Stovepipe under negative pressure?

[toddm]

A complicated question. Sorry. The "chimney" in my passive solar house is actually a 5'x5' vertical chase designed to move heat from the solar-heated part of the house to the rest of its rooms, mostly upstairs. It does so through an adjustable ventilator (220 cfm max) mounted in the chase and drawing air from it. The chase draws air from four registers downstairs and the ventilator distributes it through ductwork to three bedrooms and two baths. So far so good.

The chimney terminates downstairs is a "fireplace," which is to say that I welded up a quarter inch steel surround meant to look like one but actually to serve as a home for a 60kbtu/hr wood stove. The surround has glass doors and an outside air supply. It also has a plenum and a register that will move most of the radiant heat to the remote parts of the house via the chase and ventilator. My aim is genteel wood heat: everyone is fully clothed at all times, at least until they go to bed.

Belatedly I am mulling two problems involving the stove pipe, which rises 20 feet through this vertical chase. Should I be worried that ventilator, creating negative pressure in the chase, will draw smoke from the pipe? Should I be concerned it will be cooled too much for a proper draft? The stove pipe is 5", and the plenum opening is 6" so I could use duct pipe to separate chase and stove pipe. Your thoughts?

 

[dave11]

I might not be following your description very well, but I can't quite figure out a couple things. The flue from the stove rises through the chase, but never communicates with it, yes? If so, then the draw from the fan in the chase is not material. It might cool the flue too much, so you wouldn't want it running at the beginning or end of a fire.

Also, I don't follow the part about "redistributing radian heat." Do you mean convective heat?

 

[dave11]

Wait, are you asking whether the draw from the fan in the chase will keep the stove from drafting properly? It might a little, but air upstairs can return to the stove level (I assume), and since technically the house is "sealed" you are not really creating much worse of a stack effect than you have without the chase fan running.

 

[begreen]

Although I give credit for some ingenuity, in this case it sounds like it could be a bit too much. I'm not too comfortable with the design, especially the enclosed stove. But maybe I am not visualizing it well. I have never heard of installing a stove venting system in a duct chase and will have to look this up. I suspect is against code but can't quote it. In the meantime, can you post some pictures of the setup?

 

[fossil]

I don't know whether or not I'm envisioning this correctly, but it sounds like a solid fuel-burning appliance with its own flue to daylight, surrounded by a glassed-in enclosure at the bottom of a large vertical conduit from which air is removed and distributed through the living space of the home. If that's an accurate description of what you're talking about, then I'd have to say it's a non-starter. Mechanical codes typically require a 10' separation between a solid fuel-burning appliance and a simple return register. You're proposing to essentially place the entire stove inside a giant return register. Maybe I'm not reading this correctly...plaease straighten me out if that's the case. Rick

 

[toddm]

Not the best picture... The vent inside the surround leads to outside air supply through 6 inch ductwork. The vent on the bottom face of surround directs room air around the surround -- but not the stove -- and up into the chase. With glass doors mounted and closed, the stove will not communicate with the house or the vertical chase. I can't see how this is any different than a fireplace blower except for piddling cfm in my case. The ventilator is likely optional, in fact, because convection should circulate air. My question is whether I should separate the stove pipe from the chase as well by putting it inside a 6 inch duct.