Picked a very nice Mama Bear this weekend!

[Mark in VA]

Over the weekend, I purchased a very nice Fisher Mama Bear that I plan to install in the Baby Bear's place before next fall. Hopefully, the Mama Bear will give me the extra heat that I need in the house, with some longer burn times. The Baby Bear will most likely be moved to a three-sided pole barn that I plan to close in this summer and convert to a small work shop, where I think the smaller stove will be more efficient.

As I mentioned in a previous post, I'm limited for space in the house and will need to add some additional wall shielding before the Mama Bear is installed, due to it's extra depth, and I just wanted to clarify a few things about proper shielding. For years I had been under the impression that the durock and tile on the open studs was enough, but after reading many posts here on the form it's apparent that without the 1 inch air space it doesn't give me an approved method of clearance reduction.

If I understand what I've read here and in the NFPA guidelines correctly, I can safely get down to 12 inches from the combustible studs behind the durock by adding a sheet metal shield (open at the bottom and top) with a one inch air gap between the shield and the wall. By the measurements of the Mama Bear, it looks like I will have 16"- 18" from the rear corners of the stove to the tile on the adjacent walls and a little more than that to the actual corner directly behing the stove. The shield would cover both of the corner walls and would be tall enough to reach to the bottom of the thimble to shield the pipe as well.

So I guess my question is, with the heat shield I'm describing, will this be a safe installation? All advice is appreciated.

Thanks again,

Mark in VA

 

[coaly]

You will like that Mama so much better !
Sounds like you're referencing the clearance reduction table (12.6.2.1) with materials and specifications for wall protection correctly.
Duplicate of table 2 here; (broken link removed to http://www.maine.gov/dps/fmo/documents/2005Woodburningguide_001.pdf)

(e) states; 24 ga. with ventilated airspace allows a 66% clearance reduction. The table also was designed to prevent combustible surface temperature exceeding 90* f above ambient air temperature.
2013 is the current standard being used and 2016 is the next edition. Seems all the newer versions use the same specs, but put everything in sentence form leaving more for interpretation and a legal degree to understand.

As an example of what a little air space does, with your finger an inch away from a hot surface, you can go all the way down to about 1/8" without burning your finger. A quick touch burns, so that shows the insulating factor of the air space between your finger and hot surface. 1/8" being almost as good as 1 inch. Your cement board and tile works the same way transmitting heat in contact with the combustible surface behind it. If you stand a piece of cement board up close to a stove, the back feels just about as hot as the front facing the stove. That shows high conductivity, not to be confused with resistance. (R) It's all about the air carrying the heat away.

 

[Mark in VA]

Thanks, Coaly! I'm hoping that I'll like the Mama alot better too!

Not that there's anything wrong with the Baby bear, it's just too small for the area I'm trying to heat and the burn times that I need. I think putting it in the future workshop that I'm planning will work alot better for that stove too, since it's a much smaller area and I won't need continuous, 24 hour heat in the shop.

Thanks also for the advice on the wall shield. I'll work on getting one frabricated here soon.

Mark

 

[coaly]

Baby just doesn't hold enough to be giving off good heat in the morning with a pile of coals to kick it right up. Mama will not only be going in the morning, but you should gain coals with 24/7 burns until you need to open it up and burn them down for loading room. Up here, too many coals glows all day, but doesn't put out enough heat so we need to burn it down. You may not need to burn that hard where you are, so every few days you can skip loading in the morning and let the pile heat the house all day until it's time to reload. I got away with 3PM loading after a few days of hard burns when the coals built up too much. Could never wait longer than 3 since we needed it for cooking supper before 5.
When we had the Mama as the only heat source, it was only the best oak we had nonstop. I would clean out the ash near the front where it burns down the best and rake the coal pile ahead to build the next fire on. Never needed to let it die to empty ash that way. For this winter, we would have needed a Papa in it's place for our 1800+ sq. ft. There's no interior doors in my place, and one small fan in a wall to equalize the heat. Open floor plan with chimney in the center of kitchen.
I built the place to heat easy, so that's the only reason a Mama could do it. The reasons for no longer using the Mama Bear is due to needing it in a log cabin for now, and I fell into a brand new Kitchen Queen I really wanted for a long time. At least 3 times the cook top, oven, water heating and a bypass for summer cooking without heating the 900 pounds of steel stove. Someone is also normally here to load it and keep it going very steady. My best investment was a simple $10 thermometer that holds 24 hour highs and lows. I find we get a little lax on warmer days and end up with a 68 low overnight and 75 high day. On colder days in the single digits and below at night, I end up with 75 low and 77 high. That's a very small span to maintain with a wood stove but that's what it repeatedly does when it's cold enough to make it really work. Really gets difficult when temps warm up above 50. That hasn't happened yet with teens at night, low 30's days. So next month we can only wait until the house cools down too much to start a fire and suffer when it gets too hot. That's when a Baby Bear comes in handy on another chimney for those shoulder season nights.