Now before people say don't do it don't do it I know not to do it I'm just looking for answers to why. I bought my grandparents farmhouse. My pap ran a oil boiler and a coal boiler to the same flu with a stove pipe y. Some info on the place. The flu is 38ft high from where the stove pipe goes into the basement wall to the top. The liner is 12x12 clay. When my paps coal boiler broke he was to old to be going to basement anymore so they just hooked up the oil boiler to the chimney. He had the double connection for 65 years and never had a problem. So why is it against code in most places nowadays. What's so unsafe about it. The draft that the flu creates is very powerful.
2 stoves 1 flu
- Thread starter Bungiex88
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JA600L
Minister of Fire
Not knowing what appliances are being attached probably has something to do with it. Plug a flue with creosote and then let carbon monoxide fill the house from the other device.
Allow dilution air into the flue through the other appliance causing creosote buildup. Then when that creosote catches fire it will cause an uncontrollable fire because of the air going through the furnace. Risk of either not having enough volume to deal with the demand when both are running or having way to much volume when only one is ect ect. Yes many can and do get away with it and have no major problems. But there is a pretty big potential for issues there.
What he said.
My sister and her husband run a woodstove (on the first floor) and an oil boiler (in the basement) into the same flu. Husband is baffled as to why the draft is terrible and he's cleaning the chimney all the time. I'd be worried about CO and other gasses from the boiler venting into the living room as well.
Exactly what bholler states. And just to add to this somewhat.
This is largely because there is no practical way to connect another wood, gas or oil appliance to that flue without causing air infiltration into the flue through the second appliance, its connector pipe, or thimble fitting. Air infiltration slows the rate of exhaust travel up the flue while simultaneously cooling the wood exhaust gases, causing excessive creosote condensation and an increased chance of chimney fires
When dealing with oil exhaust intrusion into a chimney venting wood exhaust, other factors come into play. The sulpheric acids contained in oil exhaust blend with the aldehydes found in wood exhaust to create an extremely corrosive mixture inside the flue. This mixture attacks both the bonding agent in the mortar and the actual chimney structure itself, drastically reducing the usable lifetime of the chimney.
Finally, the combination of oil soot and wood creosote in the flue presents the most dangerous of chimney fire hazards. Oil soot ignites at extremely low temperatures, and wood creosote burns at extremely high temperatures. When ignited, this mixture "spits" burning balls of oily creosote out the top of the chimney in every direction. Thus, a chimney flue that is coated with a combination of oil exhaust and wood exhaust deposits is much more likely to experience repeated chimney fires, and those fires are much more likely to destroy the chimney and/or burn down the neighborhood.
The bottom line: The only way you can safely vent an oil-burner and a wood-burner into the same chimney is if you install two stainless steel chimney liners, one for each appliance.
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jetsam
Minister of Fire
As bholler said above, if the woodstove fouls the cap (or a bird nest plugs the flue) his boiler will be exhausting directly into his stove room.
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