Need Some Advice on Chimney Heights

[velvetfoot]

I got a new 8" flue installed in my chase today (still has to do the chase cover next Tuesday).

The installer is also going to adjust the chimney heights when he puts on the chase cover.
For whatever reason, there is negative draft going down the cold flues in the basement. It's always been that way. Have no idea why.
Checked a lot of things. I've been fighting a smokey odor on wood smoke coming down the oil burner and out through the baro damper, which I slowed down with an automatic flu damper. The smokiness coming down the 8" flue is real bad so I blocked it up until, hopefully, I get a wood boiler installed.

Anyway, I plan on having the guy adjust the three flues' heights so that the wood boiler is highest, insert next, and oil flue lowest, in the direction of the prevailing winds. My scheme kind of depends on the prevailing winds, but I feel that generally, there will be a fire in the boiler all the tie during heating season and will float above the other two, and the insert smoke will float above the oil flue. As long as the prevailing winds hold.

Waddya think?

 

[smokedragon]

More details (how tall, insulated flues, how tight is the house, etc)......

If the prevailing winds hold in your favor, it couldn't hurt. But unless you are on the coast or have an obstruction on one side, it is really hard to say the wind will always be from a certain direction. Have you tried letting in a little make up air (crack a window) before opening the insert......sometimes this helps with getting downdraft.

Hopefully others will chime in, as downdrafts in basements seem to be a problem for some.

 

[Woody Stover]

there is negative draft going down the cold flues in the basement. It's always been that way. Have no idea why.

I'm pretty sure that this is caused by the stack effect of the house itself; Warm air leaking out the top of the house is replaced by cool air being pulled down the cold flue. I'm not sure how that is remedied but someone here will know.
I've been thinking about this potential problem. I've got a masonry chimney with two flues, and was wondering it they would interact if I had stoves hooked up to both. I would probably only have one stove running most of the time, and wondered if I could have the downdraft problem you're describing, or some other problem if both were burning at the same time.

 

[billb3]

stack effect
warm air low pressure inside , cold air higher pressure outside
will both allow downdrafts when the oil burner isn't running

I have a outside air kit for my oil burner
never smell wood smoke in the basement any more

 

[velvetfoot]

"I have a outside air kit for my oil burner
never smell wood smoke in the basement any more"

That's like taking suction from a different location, like opening a window, which also works, but who wants to leave the window open all the time?

 

[Swedishchef]

Me..

I have 2 windows in my basement that are locked open, 1 inch wide. It's the only way I can prevent my stove from getting a downdraft. My house is too tight and my eir exchanger doesn't help (I would need a +ve pressure overall to prevent downdraft).
It is counter intuitive but it works for me.

ANdrew

 

[velvetfoot]

But my thermal storage tanks might block the lttle window.......

It's the only way I can prevent my stove from getting a downdraft.

Or just keep it hot (or warm, anyway) .

 

[Swedishchef]

LOL... true.

But sometimes I travel for work and since I am the only one who tends to the fire, it goes out.

Andrew

 

[velvetfoot]

But sometimes I travel for work and since I am the only one who tends to the fire, it goes out.

I hear you on that.

 

[billb3]

"I have a outside air kit for my oil burner
never smell wood smoke in the basement any more"

That's like taking suction from a different location, like opening a window, which also works, but who wants to leave the window open all the time?

How is it like leaving a window open ?
No air comes in through the pipe until the blower in the burner sucks it in.
That was the whole idea behind giving the furnace air directly from outside, so it wouldn't be using inside air that had to come in somehow.

 

[Swedishchef]

I think he simply meant that a window open gives a chance for any air sucking appliance to suck air and prevent having a negative pressure in the stack.

There could be cold air coming in your OAK for the furnace although you wouldn't necessarily be able to tell.

The fact is if a house has a negative pressure from fans sucking air out, imbalanced HVAC, etc, any appliance with a chimney can have a negative pressure. The air has to come from somewhere....

Air tight houses have their PROS but also the CONS.

Andrew

 

[velvetfoot]

I do wonder where it goes, but I haven't found it yet.

 

[Swedishchef]

clothes dryer? fan above your oven? bathroom exaust fan?

 

[velvetfoot]

Nope. Maybe something in the attic, but there's so much insulation there, it'd be hell to look for it.

 

[Mr_D]

Maybe something in the attic, but there's so much insulation there, it'd be hell to look for it.

An Infrared camera can show where conditioned air is leaving the house to the outside or into the attic. It can also find the main points of outside air coming in. You can't "see" hot or cold air but you will see the temperature effect on the materials next to it.

You should be able to see any significant air leak by pointing an IR camera around the attic inside perimeter.
Finding where the air is leaving could help reduce the problem of smoke coming in with the resulting makeup air.
Maybe the attic access hatch leaks?

I put a couple examples of infrared helping to locate thermal and air flow issues and what it looks like.
I have access to one. Maybe someone in your area has one they'd loan to you for an evening.

 

[smokedragon]

An Infrared camera can show where conditioned air is leaving the house to the outside or into the attic. It can also find the main points of outside air coming in. You can't "see" hot or cold air but you will see the temperature effect on the materials next to it.

You should be able to see any significant air leak by pointing an IR camera around the attic inside perimeter.
Finding where the air is leaving could help reduce the problem of smoke coming in with the resulting makeup air.
Maybe the attic access hatch leaks?

I put a couple examples of infrared helping to locate thermal and air flow issues and what it looks like.
I have access to one. Maybe someone in your area has one they'd loan to you for an evening.

I would love to add that to the list of tools/equipment I own. Along with a hydro splitter, tractor with a frontend loader, etc, etc.

 

[velvetfoot]

To kind of round out this thread. The chimney guy just now completed the job. I took pictures of the nice stainless chase cover, but wouldn't you know, I didn't have a memory card in the camera. Anyway below is a picture of the final product. It was my concept to have the heights graduated because of smoky oder from downdraft in the flues and prevailing winds. The tall one is the 8" chimney with a 6" insulated liner for the pellet boiler. The middle one is for the wood fireplace insert and what is seen is a single wall stainless extension of the 6" liner (was going to be a lot more to possibly match the air cooled-hoping creosote won't be an issue), and then the oil stack. As I said, world's most expensive pellet vent.