Chimney draft problems in 1824 farmhouse


  #1  
Old 09-30-12, 02:50 PM
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Unhappy Chimney draft problems in 1824 farmhouse

I have been scouring the web for information to help me with my chimney problem and I am hoping some forum readers have some ideas.

My house was built in 1824 and has the original brick chimney in the center of the house. There are four flues and three fireplaces. One flue was relined with stainless steel in the last 10-15 years to vent the oil-fired boiler in my basement. I have one large fireplace with a side bread oven which has a throat damper. The other two fireplaces are smaller "rumford" style (shallow depth) fireplaces that have no dampers. I have two chimney balloons for these which I use to keep my heat from escaping. The whole chimney is on an approximately 15-20 degree angle as it runs through the house. As far as I can see, all of the fireplace flues are unlined masonry.

My problem is this: in the large fireplace and one of the smaller ones I consistently get smoke exhausted into the room almost every time I try to build a fire. All of my smoke detectors in the house go off. Some smoke appears to be drafting up the chimney but some is coming into the room.

Things I have done so far:
  • The flues have been cleaned by a chimney professional recently (cleaning had no effect). There are no obstructions.
  • I have tried fires in 20-degree weather and in 50-degree weather and the outdoor temperature and wind conditions appear to make no difference.
  • I have tried having the windows and doors wide open and also tried having them closed, with various outside temperatures. There seems to be a slight improvement when I have my front door wide open when the weather is below freezing outside.
  • I have tried holding a piece of burning newspaper as close as I can to the throat of the fireplace and can see the flames flicker and smoke will go up the chimney.
  • I have tried various positions for the damper in the large fireplace. When it is closed the smoke is worse. When it is open, the smoke is better, but not drafting up the chimney enough to keep it out of the room.

The ironic thing is that in the second small fireplace, there is an excellent draft and I have had great fires of various sizes in it every time I light it. No "priming" with newspaper has been necessary. This fireplace that works is identical in size to the other small one that doesn't draft well.

Can anyone help me out with an idea that might solve this problem? Is it likely the same problem with both fireplaces or different problems?

Thanks!
 
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Old 09-30-12, 04:12 PM
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I'm north of you and have lived with a fireplace or wood stove most of my life, stove is running right now. But most importantly, I'm an energy auditor who has studied draft issues so there is a good chance I can explain what is happening.

You have and use chimney balloons so you are aware of the heat loss from these old beasts when not in use. Unfortunately they aren't much better when they are running, as so much of the energy the wood produces goes up the chimney, or at least should. But they can be enjoyable.

First, are all of these fireplaces on the same floor, which floor/s, and how many floor in the house. Is this chimney fully enclosed within the structure of the house or on an outside wall? Is there a set of stairs to an attic or attic hatch that is not well air sealed?

When it is warn inside and cold outside there will be a natural flow of air into the lower portions of a house and out of the upper portions, we call it stack effect. The opening and closing of windows and doors alters the in and out flow of air and can hurt or help. Dampers open when trying to start a fire.

Are you planning on using these for heat or enjoyment?

Give me their locations and I will go from there.

Bud
 
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Old 10-01-12, 12:24 PM
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Thanks for your help Bud. I put my answers below:

First, are all of these fireplaces on the same floor, which floor/s, and how many floor in the house?

The house is a two-story colonial with a walk-up attic and full basement. The fireplaces are all on the first floor.

Is this chimney fully enclosed within the structure of the house or on an outside wall?
The chimney is fully enclosed by the house - it is actually dead center in the floorplan, so not on an exterior wall.

Is there a set of stairs to an attic or attic hatch that is not well air sealed?
There is a door to the walk-up attic that is not weather sealed. The house has been fully insulated with fiberglass in the walls (drywall removed, fiberglass laid, new drywall installed) and cellulose in the attic floor.

Are you planning on using these for heat or enjoyment?
Primarily for enjoyment, especially the big one with the bread oven. Also, in an emergency for heat. We have thought about installing a hearth stove in the big fireplace which I think would require a metal liner.

Regarding stack effect, I had thought that if I held up a piece of burning newspaper inside the flue that it would "prime" the cold air with some heat and start a proper draft. Maybe I have not been putting enough effort into this.

Thanks again for your help...




 
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Old 10-01-12, 12:55 PM
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The "not well sealed door" to the walk up attic may be leaking a lot of air. The more that leaks out, the more that would be needed to leak in, thus an increased draw on those fireplaces to want to provide air into the house, aka backdraft. You can add a temporary seal for now.

If you go into the basement, and inspect around that chimney, is there an open gap allowing air to flow up? Being that big and complex we will have to speculate what amount of leakage may exist around it. Inspect from the attic as well. All combustibles need to be at least 2" away from that chimney (check local codes) and even that could still be a concern without liners. If you add anything to block the air flow it needs to be metal flashing or other fire approved non-combustible. Basically, you want to block all leaks to the outside. That will reduce the demand for incoming air and reduce the pressures affecting the fireplaces.

Adding a combustion air source in the basement for the furnace may also help.

Are there clean out doors for those flues in the basement. Check to see if air is being pulled out.

Burning a piece of newspaper to get a draft started is a common approach, but with a masonry chimney it takes a lot to warm the chimney. But here is another problem. Even if you establish a good drafe in the presence of the poor pressure conditions you currently have, as the fire dies out and the chimney cools, hot coals buried in the ash will still be producing lots of carbon monoxide, CO, a poisons gas. So, it is important to improve the draft conditions for safety as well as the reduction of unwanted smoke.

By reducing leakage to the outside, even if it is coming from the basement, you will be reducing the negative pressure in front of each fp. Bath fans, kitchen exhaust, your oil furnace all send air to the outside and complicate the draft you need. Check those areas mentioned and let me know.

Bud
 
 

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