ONE chimney for 2 Boilers?????

Can a coal boiler and a oil boiler share the same chimney? I plan to use a VF3K boiler for the main source of home heating,but if no one is home and the coal runs out I want the excisting oil system to come on line. Will one chimney work? It is a brick chimney. Anyway possible???? Anybody have ideas for electrical wireing for that?

i believe by code they CANNOT share the same chimney, at least here in penna. anyway

Most codes do not allow a solid fuel and other type of fuel share the same chimney, unless it has a separate flue. If you unhook one or the other and/or power vent your furnace if you don't use it, so it only runs when needed, some people do that.

Code won't allow it. Some people use the chimeny for coal and get a powerventer for the oil. Set the coal aquastat at 160/180 and the oil for 140/150 and if the coal goes out the oil will take over...albeit not at full heat but it's simple.

I came across an odd comment in a news report. Various state agencies here in Maine were discussing how to keep houses warm this winter, with the price of oil so high and people wanting to add wood or pellet burners. One proposal being considered was to drop the restriction on only one appliance per flue. Well, if it's that easy to drop it, how valid is the restriction in the first place????

Probably most older chimney/pipes are not sized correctly if BOTH appliances are running and you don't want to get into drafting problems or CO leaks in one or the other.

Plus you get a lot of moisture from Gas furnaces exhaust, mixed with coal/fly ash and corrode very quickly.

My sister has 2 furnaces and hot water tank (all OIL) piped into one flue, but it's like 12" diam and it increases after each one and has special Y pipes hooking them all up with baro dampers.

You wouldn't want to hook a wood stove up to an unlined chimney and most pellet stove are direct vented directly thru walls.

rberq wrote:One proposal being considered was to drop the restriction on only one appliance per flue. Well, if it's that easy to drop it, how valid is the restriction in the first place????

It is valid big time with wood, iffy with pellets/corn/cherry pits/etc. and ridiculous with coal.

Having a second appliance hooked to the chimney can act like a stuck open barometric damper, or a missing cleanout door.. both significantly reduce the available draft in the chimney to the coal appliance..

If you want to use the same single chimney for the two appliances, the best way is to disconnect the oil boiler, and turn it off, hook up the coal boiler.. But when you are going on vacation, let the coal boiler go out, and reinstall the oil boiler's flue pipe.. if you have it allready cut to size, it should only take a few minutes to swap the flue pipes..

Greg L.

I have both of mine(oil furnace and coal furnace) hooked to the same chimney,but don't listen to me.I'm the renegade in this outfit.I also have no GFI's in my house(1938 total rehab) and no 3 prong outlets but the outlets are polarized.

For the first 2 yrs.my smoke pipe was all 6" and both worked fine,even at the same time.If the coal fire ever ran low I would turn on the oil and that would get the draft really going and reload the coal and off it would go.

This year I ran 8" from the thimble and split 6" to each furnace.I thought I had poor draft because my baro would never be more than .08 but I just got a manometer and with a few pieces of paper burning the manometer read .05 and it was 68F when I tested.I got the feeling my draft will be over .1 in the cold weather.

So the bottom line is it will work fine BUT code and the insurance man say NO


One more thing if you do this clean your smoke pipe every month.As long as it's clean you'll be ok.

DON the renegade

I know this is an old thread - but good information doesn't expire

Since I cant get the idea out of my head (two appliances into one) every now and then I go back and google...which brings me back to this site - and then I google some more.

Anyways here's the NH code as of 2010 ....I recall googling maine or vermont and oil burner with coal was permitted but that may have been outdated info anyways.

http://www.nh.gov/safety/divisions/fire ... ces_2_.pdf

I've been researching the same thing and found this great pdf file from Bock's website today.

http://www.bockwaterheaters.com/technic ... _08_06.pdf

I am finally about to get my coal boiler hooked up. I was going to wait but this new house is bankrupting me on oil. I plan on using Field Controls recommendation and putting the baro for both the coal & oil in the A position as seen in the attached pdf.

How about some pictures of the K4 install?

How much fuel have you burned so far?

Rob R. wrote:How about some pictures of the K4 install?

How much fuel have you burned so far?

Sure I'll take some pics and post them to the stoker section. I'm burning a tank of oil per month and this has been a mild winter.

pics can be seen here: KA-4 New house, poor design, requires over 200F baseboard!