Why can't they share a chimmney?

[Gooserider]

Ok so trying to understand why....
We have a mason lined chimmney one for the upstairs fireplace and one for the oil furance. We want to put on an add on wood furance downstairs and tie it into the same chimmney as the oil furance as they would each have their own flues. We where told you can't do this. Why not?
What are our other options? Can you block off the upstairs fireplace somehow and then use that one or it our only option a pipe out the side of the house from the basement. Any help would be greatly appreciated and if I need to provide more information to get some answer let me know! Thank you so much for any feedback.

Seems to me like this one has led rapidly into confusion-land :-S w/ esoteric arguements about code interpretation rather than answering Brianna's question...

First off, Brianna, your description is also a bit confusing because I think you are mixing definitions... Let's start by clearing up the definitions, then try to understand your situation better.

A "FLUE" is a tube intended for passing the exhaust from an appliance, it can be made from masonry, metal, or (rarely) other things.

A CHIMNEY is a large structure, usually made from masonry, that CONTAINS one or more FLUES. In theory at least, there is no real limit on the number of flues that a chimney can have.

What it sounds like from your post is that you have ONE chimney that currently contains TWO flues, one connected to the the oil furnace in the basement, and one connected to the upstairs fireplace.

You are wanting to add a wood furnace, and are confused about not being able to tie it into the flue currently being used by the oil furnace. - Is this correct? If not, please clarify by describing your setup, especially your chimney configuration - how many flues, and what is connected to each one. (You didn't mention your hot water heater - what kind is it, and if not electric, how is it vented?)

With a couple of exceptions, such as combining a hot water heater and a furnace of the same fuel type, current day code specifically requires that you have no more than one appliance per flue. This means that you oil burner CAN NOT share the same flue. If they have seperate flues then you should be OK.

Aside from legalities, the reason is that it is NOT SAFE to do so (codes are mostly written after people died doing it some other way) - it is possible to have one appliance leak toxic flue gases out the intake of the other if you are sharing flues. This is prevented if there is only one appliance per flue.

It is probably not feasible to block off the 2nd floor fireplace to use that flue for the wood furnace, as it almost certainly doesn't have the right sort of structures to allow connecting into it in the basement.

If you only have one flue to the basement, to add a second appliance you need to come up with an alternative. The wood furnace essentially requires a straight up chimney, so it probably would do best on the existing flue. However it is possible to either replace the oil burner, or retrofit a "power vent" system to it, that will allow you to vent it out the side of your house, which is usually a relatively low cost approach.

I hope this clarifies things, and welcome to the Forums..

Gooserider

 

[Brianna]

Thank you so much for all of your help and feedback! You guys are amazing and I love this site the information has been incredible and like no where else!

 

[Gooserider]

Glad we've been able to help out. Has what we've told you so far answered your questions?

What sort of decision have you made on how to approach this?

Gooserider

 

[Brianna]

Yes they have. It looks like we are either going to have to close up our fireplace we have upstairs and seal it and run the pipe up that chimney or install a class a chimney. We are still trying to figure it out. It would be cheaper to seal the inside one but we do like having that one for ambiance. So we are hoping to figure out what we are going to do before the end of the month.
Thank you again for all your help!

 

[elkimmeg]

Just a thought may be I am missing something if so I apologise

Why not install an insert in the upstairs fire place? one with a good size glass view of the fire

Ambiance there are inserts that have optional fire screens and open door fires?

Many times the simplest solution turn out to be the best ones

 

[Gooserider]

Yes they have. It looks like we are either going to have to close up our fireplace we have upstairs and seal it and run the pipe up that chimney or install a class a chimney. We are still trying to figure it out. It would be cheaper to seal the inside one but we do like having that one for ambiance. So we are hoping to figure out what we are going to do before the end of the month.
Thank you again for all your help!

One problem you MAY run into if you try the sealing up the fireplace approach is that in most (all?) of the fireplaces that I'm familiar with, the flue structure in the chimney will end at the fireplace, with no easy way to get a flue down to the floor underneath - I suspect that it would take some MAJOR masonry work to get the flue extended down to the basement, probably far more than it would cost to put in a Class A pipe.

However from your earlier description as I understand it, you already have one flue down to the basement which is used by the oil burner. If that flue is in the right place from a "floor-plan" standpoint, I think your easiest, lowest cost option might be to powervent the oil burner out the side of the house, and use the flue for the wood burner.

Gooserider