Unlined flue + new oil furnace = ?

[mfglickman]

Curious what y'all think. Our house is a center chimney cape. None of the original fireplaces is currently functional but the flue from one is being used to vent the 2010 high efficiency hot air oil furnace. Like all the flues this one is unlined. People IRL seem polarized on the issue - either it's no big deal and not to worry or it must be lined immediately.

I'd love to hear your thoughts or advice!

Thanks
Mary

[Texas_Ranger]

Unlined flue + new oil furnace = recipe for disaster

High-efficiency furnaces, boilers, water heaters etc. tend to cool down the exhaust fumes as far as technically possible to reduce heat loss through the chimney. That means the gases can condense on the cold walls of the flue and drip/run down as a seriously nasty liquid. It's typically acidic and it will activate any old soot in the flue, potentially making it saturate the brickwork and seep through paint and everything. We had that issue with a gas water heater (not even a high efficienca model) and got huge brown stains all around the chimney (that was plaster over brick, so the mositure could seep right through the brick, plaster and paint). So... I'd strongly recommend lining the chimney! (and not with clay liners). It might work for some time and slowly wreak havoc on your walls/chimney. In our case the water heater was installed in 1998 and the stains weren't noticeable in late 2004 when my grandmother bought the house. They became obvious very quickly then, I think we had the chimney lined with stainless steel in early 2006.

[jwesevich]

Yes, exactly what Texas Ranger said. I had the Burnham rep come out and check out our setup because I was worried about the same thing,and he said the same thing.

Fortunately, steam boilers are so inefficient that it wasn't an issue for us as it was like 2k to get the flue lined. He did say that if we were still concerned, we could get a C0 detector and put it near the part of the chimney exposed in the attic.

jeff

[SkipW]

+2

Here in Maine, you cannot install any new unit without the chimney being lined, nor can two units share the same chimney. Luckily, the previous owner did both chimneys Stainless liner for boiler and Supaflu for fireplace, so when we went with the new Buderus oil fired unit for heat/hot water, we had no issues.

[jharkin]

EDIT - Ignore everything I said. Didn't realize you don't even ave a clay tile liner. Yes you need that fixed.

-----


Our 83% gas boiler is vented into a 15 year old clay lined flue. We got differing opinions as well.

Sweep says must be lined with stainless (he gets $$$).

The boiler tech says that lining is required by code but unless its a condensing unit that clay liner is OK. He also said that the acidic erosion issue is mostly an issue with gas units because of the lower flue gas temps and higher amount of water vapor in gas exhaust. Metal liners for gas must be stainless, but apparently oil units can use a plain steel liner, similar to woodstoves.

Or was it the sweep that said don't bother and the boiler guy said do?... Hmm don't remember exactly... But the bottom line is hat the boiler was installed in 2005 by the gas company and passed inspection so I imagine what they did was code legal at least in 05.

....


BTW, if your unit was a condensing furnace, it would have a power vent, usually piped into PVC directly outside, along with a dedicated outside air intake. The fact that they vented it into an existing chimney tells me that its likely a natural draft appliance and probably below 90% efficient. Lining cant hurt but may not be the dire emergency you suspect.


Go over to the "wall" forum at heatinghelp.com. Some really good HVAC pro's there who can help.
http://www.heatinghelp.com/Forum

[Texas_Ranger]

Apparently with a regular unit it depends on the way the chimney is built. In Vienna it's standard practice to connect gas boilers to unlined flues and I never heard of any issues. At the farm we had a gas water heater vented the same way and had lots of trouble. According to what I heard the difference is the height of the chimney - in Vienna you mostly have 5-storey buildings with very tall chimneys that draw well. A much shorter flue in a one-storey house won't draw nearly as well and cause trouble down the road.

Good point on the water vapor, gas does consist mostly of CH4, which means H2O after combustion, whereas oil doesn't contain as much hydrogen as far as I know. On the other hand, it might contain sulfur and other corrosive substances.

[Don M]

How is your furnace vented thru the old fireplace flue? Did they cut a hole in the floor of the fireplace fire box & simply vented it up the original flue? Is the fireplace bricked in or does it just have a piece of wood or sheet rock covering the original fireplace opening? That's how our furnce was vented in our 1700 vintage farmhouse! I was only 8 or 9 at the time but today I would be worried about CO infiltration into the room !

[mfglickman]

Hmmm, it looks like the mfr makes max 83% efficiency units (Armstrong Air, oil, furnace). The part that the service guy replaced yesterday was a controller that he said was covered in sulfur from condensation from the chimney. The furnace would not turn on b/c the part had failed.

As far as how it was done, I don't know...it's the dining room fireplace and it's covered and painted white, plaster or wallboard, but I don't know what's behind it. The other chimneys are sealed - I can see the metal sheet and can't look up it.

In the crawlspace, near the furnace, there is a little iron door that you can open to see (with a mirror) that the chimney is not lined.

There is a CO detector plugged into the dining room wall outlet. I may add one to the bedroom that's adjacent to the chimney on the 2nd floor as well, while waiting for a chimney guy to call me back.

I'll update when I have some news. Last night I turned the heat off around 1 AM and back on around 6:30 but that's not going to cut it if this winter is as hard as it has started out to be!

Mary

[Texas_Ranger]

If there is sulfuric condensation going on, I'm willing to bet you're going to have issues with your chminey fairly soon! Better get somehing done before it ruins your walls! If the flue is in good shape, CO isn't that much of an issue right now, but soot bleeding through everything is absolutely not nice! Besides, you don't really know whether the flue is in good shape.

[Tao]

I and the POs ran an oil heater through an old 2 1/2 story chimney for years. This place was a handy man special but it was all I could afford at the time. When I gathered sufficient funds for the $1800 chimney liner I had it installed professionally. Later I was replacing plaster walls and got a look at the chimney. Over the years POs had a variety of coal or woodstoves. There were 2-3 vent hole cut outs that had been carelessly patched. Some even had old newspaper stuffed in between the bricks! Its a miracle this place never burned down!
Line that chimnney!!!