Combustion air paired with power vent creates fumes after post-purge


  #1  
Old 02-16-10, 08:20 AM
J
Member
Thread Starter
Join Date: Feb 2010
Location: USA
Posts: 11
Likes: 0
Received 0 Likes on 0 Posts
Question Combustion air paired with power vent creates fumes after post-purge

Tjernlund SS1 power venter is hooked to Lennox boiler firing a Beckett AFG. When the boiler is fired frequently, as it has been during this cold, northeastern winter, exhaust fumes enter the house from the barametric damper and the intake on the burner after the burner powers down and the SS1 finishes its post-purge.

The house is only 5 years old and sealed tight. When the burner fires, the barametric damper swings completely open and draws mass amounts of air up the flu. It seems like the stack pressure can only be maintained properly by drawing lots of air through the damper. This obviously creates a pressure problem when the boiler kicks off.

After the SS1 finishes its post-purge, cold air is sucked back into the stack, picks up ugly fumes, and exits the barametric damper, drifting into the living area of my house.

First, would an outside combustion air kit help out with this problem? Field makes the CAS-2B to fit the Beckett AFG and it seems logical that this would at least mitigate the pressure problem. Tjernlund makes a forced air intake that seems a bit like overkill but would no doubt provide even more combustion air. Does anyone have advice as to whether an outside air kit would help and which one of these (or another) would be best?

Second, if an outside combustion air kit is used, won't air still rush in and out of the barametric damper? If so, is there a way I can also run this outside? I have not seen a 3-way flu system that I am describing (intake, damper, and exhaust) -- although Field's "sealed combustion system" comes close -- so I assume that the damper must stay exposed to the basement. Any thoughts on this?
 
  #2  
Old 02-16-10, 10:22 AM
S
Member
Join Date: May 2006
Location: upstate New York
Posts: 413
Received 1 Like on 1 Post
combustion fumes

I'm certainly no expert, but I have a similar installation with similar problems. What I found (through some investigation) is that the SS-1 venter has a piece outside that has to be adjusted
to block the fan output by a certain amount, according to the output of the boiler. If this isn't adjusted properly, the barometric damper will open wide to keep the burner draft at the right amount, but drawing a large amount of inside air and creating negative pressure which draws fumes back inside when the burner, and then the venter shuts off. Obviously the draft for the burner must be correct, but I found that adjusting that outside piece (don't know what to call it- look at the instructions) made a huge difference in my fume problem. My barometric now opens about 1/3 of the way. My burner tech confirms that the burner draft is OK, and my fume problem is gone. Good luck- Steve
 
  #3  
Old 02-16-10, 11:20 AM
J
Member
Thread Starter
Join Date: Feb 2010
Location: USA
Posts: 11
Likes: 0
Received 0 Likes on 0 Posts
Thanks for the input Steve. I found the SS1 manual and read the draft control chart. It looks like my draft was set too high and that I need to bring the control in toward the house. I will try this later today and hopefully the fumes will be lessened.

I would still be interested in hearing from anyone who may have an opinion on the combustion air system. Another thought I had is adding an oil flu vent between the power vent and the damper. This should prevent outside air from coming in after the burner stops firing. I don't know how to hook this up to the power vent control to make it dependent upon the post-purge timer though.
 
  #4  
Old 02-16-10, 04:53 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: United States
Posts: 2,644
Likes: 0
Received 42 Likes on 35 Posts
When a unit is power vented in tight homes it should always bring air in from outside which creates a balanced flue. The draft regulator may not be needed. The power venter has a draft adjustment. The house is going into a negative pressure.
 
  #5  
Old 02-16-10, 08:36 PM
J
Member
Thread Starter
Join Date: Feb 2010
Location: USA
Posts: 11
Likes: 0
Received 0 Likes on 0 Posts
The draft regulator may not be needed. The power venter has a draft adjustment.
I have adjusted the draft control which is on the outside portion of the power vent. When you say "the draft regulator" is not needed, are you referring to the flue vent I was proposing? This opens and closes to prevent back draft after the heating cycle.
 
  #6  
Old 02-16-10, 08:44 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: United States
Posts: 2,644
Likes: 0
Received 42 Likes on 35 Posts
It really does not. It is used to stabilize the draft in chimney vented products. Check with the manufacturer if it should even be there. There is very stable draft with a power venter.

I have adjusted the draft control which is on the outside portion of the power vent.
To what OF draft?
Again I repeat add the combustion intake air to balance the flue and avoid reducing the pressure in the home.
 
  #7  
Old 02-17-10, 07:14 AM
J
Member
Thread Starter
Join Date: Feb 2010
Location: USA
Posts: 11
Likes: 0
Received 0 Likes on 0 Posts
I will definately add the air intake system. I am considering the flue damper to prevent cold air from seeping down the stack as well. Hopefully this will mitigate my problem with fumes.
 
  #8  
Old 02-17-10, 07:44 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,532
Received 42 Likes on 38 Posts
John, just a quick comment and I am not an HVAC guy. How tight is the home? Have you had the combustion zone tested for negative pressures?

Your efforts seem to be compensation for a condition that should be corrected before the adjustments are made. When I audit a home and discover a home owner has improvised a fix, it tells me the problem is still there, just patched.

Bud
 
  #9  
Old 02-17-10, 08:59 AM
J
Member
Thread Starter
Join Date: Feb 2010
Location: USA
Posts: 11
Likes: 0
Received 0 Likes on 0 Posts
Bud - That's a good point. I do not want to put a bandaid on something that requires a cure. I plan on having a tech come in before I make any changes. I just want to arm myself with the right information so I know what questions I should ask.

The house is 5 years old and has no draft through windows or doors. While this is great for my heating/cooling bills, it doesn't allow my boiler to breathe. When the boiler kicks on, I can hold a sheet of paper up to the basement doors (double doors) which gets sucked into the opening. This tells me that the boiler needs more air.

The air intake seems to be the best way to compensate but I will get confirmationf rom a professional.
 
  #10  
Old 02-17-10, 09:26 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,532
Received 42 Likes on 38 Posts
John, having a CAZ test (combustion air zone) puts the house in a worst case condition, exhaust fans running, dryer, doors, and other possible situations that would create a worst case negative pressure that could pull harmful (or obnoxious) gasses back into your home. When you mention the suction on the basement door, you are correct in a big way. Basements are very easily sealed to become too tight. Not much air gets through those walls. Radon, mold, along with the fumes you are experiencing are issues that need to be watched and radon is totally odorless.

Energy efficiency is important, but so is breathing . Check out HRV's and ERV's along with radon venting.

Bud
 
  #11  
Old 02-17-10, 04:46 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: United States
Posts: 2,644
Likes: 0
Received 42 Likes on 35 Posts
The idea of venting anything and not bringing in combustion air just dosen't make sense whether it is needed on not. If the air inside the structure is used for combustion air where does that air ultimately come from? Outside and the heating appliance has to reheat it as it comes in cracks and crevasses. Balance the flue with adding an outdoor air pipe. The limit of area in the boiler room is 50 cu ft per 1000 btu's inputed. This is a formula from the fifties. I do believe the homes are tighter today!!!!! Some states have changed that to 100 cu ft per 1000 btu input.
 
  #12  
Old 02-17-10, 06:03 PM
T
Member
Join Date: Jan 2008
Location: Nova Scotia, Canada
Posts: 52
Likes: 0
Received 0 Likes on 0 Posts
I have the SSC1 power ventor for my hot water boiler and have been operating it for the past 12 years.
My house is very tight and I have a central heat exchanger/ventilation system.
My furnace is in a smallish room of its own in the basement and I installed a combustion air inlet to it when my furnace was installed.
I just ran a 4" insulated flextube from the inlet for about 5 feet along the ceiling and terminate it in a plastic bucket hung from the ceiling to act as a cold air trap.
Only draws in air when furnace is running.
Been working great.

There are rare occasions when I can smell fumes in the furnace room with the ventor off. It only happens during extremely windy days when the wind blows directly into the ventor outlet. In that case I just close the furnace room door, problem solved. It only happens maybe 2 or 3 times a year.

You definately need outside combustion air for your furnace.

I wouldn't run mine without it.
 
  #13  
Old 03-15-10, 12:37 PM
H
Member
Join Date: Nov 2002
Location: Massachusetts
Posts: 1,856
Received 1 Like on 1 Post
flex and the bucket

I heard of that one also during my school years..., no moving parts, never breaks down, and cheap...only drawback is if your wife can see it
 
  #14  
Old 03-15-10, 07:59 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: United States
Posts: 2,644
Likes: 0
Received 42 Likes on 35 Posts
Don't half step do it right with the CAS kit from Beckett. It will look and work better.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: