Questions about Draft

[BronxMatt]

Hi everyone,

I have some general questions about draft that I hope will benefit future researches, as well as me.

1. What are the factors that contribute to draft? I’ve read that a longer chimney will increase draft. I also read that pipe diameter, turns and horizontal runs will lessen it. I think I also read that a higher temperature gradient between indoor and outdoor temperatures will contribute (so colder outside temperature would increase draft). What else is there and can anyone clarify these factors?

2. Is draft the kind of thing where the more you get the better, or is it more of a happy medium thing. I have a pretty long chimney, and somewhat mild NYC winters compared to some of my co-members here I’m guessing. Will too much draft have an adverse impact on my burning experience?

3. In what ways can an operator control the draft? Are stove pipe dampers effective? Are there motorized accessories that can match the needs of the fire and help an efficient and steady burn?

Any other draft questions? Dump them here! I’m always scared most by the questions I don’t even know about.

Best,
Matt

 

[stoveliker]

Draft is generated by the temperature difference between the gases in the vertical flue and the outside temperature; warm gases in the flue want to rise.
It is hurt by horizontal flue sections (impedance without vertical distance, diminishing flow), elbows, etc. It is hurt by homes that are too tight (not enough air can infiltrate the home to compensate for the gas exiting the home through the flue. It is also hurt by flues that increase in diameter, causing gases to expand (and cool) and flow slower. It is hurt also by flues that don't retain heat well; cooling down of gases will diminish driving force (rising gases due to their lower density at higher temperature).

More draft is not always good; too much diminishes stove control, risks overfiring, burns wood too fast, and pumps too much heat into the flue, rather than your home.

Stove air control is effective, up to a degree. If draft is too much, a flue damper may be needed (or two).

 

[rudysmallfry]

Once you've sat in front of your over-firing stove, holding a fire extinguisher waiting for your stack to glow red while the flu temp continues to climb with the air shut all the way down, you will know that too much draft is not a good thing. 😊 Provide chimney height the stove requires and no more.

Honestly, the biggest mistake I used to make as a beginner was reloading wood onto hot coals and leaving the air open for too long which quickly created the opportunity for an over fire. Until you're comfortable with how your stove works and how to use your air controls and damper (if you have one), and how to monitor your flu temps, keep the loads small.

 

[bholler]

Once you've sat in front of your over-firing stove, holding a fire extinguisher waiting for your stack to glow red while the flu temp continues to climb with the air shut all the way down, you will know that too much draft is not a good thing. 😊 Provide chimney height the stove requires and no more.

Chimney height isn't always something you really get to choose. There are several ways to limit draft.

 

[Trevor Tahclep]

There are several ways to limit draft.

I keep reading this all over this site but principally it always seems to come down to a stove pipe damper, bholler please enumerate 3-4 other ways.

 

[bholler]

I keep reading this all over this site but principally it always seems to come down to a stove pipe damper, bholler please enumerate 3-4 other ways.

Reduce liner size, restrict the pipe add horizontal run or elbows. But really dampers are the easiest and most effective

 

[stoveliker]

Dampers are variable, all the rest is fixed. A damper therefore is useful to mitigate not only permanent system issues (height), but also weather related changes.in draft.

 

[Trevor Tahclep]

Reduce liner size, restrict the pipe add horizontal run or elbows. But really dampers are the easiest and most effective

Thank you bholler, you have fed and educated my curiosity very well.

 

[Das Jugghead]

Adding a flue damper was the most effective method of controlling draft (overdraft) I have found. My flue is 28' of insulted stainless steel liner inside a masonry chimney, I was going through a load of wood in 3-4 hours prior to installing the flue damper. Now we can run a good 8 hours of heat in moderate weather (around freezing) and 6 hours in sub freezing temperatures.