Excessive heat behind insert

Wood recycler · Nov 24, 2015

Hello, I am hoping some others here might share what they have done. I've been burning 5 yrs. Burning is my primary source of heat for the winter months of Michigan.

I have had a work in progress for several years now. Below is what I did over a period of time.

I have fireplace exterior masonry chimney. I gut the fireplace throat damper and cleaned the flue, smoke chamber and fireplace. I added a woodstove insert with a stainless steel liner. The liner goes to the top of the chimney. I poured vermiculite insulation between the liner and interior of the chimney.
Then installed the chimney liner cap.

I also insulated the brick of the fireplace walls. Finally, I placed sheet metal above the woodstove where the existing fireplace throat damper used to be. (Out of sight). The sheet metal lays horizontal sealing off the smoke chamber.

Since I have did the various insulation upgrades the woodstove performance immediately increased.

However, here is my dilema. Inside the smoke chamber it gets ridiculously hot. Since the heat radiated from the liner has no place to go. So to correct this I placed a Marvin window fan above the woodstove blowing airbags into the room. Adding the fan to the top of the wood stove greatly increased the efficency.

I burn half the amount of wood I used to prior to the upgrades.

Does anyone else have a better solution to get the excessive heat out of the smoke chamber? I don't like having the woodstove with out the surround.

Smoked · Nov 24, 2015

Seems like you have things set up pretty good to me. If you are worried about losing the heat between the stove and the plate you put in the damper area, you could move that down to the lintel and slope it down slightly to the back of the firebox. It is a larger plate but still pretty easy to build using tapcons to secure. Use Roxul on top and or above it as well.

mellow · Nov 25, 2015

I would insulate the liner so all that heat stays in the liner.

Wood recycler · Nov 25, 2015

Hmmm? I have thought about insulating the liner from the top of the woodstove to the bottom of the flue. I was also considering not insulating it and attaching long strips of aluminum cooling fins.

What I'm most interested in is getting the hot air out of the smoke chamber and back into the living space. Right now I'm only removing a little of the heat back into the room by placing a fan above the woodstove.

I have considered running 4 to 6 inch round duct work just shy of the top of the smoke chamber and using an inline ductwork to fan pull the hot air back into the living space.

With the above mentioned I considered louverin the top of the surround.

I'm not sure about adding anymore roxul. I have to give that some more thought.

Oregon aloha · Dec 1, 2015

Have you tried turning the fan around and blowing the room air into the firebox? I would think it would cool the smoke chamber better.

rwhite · Dec 1, 2015

What kind of excessive heat are we talking about? Does your insert have a blower? I just run my blower on low and never worried about it.

branchburner · Dec 1, 2015

Wood recycler said:
I poured vermiculite insulation between the liner and interior of the chimney.
I placed sheet metal above the woodstove where the existing fireplace throat damper used to be. (Out of sight). The sheet metal lays horizontal sealing off the smoke chamber.

You must also have something above the smoke chamber, too, that keeps the vermiculite from pouring down? It sounds like the smoke chamber is sealed off both above, where it narrows back down, and below, at the damper area. If it is sealed above and below I don't understand how the fan is helping remove heat.

jatoxico · Dec 1, 2015

Wood recycler said:
What I'm most interested in is getting the hot air out of the smoke chamber and back into the living space.

Move the insert forward 3/4-1 1/4". In most cases the surround will look fine and you'll never notice it from normal sight lines. That will let a lot of the heat out.

Wood recycler · Dec 1, 2015

Oregon aloha said:
Have you tried turning the fan around and blowing the room air into the firebox? I would think it would cool the smoke chamber better.

I have right now a dual metal fans sitting on top of the woodstove blowing hot air back into the room. I have another fan on the floor in front of the wood stove blowing at the face of the woodstove. And I have a ceiling fan in the same room as the woodstove.

With this undertaking I'm attempting to rid the three noisey fans and replace them with either a 2 6" duct fans or medium sized squirrel cage fan. My intent would be to insulate the smoke chamber and mount inside the smoke chamber the fans. At least that is my thought. Duct the heat back into the room using 1 6" duct with an elbow.

This would reduce the noise, increase the amount of heat in the room and finally look a bit more appealing to the eye.

Wood recycler · Dec 1, 2015

jatoxico said:
Move the insert forward 3/4-1 1/4". In most cases the surround will look fine and you'll never notice it from normal sight lines. That will let a lot of the heat out.

At current I have removed the surround and pulled the insert closer in the room. I was surprised at the difference itmade.

Wood recycler · Dec 1, 2015

branchburner said:
You must also have something above the smoke chamber, too, that keeps the vermiculite from pouring down? It sounds like the smoke chamber is sealed off both above, where it narrows back down, and below, at the damper area. If it is sealed above and below I don't understand how the fan is helping remove heat.

When I insulated the chimney the first step was to stuff the bottom of the flue (top of the smoke chamber). I used rags that I would later remove. Next the insulation was mixed with water. And bucket after bucket I filled the flue. It dries to a soft concrete. I removed the rags. My first fire was such a noticeable difference.

I would not have used the vermiculite had the insulation wrap fit down my flue. That is why I used the vermiculite. About four feet of the liner is wrapped in the smoke chamber. Which I plan on leaving intact.

To get the hot air out of the smoke chamber I am considering a putting 2 6" duct work fans near the top of the smoke chamber (heat rieses) and ducting it back down to the top of the wood stove then putting on elbows to direct it back into the room.

I removed the damper plate I had installed now it is wide open.

Wood recycler · Dec 1, 2015

rwhite said:
What kind of excessive heat are we talking about? Does your insert have a blower? I just run my blower on low and never worried about it.

The excessive heat I get from the woodstove surround removed and two fans placed above the woodstove and blowing back into the room is night and day difference

Before I removed the surround and used only the blower that came with the stove. It would take two to three loads of well seasoned hard wood to heat my living room. Maybe 2 degrees

Now with the flue insulated with vermiculite, the surround removed, two fans on top of the woodstove blowing in the room. 1 load will bring the room 5 to 6 degrees.

bholler · Dec 1, 2015

Wood recycler said:
Before I removed the surround and used only the blower that came with the stove. It would take two to three loads of well seasoned hard wood to heat my living room. Maybe 2 degrees

How big is your living room? One load in my stove brings my whole firs floor up to 68 or 70. I am also curious what insulation mix you used that is staying in place with nothing holding it in there? I have used quite a few and if mixed correctly allot of insulation will end up ontop of your insert if they are not held in place

Wood recycler · Dec 1, 2015

bholler said:
How big is your living room? One load in my stove brings my whole firs floor up to 68 or 70. I am also curious what insulation mix you used that is staying in place with nothing holding it in there? I have used quite a few and if mixed correctly allot of insulation will end up ontop of your insert if they are not held in place

The living room is 20x15. My house is 1500 sq ft. A lot of my challenge to heat the room is that the living room is next to the upstairs stairwell. So cold air pours down the stairwell into the living room. Another challenge I have is that the home is not an open floor plan. So moving hot air is a must.

I purchased a partial bag of vermiculite from off Craigslist three years ago. All I can remember is the bag was snow white colored paper bag. Sorry. And your right I do get vermiculite on top my wood stove if I move the liner too much. I am considering stuffing that fire proof wool to avoid the mess.

I'm this house the heat is never even. As probably all of us the closer to the woodstove the warmer. So I have to get heat to the other end of the house. If I get the living room at 76 or 78 the the other end of the house will be 72. Upstairs is always cool.

Wood recycler · Dec 1, 2015

bholler said:
How big is your living room? One load in my stove brings my whole firs floor up to 68 or 70. I am also curious what insulation mix you used that is staying in place with nothing holding it in there? I have used quite a few and if mixed correctly allot of insulation will end up ontop of your insert if they are not held in place

Do you have a woodstove insert in a n exterior masonry chimney?

bholler · Dec 1, 2015

Wood recycler said:
Do you have a woodstove insert in a n exterior masonry chimney?

No but reclaiming heat from the flue is not the answer. If you do get enough heat off of that flue to make a difference you will have a creosote factory

bholler · Dec 1, 2015

Wood recycler said:
I'm this house the heat is never even. As probably all of us the closer to the woodstove the warmer. So I have to get heat to the other end of the house. If I get the living room at 76 or 78 the the other end of the house will be 72. Upstairs is always cool.

Yes it is a space heater not a central heating system. Your stove room will always be hotter.

branchburner · Dec 2, 2015

Wood recycler said:
I removed the damper plate I had installed now it is wide open.

This is what I might do: rather than try to blow the warm air out of the chamber, try blowing cool floor air INTO the fireplace around and behind the insert, and then UP into the smoke chamber, where the forced entry of cool air will force the warmer air to circulate down and out. I'm not sure how this would be best done... maybe with two fans, one out in front of the fireplace, pointing in, and one IN the fireplace, pointing up?

I wouldn't worry too much about insulating the whole smoke chamber, or maybe insulate only the exterior-facing portion of the smoke chamber, if possible... that's where you would have greatest heat loss. But I would stuff as much rock wool as possible around the liner up below the vermiculite mix, just to help keep it from crumbling down any more... it could take the place of your rags that you originally had there.

rwhite · Dec 2, 2015

Doesn't this insert have a blower on it?

Wood recycler · Dec 9, 2015

I currently have fans sitting on top of the woodstove blowing out in the room. I don't think their is a natural way of getting the hot air out of the smoke chamber. The only way to naturally fet the hot air out would be to bore a hole from the living spaceinto the top of the smoke chamber. I would put a register over the hole. Doing this would provide a way for the hot air to rise up and out into the living space. However I have strong safety concerns with that idea.

Therefore I am wanting to create a small forced air circulation. Duct it out of the smoke chamber back into the living space.

This woodstove does have a blower. But the blower is a poor design from the manufacter. In a short period of time the blower becomes loud and spots turning. This happens regardless of how often it gets cleaned. The other issue with the Dan is that it simply does not move enough air.

So now I'm turning my attention to learning cfm'S. AND if their are any hvac members I would sure appreciate I ate your opinions. I'm considering a squirrel cage blower that is rated 800 cfm'S.

I think the small blowers that come with the woodstove inserts only produce something between 50 and 100 cfm'S. And this is just not enough cfm's to heat a room efficently.

As I continue to develop this I would like a variable speed fan that is thermostatically controlled.

rwhite · Dec 9, 2015

Wood recycler said:
I currently have fans sitting on top of the woodstove blowing out in the room. I don't think their is a natural way of getting the hot air out of the smoke chamber. The only way to naturally fet the hot air out would be to bore a hole from the living spaceinto the top of the smoke chamber. I would put a register over the hole. Doing this would provide a way for the hot air to rise up and out into the living space. However I have strong safety concerns with that idea.

Therefore I am wanting to create a small forced air circulation. Duct it out of the smoke chamber back into the living space.

This woodstove does have a blower. But the blower is a poor design from the manufacter. In a short period of time the blower becomes loud and spots turning. This happens regardless of how often it gets cleaned. The other issue with the Dan is that it simply does not move enough air.

So now I'm turning my attention to learning cfm'S. AND if their are any hvac members I would sure appreciate I ate your opinions. I'm considering a squirrel cage blower that is rated 800 cfm'S.

I think the small blowers that come with the woodstove inserts only produce something between 50 and 100 cfm'S. And this is just not enough cfm's to heat a room efficently.

As I continue to develop this I would like a variable speed fan that is thermostatically controlled.

I suppose I still would question how much heat your getting in the smoke chamber and how you are measuring that. any area outside of the stove jacket should be substantially cooler than the stove. I have never seen my brick surround over 140 when the stove top is around 600. If you can keep the air flow low and barely moving air from the jacket you should be good. It's not a forced air furnace.

Wood recycler · Dec 9, 2015

rwhite said:
I suppose I still would question how much heat your getting in the smoke chamber and how you are measuring that. any area outside of the stove jacket should be substantially cooler than the stove. I have never seen my brick surround over 140 when the stove top is around 600. If you can keep the air flow low and barely moving air from the jacket you should be good. It's not a forced air furnace.

I have not taken direct heat measurements. I can say with certainty that with the surround installed the the brick directly above the woodstove is hot to the touch on the living space side. With that being said. I slide a
Pair of gloves on and remove the hot surround away from the fireplace and some of the heat comes into theroom. Going further, I now have two 7" or 8" fans on top of my woodstove insert. When the fire in the stove is going hot and well, the two fans will not blow cold air. With the surround removed and two fans placed ontop the woodstove insert, I don't have to burn near the amount of wood as I do with no fan,surround in place, using the little blower fan that came with the insert.

I agree I don't have a forced air furnace sitting in my fireplace. I have a cat woodstove insert with a poorly designed small noisy blower. And the woodstove does a terrific job heating inside the fireplace and smoke chamber. And the living space only gets the front side of the woodstove for heat.

Side note
I haven't cleaned my chimney yet this year. But I generally get a softball size pile in the woodstove after sweeping it (once a season.) And I'm in the process of collecting the creosote to burn in an outdoor fire pit. From what I understand the creosote burns at a hotter temp. Not sure if I can get a hot enough fire ignite it.

bholler · Dec 9, 2015

Wood recycler said:
I agree I don't have a forced air furnace sitting in my fireplace. I have a cat woodstove insert with a poorly designed small noisy blower.

Are you talking about the vogelzang insert here? If so it is not a cat stove.

Wood recycler said:
And the woodstove does a terrific job heating inside the fireplace and smoke chamber. And the living space only gets the front side of the woodstove for heat.

That is why you should insulate around the liner in the smoke chamber then install a good sealed block off plate and insulate behind the insert. That means the heat will either come out of the fire box or go out the flue. Yes you dont get much dirt now because your flue temps are high enough if you start pulling extra heat off it wont be so clean any more

DanCorcoran · Dec 10, 2015

Wood recycler said:
I have not taken direct heat measurements. I can say with certainty that with the surround installed the the brick directly above the woodstove is hot to the touch on the living space side. With that being said. I slide a
Pair of gloves on and remove the hot surround away from the fireplace and some of the heat comes into theroom. Going further, I now have two 7" or 8" fans on top of my woodstove insert. When the fire in the stove is going hot and well, the two fans will not blow cold air. With the surround removed and two fans placed ontop the woodstove insert, I don't have to burn near the amount of wood as I do with no fan,surround in place, using the little blower fan that came with the insert.

I agree I don't have a forced air furnace sitting in my fireplace. I have a cat woodstove insert with a poorly designed small noisy blower. And the woodstove does a terrific job heating inside the fireplace and smoke chamber. And the living space only gets the front side of the woodstove for heat.

Side note
I haven't cleaned my chimney yet this year. But I generally get a softball size pile in the woodstove after sweeping it (once a season.) And I'm in the process of collecting the creosote to burn in an outdoor fire pit. From what I understand the creosote burns at a hotter temp. Not sure if I can get a hot enough fire ignite it.

You have mentioned several times that your fans are on top of the stove, blowing hot air into the room. Several people have suggested that you should put the fans on the floor, blowing cold air up under and behind the stove. The same fans will move a lot more cold air than hot air (because it is denser). You'll be moving a lot more hot air into the room this way...I urge you to try this.

Wood recycler · Dec 10, 2015

DanCorcoran said:
You have mentioned several times that your fans are on top of the stove, blowing hot air into the room. Several people have suggested that you should put the fans on the floor, blowing cold air up under and behind the stove. The same fans will move a lot more cold air than hot air (because it is denser). You'll be moving a lot more hot air into the room this way...I urge you to try this.

Hi Dan, thanks for the response. I thought I had mentioned it but maybe I didn't.ido have a dual window fan sitting on top the woodstove blowing air back into the living space. And I also have a fan on the floor blowing at the face of the woodstove. And the fans do a great job of getting air in the living space. I just don't like appearance of fans around the woodstove.

Tonight for example: I built a fire in the woodstove and purposely did not turn on the fans. The only area that was warm was in front of the woodstove. I placed my hand between the top of the stove and top of the masonry chimney and it was hot.

The members who have woodstove inserts in exterior masonry chimneys know these things. No fan moving hot air equals very little heat in the living space.

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