37' of Exterior Flue for Pappa Bear
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I was under the impression that a longer run helps draft but then I was wondering if the run was too long would the gasses at the top cool off and slow the drafting process.
They do cool, more so in an unisulated flue of course and yes, the taller the flue, the more draft. However the taller the chimney, the more heat that is required to achieve the increase in draft. Charts use degrees over ambient air temperature instead of internal temp since it is differential temperature that causes the differential pressure. If all things remain unchanged, a doubling of chimney height results in an increase of 41% flow capacity. (charts will use relative capacity factoring in temperatures) Average flue temperature is what draft is based on. So the more cooling, the lower the average flue gas temperature.
That said, there are many factors that decide if your Papa Bear has enough heat loss to heat the chimney as well as heat the area you're trying to heat. That is the key. You can always make it work, it just cuts into efficiency so a smaller stove won't have the capacity to heat both the chimney and indoor area as well.
Positive draft (low pressure) is caused by the chimney. Everything else reduces draft which is the connector pipe, elbows, spark screen, and the variable resistance of a flue damper. This is System Resistance Coefficient. Capacities are relative to a 20 foot high chimney which is arbitrarily given a capacity rating of 100. Heat loss effects are included. It is specifically for a masonry chimney with internal area of 38 to 50 sq inches. When you go by charts to find your chimney, and get the rating number, you then subtract the resistance which is given for elbows, straight pipe, tee, screen etc. The last factor is the Stove resistance itself. This is mostly due to the air intake square inch area. It varies greatly by flue diameter used. Example is a large stove like yours only has 5-20 with 6 inch and resistance value of 15-160 with an 8 inch. That's why it's difficult to give you a yes or no answer with many other factors needed.
Generally it will work OK, IF you have a rear venting stove with double wall pipe inside with minimum horizontal run. You can't expect a top venting stove with single wall pipe that includes one 90* elbow, a horizontal run and a tee (at chimney flue bottom) to work well when adding so much resistance and loosing so much heat. An internal baffle also adds to stove resistance as well as less available heat to the flue, so if one is present or added, it has to be adjusted for more heat loss out the outlet or removed entirely.
This isn't saying you won't experience stalling issues when starting on a very cold day or different weather conditions. Compensate for these factors with operation.
That said, there are many factors that decide if your Papa Bear has enough heat loss to heat the chimney as well as heat the area you're trying to heat. That is the key. You can always make it work, it just cuts into efficiency so a smaller stove won't have the capacity to heat both the chimney and indoor area as well.
Positive draft (low pressure) is caused by the chimney. Everything else reduces draft which is the connector pipe, elbows, spark screen, and the variable resistance of a flue damper. This is System Resistance Coefficient. Capacities are relative to a 20 foot high chimney which is arbitrarily given a capacity rating of 100. Heat loss effects are included. It is specifically for a masonry chimney with internal area of 38 to 50 sq inches. When you go by charts to find your chimney, and get the rating number, you then subtract the resistance which is given for elbows, straight pipe, tee, screen etc. The last factor is the Stove resistance itself. This is mostly due to the air intake square inch area. It varies greatly by flue diameter used. Example is a large stove like yours only has 5-20 with 6 inch and resistance value of 15-160 with an 8 inch. That's why it's difficult to give you a yes or no answer with many other factors needed.
Generally it will work OK, IF you have a rear venting stove with double wall pipe inside with minimum horizontal run. You can't expect a top venting stove with single wall pipe that includes one 90* elbow, a horizontal run and a tee (at chimney flue bottom) to work well when adding so much resistance and loosing so much heat. An internal baffle also adds to stove resistance as well as less available heat to the flue, so if one is present or added, it has to be adjusted for more heat loss out the outlet or removed entirely.
This isn't saying you won't experience stalling issues when starting on a very cold day or different weather conditions. Compensate for these factors with operation.
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