Grandma Bear Flu Help

[dgurr]

I have one Fisher stove now, a Honey Bear. Love it. 6 inch flu. When I was installing the stove I noticed it had a metal plate / baffle welded inside the stove & just below where the flu exits the main combustion chamber. This stove works perfectly.

Now, I have purchased a Grandma Bear 8 inch flu stove, has 2 arched "Cathedral Style" doors. When I look down the 8 inch flu, I am looking directly into the fire box. Should there be a metal plate / baffle installed below the flu?

Also, I would be very interested in anyones experiences with a product called Majic Heat Exchanger that installs in line and has an electric blower on a therostat.

Also, any idea of how many square feet this Grandma Bear will heat?

Also, is it best to load the logs / sticks / pieces of wood front to rear in this stove or cross ways - left to right or right to left?

Any advise is greatly appreciated.

Thank you in advance.

Doug

 

[zig]

I can't speak to the stove question but many here can and know as much as Mr. Fisher about them. As for the Magic Heat, just don't. Brother-in-law almost lost the garage to one. There's no way to keep creosote from plugging it up. They do throw a ton of heat; but so does a house fire.

 

[dgurr]

I can't speak to the stove question but many here can and know as much as Mr. Fisher about them. As for the Magic Heat, just don't. Brother-in-law almost lost the garage to one. There's no way to keep creosote from plugging it up. They do throw a ton of heat; but so does a house fire.

Thank you. I appreciate your opinion.

 

[coaly]

Could be before the baffle was used, could have a small one near the back that doesn't cover entire outlet. A larger baffle plate called a "Smoke Shelf Baffle" is advised depending on chimney draft.
The heat reclaimer boxes added remove needed heat from chimney flue. The object with any wood stove is to keep the inner flue temperature above 250* all the way to the top. Water vapor from combustion condenses on the flue walls below that temp allowing smoke particles to stick. This can form creosote rapidly. Double wall connector pipe allows less cooling of exhaust gasses so higher flue temperature is achieved all the way up. An insulated inner flue liner also stays warmer requiring less heat to be left up the chimney. You're better off with this type of efficient chimney system requiring less heat up the chimney and allowing the stove to transmit more BTU's to the building than the heat reclaimer that also causes a restriction in the flue. (slowing fire)

The Baffle thread has pictures and gives you information of design and a simple way to support a baffle plate. They were used in the later double door stoves to reduce smoke, and the threads purpose is to fabricate the same type baffle in single door stoves that were never equipped.
https://www.hearth.com/talk/threads...d-fisher-more-heat-less-smoke-under-25.74710/

The baffle in your Honey Bear is due to not encroaching on loading space in the smaller firebox. It does not roll smoke back into fire like a smoke shelf baffle, but does change the direction of flow above firebox.

Direction of loading is normally across the stove. The first single door models were designed with a long narrow firebox more conducive to the shape of wood. The air goes in the front between logs towards the outlet and leaves a nice pile of coals and charcoal at the rear in the morning to be raked ahead and kindle the fire on. This was also the shape of fireboxes in wood burning locomotives that worked very well. Public demand for double door stoves to be able to watch the fire required the wider double door viewing area and losses the more efficient burn of a better shaped firebox. They also used a 6 inch flue that requires less heat loss up the chimney. These are the efficiencies you sacrifice for fire viewing.

 

[coaly]

Your baffle should approximate this when done;

This was factory in the Goldilocks. This one was used since new in 1985 and not cleaned for the picture. It is 5/16 thick, the same as stove top material and has not warped or bowed at all. Notches (3 X 2) prevent stagnation of movement in corners.

"Heats approx. 1750 square feet". This was calculated with 8 foot ceiling and normal 2 X 4 insulated walls with R-11 insulation at the time. Today's construction varies and can add considerably to square heating area. Much more information is needed regarding your installation; If it's below grade with uninsulated walls, chimney construction (masonry, indoor or outdoor chimney, insulated metal, or insulated flue liner) The more efficient the chimney, the more efficient the stove. With the incorrect chimney the stove has to leave so much out it can barely heat the area it's in. It's all about how much heat the chimney requires, affecting the heat output of the stove.

 

[dgurr]

WOW. Thank you for a wealth of valuable information!

This is a new home installation with the Grandma Stove installed in basement with brand new 8 inch triple wall stainless pipe. Probably 25 feet of pipe with end cap above roof line. This pipe is being installed by a licensed fire place company.

With the above detail, what concerns should I be aware of?

What us your opinion of installing the Majic heat exchanger in this configuration?


If you say no to the Majic Heat exchanger, would you install a damper? This is a top flu, so I will also need a 90% elbo to connect to chimney.

Thank you again.

Doug

 

[bholler]

What us your opinion of installing the Majic heat exchanger in this configuration?

Dont put a majic heater in there they are horrible creosote factories that have no place on any wood stove. And yes you will want a damper

 

[coaly]

Ditto

The Cathedral Doors make it a Grandma III if there is no glass. The manual is in the sticky section at top. A damper should be installed in the first section of straight pipe within easy reach. It becomes your only control with a screen in place in Fireplace Mode. You will also find when kindling a fire with paper, cardboard and small branches, it will roar up the stack when first lit very easily. Closing the damper until the roar stops keeps the heat in the stove to ignite the larger kindling. You could slow it down closing the air intakes, but that slows the fire by depriving it of oxygen. You don't want to do that when first starting it. It needs all the oxygen it can get. Once up to temperature, you can control the rate of burn with the air intakes.

Your 8 inch flue requires a lot more heat than a 6 inch.
You should put a magnetic pipe thermometer on the single wall pipe just below where it goes into insulated chimney. In operation the stove top should be about twice the temp of the pipe. That means a 600* stove top may read about 300* to 350* at the base of chimney with controls set correctly. This is not actual flue temp, you would need a probe type thermometer which is even better and you would need that to try a heat reclaimer. Since the object is keeping the flue above 250* all the way up, you can only guess what the heat loss is all the way up. Checking the creosote formation regularly (weekly, monthly, etc...) until you know how much you create. When there's no smoke in the coal stage, temp doesn't matter, you can close damper to prolong the fire. Cold air blowing across the spark screen loads the screen up and plugs it first. Then the coolest part at the top will form creosote more than the bottom where it's hot. Once you know how much heat to leave up to keep it clean, (with damper or air intake and rate of burn) going by the thermometer as an indicator, you will know what temperature the pipe needs to be for clean burning. You will soon find where the thermometer runs mid burn, and if it's close to 300 or 350, you simply can't extract any more heat from the exhaust without going below the threshold of causing problems. You will find you simply don't have extra heat you can steal from the chimney. THEN if you must try a heat robbing device, try it. BUT you have to keep the pipe temperature the same or you will have problems clogging the screen and creosote near the top real quick. If you don't mind cleaning the chimney constantly, there is another reason you don't want one. Stove operation;

A fire will not get oxygen in a box without being connected to a chimney. The rising exhaust gasses are lighter than surrounding air and rise up the flue. The hotter the inside flue temp and colder the outside temp, the more temperature differential. That's what makes the stove work. That's why you have to consider the chimney being the engine that drives the stove. (In Georgia you're not going to get the temperature differential of up north. You have a weaker draft to start. Below zero outside a chimney and stove really starts to work better. Above 40 you have little and weak draft) Atmospheric air pressure, or the weight of air PUSHES into the stove intake to fill the void created by the rising gasses in the chimney. Cool the rising gasses, it becomes heavy, slows and doesn't allow oxygen into fire. Poor performing stove. It not only has to do with less air getting in, the velocity slows and air mixing with the burning gasses that come off the wood becomes dirty and creates poor combustion. The critical burn zone temp at flame tips drops, increasing smoke, stove temp drops, defeating the purpose of extracting more heat. That's the technical reasons you don't want one. You can see why the 250* flue temp is not just to prevent creosote. It is required for proper stove operation.

How many square feet are you trying to heat in Georgia that makes you think you need more BTU output?

 

[dgurr]

Ditto

The Cathedral Doors make it a Grandma III if there is no glass. The manual is in the sticky section at top. A damper should be installed in the first section of straight pipe within easy reach. It becomes your only control with a screen in place in Fireplace Mode. You will also find when kindling a fire with paper, cardboard and small branches, it will roar up the stack when first lit very easily. Closing the damper until the roar stops keeps the heat in the stove to ignite the larger kindling. You could slow it down closing the air intakes, but that slows the fire by depriving it of oxygen. You don't want to do that when first starting it. It needs all the oxygen it can get. Once up to temperature, you can control the rate of burn with the air intakes.

Your 8 inch flue requires a lot more heat than a 6 inch.
You should put a magnetic pipe thermometer on the single wall pipe just below where it goes into insulated chimney. In operation the stove top should be about twice the temp of the pipe. That means a 600* stove top may read about 300* to 350* at the base of chimney with controls set correctly. This is not actual flue temp, you would need a probe type thermometer which is even better and you would need that to try a heat reclaimer. Since the object is keeping the flue above 250* all the way up, you can only guess what the heat loss is all the way up. Checking the creosote formation regularly (weekly, monthly, etc...) until you know how much you create. When there's no smoke in the coal stage, temp doesn't matter, you can close damper to prolong the fire. Cold air blowing across the spark screen loads the screen up and plugs it first. Then the coolest part at the top will form creosote more than the bottom where it's hot. Once you know how much heat to leave up to keep it clean, (with damper or air intake and rate of burn) going by the thermometer as an indicator, you will know what temperature the pipe needs to be for clean burning. You will soon find where the thermometer runs mid burn, and if it's close to 300 or 350, you simply can't extract any more heat from the exhaust without going below the threshold of causing problems. You will find you simply don't have extra heat you can steal from the chimney. THEN if you must try a heat robbing device, try it. BUT you have to keep the pipe temperature the same or you will have problems clogging the screen and creosote near the top real quick. If you don't mind cleaning the chimney constantly, there is another reason you don't want one. Stove operation;

A fire will not get oxygen in a box without being connected to a chimney. The rising exhaust gasses are lighter than surrounding air and rise up the flue. The hotter the inside flue temp and colder the outside temp, the more temperature differential. That's what makes the stove work. That's why you have to consider the chimney being the engine that drives the stove. (In Georgia you're not going to get the temperature differential of up north. You have a weaker draft to start. Below zero outside a chimney and stove really starts to work better. Above 40 you have little and weak draft) Atmospheric air pressure, or the weight of air PUSHES into the stove intake to fill the void created by the rising gasses in the chimney. Cool the rising gasses, it becomes heavy, slows and doesn't allow oxygen into fire. Poor performing stove. It not only has to do with less air getting in, the velocity slows and air mixing with the burning gasses that come off the wood becomes dirty and creates poor combustion. The critical burn zone temp at flame tips drops, increasing smoke, stove temp drops, defeating the purpose of extracting more heat. That's the technical reasons you don't want one. You can see why the 250* flue temp is not just to prevent creosote. It is required for proper stove operation.

How many square feet are you trying to heat in Georgia that makes you think you need more BTU output?

Thank you again. My basement is roughly 1650 sg ft, new construction and well insulated. When I bought the Grandma Bear stove, the Majic Heat Exchanger was installed on the stove. Guy wanted to sell the stove, heat exchanger & fire screen as a package. So I now have a Majic Heat Exchanger.

Sounds like I should sell the Majic Heat Exchanger....?

Working on getting the Smoke Shelf Baffle made & installed in stove.

Thank you again for your expert opinion.

Doug

 

[dgurr]

Ditto

The Cathedral Doors make it a Grandma III if there is no glass. The manual is in the sticky section at top. A damper should be installed in the first section of straight pipe within easy reach. It becomes your only control with a screen in place in Fireplace Mode. You will also find when kindling a fire with paper, cardboard and small branches, it will roar up the stack when first lit very easily. Closing the damper until the roar stops keeps the heat in the stove to ignite the larger kindling. You could slow it down closing the air intakes, but that slows the fire by depriving it of oxygen. You don't want to do that when first starting it. It needs all the oxygen it can get. Once up to temperature, you can control the rate of burn with the air intakes.

Your 8 inch flue requires a lot more heat than a 6 inch.
You should put a magnetic pipe thermometer on the single wall pipe just below where it goes into insulated chimney. In operation the stove top should be about twice the temp of the pipe. That means a 600* stove top may read about 300* to 350* at the base of chimney with controls set correctly. This is not actual flue temp, you would need a probe type thermometer which is even better and you would need that to try a heat reclaimer. Since the object is keeping the flue above 250* all the way up, you can only guess what the heat loss is all the way up. Checking the creosote formation regularly (weekly, monthly, etc...) until you know how much you create. When there's no smoke in the coal stage, temp doesn't matter, you can close damper to prolong the fire. Cold air blowing across the spark screen loads the screen up and plugs it first. Then the coolest part at the top will form creosote more than the bottom where it's hot. Once you know how much heat to leave up to keep it clean, (with damper or air intake and rate of burn) going by the thermometer as an indicator, you will know what temperature the pipe needs to be for clean burning. You will soon find where the thermometer runs mid burn, and if it's close to 300 or 350, you simply can't extract any more heat from the exhaust without going below the threshold of causing problems. You will find you simply don't have extra heat you can steal from the chimney. THEN if you must try a heat robbing device, try it. BUT you have to keep the pipe temperature the same or you will have problems clogging the screen and creosote near the top real quick. If you don't mind cleaning the chimney constantly, there is another reason you don't want one. Stove operation;

A fire will not get oxygen in a box without being connected to a chimney. The rising exhaust gasses are lighter than surrounding air and rise up the flue. The hotter the inside flue temp and colder the outside temp, the more temperature differential. That's what makes the stove work. That's why you have to consider the chimney being the engine that drives the stove. (In Georgia you're not going to get the temperature differential of up north. You have a weaker draft to start. Below zero outside a chimney and stove really starts to work better. Above 40 you have little and weak draft) Atmospheric air pressure, or the weight of air PUSHES into the stove intake to fill the void created by the rising gasses in the chimney. Cool the rising gasses, it becomes heavy, slows and doesn't allow oxygen into fire. Poor performing stove. It not only has to do with less air getting in, the velocity slows and air mixing with the burning gasses that come off the wood becomes dirty and creates poor combustion. The critical burn zone temp at flame tips drops, increasing smoke, stove temp drops, defeating the purpose of extracting more heat. That's the technical reasons you don't want one. You can see why the 250* flue temp is not just to prevent creosote. It is required for proper stove operation.

How many square feet are you trying to heat in Georgia that makes you think you need more BTU output?

Goaly, one more time.

The Smoke Baffle Plate for a Grandma Bear lll help. I saw the directions on how to measure the width of stove & have the plate of steel cut 1/2 inch shorter. How deep of a plate does it need to be? Should I cut the 3 X 2 inch corners lout to prevent stagnation? Do the edges of the Baffle need to to turned up? Should the Baffle be parallel to the floor or at an angle front to rear, if so approx. what angle?

My stove is a top flue stove.

Thank you in advance.

Doug

 

[coaly]

See baffle thread in post #4 above. It gives how to measure smoke space and suggests to make a template with cardboard first to get the right angle and smoke space for your outlet /chimney size. Changing the angle changes the smoke space and plate size. It will be a custom size for each installation.