I am hoping through the combined wisdom of everyone, I might be able to identify a solution to a Exhaust problem on my furnace.  I know what the problem is, and the LARGE ($$$) solution, but I am looking for a temporary fix until I can save up enough money for a new furnace.  

The current set up is that the original furnace for the house is an old coal furnace, retrofitted to burn oil.  It is 1930's-40's vintage, asbestos wrapped boiler.  It stands about 4 feet tall, by 4 feet deep, by 3 feet wide.  The exhaust pipe coming off the back of the furnace goes up at a 45 degree angle to where it goes through the stone chimney in the basement of the house.  

The house was built in 1806.  It has double layer stone walls, and a two level fireplace.  The basement and the first floor have a walk-in fireplace.  The chimneys from these two fireplaces are seperate, until about 12 feet from the top of the chimney.  

The furnace pipe penetrates the basement fireplace/chimney, and then ends.  The flue gases are designed to go up.  

This is not happening all the time.  Every now and then I get the smell of burned fuel oil drifting into the first floor.  The house is pulling a draft, and bringing basement air upwards into the main house.  I am thinking until I can get a new furnace (and complete upgrade of the circulation system to more than one zone) I would like to connect the exhaust to a chimney pipe all the way out to the top of the chimney.  

I have enough room to run pipe up the chimney, as I could climb up the entire chimney if I needed it (it is that big).  Can I use 6" pipe to connect to the main exhaust where it comes through the stone wall?  That pipe is 8" or larger.  Or do I need to maintain the size of the exhaust pipe all the way up?  

Any other thoughts or ideas?

Thank you,

John

I would go with 8 or 10 inch if it were me.--- I used to have that type conversion and that is what it used, 8 inch, --- smaller might not handle the ignition blast on firing, ---just my thought, as you have a lot of pressure in the firebox when these burners ignite, then turns steady. This blast needs a pipe big enough to handle it.---trust me! -- I had a 6" pipe to start with and it would blow it off when burner ignited, was fine after that.---10" solved that.

These gas furnaces use 3 or 4 inch pvc for vents!--talk about changing times! lol!!

It sounds like the furnace gases go up the chimney to the 'common' section, then cooling down and come out the fireplace.....

If so...one idea is to have a fire in the fireplace to prevent the 'downdrafted' oil fumes.

some ideas....

You could, maybe be able to run insulated pipe from the oil furnace ALL the way to the top.

 A smaller diameter pipe may increase the exhaust speed, that would be good..get rid of HOT gases before they cool down.

I'm wondering what the creosote buildup looks like....

Shutting FP damper only slows down the fumes to a whiff instead of a gag...

My gas water heater exhaust is a one piece unit 'up the chimney', maybe they make them for oil furnaces too ?

 

Good point Jay..

shameless dude wrote: I don't think I've ever seen a walk in fireplace???

  Me neither,,Shameless,,,maybe he uses thet big thing for roastin a half beef,,,,,

okay, so we're talking about gravity-draft here, not forced-draft.

In ANY chimney, the actual concept of WHY they work, is gravity. 

An open fire, in the middle of a field, has oxygen coming in along the ground, into the fire, and as the fire burns, it heats the surrounding air, and with rising hot air, the combustion products rise.  The hotter the fire, the greater the difference in air DENSITY... the cold air is heavier, the hot air is lighter,.. that means air in the center, directly over the fire, wants to RISE.

A chimney isolates the hot exhaust air, from the cold supply air.  By keeping the hot exhaust air consolidated, for a longer time, causes it to rise considerably faster, and at the bottom, where the fire is, cold air is coming IN, thus supplying the fire with more combustion air.  Hotter fire, faster fuel burn... essentially, gravity (cold air pushing down) is 'turbocharging' the combustion process. 

The problem is, that a fireplace's fire SIZE determines the chimney size.  A chimney that's way to big for a fire, doesn't properly isolate the hot combustion air from the cold surrounding air.  Small fire requires a small chim, and vise-versa.  Your oil furnace is probably developing just-enough-waste-heat on full-blast to generate proper draft. 

Next... the chimney must NOT have any obstructions...  a bird's nest, partially blocking the cap, is sufficient to restrict airflow at the top, enough to cause the gases to 'back up' just a little, and in doing so, slow down, and lose heat, thus... not rise fast enough.

Next...

The house is old.  It was built before all these fantastic insulating windows and tight-sealing doors... and to have proper draft up the chimney, there must be cold air at the fire.

If you crack open an outside window for a few minutes and the furnace smell goes away, you need more combustion supply air.

And yes, if you install a liner in the chimney, to size it down commensurate with the furnace, it WILL improve the surface area/fire heat ratio  required to enforce natural draft...

What I would do, is consider a high-efficiency forced-draft furnace, and pipe PVC exhaust out through the wall, or drop PVC down the chimney, and then seal the top of the chim to it.  I would NOT personally bring in the combustion air separate from the outdoors, instead I would pipe the intake to low near the basement floor.  By doing so, the furnace will draw in any subterranean gas products, radon, etc, and burn, and eject it out the chimney, helping to restore the original air-quality circumstances that an uninsulated house naturally got from the presence of a chimney.