addition to your setup. Congratulations

 

[begreen]

I think I'm following the discussion alright... I'm just sitting back, eating popcorn, watching the discussion. It's nice to see a vigorous discussion on something.

I've decided to hold off on the fans for now, mostly cause I blew the budget going for the BK Ashford 30. Easy enough to add them later if necessary.

Good plan.

 

[SculptureOfSound]

You would do well to study up on how efficiency is measured. By reducing flue temperature at the same velocity, higher efficiency is achieved. That's what the fans do when they blow across the flue collar and suck the heat right out of it. A cooler flue collar increases the temperature differential between the collar and the hot flue gasses causing more heat to continually be absorbed by the flue collar and blown into the room as hot air.

I think you will eventually understand the thermodynamics involved if you keep studying and learning. This will help you increase the efficiency of your stove as you gain experience with operating the controls that are user adjustable. You will learn when the fans are counter-productive and when they can best be used to your advantage. I know it's not always intuitive but stick with it and you'll get the hang of it.

So if considering an insert that is surrounded by insulation... can you over insulate it with regards to efficiency? Or would you just want your fan to be running faster to bleed off the extra heat trapped in what has effectively become another "shell layer" on the unit?

I'm considering a slightly smaller insert so that I can heavily insulate the sides, back (and potentially the top...while still leaving an inch or two clearance on top) because I don't want to heat my external masonry. What's the best approach here to maximize efficiency?

 

[WoodyIsGoody]

So if considering an insert that is surrounded by insulation... can you over insulate it with regards to efficiency? Or would you just want your fan to be running faster to bleed off the extra heat trapped in what has effectively become another "shell layer" on the unit?

There are two components to efficiency.

1) How complete the combustion is. If all the volatile components are not combusting, efficiency will suffer. High firebox temperatures (or an active cat) are both good solutions to that. So insulation helps in this regard.

2) How much of that heat makes it into the room. If most of it just goes up the chimney, efficiency suffers even when the combustion is substantially complete. Insulation can make this worse. The trick is to scavenge the heat after combustion is complete while leaving just enough heat in the flue to maintain adequate draft and avoid condensation. And that's why fans are so beneficial. It provides a knowledgeable operator one more tool to increase efficiency through the burn cycle. Fans should not be left on continuously but used judiciously to increase efficiency and comfort.

I'm considering a slightly smaller insert so that I can heavily insulate the sides, back (and potentially the top...while still leaving an inch or two clearance on top) because I don't want to heat my external masonry. What's the best approach here to maximize efficiency?

That's a good question for a new thread. Like most things related to wood-burning, it's dependent upon the particular stove and the particulars of your installation. In general, a highly insulated setup will be more dependent on fans, especially with an insert.

If you post some photos and a bit more detail in a new thread I bet you'll get some good feedback (and some not-so-good feedback). But such is the nature of a free/open forum where anyone can post their opinion whether it's well grounded or not. It's up to each individual to filter the wheat from the chaff.

 

[SculptureOfSound]

That's a good question for a new thread. Like most things related to wood-burning, it's dependent upon the particular stove and the particulars of your installation. In general, a highly insulated setup will be more dependent on fans, especially with an insert.

If you post some photos and a bit more detail in a new thread I bet you'll get some good feedback (and some not-so-good feedback). But such is the nature of a free/open forum where anyone can post their opinion whether it's well grounded or not. It's up to each individual to filter the wheat from the chaff.

I did just that (although the thread turned into a bit of a rambling monster as I wrack my brain - https://www.hearth.com/talk/threads/gotta-decide-tonight.163315/.

Would love to hear your thoughts Woody. One thing I really am curious about - never studied thermodynamics and am having a hard time making heads or tails of the info I'm finding - is approximately how many BTUs are being lost when people report their external masonry which must be 4-8" thick from the back of the firebox is 20 or 30 degrees higher than ambient temps. If I could get a rough approximation of what this is actually translating to in BTUs it would help me evaluate the actual gains of heavy insulation, and greatly help me with my choice.

 

[WoodyIsGoody]

Another benefit of the fans is they vacuum up the cooler air near the floor. If you don't have an outside air intake, air intake of the stove achieves this function to a limited degree. But the stove fans typically move more air than the natural draft of the stove. I estimate on a med-low burn the normal sized BK's have a natural draft of about 5-7 cfm. The fans are capable of vacuuming a LOT more air than this. So, even on a very low fan setting, they can increase comfort by reducing the temperature stratification of the air in the room. If you have a ceiling fan in the room this won't matter as much but, if not, you can achieve more comfort, more quickly with a slightly lower overall burn rate.

For example, say your family took a weekend get-away and it's been a day or so without the stove active, the house will have cooled down (quite a bit if it's colder out). Now you build a fire and burn on med-high to bring the house back to 72F. After an hour or so the air might be 70F but the walls are still 64F and the windows are colder yet. So there are cold air convection currents flowing down the wall(s) and onto the floor. Rather than continuing to burn on med-high, lower the thermostat slightly and turn the fans on a med-low setting. After a while the thermostat will naturally open a bit due to convection cooling of the fans. Counter-act that by turning the thermostat down a bit more about 5 minutes after turning the fans on. You will find your house gets warmer and more evenly comfortable (without that cold layer by the floor) and heats up faster all while making your load of wood last longer. Turn the fans off when you have achieved the desired comfort level and the thermostat will automatically turn even lower now with the fans off. The "free lunch" you got was recovering heat that would have gone up the flue. Of course, it probably cost $0.0025 in electricity to run the fans.

If all that sounds like too much work you can just burn on high or medium-high without the fans on and lower the thermostat once the room becomes more comfortable but realize this method will consume your load sooner. Recognizing that cutting and transporting wood and bringing it inside is work too, I propose the former strategy of maximizing useable btu's is less labor intensive and offers more comfort and reduces cold air stratification more quickly and with less wood.

 

[SculptureOfSound]

Very clearly said Woody,and I agree; definitely seems like less work when evaluating the big picture.

 

[Highbeam]

Another benefit of the fans is they vacuum up the cooler air near the floor. If you don't have an outside air intake, air intake of the stove achieves this function to a limited degree. But the stove fans typically move more air than the natural draft of the stove. I estimate on a med-low burn the normal sized BK's have a natural draft of about 5-7 cfm. The fans are capable of vacuuming a LOT more air than this. So, even on a very low fan setting, they can increase comfort by reducing the temperature stratification of the air in the room. If you have a ceiling fan in the room this won't matter as much but, if not, you can achieve more comfort, more quickly with a slightly lower overall burn rate.

For example, say your family took a weekend get-away and it's been a day or so without the stove active, the house will have cooled down (quite a bit if it's colder out). Now you build a fire and burn on med-high to bring the house back to 72F. After an hour or so the air might be 70F but the walls are still 64F and the windows are colder yet. So there are cold air convection currents flowing down the wall(s) and onto the floor. Rather than continuing to burn on med-high, lower the thermostat slightly and turn the fans on a med-low setting. After a while the thermostat will naturally open a bit due to convection cooling of the fans. Counter-act that by turning the thermostat down a bit more about 5 minutes after turning the fans on. You will find your house gets warmer and more evenly comfortable (without that cold layer by the floor) and heats up faster all while making your load of wood last longer. Turn the fans off when you have achieved the desired comfort level and the thermostat will automatically turn even lower now with the fans off. The "free lunch" you got was recovering heat that would have gone up the flue. Of course, it probably cost $0.0025 in electricity to run the fans.

If all that sounds like too much work you can just burn on high or medium-high without the fans on and lower the thermostat once the room becomes more comfortable but realize this method will consume your load sooner. Recognizing that cutting and transporting wood and bringing it inside is work too, I propose the former strategy of maximizing useable btu's is less labor intensive and offers more comfort and reduces cold air stratification more quickly and with less wood.

Even old highbeam can agree with that! Your description of the intense thermostat management required to use the fans for gaining efficiency is the important caveat. Even a caveman can use fans to increase comfort.

 

[WoodyIsGoody]

Even old highbeam can agree with that! Your description of the intense thermostat management required to use the fans for gaining efficiency is the important caveat. Even a caveman can use fans to increase comfort.

Comfort, yes, but it takes a little more knowledge to use the fans to reduce wood consumption. Because you need to know to turn the thermostat down a touch when applying the fans.

 

[begreen]

Comfort, yes, but it takes a little more knowledge to use the fans to reduce wood consumption. Because you need to know to turn the thermostat down a touch when applying the fans.

Though only applicable to the stoves that have a thermostat.

 

[WoodyIsGoody]

Though only applicable to the stoves that have a thermostat.

True. It's pretty hard to turn the thermostat down if it doesn't have one!