New Installation with Fisher Mama Bear

[Unclear]

Hello everyone, I have been a short time lurker reading articles about wood head and quickly discovering that this is something I want to tackle. I have a home built in the late 80's with a fireplace on 1st floor and spot for wood stove in basement. The i.d of the basement flue is 7". The stove: I was able to scoop up a Fisher Mama Bear for very cheap and seems to be in great condition.

I would like to build a concrete hearth and get it attached to the chimney.

1st. question.
recommendations on pipe setup with stove i.d to be 6" and chimney flue opening 7" i.d.
2nd. hearth size recommendations.
I have the original documentation about recommended hearth sizes and wondered if anything has changed.
3rd. Any lessons learned about pouring a concrete hearth size, height?

Looking around the net for a 7" stove pipe reducer and not getting any luck. Not seeing anything 7" at all. Any thoughts?

thanks ahead of time. looking forward to becoming a wood heat aficionado.

 

[chimneylinerjames]

recommendations on pipe setup with stove i.d to be 6" and chimney flue opening 7" i.d.

What size is the flue outlet on the stove? Always use that same size for the stove pipe. One problem you may have is if the outlet is 6", 28 square inches, venting into a 7" flue, 49 square inches, you will not have optimal draft. The flue is almost double the size of what you need. What is best is line the chimney with a chimney liner the same size as the flue outlet on the stove.

As for the hearth, in your case with a concrete floor already, it doesn't matter how high the hearth is. It will be up to you, what is a comfortable height to load wood?

There are 6x7 and 7x8 reducers online, even home depot should have them, even tho of lesser quality many times.

 

[coaly]

What size is the flue outlet on the stove? Always use that same size for the stove pipe. One problem you may have is if the outlet is 6", 28 square inches, venting into a 7" flue, 49 square inches, you will not have optimal draft. The flue is almost double the size of what you need. What is best is line the chimney with a chimney liner the same size as the flue outlet on the stove.

As for the hearth, in your case with a concrete floor already, it doesn't matter how high the hearth is. It will be up to you, what is a comfortable height to load wood?

There are 6x7 and 7x8 reducers online, even home depot should have them, even tho of lesser quality many times.

This stove would normally have a 6 inch outlet. (Some single door Fisher's were special built with 8)

Your flue square inch figures are incorrect.
Square inch is calculated by radius (half the distance across) squared (times itself) X pi or 3.14.
6 inch = 28.26
7 inch = 38.46
6 to 8 inch would be almost twice the square inches.
Not great to increase, but not a draft killer for the Mama Bear. A Baby Bear would struggle.

Home Depot, Lowe's and Tractor Supply sticks with common 6 and 8 inch. Dura Vent makes it, they even make entire chimneys in 7 inch. (but not stocked at the big box stores)
Check out Ace Hardware for 6 X 7 increaser. They have one of the best selections of connector pipe fittings and stove boards. They have oval adapters as well.

Home Depot; "lesser quality" ? They retail Dura-Black by Dura-Vent. (with the best price) The best double wall and single wall connector pipe made.

 

[coaly]

I have the original documentation about recommended hearth sizes and wondered if anything has changed.

Welcome to the forum,
If you do indeed have an owners manual for the model II or VI (yours is one of these) PLEASE let me know so we can get it scanned for the Fisher Wiki section of manuals. Thanks !

 

[chimneylinerjames]

Square inch is calculated by radius (half the distance across) squared (times itself) X pi or 3.14. 6 inch = 28.26 7 inch = 38.46

You are right it is 28.26", but i was figuring his current flue is square 7x7, that would be 49 square inches. But if it was round yes it would be 38.46"

As far as lesser quality, I thought they were the same band name so it didnt matter. But after an install I did and I used the same brand name, got all the pipe from a stove shop but I forgot the tee. So we bought one at Lowes or Home Depot, cant remember. We installed everything, lit the fire. The pipe was fine, the tee got red hot. Since then I never buy black pipe from big box stores. Lesser quality. Cant really agree that Home Depot sells the "best pipe made", I have used many other pipes that were better.

Same goes with lots of other items in those stores, that is why you will find model numbers only in those stores and not in any other places, specially made for Big Box stores.

 

[Unclear]

Thanks for the quick and informative responses! So should I run 7" all the way to the stove then reduce or try to run 6" up to the flue opening? Still on the hunt for the 7" to 6" reducer. Have a lead to a local chimney supply for the part. Hope they have it!

thanks again everyone.

 

[Unclear]

Just off the phone with my local chimney supply and she states that they could get the reducer but I should re-line my entire flue with 6". She states that I should re-line the chimney and the draft issues would make my stove work inefficiently. What is actually involved with installing a new liner? As Coaly said "not a draft killer". Would you guys use a reducer and go with it?

I actually got my manual from this site! Thanks....

 

[coaly]

Then you don't have a manual for that stove. The manuals there are for pre 1980 unlisted, and post 1980 listed double door III.
Yours is a UL listed stove made after 1980. Probably a II, since the VI would have a tag on the rear shield and you would know what you have. There is no III in a single door Bear series, only Fireplace Series III.

I'd certainly connect up what you've got with 6 inch (including a pipe damper in-line) since that is the connecting pipe you need for the connection to the thimble, regardless of the chimney flue. The only thing the larger flue is going to do is require you to let more heat up to stay clean, and "pull" the intake air into the stove. (It's not actually pulling air in, the rising gasses create a low pressure in the stove that barometric air pressure pushes combustion air into to fill the void)

When these stoves were invented, there were no liners. They were invented to set on a hearth, block the face of fireplace off with a steel plate with a 6 inch hole in it. The pipe simply went up the flue a bit, and they worked better than the fireplace and cast iron leaky stoves of the day. Fireplace flues are normally 10 X 10 or larger, and they worked ! Granted, they had to run them harder using more wood, both to keep them going, and clean. IF you have a round flue all the way, the difference to making it perfict is marginal. Like chimneylinerjames said, if you have a square flue, the area inside is much more. HOWEVER take into account that a square flue doesn't actually USE all this area for gasses to rise in either. The smoke swirls in a CIRCLE as it rises, It doesn't use the corners ! So if you don't count the corners as wasted space, it's still a minimal difference. If I were in the business of chimneys and relining, I guess I would let the numbers speak for themselves, since most customers wouldn't know how much of the inside of a square flue is used. Many, Many 6 inch stoves are connected to 8 inch chimneys and the owners figure the extra cost or time of cutting wood is not worth the liner cost. With the advent of newer stoves that absolutely require a 6 inch flue, many reline now for some wood savings, and are ready for a new stove when the time comes.

Ace Hardware has the increaser you're looking for. Crimped on the 7" side, 24 gauge. (same as DuraVent, not quite as thick as Selkirk's Heatfab 22 gauge. At least our local store stocks them.

 

[coaly]

Here you go;
http://www.acetogo.com/product/increasr-lg-cr-blk24g6x7.html

I was amazed our store had odd ball stuff like 6X5 and 6, 7, and 8 oval to round adapters ! That's hard to find even in some stove shops without ordering.
Here's the selection most stores have on the shelf !
http://www.acetogo.com/class/heating-and-cooling-supplies/vent-pipefittings/black-pipefittings.html

 

[coaly]

The reason I say "not a draft killer" is because you have enough firebox cubic area for that chimney. (Grandma that heats the same size area and has equivalent surface area has 8 inch outlet, only for open door burning, and works fine reduced to 6 inch flue - against code - but works, and there are PLENTY reduced like that) Just an example of the same size stove made with 8 inch outlet.
The Baby Bear with lower BTU output would have to put more up the stack, lowering the useful BTU to the building.

Notice my comment above; There were Mama and Papa Bears built with optional 8 inch outlets. If one of these chimney guys or inspectors saw one in your home, they would tell you it NEEDS an 8 inch flue ! Same stove ! proof that codes can't be written for every circumstance.

Here's a picture of two 8 inch single door stoves ordered that way. Technically codes do not allow reduction in the size of flue smaller than the stove outlet. Talk to the guy who designed and builds them, you will get a different answer.
(or later, Fisher International research and development)



Here's the stoves;

 

[Unclear]

Guys! This is amazing information, I really appreciate your assistance here. I will be sure to post "finish" pictures of my project and the stove as I want to clean it up and re-paint.

Do you guys have any opinions of what kind of concrete is best to use in this application. I was simply going to build a frame and place wire grid in the mold for strength and pour full of concrete. Wasn't sure if there were any precautions I could use with the heating aspect.

thanks again for the information. You guys are truly awesome...

 

[coaly]

The lower, the better for heating. The higher the better for loading. Just keep it away from the ceiling.

The "pound" mix of cement is not what it weighs or what it will carry, it's the wieght it takes to crush it. A couple hundred pound stove won't deform any cement mix, they are all into the thousands of pounds.
As in "3500 # Footer Mix". Just don't set the legs or ball feet directly on cement. It contains lime and can corrode metals.