Outside temperatures and effect on draft

[mar13]

This is more of a theoretical question because I can't change my outside temperatures. Anyhow, I live in a relatively mild climate (near freezing is a cold winter morning, more often upper-mid 40s and wet), but I read reports about how people's stoves take off in cold weather. When nerding out on Gulland's webpage (http://www.gulland.ca/fhs/temperature.htm ) about drafts, he has a chart for pressure differences for different temperatures differences (average stack temperature vs. outside temperature) for different stove heights. Below is a graph of his chart's table for a 20 foot stack (perhaps relative to midpoint of house pressure?)

Anyhow, doing a bit of interpolation, I plugged in the difference between 300 degrees ( stove pipe averaging 350 degrees, outside 50 degrees, 350-50=300) and 350 degrees (stove pipe averaging 350 degrees, outside 0 degrees , 350-0=350). My estimates for pressure differences were 28.1 and 31.4, respectively. Is that a big difference? Or is it an issue of circular feedback where a little extra draft increases air, which increases fire heat, which increases the draft further.

I do see that the effect of the delta in temperature is greatest for the lower values, and I have no real idea what is the "average" value of my stack temperature.

Sorry if I made your head hurt. It's just something I'm curious about.

 

[jetsam]

Temperature differential influences draft. We tend to talk as if it's the only factor because it's easy to observe and measure.

However, it is not even always the biggest factor. Ask anyone who lives in an inversion zone!

 

[mar13]

Temperature differential influences draft. We tend to talk as if it's the only factor because it's easy to observe and measure.

However, it is not even always the biggest factor. Ask anyone who lives in an inversion zone!

And then I wonder about humidity, such as cool foggy days vs. cold crisp (low dew point) days.