How to combat condensation in chimney?

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  #41  
Old 02-25-15, 11:42 AM
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Do you know how many btus are produced by 0.4 nozzle that are left in the volume of gas at 200f and how many are required to heat an outside flue above the dew point.
No, I do not. I've never even thought about calculating it!

My gut feel is the only thing I'm going on.

Let's just do a 'ballpark what if' scenario. These are off the cuff GUESSES.

Let's say the firing rate is 1 GPH. That's 140K BTUH.

Let's say 85% combustion efficiency.

So 15% of the heat is up the chimney at some velocity. 21K BTUH.

Not all of that heat is going to go into the chimney, the majority of it will be pumped out to the atmosphere.

But let's say that HALF of the heat goes into the chimney structure just for sake of argument. Make it a nice round 10K BTUH. (about 3kW)

Consider the mass of the chimney and the temperature extremes it's exposed to.

Does your gut feeling tell you that you can heat that chimney to 130F with 10K BTUH ?

Mine doesn't.

maybe a source of outside cold air entering the flue.
No, not possible. It's a 6" double wall chimney (INSULATED) with a 4" CONTINUOUS LINER (also insulated) inside of it.

Unless you mean the air that comes in the baro damper... nothing I can do about that!

should no way no how be condensing unless you still have very short burner on times and very long burner off times to allow the chimney material to cool to the dew point temperature
Tell that to the chimney!

GROSS gas temp at the breech is about 370F. Where the pipe enters the base of the chimney, the gases are already at about 220F due to dilution air from the barometric damper.

Burner run times average about 7 minutes, a bit longer when very cold of course, a bit shorter when milder.

It condenses LESS when the weather is warmer in spite of the shorter run times.
 

Last edited by NJT; 02-25-15 at 02:03 PM.
  #42  
Old 02-25-15, 12:40 PM
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Let's say the firing rate is 1 GPH. That's 140K BTUH.
Let's say 85% combustion efficiency.
So 15% of the heat is up the chimney at some velocity. 21K BTUH.
It's worse. The 140,000 Btu/gal is the higher heating value of the fuel, which includes the latent heat of the moisture in the flue gas. The lower heating value is about 9,000 Btu/gal less.
 
  #43  
Old 02-25-15, 05:26 PM
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The baro damper could be eliminated if you have a one story house and a insulated flue from top to bottom especially when the burner is a Reillo as it will tolerate a large swing in over fire pressure .My gut feeling is a seven minute burn time which is considered short cycling is the source of your condensation .
 
  #44  
Old 02-25-15, 05:34 PM
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The baro damper could be eliminated if you have a one story house and a insulated flue from top to bottom
No kiddin? You mean I can just wrap it up in aluminum foil like I seen the hacks do? Gosh, I didn't know it was that easy!


especially when the burner is a Reillo
But it's not, and won't be.


a seven minute burn time which is considered short cycling
By whom is it considered?


How about we just agree to disagree and quite while we're ahead?
 
 

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