Chimmney placement

Started by Dustin, August 14, 2006, 04:25:50 PM

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Dustin

The house I'm planning to build is a two storey with a one storey bumpout that will be the living room. I'm planning on putting a woodstove in the living room. Is there an issue with this? Will I be in danger of backdrafts if I don't put the chimney in the main 2 storey portion?
Would having the woodstove direct vent from the outside make a difference?
Here's picture:


JRR

#1
If you've got to have the stove in the bump-out, I would think at the other end of the bump-out (near the main bldg) would be better.  (In the center on the main bldg would be the best of all of course.)  You currently have the chimney at the lowest point of all the roof system ... the higher you place it the better.

And I think there is some design-rule that says the chimney is supposed to extend 2' above the highest roof ridge ... that would be 2' above the main roof apex ... gonna look pretty tall anywhere on the bump-out.

Maybe you could compromise by locating the stove to the other end of the bump-out and by elbowing exhaust vents under the ceiling ... end up with the chimney piercing the side/slope of the main roof, say half-way up.

EDIT CORRECTION:  Elbows should be avoided!


glenn-k

As I recall the chimney spec, it is 2' above the highest point within 10 feet of it.

jraabe

The spec Glenn notes is the most common rule of thumb for chimneys. If you are in a breezy area with the chimney on the leeward side of a taller structure you may wish to get the outlet taller than the rule of thumb suggests. You don't want a chimney in the rolling eddy currents.

JRR

#4
Agreed, but there may be some additional considerations when there is more than one roof level:
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http://www.woodheat.org/chimneys/trichim.htm
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.. in particular, included in the above:

"Don't make the mistake of locating a chimney low on the eaves of a cathedral roof, or in a one story section of a two story house. If the chimney exits the warm part of the house below its highest level, the house might function as a better chimney than the chimney."
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...and:

"If the top of the chimney is lower than the highest living space in the house, cold air will leak from the fireplace when there is no fire burning in it. Simply raising the chimney rarely helps because of excessive cooling."
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(.. The emphasis is mine.  I believe "fireplace" and "woodstove" would be interchangeable words.)


jraabe

#5
A fireplace or woodstove can backdraft, which is what I think the author is saying. Air (usually colder than inside) can be pulled back down the chimney and into the living space through the firebox doors or air intake vents. Nobody likes this - it smells of the chimney and creosote and, if the last fire is smoldering, can contain carbon monoxide (a truly bad actor!)  :P.

Thinking this won't happen if you have the chimney in the right place (centered on the tallest gable) or high enough (at least 2' taller than that ridge line) is a fallacy.  :-[

Airflows inside a modern house are very complex and the stack effect (lift of the chimney air) can be overcome by such things as downdraft range hoods, dryer fans, etc. as well as wind and outside air flows.

This gets into another thread that has been discussed before - indoor air pollution, backdrafting and sealed combustion appliances. I just don't want people to think that there is a magic location for the chimney that will make these problems go away.

Dustin

What I thought. I also read that www.woodheat.com article and am now trying to figure out where I can squeeze the woodstove in the kitchen.
Or I can swap the kitchen with the living room, but then there's not enough room for the dining are, so the dining area is in the living room.
This is the existing plan:






Dustin

This is the "possible fix", moving the kitchen to the bumpout, though I'm not sure if I like having the dining room table there. I thought I might expand the island (add a semi circle to the chair side), but then nobody would ever use the dining area, just the breakfast area on the island.... My wife also is not keen about having the front door open into the kitchen, but I'm not too keen about it opening to the dining area.


Amanda_931

Why do you want a woodstove/fireplace at all?

Because you've always liked them, cannot imagine a house without one.

This will be a major part of your home's heating.

I'm sure that there are lots more good reasons.

You could look at the heated cob bench, possibly going across the top of your plan.  but you'd have the same spacing problems as putting it in the bumpout.

This is from the blurb on the new edition of the book--might be a book now, it was a pamphlet before.

QuoteThey save a lot of fuel, and completely rearrange our concepts of house heating, of wood burning, and of dependency on coal, oil, hydro or nuclear power for our comfort. Rocket Stoves can be built at home by relatively unskilled people. Rocket Stoves are the ultimate in efficiency, reducing wood to carbon dioxide and water vapor, with a little ash. Coupled with heat storage in a cob bench bed or floor they provide gentle heat for up to two days without an all night smoldering fire that poisons the neighbors and heats mainly the sky. They are quite safe for small children as there are no dangerously hot surfaces.

http://www.dirtcheapbuilder.com/rostforcobbu.html

That is, they are safe as long as you have enough stuff on the top--there is a story about an early one catching whatever was on the early part of the bench on fire.

But "used as directed," perfectly safe.


Dustin

I like the rocket stove ("dirt" cheap masonry stove) idea, but it would not work in this house on a basement....too heavy and too combustible in a wood house.  Now a home like Glenn's...or a rammed earth house...
I could put the one storey section on a slab, and the two storey section over the basement, but then I'm running into the same problem again.  


bartholomew

Nice plan Dustin. If I was you I'd just more or less center the stove in the living room end wall and have the chimney exit near the ridge. It is true that in some cases "the house might function as a better chimney than the chimney". However, for that to happen the house has to have significant holes and cracks in the attic to allow air to escape. Since you are building new, just take care to make sure the attic and second floor walls are sealed up tight. If air can't rise out the top of the house, it won't pull air down the chimney. But as John says, ventilation fans can still easily overpower a chimney. To avoid that you have to make sure the ventilation system is balanced, with equals amounts of air pulled in as is pushed out. You could also consider a stove with its own direct air intake. If I remember, the woodheat.org guy doesn't think that is ever necessary. But as with the "house functioning like a chimney", I think he might be underestimating the air-tightness of modern construction.

Amanda_931

But if you're wanting a fire for heat, or good looks in a cold climate, then end wall placement, particularly of a fireplace, but to a lesser extent a wood stove, is the kind of thing that gives fireplaces a bad name.

I once read a serious condemnation of all fireplaces that went approximately--"since they and their chimneys are always outside the building, they lose heat horribly and transmit cold into the house through the stone or brick" as if there could be no other placement.  

Which is why I liked John's little bumpout (bum-pout?) with a trombe wall so much.

Dustin

I agree central placement of a wood stove is a good idea. Finding a way to put the chimney in the middle of the house when you didn't plan for it is...a problem. Since I grew up in Southern CA where heating is never an issue and central air is king, I had to educate myself.  The fire would be lit a couple times a year for decorative puroses. This is just another example of me catching up to moving to another climate....  My first experience with a woodstove has been at our ranch. They have some very interesting little cabins there. I think there were modular pre-manufactured units, say in 4 sections, trucked up and bolted together. Very wierd. Quality is like a mobile home.  I'll have to post the plans and pictures sometime.

I may settle for just putting the woodstove at the far end of the bumpout in the middle, if not I've got to re-do some plans, because things are going to have to move around.
Thanks,
Dustin





jb52761

My two cents.....I installed my stove by myself last fall in my cabin. Had never done it before, so I did alot of research online, etc......it worked GREAT all last winter and I see no probs. The first few weeks of burning, I put in a carbon mon. detector to be sure.....no alarms. I found a wealth of info here   www.hearth.com  ...they have a great forum just like this one, helped me out alot.....I'll try to send a pic.......jb



JRR

Got pumice?

Here's a discussion of chimney subject from old episode of This Old House that includes chimney insulation.
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http://www.thisoldhouse.com/toh/knowhow/heatingcooling/article/0,16417,216596,00.html