Improving draft

[pyper]

My stove doesn't draft well enough. It's got a liner in a masonry chimney. It's not very tall. I don't know exactly, but probably only 10 or 12 feet. It's also on a T. What is the best way to improve things?

It would be possible to remove the T with the short leg kit (pushing the stove back into the fireplace). How much would that probably help?

Is it possible to extend the chimney?

Oh, it's an old house, so it's not too tight.

 

[logger]

I'd first try opening a nearby window to help with draft. Removing the 90 degree elbow would def help too. However, I really think its the height of your chimney that could be the biggest problem. It is possible to find a mason to make it taller. Best of luck.

 

[LLigetfa]

Lowering the neutral pressure plane in the house might help. Insulating the liner should help. Extending the flue might help. Burning a little hotter might help.

 

[dougand3]

Could try: Flue exit out top, w/o the T. Straight up will improve draft. Is liner insulated? If not, could make a big difference. They have pour in hi temp insulation (vermiculite type material), thermal ceramic blankets (rated to 2100*F), rock wool/roxul (don't know it's temp rating). Is there a block off plate (above stove, near damper)? You may get good results blocking off bottom and top of chimney with proper insulation - the liner stays hotter inside the masonry chimney.

 

[begreen]

The Castine needs a strong draft for good operation, especially when connected rear-exit. I would want at least 16 ft on that flue. Options could be extending the masonry, extending the liner or perhaps tying into 4 ft of class A. Can you post a picture of the chimney so we can see what might work? The liner should be insulated and the horiz run to the tee kept as short as possible and pitched uphill toward the chimney with at least a 1/4"/ft pitch. More pitch is even better.

 

[pyper]

Thanks!

The horizontal run is basically just the T itself. A few inches. I'm going to stop by Lowes and special order some Roxul. I have some pieces of flashing blocking off the bottom of the flue, but that's obviously not very effective. After I get the Roxul I'll stuff some up there and perhaps use the pourable stuff from the top. Roxul's website says it's completely non-combustable and won't melt to something like 2500F. They mention using it to insulate chimneys.

As far as pressure, I don't think that's the problem. Until Monday there was a 1" hole in the back of the fireplace where the gas line used to run. All the windows leak too, and the doors. The other night when it was really windy I could feel the air moving through the house. More projects!

I'll see about taking a photo of the chimney. It's exterior, on the short side of the roof. It's about six feet wide, with three flues. When I stand on the roof, it's about belly high. There's a large metal pan over the whole thing which would make things slightly more complicated.

This is approximately to scale:

 

[begreen]

This could be a tough one. With it's shallow firebox, the Castine really likes a good draft.

 

[Stump_Branch]

Bigger brother to yours, same setup. I ended up pulling the liner, insulating with kaowool, then i made a 3ft extention out of black stove pipe, more kaowool and then more larger pipe. Basically poor mans class A pipe like begreen mentioned.

This all worked for me and i did notice an improvement in the draft and controllability of the stove(s). However i cant tell you which one did the most as i did them both at the same time.

Try a section of plain stove pipe at the top, its a cheap way to determine if this will be the fix. If it is the cure, get a real piece of insulated pipe up there since the top is typically where most creosote will form.

adding liner insulation i think helps with keeping draft up during cold starts and when the fire is dying down. My opinion though.

Good luck.

 

[Kevin*]

The install manual that came with my chimney and stove said the 1 90 deg bend reduces the effective draft by 5 ft. My stove needs 12-15 ft of effective draft. Removing the bends in the system is the best and often the cheapest way to get better draft. Also you cap should be checked, no cap or a damaged cap can hinder the draft.

 

[Backwoods Savage]

The install manual that came with my chimney and stove said the 1 90 deg bend reduces the effective draft by 5 ft. My stove needs 12-15 ft of effective draft. Removing the bends in the system is the best and often the cheapest way to get better draft. Also you cap should be checked, no cap or a damaged cap can hinder the draft.

5' is the largest I've ever seen listed. Most claim 2-3' with each 90 degree bend.


Pyper is it possible you could buy some single wall pipe and stick, say, two lengths on top of your chimney. That might tell you if the extra height would improve your draft. You would not have to buy the black pipe but just the cheaper stuff or even galvanized.

 

[Stump_Branch]

From your manual "Chimneys shorter than 14 feet (4.27 m) may not provide adequate draft. Inadequate draft can result in smoke spillage when loading the stove, or when the door is open. Poor draft can also cause back puffing (ignition of gas build-up inside the firebox) and sluggish performance. The minimum height does not, in itself, guarantee proper chimney performance."

and you are 10' with a 90 degree bend in a tee set up? How did that ever pass inspection? and why did not the installer or the company selling you the stove ask your chimney configurations before selling you a stove doomed to fail

Most stoves will claim the `4 feet min. its a 'general' rule of thumb (size dependent) as this is the height required to generate a draft. some companies measure from the stove collar, others from the floor of the fire box.

however the amount of feet to take off from 90 degree bends is also just a 'rule of thumb'

I have what sounds like the exact same setup. EXACT, minus the stove and overall height. note sure how that would violate code, rather just perform poorly.

Cheapest diagnostic here is as backwoods mentioned, a few extra feet of pipe. should this work. a permanent fix, real exterior stove pipe, should be in order.

good luck.

 

[begreen]

Not disagreeing with following the mfg recommendations, but that is not a code violation.

 

[amellefson]

I bought a 2' piece of single wall galv earier this season. I have a similar chimeny height, 14' just below the ridgeline. It helped somewhat but I think that a lower block off plate with top and bottom insul sounds like the next easiest thing. I hate to pull out the liner to insul the whole thing. Good luck. It is definately a learn as you go process.

 

[begreen]

I haven't seen a code requirement for chimney height. There is a difference between what will fail inspection and what will function well. Not that these goals are mutually exclusive, but the terminology used implied that it would fail inspection and it would not afaik. In other words, code compliance does not guarantee good draft.

 

[pyper]

and you are 10' with a 90 degree bend in a tee set up? How did that ever pass inspection? and why did not the installer or the company selling you the stove ask your chimney configurations before selling you a stove doomed to fail

The company I bought it from was the company that installed it and they came out and looked things over before they sold it to me. I have no idea what they think or why they might do what they do.

Where I live they aren't big on inspections.

I think "doomed to fail" is a bit of an exaggeration. It works, just not as well as it should.

For those arguing about the manufacturer's recommendation -- you'll note that it is not specified as a minimum requirement. In fact, it says chimneys shorter "may not" provide enough draft.

I think my plan then is to insulate and seal the smoke chamber and flue, and test a longer length of pipe to see how much difference that makes. My wife still might want to take out the T just to push the stove further into the fireplace for the appearance.

 

[Stump_Branch]

Pyper, for reference the only reason i didnt push my oslo back into the fireplace (had short legs) was i wanted to use the side door. You dont have that issue so could be a wise move.

Does the castine have a blower option? Depending on how far it has to sit back in there, might be worth considering to get the heat out in the room.

Good luck, youll have to report back with your findings and any pictures.