State of Maine - 2 appliances vented in the same chimney

[PassionForFire&Water]

The State of Maine allows for the venting of an oil furnace and biomass appliance in the same chimney.

Having no experience in doing this, I'm wondering what the most recommended (safe) physical setup would be to:
- connect a power vented biomass boiler to a chimney that also has an oil furnace hooked up to it
- connect a natural draft biomass appliance to a chimney that also has an oil furnace hooked up to it

Are there any other states that allow this?

 

[BoilerMan]

This is an interesting topic. It is my understanding that in Maine the only way this is allowed is if it were installed and working properly before 1995. This is basically their grandfather law, although the state has gone back and forth on this a few times. I do know from expierence that you would want a natural draft boiler if it connected to a flue serving another appliance, a power drafted boiler can make funny things happen with oil if the barometric pressure is right........... I do not know of any insurance company that will touch a shared chimney situation though, I do not however, believe it's dangerous especially if the flue is tall and drafts well and is an 8x10 or larger. If you do choose to do it, put the biomass on a takeoff above the oil so any creosote will not build up in the oil vent pipe.

Taylor

 

[maple1]

My boiler is oil & wood (natural draft), combo. It has two separate flues out the back. They both go into the same chimney (7in. stainless, 30 ft. high). However, the oil takeoff needed to be above the wood takeoff - oil over wood. I don't know the exact science behind that, but that is how it had to be done.

 

[tom in maine]

We lobbied for years over venting 2 devices into a single flue.
The former fire marshall of the state tacitly accepted the concept without making it legal.

More recently, it was disapproved of by the current fire marshall.

What changed was a long time politician in Northern Maine got nailed on this issue.
He pushed it through the Maine legislature where Dick Hill (the inventor of the gasifier and former Maine Solid Fuel Board member)
got nowhere.

It is only for grandfathered installations(pre-1995).

There were never any issues caused by the practice, but it took a politician who got nailed by a code person to make the change!
I am not sure if we should be happy or not...

 

[BoilerMan]

I am not sure if we should be happy or not...

I agree it's alot of politics...... As an electrician, I've been ALOT of basements in the state, as well as other states, and I've seen hundreds of wood and fossil fuel on a common flue. Personally I think it's a non issue, the barometric damper on the oil will cool the flue........ but it also dilutes the smoke from the wood, so it's a catch 22 (this has been debated on here many times). In the event of a chimney fire though I'd like to have the ability to suffocate the flue as much as possible. So a thimble or something to cover the baro in the oil vent pipe might be in order. Not an issue for me though, one flue = one appliance here, it's the only question the insurance company asked when I said I heat with wood.
As has been stated some wood - oil combo units have two vent connections on the back, if it is not allowed to share a flue they can have two vents into two flues, or can be connected to the same flue.

Taylor

 

[Don2222]

Hello

I had an Oil Boiler and a Wood stove connected to one block chimney with one clay lined flue. When the boiler with the burner fan came on it would put stress and pressure on the seals of the air tight wood stove. If I was reloading a stove that had a small fire, the burner on the boiler would cause a back draft and I would get smoked. Then the wood stove seals went bad and I would get smoke everytime the boiler came on. So in general it is certainly not a good idea. Since then, I installed a stainless steel chimney flue for the boiler and now it works much better. It cost me $2500.00 for the new chimney but worth it and now the fire department and the insurance company is happy!