Are Exposed chimney block chimnys Legal? Why are they creosote factories?

[elkimmeg]

Recently two of the worst creosote picture posted, were taken looking down masonry chimney block chimneys
Forum member Struggles live in constant fear of chimney fire danger till he lined his. I have been pondering why this is occurring in the chimney block setups with 8/8 flues in exposed chimneys?

A nominal brick measures 3, 5/8” Chimney block 3,1/8”
Is it that ½” reduced masonry thickness? Does that reduction promote more cooling within the chimney? Are these chimneys code compliant? Code calls for 4” masonry, which in reality 3,5/8”. There are no code exceptions for reducing this requirement to 3,1/8”

Another factor here might be that chimney block chimneys having more than one flue seen to work better? The furnace and or hot water heater are connected to the adjacent flue and do provide residual heat within the chimney. That may aid in both the wood stove draft and the burner’s draft. It seems the stand-alone exterior chimney is the most effected by creosote development.

Next factor: As wood stoves become more efficient, their draft requirements become more critical. Could it be that they are producing less heat in the draft cycle and more to the living space? They are not producing enough heat in the chimney, to draft correctly? Evidence of this, is the increased post complaining about poor performances in inserts installed in exposed exterior chimneys. Even code recognized this, when they amended the cross-sectional codes to reduce the area requirements of exterior locations.

At some point the wood used has to be questioned. We all know mister woodman sells seasoned wood, that is not ready for prime time. At some point the user practices have to be examined. In the effort to obtain longer burn times, are they dampering down too soon? Are they using wetter that dry wood? Have they choked down the air supply too soon with less than dry wood?

 

[slowzuki]

Can't comment on too much except exposed block chimneys really have to have a high heat input to maintain their temps above condensing. They are actually an excellent low cost condensor by nature so why do we try to use them as chimneys?

Newer efficent stoves may be able to be operated at lower stack temps but they also produce much less "junk" to form creosote. A catalytic stove would be getting pretty close to being able to used with a condensing flue without worry of acid attack. Of course it doesn't burn this clean throughout the operating cycle so it wouldn't work in real life.

I think the advent of vapor barriers and tight homes contributes to the weaker drafts seen now. You can see the effect of an opening door on the flame pattern in the stove/insert and the flue become a good relief vent of the house.

 

[begreen]

Can't comment on too much except exposed block chimneys really have to have a high heat input to maintain their temps above condensing. They are actually an excellent low cost condensor by nature so why do we try to use them as chimneys?

I'm with Elk, if one installs a new exterior chimney for a stove or fireplace it should be required that it is safely and properly insulated. If you want a big condensor on the side of your house, consider turning it into a still instead. (now there's a thought.)

 

[Harley]

Aside from the thickness difference, could it be block chimneys cool quicker because they are "less dense" as compared to brick, and simply don't hold the heat as well?

 

[webbie]

What is legal and what should be legal are two different things.
I have long said that the brick industry must have a good lobby since most masonry structures cannot properly function in the way intended (cracked tiles, etc.).

I doubt we will see a change soon, so it is up to the customer to educate him or herself and build properly insulated or interior chimneys.

 

[struggle]

I would say after my creosote run with an outside chimney that if and when we pursue a new home I would like to get one that could have an interior set up instead of exterior. It just seems to make sense that way after all the reading here.

Since my upstairs unit is a mass cavity type fire place (has a heated area, air chamber, all around the fire box, Cozy Heat) It requires a large concrete chimney.

I sometimes think the outside chimney is just a matter of not wanting to lose inside interior footage, the ashtetics of an outside chimney (looks nice) and the fact that most fireplaces at least around where I live are only used as a novelty so they are not primary heaters.

After spending much time on this site it is clear that true wood burners for primary heat really work under a different set of circumstances for what set up works best. Location location location

Thankfully I have no problem with the draft on our chimney and it actually drafts to much but I can control it with a dampener in the pipe but it still seems to pull to hard so I use less wood to slow it down instead of cramming the box full.

 

[Harley]

I sometimes think the outside chimney is just a matter of not wanting to lose inside interior footage, the ashtetics of an outside chimney (looks nice) and the fact that most fireplaces at least around where I live are only used as a novelty so they are not primary heaters.

Interesting... not to go off topic too much, but I generally assumed that many chimneys were on an outside wall due to cost, or that that were added on afterwards, which might have made it impractical to centrally locate..... Elk, or any other builder-type - does that make sense or did I just kind of make that up?

 

[BrotherBart]

In 1977 when I had my first house built I had to go to war with the builder to keep him from putting a masonry chimney on the house. I wanted to put in a wood stove and single/double wall chimney straight up inside after the house was completed. He raised hell saying "But what if something happens to you before we close? I will never be able to sell that house without a fireplace.". I told him if he put a fireplace in it I would see him in court given that I had already fronted some of the money for the house and a mortgage locked for the rest.

The house was finished without a fireplace and the stove was installed the day after closing but man was it a battle with that guy. And I was paying him the same price that he charged to build the darn thing WITH a chimney.

 

[Eric Johnson]

I can remember back when having a chimney with any kind of a liner was seen as pretty darn fancy. Plain brick chimneys in old farm houses is what I grew up with. No problems until we started using airtights in the early '70s.

 

[BurningIsLove]

Im curious to hear whether its even possible to get a (new) brick chimney anymore for less than the cost of a luxury car. When I put in my chimney in 2005, I wanted brick on the exposed section above the roof peak for looks, even that was astronomically expensive. When my parent's house burned down 20 years ago, even then it took months to find real brick to replace the chimney. Large concrete blocks (with a liner) was the only option I was given.

As far as the creosote conversation goes, I certainly worry about it far more with my concrete chimney than if I had a vertical, well drafted, interior stove pipe. My chimney is in a garage, so it certainly takes a while to get the stack up to temp if I've been away and the stove has been cold for more than 12 hours. But once it is up to temp, it has many advantages like retaining its heat for long periods and providing radiant heat to the garage & upstairs shop. This more than halves the temperature delta between the ambient temp and the stack temp.

If I had the same setup except an exposed, exterior block chimney, then I'd be very concerned about creosote buildup, not to mention poor drafting/operation of the stove. But as far as making this illegal, I dont think that would be possible since it would prevent someone who buys a house w/o chimney from installing one. I know if would have been impossible for me to add an interior chimney in my house without the garage addition.

Also to the point of an adjacent flue which services a hot water/oil/gas furnace, this has almost no impact from experience. I also have a double flue, block chimney, where the adjacent flue services my oil furnace. When I first installed the chimney prior to the wood stove install, my oil furnace provided primary heat. It was on so intermittently that even after several days of continual operation, there was no appreciable heating of the stack. For reference, the surface temp of the stack w/ the wood stove hovers around 110 degrees.

 

[begreen]

You can retrofit an insulated stone or masonry chimney to a house. I don't think they should be illegal, just insulated.

 

[slowzuki]

The old farm houses I grew up around all had old pot bellies and cookstoves in them and they got creosote too in the spring and when burning wet wood but the old timers would set a good fire to purposely burn the creosote out of them.
Ken

I can remember back when having a chimney with any kind of a liner was seen as pretty darn fancy. Plain brick chimneys in old farm houses is what I grew up with. No problems until we started using airtights in the early '70s.

 

[elkimmeg]

guys you are missing the point chimneys can be built with solid 4" blocks or bricks its the 3,1/8" chimney block were are discussing which is 1/2' less than code and commoin blocks and bricks