Does a vacu-stack help in non-windy situations?

[shaggymatt]

I've been getting no assistance with the dealer and installer on my recently installed Osburn 2400i. The stove backpuffs when there is any fire in the firebox. If there are hot coals, it is fine. Once the wood catches, it starts smoking into the house. We've been through all the normal remedies.

Last I head from the installer (4 weeks ago) he suggested that the vacu-stack also solves backpuffing issues when there is no wind. Does anyone have any feedback in regards to this?

 

[Webwidow]

not that I have ever witnesses

 

[thechimneysweep]

Can't happen. It is the flow of air around the cap that causes the negative pressure (Bernoulli's Principle). No airflow, no increase in updraft.

 

[shaggymatt]

Thanks. That is what I thought.

 

[swestall]

What were all the "normal remedies"? What size is the flue and how is it drafting?

 

[webbie]

If they have not already, folks might want to look at this study - according to it, a regular cap helps as much or more than certain "advertised" caps.
https://www.hearth.com/econtent/index.php/wiki/Effect_of_wind_on_chimney_caps/

 

[shaggymatt]

What were all the "normal remedies"? What size is the flue and how is it drafting?

From my previous post in this thread: https://www.hearth.com/talk/threads/11372/

I recently had an Osburn 2400i(nsert) installed into my newly purchased house. The installer put in a 6” liner into my exterior brick chimney. The house is a split level, the stove is in a basement which is about half way underground.

I have about 4 cords of well seasoned wood. Have been through about a 1/2 cord so far this fall. The wood is dry, always ignites within a minute. The stove lights easily, I can start a fire with 5-6 pieces of newspaper, some branches, and a piece of cordwood, and the fire is well on its way with no further attention. This is not when I have the drafting problem. I cannot load the stove with any additional wood until the flames are entirely gone, and only embers are left in the stove. Normally this isn’t a huge problem, but if we want to put on one more piece of wood before bed, leaving to go somewhere or whatever, that is when we run into problems. In other words, if there is an established fire, you can’t open the door without smoke pouring into the room.

This occurs when there is no wind, or there is wind, so it isn’t a wind issue with the cap. The brick portion of the chimney goes higher than the roofline already (off the top of my head - it is dark right now as I type). The installer then left ~1.5 feet of pipe exposed and put the cap in place. For this reason, I don’t think that it is a height issue. I’ve opened windows in the house attempting to equalize pressures, again no luck here.

I *think* that the problem really has come in from where the exhaust outlet on the Osburn is located. It is very far to the front of the stove. When he installed the stove, he couldn’t get the liner to line up with the exhaust port. So he had to go to a metal shop and have a (beautiful - at the cost of just over $100) stainless steel double bend elbow made. So it goes up, bends 90 degrees, back another 8-10”, and makes another 90 degree bend to line with the liner.

Once loaded, the stove burns great. I’ve only had to clean the glass when I performed the low temperature break in burns to cure the paint. I’ve burned the stove for upwards of two weeks, heating the entire house. I’m very happy with the performance, just not the smoke in the house. I did notice that from the previous homeowner, there is a lot of soot on the bricks directly above the fireplace opening.

Thoughts? Many thanks!

And I should add that the liner is insulated.

After talking to the installer four weeks ago, he said that the bends would have nothing to do with the backpuffing. At this point, I think that the only thing I can do is to send a threatening letter with some mention of legal recourse to get them moving on this. I imagine that I need him to check the baffle position? I'm technically inclined, but don't know much about stoves, and the Osburn manual is horrible. As 'webmaster' said in the previous thread, I can do the temporary extension on the chimney, perhaps I'll try that this weekend. I mentioned the height to the installer as a possible problem, and he didn't think that was it, as it is higher than the roofline, and the closest tree is about 20 feet away.

 

[Metal]

Possible problems that could be affecting draft:
1. Height (although it doesn't sound like that is it)
2. Uninsulated liner in an exterior chimney (insulation would help draft, which should help eliminate the puffing)
3. Installation of nonstandard double 90 El (without seeing it it is hard to say how much restriction it is adding, but it is adding some no matter what)
4. What type of cap is installed (some caps can be restrictive and inhibit draft)
5. Negative pressure in house (sounds like you have checked this, if it was a problem you could try adding an outside air kit (OAK))
6. Dirty chimney (maybe those low heat break in fires creosoted the pipe?)

 

[shaggymatt]

Possible problems that could be affecting draft:
3. Installation of nonstandard double 90 El (without seeing it it is hard to say how much restriction it is adding, but it is adding some no matter what)

Did you mean nonstandard 90º elbow here? I honestly still think that the issue is coming from the elbow, although he doesn't think so.

And the cap is just a stainless steel cap, with bird grating around it, and a cap. Nothing special.

 

[Metal]

This is from you manual

"1.5.3.3 Exterior Chimney
Chimneys constructed outside of the home on an exterior wall should be avoided if possible, especially in
colder climates. Exterior chimneys may not draft well and in fact may down draft (reverse flow) due to the
difficulty in heating them up to operating temperature while trying to evacuate the stack gases. All else
being equal, cooler chimneys will have less draft than hotter ones; this may lead to creosoting and poor
performance. If an exterior chimney is used to remove the stack gases the best results will be obtained by
using a connector vertically off the unit to the highest possible point before elbowing off horizontally to the
chimney. For efficiency and safety reasons the stove must not be installed with an insulated chimney
connected directly to the appliance."

Notice how it states:

"If an exterior chimney is used to remove the stack gases the best results will be obtained by
using a connector vertically off the unit to the highest possible point before elbowing off horizontally to the
chimney."

In your situation, you are elbowing off twice immediately off the stove. I still think that double elbow may be your problem.

 

[shaggymatt]

Thanks. They HAD to do the elbow how it was done, otherwise, the stove wasn't going in. They used a power chisel to get out a bunch of brick to get the unit in, and the elbow, I don't think that they could take out much more in the front. I would think that it is pretty standard to build a fireplace with the bed directly under the main open part of the chimney, so why do the stove manufacturer's put the exhaust port so far forward on the stoves???

They used the insulation that you pour down into the chimney after the liner was in place, so it isn't insulated all the way to the elbow even.

You have to forgive my ignorance, as I'm new to all of this, and learning a lot from here. I feel like I am better educated though than the installer from reading everything on here! At least I can talk with a sense of confidence to him!

 

[Metal]

No one here thinks you are ignorant, we just ask every question we can think of to try to get a better picture of what the problem could be. According to this picture from the manual, it doesn't look like they could have moved the flue back much further. The company sounds like they did everything else well, i.e. installation and insulating the liner.

The manual shows a specific way the baffle/bricks should be installed. I would check to make sure everything looks correct in that area (page 10 & 11 in the manual).