Condensation problem

[muncybob]

I have a call into AHS but wanted to put this here for some ideas. My Wood Gun has the optional oil boiler attached to it. When first installed the oil tech said I was gettintg condensation due to the induced draft keeping the stack temps too low. Carl @ AHS told me how to defeat the induced draft fan when oil was running and this certainly did kick the the stack temps up and we mad adjustements to oil burner. This took place last year and we were well into wood burning mode so I only ran the oil for a couple of hours and at the time the condensation issue seemed to be solved. So far this year we have burned only oil due to the relatively mild outdoor temps and after a couple of days I am getting condensation again. Stack temp with the oil running is about 450 to 500 degrees. Initially I started to think that this is a design flaw but AHS states this is the first time they have come across this....any ideas?

 

[bigburner]

where are you getting condensation? If the boiler is sweating then the return temp is to low. 500 degree stack temp should be fine unless it's dumping into a large chimney. need more information!

 

[muncybob]

I'll explain the WG set up in case you are not familiar. The exhaust stove pipe exits the boiler and goes into what they call the "cyclone". The cyclone has piping that goes vertically into a "T" and then horizontaly to the chimney(about a 4' run with a slight incline). The bottom of the cyclone contains an ash drawer. This is where the condensation is ocurring. All stove pipe from the cyclone to and including the chimney liner are 6"SS. The chimney is apprx. 30' high from basement to top.

 

[Chris Hoskin]

check stack temps AFTER the cyclone if you are not already. Sounds like you may be loosing enough stack temp there to cause condensation. Sounds like you've got an ideal chimney, but may want to confirm draft too.

 

[muncybob]

check stack temps AFTER the cyclone if you are not already. Sounds like you may be loosing enough stack temp there to cause condensation. Sounds like you've got an ideal chimney, but may want to confirm draft too.

The stack thermometer is after the cyclone...it's in the vertical stove pipe above the cyclone that connects into the "T".
How would I confirm draft...what exactly am I looking for? I can actually hear the oil burner running when outside the house...sound is coming from the top of the chimney much in the way I can hear the wood burner wehn running. I had thought I could hear it due to the draft?

 

[Chris Hoskin]

sorry, should have said 'adequate draft'. Your oil tech can measure draft to confirm that is is within Woodgun's specified range. Chances are with that chimney you have plenty of draft.

moisture in the chimney comes from two places: condensation of water vapor in the flue gas because stack temps are too low (uninsulated liner, cold/outside chimney, etc.); the other is rain getting past your chimney cap.

 

[muncybob]

The outside chimney is not insulated(not enough room). I've been checking daily for a pattern as I was hoping it was rain water but it's been there on dry days too. The cool chimney temps would make sense if we were getting condensation when burning wood too??, but we are not.

 

[Fred61]

Are you sure the condensation is occurring all the time or could it wet only when starting with a cold boiler. That's a wicked long path and a lot of mass between the oil nozzle to the cyclone and the exhaust temp could be dropping upon starting with a cold boiler. If you can, try to see if is condensing after the boiler is up to temp.

 

[muncybob]

The boiler has been "on" for 2 weeks now so it has not dropped below 160* in that period. Twice condensation has shown up in the last 2 weeks.

 

[Singed Eyebrows]

The boiler has been "on" for 2 weeks now so it has not dropped below 160* in that period. Twice condensation has shown up in the last 2 weeks.

Bob, Is it possible the cyclone is dropping "part" of the flue gases temp enough to condense? while still giving good after cyclone temps. If this is the case you might need to wrap the cyclone/ insulate the drawer to keep it all hot, Randy

 

[Fred61]

Randy may be on to something. The cyclone is the first low temp or room temp thing that the gasses pass through and it's not a wimpy piece of sheet metal. It has some mass to it so it's not going to heat up instantly. I think the gases could pass through it and condense on the surfaces without significantly reducing the temperature of the exhaust. I have a similar situation with a bathroom exhaust fan. The pipe is exposed to the cold air in the attic and produces enough condensation so that I need a drain in a low spot on the pipe although the temp does not show a significant drop.

 

[muncybob]

OK, but why would this happen only when burning oil? The stack temps are a bit higher with oil than wood. Suggesting wrap the cyclone with fiberglass insulation?

 

[Fred61]

OK, but why would this happen only when burning oil? The stack temps are a bit higher with oil than wood. Suggesting wrap the cyclone with fiberglass insulation?

Daaa! Higher air speed with induction fan running????

 

[muncybob]

But I was told to increase my stack temps when burning oil to defeat the fan for lower draft. I was getting the condensation with the fan running.

 

[bigburner]

This is interesting! More questions. Do you have a barometric damper on this unit. Oil burners are super sensitive to draft. Trouble shooting is know ALL the facts then it's easy to fix. if you called me out to fix this I would start at the beginning by asking a bunch of question [ like this forum is doing] Then I would start checking all the basics first. Line voltage, fan condition, oil filter, overall appearance to look for clues, look down or up the chimney,pumps, cyclone etc, combustion air etc. Then it being oil, a stack test should be next to determine if the burner is set correctly. lets assume that the draft is correct & burner is set correctly both air & nozzle. my guess is the problem is also gone.

 

[Fred61]

How did you increase your stack temperature? You've probably noticed that when the induction fan is running that it draws quite a bit of air through the oil burner. I assume when you defeated the induction fan when burning oil you had to increase the intake air on the oil burner otherwise it would be burning extremely rich. The inverse is that when you are burning wood, more air is entering the unit (at the new setting) through the oil burner that should be coming in through the air intake for better combustion.

 

[Singed Eyebrows]

My guess is that when burning wood the cyclone is heated thouroughly & isn't when burning oil. If rain is not the culprit & you say it isn't then it seems a cold cyclone might be. You might want to try wrapping the cyclone, Randy PS , the flue gasses are not cold going into the cyclone & when leaving the cyclone so if you are getting water out of it....

 

[muncybob]

"This is interesting! More questions. Do you have a barometric damper on this unit. Oil burners are super sensitive to draft. Trouble shooting is know ALL the facts then it’s easy to fix. if you called me out to fix this I would start at the beginning by asking a bunch of question [ like this forum is doing] Then I would start checking all the basics first. Line voltage, fan condition, oil filter, overall appearance to look for clues, look down or up the chimney,pumps, cyclone etc, combustion air etc. Then it being oil, a stack test should be next to determine if the burner is set correctly. lets assume that the draft is correct & burner is set correctly both air & nozzle. my guess is the problem is also gone.
"
No, there is no damper. The oil tech set up the burner and coducted draft test, etc. ...seemed to be OK but we really did not run oil enough to see the problem I guess.

Fred, the stack temp rose considerably when the draft fan was defeated and yes, air intake was adjusted accordingly. A larger nozzle was also installed and the pressure was increase to 200 PSI, both done I'm told to get stack temp higher. I guess the possible situation is that perhaps the oil burner is not running long enough now?
Jeff at AHS has me doing a few things this weekend to narrow down the problem...mainly he's looking to increase burn time. I'm not sure why I didn't think of this, but I will be babysitting the cyclone during burns to see if indeed it's geting hot and if not where is the heat stopping at. I guess I should not be surprised to feel that it's not getting hot and assuming this...why isn't it? Was going to start burning wood this weekend but we'll hold off until this is resolved.

 

[muncybob]

My guess is that when burning wood the cyclone is heated thouroughly & isn't when burning oil. If rain is not the culprit & you say it isn't then it seems a cold cyclone might be. You might want to try wrapping the cyclone, Randy PS , the flue gasses are not cold going into the cyclone & when leaving the cyclone so if you are getting water out of it....

I'll be wrapping as long as it's actually getting hot...I'll be checking it good tonight! What I'm concerned about is, according to AHS I'm the first person to report this problem but I know I'm not the 1st person with an oil burner.

 

[Singed Eyebrows]

My guess is that when burning wood the cyclone is heated thouroughly & isn't when burning oil. If rain is not the culprit & you say it isn't then it seems a cold cyclone might be. You might want to try wrapping the cyclone, Randy PS , the flue gasses are not cold going into the cyclone & when leaving the cyclone so if you are getting water out of it....

I'll be wrapping as long as it's actually getting hot...I'll be checking it good tonight! What I'm concerned about is, according to AHS I'm the first person to report this problem but I know I'm not the 1st person with an oil burner.

Bob, I think Fred was also correct, that there is a different/longer smoke path for the oil gun & the gasses might be entering the cyclone cooler than the wood burning. Maybe I misunderstood you, you want to wrap so it gets hot, not if it gets hot. I'll bet the coolest part (drawer & underside of cyclone) will be the most difficult to insulate, this is where I think it's condensing, Randy

 

[muncybob]

Looks like you guys are right. Wife just called and did the "hands on" test right at the end of the oil burn cycle. Bottom(drawer area) was warm but was touchable...the higher up she went the hotter it got until she could not touch without a possible burn. I've never checked out the drawer area like this when burning wood but I will this year. AHS seems to think that if the burn time was extended(either increasing via aquastat differential dial{is already at +20} or with smaller nozzle) condensation would not be an issue. Sound reasonable? In any case tonight I will make the dial adjustment for a longer burn time and will see what I can do to insulate the bottom of the cyclone.

 

[Fred61]

Place a batt of insulation in the drawer.....Just don't forget it!!

 

[Singed Eyebrows]

I would insulate the entire cyclone Bob so the heat from the top doesn't just radiate out, Randy

 

[Fred61]

Randy's right but don't be discouraged if you initially get a little condensation. That cyclone is pretty massive. I'm sure you noticed that if you installed it!! It's going to heat up alot slower than your flue.

 

[muncybob]

Well...problem solved!

I'm not sure why it didn't dawn on me to insulate the cyclone, but that was the fix! I have just temporarily insulated it with R-13 faceless fiberglass but the long term fix will be to insulate it with the special very high temp blanket type insulation. I am surprised at how much warmer the bottom of the cyclone is, I'm now experimenting with the aquastat differential dial to get lower without any condensation.

My next question is, if the temp difference in the cyclone caused condensation there am I getting condensation in my exterior non-insulated SS chimney liner? I don't have room for insulation.